C H R O N I C S T R E S S A M O N G A D O L E S C E N T S C O N T R I B U T I N G F A C T O R S A N D A S S O C I A T I O N S W I T H

A C A D E M I C A C H I E V E M E N T

Karin Schraml

Doctoral Thesis in Psychology at Stockholm University, Sweden 2013

Chronic stress among adolescents Contributing factors and associations with academic achievement

Karin Schraml

© Karin Schraml, Stockholm University 2013 ISBN 978-91-7447-680-4 Printed in Sweden by US-AB, Stockholm 2013 Distributor: Department of Psychology, Stockholm University Cover illustration by Karin Schraml

Knowing is not enough, we must apply.

Willing is not enough, we must do.

J.W.Goethe

Abstract

According to recent nationwide surveys there have been dramatic increases

in stress and serious stress-related health problems among Swedish adoles-

cents. The aims of the present thesis were to investigate the prevalence of

perceived chronic stress among sixteen-year-old adolescents who attended

their first year at high-ranking high schools in the Stockholm area, to exam-

ine if factors that have been found to be relevant in the development of

chronic stress among adults also contribute to chronic stress among adoles-

cents, and to investigate the associations between chronic stress and sleep-

related variables and academic achievement. Data were collected by means

of self-report instruments. The main outcomes showed that a substantial

number of individuals (30%) reported to perceive severe stress symptoms.

The highest degree was perceived by 8% who suffered from symptoms to an

extent which otherwise only has been observed among adult clinical burnout

patients. Besides, 15% reported severe stress symptoms throughout high

school and were thus considered to suffer from chronic stress. Perceived

high demands, low global self-esteem, sleep disturbances and low social

support were crucial factors in explaining stress symptoms. Another finding

showed that perceived chronic stress was associated with adolescents’ aca-

demic achievement. A closer look at the potential contribution of sleep-

related variables to academic achievement revealed further that, apart from

severe stress symptoms, social jetlag was involved in predicting variation in

academic achievement. Overall, the findings indicated that there is a high

prevalence of chronic stress among adolescents. The results should be taken

seriously, as young people’s sense of well-being during this period impacts

both their successful transition into adulthood and their life course. Future

research options and potential practical applications in terms of chronic

stress prevention were suggested and discussed.

Acknowledgements

I would like to take this opportunity to thank all the people who have helped and

supported me through my thesis work.

My warmest gratitude goes to Aleksander Perski, my main supervisor. Thank

you for believing in me, for encouraging and supporting me and my ideas and

for guiding me through my time as a Ph.D. student. Besides your invaluable

expertise, I am very grateful for your optimistic way of seeing things, your gen-

erosity and your contagious enthusiasm. Working with you has sparked my great

interest in combining clinical psychological practice and research.

Thank you, Giorgio Grossi for always being encouraging and supportive, and

for sharing the experience of implementing chronic stress prevention workshops

among high school students with me.

I am especially grateful to my friend and dearest colleague, Johanna Schwarz.

Thank you, Johanna, Lena Låstad and Anne Richter for standing by my side

with scientific and non-scientific support.

In general, I would like to give credit to the entire staff of the Stress Research

Clinic. Thank you for always providing such an extraordinarily welcoming,

caring and friendly climate!

I furthermore wish to record my thanks to all my colleagues at the Stress Re-

search Institute. A special thank to my research assistant/Ph.D.-student col-

leagues and friends. It was a pleasure sitting in the same boat with you. In par-

ticular, I would like to thank Cecilia Stenfors, Malena Ivarsson and Maria

Baltzer, with whom I have shared my office/corridor and many inspirational

conversations. Thank you, Veronika Klevegren for always having an open door.

I would like to extend my appreciation to my co-supervisors Maarit Johnson

and Joakim Westerlund for their valuable remarks on my thesis. Thanks to in-

spiring role models and encouraging friends/colleagues, Petra Lindfors, Marie

Söderström, Kerstin Jeding, Walter Osika, Töres Theorell, Torbjörn Åkerstedt,

Göran Kecklund, Arne Lowden, Michael Ingre, Constanze Leineweber, Linda

Hanson, Anna Zyto, Maria Eriksson, Victoria Blom, Margareta Simonsson-

Sarnecki and Irena Makower.

Finally, I am infinitely grateful to my friends, who enjoy life with me outside

of academia, and to my kindhearted family. Most importantly, I would like to

give thanks to my parents for their loving support throughout my life. Thank

you, my amazingly talented, intelligent and loving sister, Christina, who is al-

ways there for me and who is a source of inspiration to me. Last but not least,

“Danke Oma!”

List of Studies

This thesis is based on the following studies:

I. Schraml, K., Perski, A., Grossi, G., & Simonsson-Sarnecki, M.

(2011). Stress symptoms among adolescents: The role of subjec-

tive psychosocial conditions, lifestyle, and self-esteem. Journal

of Adolescence, 34 (5), 987-996.

II. Schraml, K., Perski, A., Grossi, G., & Makower, I. (2012).

Chronic stress and its consequences on subsequent academic

achievement among adolescents. Journal of Educational and

Developmental Psychology, 2 (1), 69-79.

III. Schraml, K., Schwarz, J.F., & Perski, A. (submitted). The role of

social jetlag and stress in academic achievement among adoles-

cents.

Contents

Introduction .......................................................................................................... 1

Aims of the thesis ............................................................................................ 2

Theoretical framework ......................................................................................... 3

Adolescence and stress .................................................................................... 3

Stress theory .................................................................................................... 5

Stress – a physiological reaction ................................................................ 6

Psychological stress.................................................................................... 6

Chronic stress and burnout ......................................................................... 7

Chronic stress among adolescents ................................................................... 9

Factors that may contribute to chronic stress among adolescents ............ 10

Chronic stress, sleep, and academic achievement .................................... 18

Methods ............................................................................................................. 21

Participants and procedure ............................................................................ 21

Measures ....................................................................................................... 21

Statistical analyses ........................................................................................ 24

Summary of studies............................................................................................ 26

Study I - Stress symptoms among adolescents: The role of subjective

psychosocial conditions, lifestyle, and self-esteem ....................................... 26

Background and aim................................................................................. 26

Method ..................................................................................................... 26

Main findings and conclusions ................................................................. 27

Study II - Chronic stress and its consequences on subsequent academic

achievement among adolescents ................................................................... 29

Background and aim................................................................................. 29

Method ..................................................................................................... 29

Main findings and conclusions ................................................................. 30

Study III – The role of social jetlag and stress in academic achievement

among adolescents ........................................................................................ 32

Background and aim................................................................................. 32

Method ..................................................................................................... 33

Main findings and conclusions ................................................................. 33

Discussion .......................................................................................................... 35

Summary of the findings ............................................................................... 35

Factors that play a crucial role in chronic stress among adolescents ............ 36

Chronic stress, sleep and academic achievement .......................................... 41

Gender differences ........................................................................................ 43

Limitations and methodological considerations ............................................ 45

Implications for future research .................................................................... 47

Practical implications – preventing chronic stress among adolescents ......... 49

Concluding remarks ........................................................................................... 53

References .......................................................................................................... 54

1

Introduction

“While all life requires stresses and strains in the everyday give-and-take of de-

mands, chronic stress is a state of persistent excess of demands over resources. To

struggle, to achieve and to strive are admirable and essential characteristics. Yet,

without moderation the struggling goes awry, rendering the body and mind suscep-

tible to health and disease problems” (Thoreson & Eagleston, 1983, p. 54).

In modern Western society, chronic stress is a major public health prob-

lem (Levi, 2005; Perski, 2006; Shirom, 2003) because it increases the risk

for stress-related health implications and diseases. In Sweden, stress-

related health problems, such as clinical burnout, are among the most

common diagnoses for long-term sick leave among the adult working

population, leading to high costs for society as well as individual suffer-

ing (Lidwall, 2010; Socialstyrelsen, 2003).

It is not only adults who suffer from prolonged stress. Recent nation-

wide surveys indicate that there have been dramatic increases in reports

of stress and serious stress-related health problems among Swedish ado-

lescents (Ahrén, 2010; Bremberg, 2006; Hagquist, 2010; Socialstyrelsen,

2009). Over the past 20 years, the number of sixteen-year-olds reporting

stress, fatigue, and psychosomatic complaints as well as psychological

and physical tension has been steadily rising (Bremberg, 2006; Hjern,

Alfven, & Östberg, 2007; Östberg, 2001; Socialstyrelsen, 2009), indicat-

ing an increasing prevalence of chronic stress among younger age groups.

Adolescence usually involves a high number of physiological, social,

and psychological changes. During these years the choices that are made

and the behaviors that emerge have the potential to influence the rest of

one’s life (Eccles, Brown, & Templeton, 2008; Mortimer, Zimmer-

Gembeck, Holmes, & Shanahan, 2002). Young people’s sense of well-

being during this period impacts not only their successful transition into

adulthood but also their life course and adult options. Therefore, to pro-

vide adolescents with the optimal preconditions for their future life and to

maintain their health and well-being in the long run, by preventing chron-

ic stress is and, in fact, must be of great public concern (KVH, 2010;

SBU, 2010).

In order to do this an increased understanding of chronic stress among

adolescents is called for. Adolescent well-being and health are dependent

2

on a variety of factors, including individual (physiological, psychological,

and social factors), contextual (e.g., socio-economic status, school con-

text, and family structure), and societal factors (e.g., labor market condi-

tions and societal values). However, because many of these factors were

beyond the scope of what is feasible for an exhaustive investigation of a

broad and complex research topic such as chronic stress in a heterogene-

ous and complex population, like adolescents, the present thesis was lim-

ited to the following aims.

Aims of the thesis

The general aims of the present thesis were to investigate the prevalence

of chronic stress among sixteen-year-old adolescents who attended their

first year of high school at high-ranking high schools, to further examine

if factors that have been found to be relevant in the development of

chronic stress among adults also contribute to chronic stress among ado-

lescents, and to investigate the associations between adolescent chronic

stress and sleep-related variables and academic achievement.

The specific aims of the present thesis, which were covered by three em-

pirical studies, were

I. to investigate the prevalence of severe stress symptoms

among adolescents, to better understand the factors that may

contribute to stress symptoms in adolescents and to explore

gender differences.

II. to examine the link between chronic stress and adolescents’

academic achievement.

III. to investigate whether variability in academic achievement

among high school students can be explained by chronic

stress as well as whether a number of sleep-related variables

also influence adolescents’ academic achievement.

3

Theoretical framework

The subsequent section provides a theoretical background to the empiri-

cal studies that this thesis is based upon. To begin with, adolescents, who

are the target group of this thesis, and the challenges they face are de-

scribed. Thereafter, a short introduction to the concept of stress and

chronic stress is presented, followed by a description of burnout, which is

one of the possible health consequences of chronic stress. Next, the litera-

ture on different factors that have previously been related to stress is in-

troduced. Finally, a discourse on the research on chronic stress, sleep, and

academic achievement is provided.

Adolescence and stress

The study of adolescence from a scientific point of view started in the

20th century. Adolescence (Latin: adolescere: to grow up, to nourish)

refers to a transitional period of physical and psychological development,

the individual’s transition from childhood to adulthood (Arnett, 1999).

Typically, adolescence is associated with a number of major changes and

challenges that normally occur as one emerges into adulthood (Eccles et

al., 2008; Frydenberg, 2002; Seiffge-Krenke, 2000).

The changes include physiological changes that are connected with the

onset of puberty and physical growth, affecting sex organs, bodily dimen-

sions in terms of height and weight, and brain structure. Psychological

changes take place, which concern cognitive advances in abstract think-

ing and reasoning capabilities. Personality and identity development is

another key aspect of adolescence, as existential thoughts and questions

of personal values, commitments and expectations begin to receive more

attention and the desire for autonomy and independence becomes more

central. Also, social and contextual changes are happening, concerning,

for example, the parent–child relationship, the importance of the peer

group, intimate relationships, and school transitions. These changes and

challenges are faced by all young people to a greater or lesser extent,

which leads to greater or lesser degrees of stress (Eccles et al., 2008;

Frydenberg, 2002).

4

Other potential stress sources concern the school context, where ado-

lescents usually spend most of their time (Modin & Östberg, 2009;

Modin, Östberg, Toivanen, & Sundell, 2011; Salmela-Aro, Kiuru,

Pietikäinen, & Jokela, 2008). Additionally, adolescents may have to deal

with accumulated stress from increased academic pressure, economic

constraints, interpersonal conflicts with peers or parents or from unfore-

seen major life events that could affect anyone at any time, such as di-

vorcing parents, severe illness, or the death of a significant other. Moreo-

ver, there are a number of general potential stressors which are character-

istic of modern Western societies, such as high degree of individualiza-

tion, which provides personal freedom but also increased uncertainty.

Also high youth unemployment and job insecurity are prevalent stressors

in today’s society. Furthermore, technological advances such as global

communication and instantaneous access to information and social media

provide both advantages but may also be sources for stress (Bremberg,

2006; Eccles et al., 2008; Wiklund, Bengs, Malmgren-Olsson, & Öhman,

2010).

Although the transition from childhood to adulthood basically de-

mands the same from young people today as it did twenty years ago, in

Sweden, several investigations and surveys have pointed to an increase in

stress and mental health problems among adolescents over these years

(Ahrén, 2010; Bremberg, 2006; Socialstyrelsen, 2009). Mental health

problems refer to depressive symptoms, sleeping difficulties, worries, and

psychosomatic symptoms. Based on an exhaustive review of several na-

tional studies, Bremberg (2006) found that worry and anxiety, sleep dis-

turbances, tiredness, and tension and pain were increasing among 16- to

24-year-olds. It has also been found that the increase in psychological

problems and stress-related disorders is more common among girls than

boys (Ahrén, 2010; Bremberg, 2006; Haquist, 2009).

In an investigation among 10- to 18-year-olds, 42% reported that they

felt stressed at least once a week and 21 % reported that they felt stressed

several times per week; in addition, every third adolescent reported suf-

fering from psychosomatic problems such as headaches, stomach aches,

and problems falling asleep (Östberg, 2001). A more recent internet-

based investigation on adolescent psychosomatic health revealed that a

high percentage of participants felt stressed very often or often (47%

among girls and 29% among boys), that psychosomatic health was dete-

riorating among the participants (between 2007 and 2010) and that older

adolescent girls reported psychosomatic symptoms to a high degree

(Friberg, Hagquist, & Osika, 2012).

Skolverket’s (2010), the Swedish National Agency for Education, lon-

gitudinal survey on school children’s attitudes towards school showed

that, in 1997, 25% of high school students reported that they often or

5

constantly felt stressed, reaching a peak of 41% in 2000 and finally level-

ing out at 36% in 2009. In 2009, every other girl and every fifth boy re-

ported feeling stressed in school.

In an investigation among fifteen-year-olds, it was observed that the

number of adolescent girls to report perceiving at least two disturbing

psychosomatic or psychological symptoms per week had increased from

30% to 50% between 1985 and 2001, where it remained since then. The

measurement among boys went from 15% to 30% over this period. When

asked about their self-rated health, in 2009, only 28% of the girls reported

perceiving that their health was good as compared to 49% of the boys

(SFI, 2011).

Furthermore, the number of young people to complain of daytime fa-

tigue and sleep disturbances has increased dramatically in the past dec-

ade, with the prevalence of sleeping problems reaching the same level as

for adults in 2009, between 20% and 25% (Socialstyrelsen, 2009). Ac-

cording to the “Survey of living conditions among children,” a national

longitudinal survey conducted among Swedish children and adolescents

every other year, the percentage of girls with sleeping problems rose from

9% to 13% between 1980 and 1997, and suddenly increased to 27% in

2003. For boys a similar development took place, going from 6% in 1980

to 12% in 1997, and finally to 19% in 2003 (Bremberg, 2006 in reference

to SCB).

As a consequence of these developments, there has been an increase in

the number of young people who are hospitalized for mental health prob-

lems (Ahrén, 2010; Socialstyrelsen, 2009). In fact, in 2006 adolescents

and young adults constituted the largest group of psychiatric patients in

Stockholm (Dalman & Wicks, 2006). The high proportion of young indi-

viduals suffering from stress and stress-related health problems has to be

taken seriously.

Stress theory

Beginning in the early 1920’s, stress research has a short history. It is and

may always be a complex and difficult concept to define. Depending on

the research approach, stress can refer to the direct influence of harmful

stimuli, physical strain, subjectively perceived threats, physiological reac-

tions or psychological states. Common to all definitions of stress, howev-

er, is that it represents an imbalance that is rooted in the need of the indi-

vidual to adapt to environmental changes and demands (Butler, 1993).

6

Stress – a physiological reaction

Hans Selye was the first to speak of stress as a non-specific physical re-

sponse to any demand for change (Selye, 1936). Selye had observed that

certain physical and emotional stimuli (stressors) resulted in physiologi-

cal responses that were intended to restore a physical balance, known as

homeostasis. Based on this observation, he formulated a process model,

called the general adaptation syndrome (GAS) and which consists of

three phases. In a first immediate reaction (the alarm stage), when con-

fronted with a stressor, the body mobilizes energy and resources to re-

spond to the stressor. The second stage is the resistance stage, where the

increased arousal is maintained and followed by adaptation to the stress-

or. However, if the stress does not abate, the body’s resources and energy

deplete, leading to the exhaustion stage in which the risk for negative

health outcomes increases (Selye, 1936, 1978).

The body’s constant striving to maintain homeostasis is a process

called allostasis (McEwen, 2006; Sterling & Eyer, 1988). If stressors

challenge homeostasis, the organism reacts with a so-called allostatic

response. The allostatic, or physical stress response, is characterized by

the activation of two bodily systems, the sympathetic adrenal medullary

(SAM) system and the hypothalamic–pituitary–adrenocortical (HPA)

axis. Acute stress activates the SAM-system, which aims to prepare the

body for dealing with a threat through what Cannon (1922) coined as the

“fight-or-flight” response. Accordingly, cardiovascular activity and the

secretion of epinephrine and norepinephrine are stimulated (Folkow,

1997; Lundberg 2005). The reaction is immediate, short lived, and adap-

tive in order to re-establish homeostasis. Parallel to this, the HPA-axis

also becomes activated, which stimulates the release of cortisol from the

adrenal cortex. Cortisol increases gradually after stimulation of the HPA-

axis, indicating that the reaction is less immediate. Moreover, the activa-

tion of the HPA-axis is associated with more affective stress and with the

long-term adaption of an organism to stress (Sapolsky, Romero, &

Munck, 2000).

The physiological reaction described above is similar for all mammals

when they are facing an immediate physiological threat that could cost

one’s life if an organism does not react by either fighting or fleeing

(Sapolsky, 2004).

Psychological stress

In humans, psychological states also have a role in activating the physio-

logical stress reaction. An individual’s evaluation of a situation as stress-

ful or not affects whether a situation evokes stress or not. Whether a situ-

7

ation is experienced as stressful is dependent on earlier experiences, af-

fective states, personality, available resources, and the interpretation of

events.

According to the transactional model, stress is a dynamic process in-

volving an interaction between the individual and the environment (Laza-

rus, 1993, 1999; Lazarus & Folkman, 1984). The process whereby indi-

viduals appraise their situation is therefore central. It involves a primary

appraisal where the relevance of the situation for one’s well-being is

evaluated in terms of the potential threat or challenge that is posed. It is

not only negative events but also positive events that can set this process

in motion, as both may involve the need to adapt to changing or new cir-

cumstances and therefore evoke stress. This is followed by secondary

appraisal, another cognitive process, where the internal and external re-

sources for handling the situation are evaluated (Lazarus, 1993; Lazarus

& Folkman, 1984). Thus, stress is occurring when there is an imbalance

in terms of the actual and/or perceived resources not being adequate to

counter actual and/or perceived demands (Butler, 1993; Lazarus &

Folkman, 1984).

Coping is defined as an individual’s behavioral or cognitive efforts to

handle stress-evoking internal and external demands (Lazarus &

Folkman, 1984). Usually a distinction is made between active, problem-

focused coping, which aims at addressing the sources of stress, and pas-

sive, avoidant or emotion-focused coping, which aims at regulating dis-

tressing emotions. The effectiveness and adaptability of each type de-

pends on the nature of the stressor (Butler, 1993; Lazarus & Folkman,

1984).

Taken together, the research and theory suggests that there is a con-

stant interplay between physiological, psychological, and environmental

factors that influences whether stress is elicited or not, which (if any)

stress symptoms are evoked, and how the individual reacts to stress. It is

this complex interplay of multiple factors, along with the variation be-

tween individuals that makes it difficult to definitively explain the causes

and effects of stress processes. It is, however, well understood that pro-

longed stress and strain, also called chronic stress, eventually have a neg-

ative impact on health and may cause serious mental and physical diseas-

es (Perski, 2006; Theorell, 2004).

Chronic stress and burnout

The allostatic response is an important physical reaction that protects the

body from external and internal stress. It usually decreases together with

decreasing stress, but if the imbalance between spending and regaining

8

energy persists over a long period of time, allostatic load may result

(McEwen, 2006; McEwen & Stellar, 1993). More specifically, allostatic

load occurs when too few essential anabolic processes are taking place,

which implies a lack of energy regeneration. Allostatic load is often de-

scribed as the wear and tear on the body that results from chronic overac-

tivity of the allostatic system.

This kind of prolonged stress is then referred to as chronic stress,

which is associated with severe stress symptoms such as somatic symp-

toms, emotional and physical exhaustion, and sleep and cognitive diffi-

culties. Chronic stress and its associated symptoms eventually lead to a

depletion of the body’s energy. The degree to which this occurs has been

associated with a stage of exhaustion that carries with it an increased

susceptibility to negative health outcomes, such as a heightened risk for

cardiovascular morbidity, diabetes, immunosuppression, and affective

disorders (Sapolsky, 2004). Not least of all, one of these possible nega-

tive health outcomes is burnout.

To date, there is no generally accepted definition of burnout, which

constitutes a problem for science and intervention attempts (Weber &

Jaekel-Reinhard, 2000). The term burnout has been used in different

ways in different contexts. Freudenberger (1974) was the first to describe

burnout from a clinical perspective, describing it in terms of physical and

emotional symptoms. Burnout has also been defined as a work-related

multidimensional syndrome, most notably by Maslach and her colleagues

(Maslach 2001; Maslach & Jackson, 1981; Maslach & Leiter, 1997).

From this perspective, burnout refers to a psychological condition in

which a sequential progression of emotional exhaustion, depersonaliza-

tion, and reduced personal accomplishment is experienced in relation to

an occupational setting (Maslach, Schaufeli, & Leiter, 2001). Coming

from another perspective, Pines and her research associates have extend-

ed the definition of burnout to potentially apply to situations beyond the

occupational setting that are emotionally demanding, where an individu-

al’s sense of importance and influence are strained, and decreases in self-

esteem can eventually result (Pines & Aronson, 1988; Pines & Keinan,

2005). According to Hallsten, Josephson, and Torgén’s (2005) burnout

theory, performance-based self-esteem contributes to the process of burn-

ing out. Cherniss (1980), who conceives of burnout as entailing further

consequences, describes it as a process that starts with a perceived imbal-

ance between demands and resources, followed by a lack of adequate

coping strategies, and then an experiencing of disturbing symptoms such

as tension, anxiety, and exhaustion, which finally leads to negative

changes in attitude and behavior.

In the context of this thesis, the term burnout refers to the definition of

Melamed, Kushnir, and Shirom (1992). They conceptualized burnout as

9

an individual’s negative affective response to chronic stress, a response

that comprises experiencing severe stress symptoms in three areas: emo-

tional exhaustion, physical exhaustion, and cognitive difficulties

(Melamed et al., 1992; Melamed, Shirom, Toker, Berliner, & Shapira

2006; Shirom, 2003). Emotional exhaustion refers to experiencing a lack

of energy in relation to social interaction, while physical exhaustion man-

ifests itself in tension and an inability to accomplish everyday tasks.

Cognitive difficulties are characterized by decelerated cognitive process-

es, impaired memory and concentration problems. In this definition of

burnout, the individual’s initial unsuccessful attempts to cope with stress,

and successive increasing efforts to protect resources, gradually lead to

more and more stress symptoms, including physical exhaustion, concen-

tration problems, listlessness, and tension. According to Shirom (2003),

the core feature of burnout is “the gradual depletion over time of individ-

uals’ intrinsic energetic resources” (p. 245), due to long-term stress expo-

sure. The prevalence of severe stress symptoms can be measured by

means of the Shirom-Melamed Burnout Questionnaire (Lundgren-

Nilsson, Jonsdottir, Pallant, & Ahlborg, 2012; Melamed et al., 1992).

This last definition of burnout fits with the diagnostic criteria of ex-

haustion syndrome, also called clinical burnout, which, in Sweden was

designated as a stress-related disease in 2003, and in 2005 was added to

the ICD-10 (code F43.8) as an established medical diagnosis (Schaufeli,

Leiter, & Maslach, 2009; Socialstyrelsen 2003). The criteria include dif-

ficulties concentrating, reduced ability to cope with stress, emotional

distress, and sleep disturbance as well as somatic symptoms, such as

muscle pain, palpitations or dizziness, which cause significant clinical

suffering for the individual (Armon, Shirom, Shapira, & Melamed, 2008;

Jonsdottir et al., 2012; Schaufeli et al., 2009; Socialstyrelsen, 2003). As

exhaustion syndrome is considered to be the result of complete energy

erosion, recovery only comes slowly even after the energy draining stress

source has disappeared. It is among the most common diagnoses for long-

term sick leave among the Swedish adult working population (Lidwall,

2010; Socialstyrelsen, 2003). It is a serious disease that carries with it

individual suffering and societal costs.

Chronic stress among adolescents

As mentioned above, besides causing individual suffering, chronic stress

increases the risk for stress-related ill-health in the long run (Theorell,

2004). There may be a substantial risk that today’s adolescents who expe-

rience serious stress-related symptoms over a prolonged time will become

10

tomorrow’s adult patients at stress clinics (Perski, 2006). In order to pre-

vent adolescents from ill-health due to chronic stress, it is important to

increase our understanding of chronic stress and the factors that may elic-

it chronic stress among adolescents. In the present thesis, the contribution

of factors that have been found to be relevant in the experiencing of

chronic stress among adults are examined in more detail, namely, subjec-

tive psychosocial conditions, self-esteem, lifestyle routines, and sleep

(Perski, 2006).

Because stress-related health problems emerge over an extended peri-

od of time, a fully developed exhaustion syndrome might not be expected

to be prevalent among younger populations (Thoreson & Eagelston,

1983). Therefore, an investigation of the more immediate associations

between chronic stress and another relevant life domain, i.e., academic

achievement, was of interest in the present thesis.

Factors that may contribute to chronic stress among

adolescents

Psychosocial conditions – demands, control, and social support

The job demand-control-support model, which is derived from research

among the adult working population, can and has been applied to adoles-

cents, who “work” in schools (Gillander-Gådin & Hammarström, 2000;

Modin et al., 2011). According to the model, perceived high work de-

mands and low influence (control; decision latitude) over one’s work

situation are positively associated with elevated levels of stress (Karasek

& Theorell, 1990; Theorell, 1996) and chronic stress (Lindblom, Linton,

Fedeli, & Bryngelsson, 2006). It also poses that a higher risk of psycho-

logical strain and physical illness is to be expected among individuals

who face high demands but who perceive having little control or social

support for handling these demands (Karasek & Theorell, 1990; Theorell,

1996).

The demands that school places on students are comparable to those

faced by working adults (e.g., with regard to high workload, deadlines,

and performance) (Gillander-Gådin & Hammarström, 2000; Modin et al.,

2011). According to the latest results of the “Survey of living conditions

among children,” the perceived demands of adolescents were most often

connected to school-related work, such as tests and homework (SCB,

2007; 2012). In fact, 60% of high school students reported feeling

stressed over school-related tasks and academic demands (50% among

boys and 71% among girls). Furthermore, 55% reported that they felt

stressed over the high demands they placed on themselves (68% among

girls and 42% among boys). Fifteen percent felt stress over their parents’

11

demands and 32% felt stress over their teacher’s demands and expecta-

tions (SCB, 2012), which is in line with the findings of Huan, Lay-See,

Ang, and Wan-Har (2008), who showed that high school students’ aca-

demic stress is both related to the demands they put on themselves and to

external demands from their parents.

It has also been found that students who rated school-related demands

as one of their main sources of stress were more likely to worry about

their studies and felt overwhelmed by their workload (Huan et al., 2008).

Ollfors and Andersson’s (2007) study among Swedish youths showed

that the combination of greater commitment to school work and perceiv-

ing that demands on school performance were high were associated with

greater stress. Worries over school achievement and feeling that school

work is too demanding as well as the pressure to achieve good grades

were shown to be particularly associated with psychosomatic symptoms

(Murberg & Bru, 2004).

Concerning perceived control, Modin et al. (2011) found that high lev-

els of control could mitigate the negative impact of high levels of per-

ceived school-related demands on subjective health among fifteen-year-

old adolescents. Based on the results of interview studies, Bremberg

(2006) concluded that adolescents associated stress mainly with high

academic demands and lack of control over school-related work, in the

form of, for example, unclear instructions and multiple tasks. The inter-

viewed students mentioned that high workloads forced them to frequently

skip regenerative or social activities.

While some studies indicate that there are no differences between girls

and boys when it comes to the degree of stress they perceive over school-

related demands (deAnda et al., 2000; Seiffge-Krenke, Aunola, & Nurmi,

2009), others point out that females report experiencing significantly

more stress symptoms due to school-related worry than males (Murberg

& Bru, 2004). According to Dedovic, Wadiwalla, Engert, and Pruessner

(2009), females were found to perceive less control than males, which, as

they posited, was due to differences in socialization processes. Compared

to boys, girls are more closely supervised and are not granted as much

autonomy from adults and thus have fewer opportunities of exerting in-

fluence (Dedovic et al., 2009).

As the experiencing of high demands increases during adolescence,

social support and interpersonal relationships tend to deteriorate. Murberg

and Bru (2004) emphasized the fact that school is the primary social

meeting place for adolescents and where the number and quality of inter-

actions with peers have a crucial impact on their well-being. Supportive

relationships are considered to be a buffer against stress (Haraldsson,

2010; Langstedt, Asplund, & Gillander-Gådin, 2009; Rudolph, 2002).

Moreover, because social relationships in general can be a cause for con-

12

flicts, they constitute a potential source of increased stress symptoms,

especially among adolescent girls (Byrne, Davenport, & Mazanov 2007;

Rudolph, 2002). Brolin-Låftman and Östberg (2006) found that strained

relationships with both parents and peers had a stronger impact on health

among adolescents than did supportive relationships. Also, perceived lack

of social support and perceived social isolation have been associated with

an increased risk for stress and affective problems (Brolin-Låftman &

Östberg, 2006; Hankin, Mermelstein, & Roesch, 2007). With increasing

age, adolescents tend to more often turn to their friends rather than to

their parents for social support (Aldwin, 2007). Especially for girls, sup-

portive peer relationships have been shown to be important (Langstedt et

al., 2009; SCB, 2011). Females have been found to be exposed to higher

levels of interpersonal stress than the males and to react more negatively

when experiencing social stressors (Murberg & Bru, 2004; Rudolph,

2002; Stroud, Salovey, & Epel, 2002). It is the girls rather than the boys

who tend to blame themselves for problems in relationships. Moreover,

girls are usually more occupied with worries and concerns about others’

well-being (Murberg & Bru, 2004).

In sum, recent research indicates that perceived demands as well as re-

sources such as perceived control and social support play an important

role in the experience of stress. However, it is not only the perception of

the psychosocial conditions that is associated with stress but also the per-

ception of one’s self.

Self-esteem

Disturbances in self-esteem are believed to essentially contribute to the

high prevalence of stress and stress-related health complaints (Birndorf,

Ryan, Auinger, & Aten, 2005; Rhee, Holditch-Davis, & Miles, 2005;

Stinson et al., 2008). Even though there are several different theories

about self-esteem, all of them are based on the concept that self-esteem

corresponds with individuals’ perception of their own value. The concep-

tion of self-esteem that is used in the present thesis is referred to as global

self-esteem, which is defined as one’s overall positive or negative attitude

towards the self (Pyszczynski, Greenberg, Solomon, Arndt, & Schimel,

2004; Rosenberg, 1972; Tarafodi & Swann, 1995). High global self-

esteem is indicated by positive self-evaluations, characterized by having

an accepting attitude towards one’s self. In contrast, low global self-

esteem is indicated by negative self-evaluations, characterized by self-

doubts and self-rejection (Baumeister, Campbell, Krueger, & Vohs,

2003). It has been proposed that every person acts according to a univer-

sal human need to protect their feelings of being valuable and increase

13

their sense of worth (Pyszczynski et al., 2004; Rosenberg, Schooler, &

Schoenbach, 1989; Schütz, 2003).

Self-esteem is a central aspect of humans’ self-understanding and it is

essential for psychological well-being and functioning. During adoles-

cence, however, it dips (Moksnes, Moljord, Espnes, & Byrne, 2010; Rob-

ins & Trzesniewski, 2005). Adolescent decline in self-esteem is thought

to be due to an increase in self-consciousness and in the ability to think

abstractly about one’s self (Moksnes et al., 2010). Leaving behind the

childlike, unrealistically positive self-view, external feedback and social

comparison are brought into the equation when adolescents evaluate their

self-worth. Many of the changes that come along with adolescence (relat-

ed to puberty, body image, academically more challenging environments,

and more complex social and intimate relationships) pose further chal-

lenges to self-esteem (Robins & Trzesniewski, 2005).

High global self-esteem has been identified as a crucial factor in pre-

venting stress and mental health problems such as depression (Avison &

McAlpine, 1992; Major, Barr, Zubek, & Babey, 1999; Rector & Roger,

1997), while low global self-esteem has been shown to be associated with

stress symptoms and ill-health (Birndorf et al., 2005; Kernis, 2006;

Kivimäki & Kalimo, 1996). In a prospective study among young adults,

high self-esteem was shown to be a buffer against emotional exhaustion

and was positively associated with personal accomplishments ten years

later (Salmela-Aro & Nurmi, 2007).

Even when experiencing the same objective situation, the cognitive

and affective reactions of individuals with high and low self-esteem have

been found to differ from each other (Campbell & Lavallee, 1993). Stud-

ies suggest that high self-esteem may foster the individual’s self-efficacy,

which is the belief in one’s abilities and competence to handle stressful

situations (Bandura, 1997, 2000; Dumont & Provost, 1998). Other char-

acteristics of those with high self-esteem, according to Locke, McClear,

and Knight, (1996), is that they tend to appraise stressful events as chal-

lenges rather than threats and experience less fear of failure. It is there-

fore perhaps not surprising that individuals with high self-esteem have

also been found to use more adequate coping strategies (Moksnes et al.,

2010). In contrast, Chapman and Mullis (1999) observed that adolescents

with low self-esteem tended to ventilate their feelings and avoid problems

rather than directly dealing with difficult, stressful situations. Hence, they

tended to utilize emotional, avoidant coping strategies rather than active

problem-solving strategies.

Individuals low on self-esteem are more insecure about themselves

and thus their self-beliefs fluctuate over time and depend on the circum-

stances, which tends to make them more sensitive and reactive to their

social environment. Their self-view and their mood are highly dependent

14

on external feedback. Both the negative and the positive feedback they

encounter are crucial to shaping how they feel about themselves (Camp-

bell & Lavallee, 1993). High self-esteem individuals, on the other hand,

are less disturbed when facing a particular stressful situation because they

hold a consistent self-view which does not get disrupted so easily by

changing circumstances (Spencer, Josephs, & Steele, 1993).

In their meta-analysis on self-esteem among adolescent girls and boys,

Kling, Shibley-Hyde, Showers, and Buswell (1999) revealed that, even

though the overall differences were small, boys scored higher on global

self-esteem than girls, with the largest effect emerging in late adoles-

cence. In a study by Harter (1993), it was found that girls’ global self-

esteem in general was lower than that of boys.

Global self-esteem has to be distinguished from lower order factors

that represent contingent aspects of self-evaluation, also called domain-

specific self-esteem (Crocker, 2002; Crocker & Wolfe, 2001; Kling et al.,

1999; Major et al., 1999), where the target of the evaluation is not the self

as a whole but a specific domain of the self. Harter’s (1993) research

among adolescents also highlights a contingent component of self-

esteem. As stated by her, perceived competence in domains which the

individual perceives as important as well as the approval by significant

others are essential determinants of adolescents’ self-esteem. Individuals

with low self-esteem usually do not receive sufficient approval or only

receive contingent social approval, which depends on the fulfillment of

external expectations (Harter, 1993).

One example of contingent self-esteem, which has been shown to play

a crucial role in the development of chronic stress by increasing the risk

of psychological and physiological exhaustion, is performance-based

self-esteem (Blom, 2012; Hallsten, Bellaagh, & Gustafsson, 2002;

Hallsten et al., 2005; Hallsten, Voss, Stark, Josephson, & Vingård, 2011;

Perski, 2006). According to Hallsten et al. (2005), performance-based

self-esteem relies on the belief that one’s self-worth equals one’s perfor-

mance and is a prerequisite for burnout.

Typically, individuals with high performance-based self-esteem have a

strong need to prove their competence and to exert maximum effort in

order to feel worthy. Because failures and setbacks are particularly detri-

mental to the self-esteem of these individuals, they put a great amount of

effort into performing well and striving for success (Hallsten et al., 2005).

Stress then develops as a result of one’s self-worth being threatened by

the risk of not succeeding because failure would be tantamount to not

being good enough. Consequently, deriving one’s self-esteem from ex-

ternal sources, such as performance outcomes and recognized success,

means not only that it is vulnerable, but also that the individual is ex-

posed to a higher risk for negative health outcomes (Blom, 2011; John-

15

son, 1997; Johnson & Forsman, 1995). Performance-based self-esteem

has been found to be more prevalent among women (Blom, 2012;

Hallsten et al., 2005). Also, in an interview study among adolescent girls,

it was observed that they perceived their value as a person to be highly

related to their accomplishments (Wiklund et al., 2010). Ruble, Greulich,

Pomerantz, and Gochberg (1993) showed that women tend to be more

concerned about future success and that they show more maladaptive

attributions for success and failure, which prevents them from feeling

content with themselves and their performance. It is possible that their

greater concern with success is due to having high performance-based

self-esteem.

In conclusion, self-esteem, the overall attitude that individuals have

towards themselves, influences their appraisals of situations, the actions

they take, and, consequently, their experience of stress. The next section

focuses on the things people actually do on a daily basis, because, accord-

ing to research on lifestyle habits, behavioral routines have also been

shown to be associated with stress, well-being and health.

Lifestyle factors

Lifestyle factors, such as eating habits and physical exercise, often take

root in adolescence and are difficult to change later in life. While a

healthy lifestyle can help prevent physical stress reactions, an unhealthy

lifestyle has been associated with greater susceptibility to stress and other

negative health outcomes (Lien, 2006; Sundblad, Jansson, Saartok,

Renström, & Engström, 2008; Wiles et al., 2008). Breakfast skipping, for

example, has been associated with other health compromising behaviors

(Keski-Rahkonen, Kaprio, Rissanen, Virkkunen, & Rose, 2003). Several

studies have found positive associations between physical exercise and

physical and psychological well-being (Nabkasorn et al., 2005; Wiles et

al., 2008). At least one hour of moderate physical activity per day seems

to be necessary in order to maintain health (Wiles et al., 2008). Physical

exercise has also been found to work against depressive symptoms

among adolescent females (Nabkasorn et al., 2005). In a study by

Sagatun, Sogaard, Bjertness, Selmer, and Heyerdahl (2007), the physical-

ly active sixteen-year-olds reported better well-being in terms of mental

health than their physically inactive counterparts. However, these results

were not found to be consistent at follow-up three years later. Earlier

research has shown that adolescent girls skip breakfast more often, smoke

more frequently, and engage in physical exercise less often than boys

(Östberg, 2001). Moreover, this study found that unhealthy lifestyle hab-

its become more common with increasing age.

16

Besides the investigated associations between lifestyle, stress, and

health, an essential factor that has come to play a crucial role in research

on stress and burnout is disturbed sleep.

Sleep and recovery

Sleep is an antagonist to stress; it is when anabolic, energy providing

processes occur that prevent wear and tear to the body (Ekstedt, 2005). It

is essential for brain functioning, health, and overall well-being. Dis-

turbed sleep and impaired recovery are among the most important and

early symptoms of clinical burnout, as they play key roles in the depletion

of energy (Ekstedt et al., 2006; Shirom, Melamed, Toker, Berliner, &

Shapira, 2005; Söderström, 2012; Söderström, Ekstedt, Åkerstedt, Nils-

son, & Axelsson, 2004; Sonnenschein, Sorbi, VanDoornen, Schaufeli, &

Maas, 2007). Armon et al. (2008) found a bidirectional relationship be-

tween burnout and insomnia, in that they contributed to each other’s de-

velopment and intensification over time. Because poor sleep quality,

sleep deprivation, and sleep disturbances have been associated with

chronic stress among adults (Armon et al., 2008; Ekstedt, 2005; Lund,

Reider, Whiting, & Prichard, 2010) it is essential to take sleep and recov-

ery into account as relevant factors when studying chronic stress among

adolescents.

Recent investigations show that many adolescents do not obtain an ad-

equate amount of sleep (Dagys et al., 2012; Fuligni & Hardway, 2006;

Roberts, Roberts, & Doung, 2009; Saxvig, Pallesen, Wilhelmsen-

Langeland, Molde, & Bjorvatn, 2012). In fact, the number of young peo-

ple who complain of daytime fatigue and sleep disturbances has increased

dramatically in the past decade and is now at the same level as for adults

(Socialstyrelsen, 2009). In research on adolescent sleep and its associa-

tions to stress and well-being, sleep disturbances and insufficient sleep

have been found to affect daily functioning by negatively impacting aca-

demic performance and social interaction, an effect that can in turn give

rise to stressful experiences (Bernert, Merrill, Braithwaite, VanOrden, &

Joiner, 2007). Looking at it from another direction, stress has been found

to interfere with individuals’ ability to obtain adequate sleep, according to

Fuligni and Hardway (2006). Their findings showed that stressful de-

mands during the day were associated with less sleep during the night and

higher levels of anxiety, depressive feelings, and daytime fatigue during

the subsequent day. In another study, adolescent sleeping problems have

been shown to be associated with stress, decreases in social functioning,

and reduced quality of life (Lund et al., 2010), while yet another found

poor sleep quality and insufficient sleep quantity to be associated with

health complaints (Pilcher, Ginter, & Sadowsky, 1997). Moreover, occa-

17

sional and persistent sleeping problems have been associated with con-

centration problems (Ipsiroglu, Fatemi, Werner, Paditz, & Schwarz,

2002).

From a behavioral perspective, sleep is equivalent to “going to sleep,”

which implies a reversible perceptual disengagement from the environ-

ment (Ekstedt, 2005). However, individuals cannot force themselves de-

liberately to sleep; there are several physiological factors involved, as

described by several studies (Ekstedt, 2005; Söderström, 2012). When it

comes to adolescents, it is essential to keep in mind that their sleep is

opposed by biologically based phase changes in their circadian rhythm

during puberty, which makes it physically harder to maintain earlier bed-

times (Auger, Burgess, Dierkhising, Sharma, & Slocumb, 2011;

Brandalize, Felden-Pereira, Leite, Lorenzi-Filho, & Mazzilli-Louzada,

2011; Randler, 2011; Wolfson & Carskadon, 2003). This is compounded

by the fact that adolescents tend to wish to stay up later to engage in so-

cial and other stimulating activities and therefore choose to go to bed

later (Dahl & Lewin, 2002). In more conceptual terms, a reorientation, or

phase shift, towards more evening activity, or eveningness, commonly

occurs during adolescence, which is presumably caused by both biologi-

cal and social factors (Besoluk, Önder, & Deveci, 2011; Roenneberg,

Wirz-Justice, & Merrow, 2003; Wittmann, Dinich, Merrow, &

Roenneberg, 2006). In general, male adolescents have been found to be

more evening oriented than female (Randler, 2011).

Evening chronotypes are more active later in the day than intermediate

or morning chronotypes. With school days starting early, a problem arises

for evening chronotypes when their typically late bed times and required

early wake-ups combine to lead to less sleep and create an increasing

sleep debt over the course of the school week (Auger et al., 2011;

Mecacci & Rocchetti, 1998; Taylor, Clay, Bramoweth, Sethi, & Roane,

2011). Consequently, on average, evening chronotypes usually get less

sleep per school night compared to morning chronotypes (Roenneberg et

al., 2003).

Moreover, evening chronotypes are at higher risk for experiencing a

phenomenon known as social jetlag (Roenneberg et al., 2003; Zimmer-

mann, 2011). Social jetlag refers to a pattern that implies a drastic varia-

bility between a person’s weekday (school day) and weekend sleeping

schedules. It refers to the individual’s tendency to increase the weekend

sleeping time in order to compensate for a sleep debt accumulated during

the weekdays, often in combination with staying up even later and sleep-

ing in. This shift in sleeping times over the weekend results in a disturb-

ance in circadian rhythms, which then makes it difficult to get up at the

regular times during the school week (Dahl & Lewin, 2002; Roenneberg

et al., 2003; Wittmann et al., 2006). For students returning to school after

18

the weekend or days off, the symptoms of this can be similar to jetlag, as

they may experience severe tiredness, irritability, lack of energy, lack of

appetite, and problems concentrating.

Taken together, sleep and recovery have previously been found to be

of particular relevance to adolescent stress and well-being. Previous re-

search has focused on sleep-related factors and their impact on academic

achievement among adolescents, which is further referred to in the next

section. Because the rather new concept of social jetlag has not been ex-

haustively investigated, another purpose of the present thesis was to take

a closer look at its associations with adolescent stress and academic

achievement.

Chronic stress, sleep, and academic achievement

In Sweden, school is compulsory for children between the ages of seven

and sixteen. Following this, a minority of adolescents choose to enter

directly into the labor market, while about 90% choose to either pursue

vocational training or enroll in an academic track in high school (usually

a three-year education) (Skolverket, 2010). While continuing on to high

school is optional, its successful completion is necessary in order to get

accepted to tertiary education, which usually also involves having com-

pleted an academic track. If the goal is to enter a high-ranking tertiary

educational program, good final grades, which are based on students’

total academic performance throughout high school, are crucial for selec-

tion. About 30% of high school students in Sweden and almost 40% of

high school students in Stockholm in particular do not finish their high

school education (Ahrén, 2010; KFA, 2009).

Academic achievement can be considered to be an important domain

in the life of high school students, as it profoundly affects young people’s

transition into adulthood in terms of access to higher education and voca-

tional careers. Academic achievement is also considered to be a reliable

indicator for future health and well-being (Brolin-Låftman & Modin,

2012; Schmidt & Padilla, 2003).

Chronic stress symptoms, such as emotional and physical exhaustion

as well as cognitive difficulties, might complicate the accomplishment of

academic tasks, such as exams, participation in school lessons, project

work, and homework, which typically are the basis for grades and aca-

demic achievement. It would therefore not be surprising if chronic stress

was related negatively to academic achievement. However, little attention

has been paid thus far to the effects that the experiencing of chronic stress

has on adolescents’ academic achievement.

19

There are, however, several neuropsychological investigations which

suggest that chronic stress has a considerable negative association with

brain functioning throughout a person’s lifespan (Marin et al., 2011). This

functioning should be important in the school environment as a number

of factors are crucial to performing school-related tasks, including cogni-

tive processes regarding learning, attention, and concentration, as well as

one’s capacity for complex thinking, working memory, problem solving,

and creativity.

During adolescence, the prefrontal cortex, the most evolved brain re-

gion that serves higher order cognitive abilities, such as executive func-

tioning, is still developing (Arnsten, 2009; Lupien, McEwen, Gunnar, &

Heim, 2009). It is also the brain region that is most sensitive to the detri-

mental effects of stress exposure. In fact, in otherwise healthy individu-

als, chronic stress has been found to disrupt working memory, problem

solving, creativity and other prefrontal cortex-related processes (Liston,

McEwen, & Casey, 2008). Liston et al. (2009) compared the performance

of twenty university students, who were experiencing prolonged psycho-

social stress for four weeks as they prepared for a major academic exami-

nation, with twenty control students who did not perceive stress. Experi-

encing psychosocial stress selectively impaired attentional control and

disrupted attention shifting.

Moreover, prolonged stress implies an accumulation of neurocognitive

deficits over time (Arnsten, 2009). The effects of chronic stress on the

brain may also explain the cognitive impairments of clinical burnout pa-

tients. In fact, cognitive difficulties are included in the definition of burn-

out (Melamed et al., 1992; Socialstyrelsen, 2003) and have been found to

be among the most pronounced and handicapping symptoms among clin-

ical burnout patients (Jonsdottir, et al. 2012).

As indicated by the studies described above, chronic stress seems to

have an impact on cognitive functioning and thus on cognitive perfor-

mance. However, psychological studies on this matter are rare. Kaplan,

Liu, and Kaplan (2005) showed that stress was linked with both emotion-

al adjustment and with academic performance among adolescents. A

bidirectional negative relationship between stress and academic achieve-

ment has also been observed (Gustafsson et al., 2010). In this study, in-

ternalized problems, such as stress, anxiety, and depressive mood, were

associated with negative effects on academic achievement; poor academ-

ic achievement, in turn, was shown to be associated with mental health.

While the relation between self-reported chronic stress symptoms and

academic achievement is rarely investigated, a growing number of studies

have discovered the importance of sleep and recovery for processes of

learning, memory, and academic achievement (Dahl & Lewin, 2002;

Walker, 2008; Wolfson & Carskadon, 2003). Insufficient sleep duration

20

has been linked to decreases in academic performance (Beebe, Rose, &

Amin 2010; Kelly, Kelly, & Clanton, 2001; Lund et al., 2010; Roberts et

al., 2009; Wolfson & Carskadon, 2003). In their longitudinal study

among 4175 adolescents, Roberts et al. (2009) found that amount of sleep

was related to alertness during the day and, consequently, the ability to

concentrate and perform school-related tasks. Despite finding an associa-

tion between sleep quality and school performance, Meijer, Habekothe,

and Wittenboer (2000) found that objective sleep duration did not have

any impact on school performance. Also, the experience of sleeping diffi-

culties and/or sleep quality have been associated with academic achieve-

ment (Buboltz, Brown, & Soper, 2001; Curcio, Ferrara, & DeGennaro,

2006; Fuligni & Hardway, 2006; Lund et al., 2010; Saxvig et al., 2012).

Moreover, academic achievement among evening chronotypes was found

to be worse compared to morning chronotypes (Besoluk et al., 2011;

Gomes, Tavares, & deAzevedo, 2011; Howell, Jahrig, & Powell, 2004;

Wolfson & Carskadon, 2003; Yeung, Chung, & Cy Chan, 2008). Howev-

er, research on the association between the consequences of not going to

bed at a regular time throughout the entire week, i.e., social jetlag, and

academic achievement are lacking.

21

Methods

The present thesis is based on three empirical studies which make use of

questionnaire data that have been collected among students from Swedish

high schools within the project “Stress prevention in high school” (Perski,

Schraml, Grossi, Makower, & Ivarsson, 2010). Collaboration was estab-

lished with three academically high-ranking high schools from suburban

areas of Stockholm. The samples are described below, followed by a

description of the measures and statistical analyses.

Participants and procedure

In all of the studies, questionnaire data were collected among sixteen-

year-old (+/− one year) high school students during their first year in high

school (in February), after approval by the local ethics review board. All

participants were students in an academic high school track. Prior to the

data collection, students and parents were informed in writing about the

study’s aims and procedures and their consent was requested. Participa-

tion was voluntary. The data collection was organized in collaboration

with the school staff. During a designated school lesson, all of the partic-

ipating students answered the questionnaires individually and in silence

in the presence of a school staff member. The average completion time

for the questionnaires was approximately thirty minutes. In all three stud-

ies, missing and incomplete data were deleted. In Study II and Study III,

participants were asked to answer questionnaires on two occasions, at the

age of sixteen in their first year of high school and again two years later

at the end of high school.

Measures

The data used in all three studies are based on a set of established scales

and questions that were collectively distributed to the participants as a

“stress screening questionnaire.” First, the Shirom-Melamed Burnout

Questionnaire (SMBQ) is described, which was used to assess severe

22

stress symptoms throughout all three studies. Thereafter, the other applied

scales are presented in alphabetical order. Finally, single items are men-

tioned, followed by a description of the applied indicators for academic

achievement, i.e., final grades.

To measure the prevalence of severe stress symptoms and chronic

stress among adolescents, the Shirom-Melamed Burnout Questionnaire

was used, which contains 22 items (graded 1–7) that measure different

facets of chronic stress by focusing on the depletion of an individual’s

energy resources (Melamed et al., 1992). Respondents were asked to rate

the degrees of physical, emotional, and psychological stress symptoms

which they were experiencing (e.g., “I feel physically exhausted”; “I have

difficulties concentrating”; ”I feel restless”; “I feel like I have had

enough”) (Shirom & Melamed, 2006). High scores indicate an intense

degree of perceived stress symptoms. An overall chronic stress or burnout

index can be calculated. Throughout this thesis, as in previous studies, a

rating of 4 or above is considered to be indicative of serious stress symp-

toms (Grossi, Perski, Evengård, Blomkvist, & Orth-Gomér, 2003). The

indications of chronic stress differed among the studies. In Study I, the

term chronic stress was used to describe the prevalence of extremely pro-

nounced stress symptoms (indicated by a rating of 5 or above), which

have otherwise only been observed in clinical burnout patients and there-

fore were interpreted as indicative of prolonged stress (Perski, 2006). In

Study II, chronic stress was indicated by the prevalence of severe stress

symptoms at more than one time point. In Study III, the mean value of

perceived stress symptoms from two time points was used to indicate the

prevalence of severe stress symptoms. The Cronbach’s α coefficient for

this scale was determined to be between 0.90 and 0.94 for the different

studies.

Perceived demands, control, and social support, which are important

stress-related variables according to Karasek and Theorell (1990), were

measured by 17 items (graded 1–4) in an adapted version of the question-

naire (instead of referring to the workplace, the questions referred to high

school students’ life situation). Demands were measured using an index

of five items concerning qualitative and quantitative demands, such as

time pressure and conflicting demands (e.g., “Do you feel life is too de-

manding?”; “Are there many conflicting demands in your life?”). High

scores indicated that the perceived demands were high. The Cronbach’s α

coefficient was between 0.80 and 0.84 for the different studies. The con-

trol index included six items to capture such areas as skill discretion and

authority over decisions (e.g., “Can you make decisions about your life

on your own?”; “I constantly need to learn new things in order to deal

with my life”). Low scores indicated a lack of perceived control. The

Cronbach’s α coefficient was between 0.30 and 0.54. Social support,

23

which focuses on the social climate in school, was measured by an index

of 6 items (e.g., “I get along well with my schoolmates”; “There is a good

sense of togetherness in my class”) (Theorell, 1996). High scores indicat-

ed that social support was high. The Cronbach’s α coefficient was be-

tween 0.70 and 0.76 for the different studies.

Sleep disturbances/difficulties were examined by a nine questionnaire

index (Study I) and an eight question index (Study II and Study III)

(graded 1-5) taken from the Karolinska sleep questionnaire (KSQ) (e.g.,

“I have difficulties falling asleep”; “I do not feel well-rested when I wake

up in the morning”; “I experience disturbed sleep”) with lower scores

indicating more pronounced sleeping difficulties (Kecklund & Åkerstedt,

1992). The Cronbach’s α coefficients were 0.67 (Study III), 0.71 (Study

II), and 0.73 (Study I).

The Performance-Based Self-esteem scale (PBS scale) (Hallsten et al.,

2005) consists of four items (graded 1–4) and was used in Study I and

Study II to assess to what degree the respondents’ self-esteem was based

on performance and success (“I think I sometimes try to prove my worth

by being competent”; “My self-esteem is far too dependent on my daily

achievements”; “At times, I have to be better than others to be good

enough myself”; “Occasionally I feel obsessed to accomplish something

of value”). High scores indicate high performance-based self-esteem. The

Cronbach’s α coefficient was 0.80 in Study I and 0.81 in study II.

The Rosenberg self-esteem scale (RSE scale), the most extensively

applied instrument for the assessment of global self-esteem among ado-

lescents, was utilized (Baumeister et al., 2003; Butler & Gasson, 2005;

Rosenberg, 1972; Vispoel, Boo, & Bleiler, 2001). It consists of 10 gener-

ally formulated items (graded 1–4) which enable a global self-assessment

(e.g., “Sometimes I feel rather worthless”; “There is nothing I could be

proud of”; “In general, I am quite content with myself”). In this assess-

ment high scores indicate high global self-esteem, which reflects a re-

spondent’s overall feeling of being good enough. The Cronbach’s α coef-

ficient was 0.90 in both Study I and Study II.

Some single items were used as indicators for lifestyle variables, such

as breakfast and lunch routine (“How often do you skip breakfast?”;

“How often do you skip lunch?”; graded from 1=every day to 5=never)

(Study I), degree of physical exercise (“To what extent do you exercise

physically?”; graded from 1=no physical exercise to 5=intense physical

exercise) (Study I), and alcohol and tobacco use (“How often do you

drink alcohol?”; “How often do you consume nicotine?”; graded from

1=every day to 5= never) (Study III). Study II included a question about

life satisfaction (“In general, how satisfied are you with your current life

situation?”; graded from 1=very unsatisfied to 5=very satisfied) and one

item on self-rated health (“How would you say your general health has

24

been during the past year?”; graded from 1=bad to 5=very good). Moreo-

ver, one question about subjectively perceived sleep duration/sleep quan-

tity was asked in both Study II and Study III (“Do you believe that you

get enough sleep?”; graded from 1=no, not nearly enough to 5= yes, defi-

nitely enough). More conclusive information on participants’ sleep-

related variables was collected in Study III, where, in addition to subjec-

tive sleep quantity, sleep quality was measured (“How would you esti-

mate the quality of your sleep?”) on a scale from 1 to 5, with higher

scores indicating better sleep quality. Also, information about the partici-

pants’ average bed and rise times during the week and during the week-

end was collected. They were also asked to estimate their average sleep

onset latency (that is the length of time that it takes to fall asleep). The

answers were used to calculate sleep duration, in terms of the average

number of hours spent in bed daily on weekdays and on weekends. Also,

the data were used to define the participants’ degree of social jetlag,

which was determined according to the absolute difference between the

time of mid-sleep (midpoint between sleep onset and rise time) on school

days and on weekends (Roenneberg et al., 2003; Wittmann et al., 2006).

Higher values indicate a higher degree of social jetlag.

Finally, academic achievement, which was the outcome variable of

most interest in Study II and Study III, was indicated by the students’

final grades. The final grades are based on students’ total academic per-

formance throughout high school and access to these public data was

provided by the participating schools. In these studies, the final grades

varied from 6.20 to 20 points, with a mean of 16.80 (SD=2.36) in Study

II and a mean of 16.92 (SD=2.36) in Study III with higher values indicat-

ing better grades.

Statistical analyses

Study I had a cross-sectional design and the first aim was to survey the

prevalence of severe stress symptoms and chronic stress among adoles-

cents. In the analysis of the SMBQ questionnaire data, minimum cut-off

scores were set to demarcate at what point both stress and chronic stress

were perceived, which were based on earlier studies and clinical settings

(Grossi et al., 2003; Perski, 2006). A simple frequency analysis for both

males and females was then carried out. By conducting a one-way ANO-

VA, three stress groups (representing non-stressed, stressed, and chroni-

cally stressed adolescents) could be compared, and post hoc tests

(Scheffé) of the least significant differences were performed on all pair-

wise comparisons. Also, to investigate gender differences, a one-way

25

ANOVA was conducted. The further aim of Study I was to determine

which factors may contribute to or exacerbate stress symptoms in adoles-

cents. To do this, a linear stepwise regression analysis was conducted.

The independent variables were added one by one into the model to test

whether they were statistically significant. The purpose of this statistical

analysis was to examine the order of entry of the predictors into the mod-

el, as well as the relative strength of the relations between the predictors

and the outcome. The statistical analyses in Study I and Study II were

carried out using the Statistical Package for Social Sciences (SPSS) ver-

sion 16.0 for Windows.

The design of Study II was longitudinal. According to their responses

on the SMBQ items at time 1 and time 2, and using the cut-off point of 4

or more, the students were categorized into three different stress groups: a

no-stress group, a transitory stress group, and a chronic stress group. In

the first step, data were explored by means of descriptive statistics, and a

multivariate analysis (gender x stress groups) of variance was conducted.

In addition, the differences between the final grades in the three stress

groups were investigated by means of an analysis of variance. Finally, a

logistic regression analysis was conducted to determine the relative im-

portance of the various risk factors that may contribute to chronic stress.

In Study III, which had a longitudinal approach, descriptive analyses

were conducted for a number of sleep-related variables among the overall

sample (bed and rise times, sleep latency, sleep duration on school days

and weekends, chronotype, and social jetlag). Among the subsample of

those whose final grades were available and who had also filled in the

questionnaire at both time 1 and time 2, the contribution of stress symp-

toms, gender, sleep duration, sleep difficulties, sleep quality, sleep quan-

tity, and social jetlag in predicting academic achievement was investigat-

ed. The analyses were based on average values over the two test points.

Multilevel mixed effects regression models were utilized with a random

intercept for school, using the analytical method “xtmixed” within the

statistical package STATA 12.1. Academic achievement was treated as

the dependent variable and stress symptoms, gender, sleep duration, sleep

difficulties, sleep quality, sleep quantity, and social jetlag were subse-

quently added to the model. Each model was then tested against the hith-

erto best-fitting model using likelihood ratio testing (Rabe-Hesketh &

Skrondal, 2008). Finally, the best-fitting model was estimated using re-

stricted maximum likelihood.

26

Summary of studies

Study I - Stress symptoms among adolescents:

The role of subjective psychosocial conditions,

lifestyle, and self-esteem

Background and aim

Over the past 20 years, the number of sixteen-year-olds reporting stress,

fatigue, psychosomatic complaints as well as psychological and physical

tension has been steadily rising, especially among adolescent females

(Bremberg, 2006). There is also an increasing number of Swedish adoles-

cents and young adults who seek psychiatric health care (Dalman &

Wicks, 2006; Socialstyrelsen, 2009). This alarming trend has stimulated

great public concern, especially since it may lead to the development of

chronic stress. Chronic stress is associated with deteriorating energy re-

sources (Shirom, 2003). If an imbalance between spending and regaining

energy persists over a long period of time, severe stress symptoms, which

are characterized by emotional exhaustion, physical exhaustion and cog-

nitive weariness, may occur, which eventually lead to negative health

outcomes, such as exhaustion syndrome.The aim of Study I was to survey

the incidence of severe stress symptoms among adolescents in order to

better understand the factors that may contribute to these symptoms and

to examine gender differences.

Method

The data collection took place at two high schools over the course of one

week in February 2006. The sample included 304 first-year high school

students, of whom 159 were males (52%) and 145 were females (48%).

They participated by responding to a stress screening questionnaire that

included questions regarding stress symptoms, perceived demands and

control, and social support as well as self-esteem and lifestyle variables,

such as sleep, eating habits, and physical exercise. At both schools the

27

response rate was very high (98%) even though participation was volun-

tary.

Main findings and conclusions

About one-third (32.9%) of the participants reported a high degree of

stress symptoms. This group consisted of 68 girls (45.9% of all girls) and

32 boys (20.5% of all boys). Twenty-five of the participants (8.2% of all

participants) reported a very high degree of stress symptoms – levels

which are similar to those reported by patients who suffer from exhaus-

tion syndrome – and which were therefore considered to be indicative of

chronic stress in this study. More than five times as many girls (n=21)

than boys (n=4) were in this group. In other terms, 14.2% of all the fe-

males exceeded the cut-off score for chronic stress compared to 2.6%

among the males.

Next, the participants were categorized into three groups (no-stress,

stress symptoms, and chronic stress groups) depending on their degree of

perceived stress symptoms. By conducting a one-way ANOVA these

groups were then compared with regard to stress-related variables. Post

hoc tests revealed that all three groups were significantly different from

one another in respect to demands, social support, and eating habits. The

chronic stress group reported more negligent eating habits as well as ex-

periencing significantly higher demands and less social support than the

stress symptoms group who, in turn, reported less regular eating habits

and experiencing higher demands and less social support than the no-

stress group. Moreover, the individuals in the no-stress group reported

significantly higher global self-esteem, less performance-based self-

esteem, and less sleep disturbances than those in the other two groups.

Concerning perceived control, students in the no-stress and stress symp-

toms groups did not differ significantly from each other, whereas the

chronic stress group experienced significantly less control.

In regard to gender differences, the study revealed that girls reported

stress symptoms to a significantly higher degree than boys. They showed

lower levels of global self-esteem, higher performance-based self-esteem,

experienced higher demands, and perceived more sleeping difficulties

compared to the boys.

Another purpose of the study was to identify the relative contribution

of the studied factors to stress symptoms. To get an overview of the asso-

ciations between the investigated stress-related variables, a correlation

matrix is provided in Table 1.

28

Table 1. Partial correlations among study variables (n=285), control variable: gender.

1 2 3 4 5 6 7 8

1 Stress symptoms 1 2 Global seª -.503** 1

3 Pbseº .245** -.250** 1

4 Demands .617** -.354** .418** 1 5 Control -.213** .113 -.012 -.178* 1

6 Social support -.344** .252** -.092 -.249** .256** 1 7 Sleep disturbances .540** -.357** .229** .534** -.176* -.183** 1

8 Eating habits .321** -.208** .101 .229** -.023 -.125 .377** 1

9 Physical exercise -0.051 0.029 .194** .066 -.009 .045 -.043 -.158*

*p<.01;**p<.001 ;ª self-esteem;º Performance-based self-esteem

The results of a stepwise multiple regression analysis revealed that per-

ceived demands, global self-esteem, sleep disturbances, low social sup-

port, and negligent eating habits were significant predictors, which to-

gether explained as much as 56.3% of the variance in stress symptoms

(Table 2). Performance-based self-esteem, control, and physical exercise

did not emerge as significant predictors in the regression analysis.

Table 2. Significant predictors in the linear stepwise regression analysis with stress symptoms as the dependent variable.

Predictors B SE Beta t p

Demands .583 .078 .369 7.481 <.001

Global self-esteem -.391 .068 -.260 -5.782 <.001

Sleep disturbances .312 .082 .195 3.820 <.001

Social support -.301 .091 -.137 -3.302 .001

Eating habits .077 .036 .091 2.134 .034

The fact that serious stress symptoms were reported by more than 30% of

the investigated high school students indicates that this phenomenon

should be seen as the first phase of a potentially prolonged state involving

future health implications, such as exhaustion syndrome.

29

Study II - Chronic stress and its consequences on

subsequent academic achievement among

adolescents

Background and aim

Chronic stress has been associated with stress-related symptoms among

adults and may lead to negative health outcomes, such as exhaustion syn-

drome. However, it is not only adults who suffer from prolonged stress,

as research has shown that every third adolescent reports severe stress-

related symptoms (Study I). Since the chronic depletion of energy emerg-

es over an extended period of time, finding a fully developed exhaustion

syndrome among young populations is difficult to expect. However,

chronic stress may have more immediate consequences on adolescents

(Thoreson & Eagelston, 1983). While the pernicious consequences of

chronic stress on health are recognized, research has not focused on the

importance that chronic stress may have in other important life domains,

such as in adolescents’ academic achievement. The aim of Study II was

to investigate how academic achievement, in terms of final high school

grades, is associated with perceived chronic stress symptoms, and to in-

vestigate which factors may constitute a heightened risk for chronic

stress.

Method

The initial sample consisted of 456 sixteen-year-old high school students

from two different high-ranking high schools who answered the stress

screening questionnaire at the beginning of their time in high school. In

this first round of data collection, which took place in February 2006 for

the first school and February 2008 for the second, 171 and 285 high

school students participated, respectively. Two years after the first round,

at the end of high school, a second round of data collection took place at

each school where 119 students from the first school and 176 from the

second voluntarily participated again in the study, yielding longitudinal

response rates of 70% and 62%, respectively, and 65% combined. In

order to control for attrition effects, the data from the students who did

not participate at time 2 were analyzed. Compared to those who partici-

pated on both measurement occasions, no significant differences were

found on any of the examined variables. After excluding incomplete and

missing data, the data from 273 participants remained for the analyses.

30

Academic achievement, the outcome variable of most interest, was indi-

cated by the students’ final grades at the end of high school.

Main findings and conclusions

Based on the prevalence of perceived stress symptoms at both time

points, three stress groups were defined, a no-stress group, a transitory

stress group, and a chronic stress group. Among all of the investigated

high school students, 41 students (15%) (31 girls and 10 boys) were

found to be chronically stressed, as they reported experiencing serious

stress symptoms both at the beginning and in the end of high school. Fif-

ty-nine students (22%), 39 girls and 20 boys, perceived severe stress on

just one of the measurement occasions. Taken together, 100 high school

students (37%) perceived stress symptoms at least once during their time

in high school. The remaining 63% of the study’s participants (67 girls

and 106 boys) did not feel stressed at all. In regard to gender differences,

the results were in line with previous studies, indicating that stress symp-

toms are more prevalent and more pronounced among girls, who consti-

tuted the majority of the chronically stressed group.

The results of a 2 (gender) x 3 (stress groups) multivariate analysis of

variance revealed significant main effects. All three groups were signifi-

cantly different from one another in respect to global self-esteem, de-

mands, sleep difficulties, perceived sleep duration, and self-rated health.

While the no-stress group reported the highest levels of global self-

esteem and self-rated health, as well as less sleeping difficulties and de-

mands, and an adequate perceived duration of sleep, the chronic stress

group reported the lowest levels of global self-esteem and self-rated

health. The chronically stressed students also perceived their duration of

sleep to be too short, had the most sleeping difficulties, and perceived the

highest levels of demands. The temporary stress group reported levels in

between the other two groups for the mentioned variables. Regarding

performance-based self-esteem and total life satisfaction, the no-stress

group differed significantly from the other two groups; they reported

lower levels of performance-based self-esteem and greater life satisfac-

tion. Compared to the other two groups, the chronic stress group per-

ceived significantly less social support. Gender differences were also

found, indicating that girls had significantly worse global self-esteem.

They further reported higher demands and poorer self-rated health than

boys. The boys perceived their sleep duration to be less sufficient than

did the girls.

According to an ANOVA, a comparison of the final grades of the var-

ious stress groups showed significant differences (F2,266=5.605, p=0.004,

31

partial η²=0.04). It was revealed that the chronic stress group achieved

significantly worse grades than the other participants (Table 3). Further-

more, there was neither a main effect for gender (F1,266=3.333; p=0.069,

ns) nor any interaction effect (F1,266=1.159; p=0.315, ns).

Table 3. Descriptive statistics for final grades in each stress group.

No-stress Transitory stress Chronic stress

M (S.D.) M (S.D.) M (S.D.)

Girls 17.40 (1.639) 17.58 (1.732) 15.55 (3.416)

Boys 16.80 (2.360) 16.11 (2.275) 15.59 (3.195)

The results of the logistic regression analysis showed that a high degree

of perceived demands, low global self-esteem, short perceived sleep dura-

tion, and poor self-rated health at the beginning of high school were rele-

vant indicators for an increased risk of chronic stress throughout high

school.

In addition to the negative long-term implications it can have on health

and well-being, chronic stress was associated with worse academic

achievement. Thus, it may have significant negative repercussions on a

young person’s future chances of being accepted into a quality line of

education.

32

Study III – The role of social jetlag and stress in

academic achievement among adolescents

Background and aim

Stress symptoms have not only been found to be highly prevalent among

high school students (Study I), it has also been shown that chronic stress

plays a role in adolescents’ academic achievement (Study II). Along with

the high prevalence of stress-related symptoms, sleep-related problems

have been rapidly increasing among adolescents over the last decade

(Socialstyrelsen, 2009). Moreover, sleep and recovery have been shown

to be associated with academic achievement (Dahl & Lewin, 2002;

Walker, 2008; Wolfson & Carskadon, 2003). In light of this, a further

investigation of the role of sleep and sleep-related variables, as well as

the importance of chronic stress, in explaining adolescents’ academic

achievement was undertaken in Study III. For adolescents, the need to

sleep is opposed by biologically based phase changes in their circadian

rhythm during puberty, which makes it physically harder to maintain

earlier bedtimes (Auger et al., 2011; Brandalize et al., 2011; Wolfson &

Carskadon, 2003). Furthermore, social and other arousing activities may

impede earlier bedtimes at this age (Dahl & Lewin, 2002). Although ado-

lescence brings with it a tendency towards more evening orientation,

there are differences in how evening or morning orientated a person is,

which is referred to as the individuals’ chronotype.

The main aims of Study III were to investigate whether variability in

academic achievement among high school students is due to stress symp-

toms, as shown in Study II, and to examine whether a number of sleep-

related variables contribute to the prediction of adolescents’ academic

achievement. The investigated sleep variables were objective sleep dura-

tion (time in bed), sleep difficulties (such as having trouble falling asleep

or waking up during the night), subjectively perceived quality and quanti-

ty of sleep as well as degree of social jetlag. High social jetlag refers to a

pattern that implies a drastic variability between a person’s weekday

(school day) and weekend sleeping schedules. Because social jetlag is a

relatively new construct, a closer look was taken at its associations with

unhealthy lifestyle habits, stress symptoms, and the other investigated

sleep-related variables.

33

Method

The overall sample consisted of 1035 sixteen-year-old high school stu-

dents from three different high schools, who answered questions about

stress and sleep-related variables. After the deletion of missing and in-

complete data, the data of 958 high school students remained for the sub-

sequent analyses. Furthermore, data from a subsample of 244 high school

students, who had answered the questionnaire on stress and sleep at two

time points, at the beginning of high school and two years later at the end

of high school, were analyzed. For this subsample, the final grades were

available. Degree of social jetlag was determined by calculating the abso-

lute difference between the time of mid-sleep (midpoint between sleep

onset and rise time) on school days and on weekends (Roenneberg et al.,

2003; Wittmann et al., 2006). Academic achievement, the outcome varia-

ble of most interest, was indicated by the final grades at the end of high

school.

Main findings and conclusions

Overall, the average sleep length of the study’s participants during the

week was less than the recommended nine hours per night, indicating that

the participants were chronically sleep deprived (Table 4). Table 4. Average bedtime, sleep onset latency, rise time, and sleep duration during the school weeks

and weekends for the overall sample (n=958).

School week Weekend

Bedtime 11:05 p.m. (SD: 50 min) 1:28 a.m. (SD: 79 min)

Sleep onset latency 27 min (SD: 26 min) 13 min (SD: 16 min)

Rise time 6:47 a.m. (SD: 26 min) 10:55 a.m. (SD: 84 min)

Sleep duration* 7 h 42 min (SD: 54 min) 9 h 26 min (SD: 74 min)

*time in bed

According to the results of a multilevel mixed effects regression analysis,

social jetlag, weekend sleep duration, chronic stress, and gender were

significant predictors for academic achievement. Specifically, being

male, having more stress symptoms, sleeping longer during the weekend,

and having higher social jetlag were associated with poorer final grades

(Table 5).

34

Table 5. Model predicting final grades (best-fitted model: Social jetlag).

Coefficient Standard error z p

Stress symptoms -.645 .174 -3.70 <.001

Male -.639 .321 -1.99 .001

Social jetlag (hour) -.329 .164 -2.00 .046

Sleep duration we* (hour) -.297 .137 -2.17 .030

Constant 23.068 1.518 15.20 <.001

SD of random effects

School .518 .427

Residual 2.214 .101

*we=weekend

In line with earlier investigations, evening chronotypes were more prone

to social jetlag. They tend to have greater shifts in their sleep/wake pat-

terns between the school week and weekend as compared to morning

chronotypes. This creates a disturbance in their circadian rhythms at the

beginning of each school week that puts them at higher risk for experi-

encing jetlag like symptoms that might impair their ability to perform

academically.

Social jetlag was associated with unhealthy life style habits, including

skipping breakfast and lunch, and smoking and drinking alcohol more

frequently. Furthermore, an association between social jetlag and per-

ceived stress symptoms was found. Social jetlag was associated with

other sleep-related variables, i.e., more pronounced sleeping difficulties,

poor sleep quality and insufficient perceived sleep quantity, as well as

actual shorter sleep duration on weekdays and longer sleep duration on

the weekends.

Undoubtedly, adequate and regular sleep timing is an important factor

when it comes to preventing adolescent stress and improving academic

achievement. Evening chronotypes, in particular, would perhaps benefit

from having regular sleep/wake schedules throughout the entire week and

later school start times in order to counteract the risk for social jetlag.

35

Discussion

The main aims of the present thesis were to investigate the prevalence of

severe stress symptoms among adolescents, to examine factors that may

contribute to chronic stress among adolescents, and to examine the asso-

ciations between chronic stress and sleep-related variables and academic

achievement. After a short summary of the empirical studies’ results, the

main findings and their implications are discussed in more detail. Next,

limitations and methodological considerations are provided. Finally, pos-

sible implications on both future research and clinical practice are con-

sidered.

Summary of the findings

Concerning the prevalence of severe stress symptoms, the results of

Study I indicated that almost one-third of the total group reported that

they experienced a high degree of stress symptoms, whereas 60% of the

adolescents did not perceive severe stress symptoms. The highest degree

was perceived by 8% who experienced especially pronounced stress

symptoms. In fact, they suffered from symptoms to an extent which oth-

erwise only has been reported by adult clinical burnout patients (Grossi et

al., 2003; Perski, 2006).

In Study II, the prevalence of chronic stress among adolescents was

investigated using a longitudinal approach. While 63% of the participants

did not perceive stress symptoms during high school, 22% experienced

severe stress symptoms once, and 15% reported severe stress symptoms

throughout high school and were thus considered to suffer from chronic

stress.

Potential differences between boys and girls with regard to chronic

stress were also looked at. It was shown that almost every other girl and

every fifth boy struggled with stress-related symptoms (Study I). Not

only were girls more prevalent among the students who perceived stress

symptoms, they also perceived more pronounced symptoms compared to

the boys. Similar gender differences were noticed in Study II, where the

majority of those chronically stressed were girls.

36

Furthermore, an attempt was made to investigate if the factors that

have been found to be relevant in the development of chronic stress

among adults also contribute to severe stress symptoms among adoles-

cents. The results of Study I found that perceived high demands, low

global self-esteem, sleep disturbances, low social support, and negligent

eating habits were significant predictors of severe stress symptoms,

which together explained a considerable amount of variation in stress

symptoms (56%). Moreover, perceived high demands, low global self-

esteem, perceived short sleep duration, and poor self-rated health in the

beginning of high school were found to be relevant indicators for an in-

creased risk of chronic stress throughout high school (Study II).

The importance of chronic stress in academic achievement was also

investigated (Study II and Study III), motivated by previous neuropsy-

chological findings on the negative impact of chronic stress on brain

functioning. In Study II, the investigation of the impact of chronic stress

on subsequent academic achievement revealed that the group which was

chronically stressed throughout high school had significantly worse final

grades compared to both students who did not perceive stress symptoms

and those who perceived stress symptoms occasionally. In addition, since

regenerative processes are especially crucial for cognitive functioning,

the relative importance of sleep and sufficient recovery for subsequent

academic achievement was investigated in Study III. The results indicat-

ed that, besides chronic stress, social jetlag, a factor that had not been

discussed before in this context in literature, and longer sleep duration

during the weekend predicted academic success.

Factors that play a crucial role in chronic stress

among adolescents

By increasing the knowledge about the factors that may contribute to

chronic stress, the results of the present thesis could facilitate the early

identification of adolescents at risk for chronic stress. Based on the pre-

sent findings, high perceived demands and low self-esteem are factors

that have been found to be highly associated with the perception of severe

stress symptoms and an increased risk for chronic stress among adoles-

cents. Moreover, sleep and recovery-related variables along with per-

ceived social support were relevant for severe stress symptoms. Hence,

these factors merit a more detailed description.

37

High perceived demands

In the present thesis, adolescents who perceived high demands were more

likely to suffer from chronic stress. Even though the present findings

cannot provide distinctive conclusions about the relative importance of

different domains within which adolescents may perceive high demands,

a number of possible demand-creating sources in the life of adolescents

are worth discussing.

A higher risk for psychological strain is prevalent among individuals

who perceive high demands from and low control over their work situa-

tion (Karasek & Theorell, 1990; Theorell, 1996). This is also true for

adolescents who ”work” in schools (Gillander-Gådin & Hammarström,

2000; Modin et al., 2011). In fact, besides worries about their future, ado-

lescents most often report that school-related demands are the most

stressful (deAnda et al., 2000; Murberg & Bru, 2004). To study, gain new

insights, and learn new skills are the main purposes of attending school,

which naturally puts demands on the individual in terms of time and ef-

fort. Thus, being a high school student is inescapably demanding to some

degree. This is evidenced by the results of a recent national Swedish sur-

vey, which indicate that many high school students, to be precise 60%

(50% boys and 71% girls), feel stressed by demands related to school

issues and academic tasks (SCB, 2012).

One explanation for this high degree could be that the fact that final

grades are based on the students’ total academic achievement throughout

high school is perceived as extremely demanding and thus contributes to

an increased risk for chronic stress. Final high school grades are crucial in

determining an adolescent’s academic future by facilitating admission to

high-ranking tertiary education. This is especially relevant for high

school students in an academic track, who usually aspire to enter tertiary

education. Consequently, adolescents are asked to excel academically

throughout the entire school period, which may lead some to feel pres-

sured constantly. To perceive constant pressure to succeed academically

may then imply a prolonged imbalance between spending and regaining

energy, which may result in chronic stress symptoms.

It could, however, also be true that some students lack adequate strate-

gies for coping with the demands they perceive. Instead of using active

strategies, such as solving tasks or asking others for help, they may strug-

gle with aversive feelings related to the source of stress, associated with

avoidant behaviors like procrastination or distraction. According to

Modin et al. (2011), it is the students who lack strategies for dealing with

high demands who are especially at higher risk for negative health out-

comes.

38

It might, however, be the case that the demands placed upon and per-

ceived by today’s adolescents are different from the demands faced by

earlier generations. For instance, changes in the school system and school

environment may play a crucial role in shaping adolescents’ demands and

stress perceptions (Ahrén, 2010). Moreover, cultural and societal changes

may force young people today to develop and apply other coping strate-

gies in order to maintain well-being. According to Eccles et al. (2008),

today’s adolescents grow up in a climate of uncertainty about their op-

tions and the impact their choices have on their future life owing to the

more transient and less rigid social norms which are typical for modern

Western, heterogeneous societies. One’s life course is in fact less predict-

able in a post-industrial individualistic society, like in Sweden (World

Values Survey, 2005/08). A high degree of individualization implies a

culture that places a high value on individual freedom and self-

expression, which is an advantage in many respects (Bremberg, 2006).

However, to live according to the saying “man forges his own destiny”

places high demands on oneself for taking responsibility that the “right”

decisions are made. In the face of today’s innumerable possibilities, this

may overstrain the decision-making capabilities of some adolescents. In

fact, to pick one alternative always implies abandoning other ones.

In particular, adolescents are often concerned with the decisions and

plans that could affect their occupational futures (Eccles et al., 2008;

Mortimer et al., 2002) and worries about their future career prospects are

both common and entitled due to an increase in youth unemployment

rates (Bremberg, 2006).

Moreover, social comparisons based on unrealistically high standards

might be a source of perceived high demands and prolonged stress

(Wiklund et al., 2010). Even though “nobody is perfect” is an established

expression, societal standards and discourse in the media point more of-

ten than not to the opposite, reinforcing that striving for perfection is a

necessary precondition for a happy and fulfilled life. Consequently, indi-

viduals may struggle and strive to become somebody who they think they

are supposed to be. It is not only impossible to have “everything under

control,” vulnerability and imperfection are inescapable parts of being

human. Based on interviews conducted among adolescent girls, Wiklund

et al. (2010) found that young girls feel a considerably high degree of

pressure to achieve individual success and perfection as well as to man-

age challenges and overcome barriers on their own. Girls have also tend-

ed to equate their self-worth with achievement outcomes (Wiklund et al.,

2010), an observation which is in accordance with what Hallsten et al.

(2005) described as high performance-based self-esteem and which in

previous research has been associated with a heighted risk for burnout

(Blom, 2012; Hallsten et al., 2011). In fact, in the present thesis (Study I)

39

high performance-based self-esteem was significantly correlated with

high perceived demands, indicating that individuals who perceived high

demands also tended to base their self-worth on performance and success,

or vice versa. According to earlier investigations, extremely high com-

mitment to school work in combination with high perceived demands was

found to be related to stress, worries about school, and the feeling of be-

ing overwhelmed by school-related tasks (Huan et al., 2008; Ollfors &

Andersson, 2007). It may be possible that these high levels of commit-

ment result from deeper-seated fears of failure, inadequacy and being

evaluated as ”not being good enough”. That is to say, individuals’ strong

performance drive could be fueled by low self-esteem. Obviously, ado-

lescents who perceive their own value as being partly dependent on their

performance also perceive higher demands put on them.

Low self-esteem

Global self-esteem was found to be associated with stress symptoms and

chronic stress in the present thesis, confirming the results of earlier inves-

tigations that high self-esteem is a buffer against stress (Rector & Roger,

1997). An individual’s self-esteem might not only influence if a situation

is perceived as threatening and stressful but might also determine in

which ways the individual deals with demands. Thus, individuals with

high global self-esteem might perceive themselves to be more capable of

dealing with stressful situations.

In other words, according to the transactional stress model (Lazarus &

Folkman, 1984), individuals with high self-esteem seem to have ad-

vantages in regard to the processes of primary and secondary appraisal,

and consequently experience less stress. According to Locke et al. (1996),

individuals with high self-esteem tend to appraise stressful situations as

challenges rather than threats. Thus, they perceive the same situation as

less demanding than do individuals with low self-esteem, who not only

feel threatened by experiences of and thoughts about failure but also tend

to perceive their coping resources as insufficient.

Inadequate coping increases the feeling of being incapable of solving

problems and successfully dealing with stressors and of having access to

resources for eliminating sources of stress. Thus, it impairs self-efficacy

and, consequently, decreases self-esteem (Liu & Kaplan, 1999). High

global self-esteem, on the other hand, implies a higher self-efficacy in

stressful situations and the ability to use more adequate coping strategies

(Bandura, 2000; Moksnes et al., 2010), which is a protector against

chronic stress. This is in line with Salmela-Aro and Nurmi (2007), who

concluded, based on the association between self-esteem among universi-

ty students and their vocational careers ten years later, that self-esteem

40

improves individuals’ beliefs in their competencies, which supports the

use of more active coping strategies in demanding situations.

Lack of social support

The degree of social support perceived by the adolescents influenced

their perception of severe stress symptoms. The chronically stressed stu-

dents perceived the least social support. This result underpins earlier stud-

ies, which point to the stress-preventive impact of supportive relation-

ships (Brolin-Låftman & Östberg, 2006; Haraldsson, 2010; Langstedt et

al., 2009), especially for girls. The relations adolescents have with their

peers in school are important for their health and well-being. Moreover,

especially strained relationships have previously been shown to have a

negative impact on health (Brolin-Låftman & Östberg, 2006). In order to

prevent adolescents from health complaints and chronic stress, it is there-

fore important to provide a school context that counteracts social rejec-

tion and social isolation. In this respect, accessibility to significant others

as well as being able to view oneself as being significant to others seems

to be of importance. Perhaps, individualistic, competitive values impede

the possibility and perception of connectedness to others. This, however,

remains a question for future research.

Insufficient sleep and recovery

Not surprisingly, sleep and sufficient recovery played a crucial role in

predicting severe stress symptoms among adolescents. Sleep is essential

for the anabolic (energy providing) processes in the body. Lack of sleep

or bad sleep quality prevents adequate recovery after effort and has been

found to be a risk factor in the development of clinical burnout (Ekstedt

et al., 2006; Shirom et al., 2005; Söderström, 2012; Sonnenschein et al.,

2007). In the present thesis, it was shown that perceived sleeping difficul-

ties and the perception of not getting sufficient sleep duration were asso-

ciated with severe stress symptoms among adolescents. It was further

revealed that sleeping difficulties were highly associated with the percep-

tion of high demands (Study I), which indicates that the perception and

cognitive preoccupation with stressful demands may impair sleep. Ac-

cording to Söderström (2012), sustained cognitive activation in the form

of, for example, worries and rumination makes it more difficult to initiate

and maintain sleep and sufficient recovery, which, according to the find-

ings in the present thesis, also seems to be the case for adolescents.

Of particular interest was the novel finding that, besides sleeping diffi-

culties and perceived lack of sleep duration, social jetlag was associated

with the perception of severe stress symptoms (Study III), indicating that

having disturbances in the circadian rhythm and related jetlag-like symp-

41

toms on a weekly basis stresses the organism and, in the long run, may be

responsible for an increased susceptibility to chronic stress among ado-

lescents.

Taken together, the investigated factors were not only associated with

the perception of severe stress symptoms but were also partly associated

with each other, indicating that there are multiple influences which to-

gether account for a heightened risk of chronic stress among adolescents.

Chronic stress, sleep and academic achievement

At the end of high school, the academic achievement of chronically

stressed high school students was shown to be significantly worse com-

pared to that of non-stressed or occasionally stressed students (Study II).

This is an interesting finding because academic achievement has a crucial

impact on young people in terms of their future occupational and educa-

tional options. This is especially relevant for high school students who

are in academic high school tracks, because their successful completion

of high school is a requirement for access to tertiary education.

In accordance with theories about stress physiology, increased effort

and strain over a limited period of time, which is the case during short-

term stress, permits the organism to recover and regain energy after de-

creasing stress (Lundberg, 2005; Sapolsky, 2004) and thus does not imply

allostatic load (McEwen, 2006). If an imbalance between spending and

regaining energy persists over a prolonged time, as with chronic stress,

anabolic and regenerative processes are prohibited. Prolonged stress is

accompanied by severe symptoms, such as emotional exhaustion, physi-

cal exhaustion, and cognitive weariness (Melamed et al. 1992), which

have a negative impact on academic achievement. This is in line with

results from neuropsychological findings, indicating that chronic stress

impedes optimal brain functioning, which then can lead to cognitive dif-

ficulties and impairments (Arnsten, 2009; Liston et al., 2008). Based on

the present findings, the conclusion is therefore made that chronic stress

leads to worse academic achievement, because the symptoms associated

with chronic stress make it harder for the individual to accomplish

school-related tasks and maintain academically high standards.

It should be mentioned that the effect of chronic stress on subsequent

academic achievement was small, indicated by a small effect size

(η²=0.04). However, chronic stress had an effect in the investigated group

of elite high school students which may suggest there would be even

stronger effects in other, more diverse adolescent populations. It could,

however, also be the case that adolescents from the academic high school

42

track in particular are more concerned about school-related issues and

academic achievement and thus experience more stress related to those

concerns as compared to students from other educational programs. A

recent study conducted by Samela-Aro and Tynkkynen (2012) indicated

that it was adolescents from an academic educational track rather than

those from a vocational track who tended to develop school burnout

symptoms. Determining more specifically what the prevalence and im-

pact of chronic stress is on achievement in adolescent populations from

other educational programs is a task for future research.

Otherwise, the big-fish-little-pond effect (Marsh & Hau, 2003) might

be useful in providing an explanation for the associations found between

chronic stress and poor academic achievement. According to this theory,

it is better to be a big fish in a little pond than a little fish in big pond,

referring to the fact that the academic self-concept of high-achieving

students is lower in a high-achieving, competitive educational context,

compared to the academic self-concept of equally able students who are

educated in an average-ability school. With respect to the present find-

ings, this would mean that, after entering the high-ranking elite high

schools, some of the initially equally able adolescents may feel especially

challenged and stressed in a more selective and high-achieving school

context. When being among other high-achieving students, it is probably

tougher to sustain one’s position as an excellent student. Consequently,

based on the perception of facing higher demands in combination with

insufficient resources, perhaps also in combination with perceiving one-

self as “not being good enough” any longer, prolonged stress may result,

which then impairs performance.

Indeed, the perception of not being able to live up to one’s own or oth-

ers’ expectations in terms of academic performance can feed into a vi-

cious circle that leads to even more stress and performance-disturbing

symptoms. In fact, Gustafsson et al. (2010) found a bidirectional relation-

ship between stress and academic achievement, where academic

achievement decreased due to stress and affective symptoms and poor

performance evoked stress and affected mental health.

Moreover, in previous research, sleep and sufficient recovery have

both been described as resources against the negative impact of chronic

stress on health (Ekstedt, 2005; Söderström, 2012) and are considered

necessary for cognitive processes, such as learning and memory (Dahl &

Lewin, 2002; Walker, 2008; Wolfson & Carskadon, 2003). To examine

this potential impact, in Study III, the relative contribution of different

sleep-related variables were taken into account when studying adoles-

cents’ academic achievement. It was found that, besides chronic stress,

degree of social jetlag contributed to the prediction of adolescents’ aca-

demic achievement at the end of high school. Longer sleep duration dur-

43

ing the weekend was associated with poorer grades, which may have

been the consequence of an accumulated sleep debt during the week.

The finding that social jetlag contributed to worse academic achieve-

ment should be highlighted in particular because it is a novel and interest-

ing outcome. Social jetlag results from the individual’s tendency to shift

sleeping times between weekdays and weekends drastically. This implies

a disturbance in circadian rhythms and difficulties getting up at regular

times during the school week in combination with symptoms of tiredness,

irritability, lack of energy, lack of appetite, and concentration problems,

i.e., social jetlag (Dahl & Lewin, 2002; Roenneberg et al., 2003;

Wittmann et al., 2006; Zimmermann, 2011). Thus, students with social

jetlag most likely start off their school days feeling tired and exhausted

while at the same time being in a constant hurry to make it to their morn-

ing school lessons in time. It stands to reason that this might inhibit one’s

chances of performing well in school.

Social jetlag was more pronounced in evening chronotypes, which is

in line with previous studies (Roenneberg et al., 2003; Zimmermann,

2011). Specifically, evening chronotypes tended to have greater shifts in

their sleep/wake patterns between the school week and weekends com-

pared to morning chronotypes. The disturbance in their circadian rhythms

may not only make it more difficult to get up at the regular time at the

beginning of each school week (Dahl & Lewin, 2002; Roenneberg et al.,

2003; Wittmann et al., 2006) but may account for a lack of alertness and

difficulties concentrating, which makes school work more demanding and

the perception of stress more likely. Consequently, it is harder for them to

academically perform properly in school.

In conclusion, evening chronotypes and especially those with high so-

cial jetlag are disadvantaged by the timing of school activities, which are

concentrated in the morning, since they are forced to both perform under

conditions where circadian factors promote sleep (Mecacci & Rocchetti,

1998; Saxvig et al., 2012) and to struggle with social jetlag symptoms.

Gender differences

The results of the present thesis indicated that girls both constituted the

majority of chronically stressed individuals and showed more pronounced

stress symptoms. This is in line with previous research and national in-

vestigations (Ahrén, 2010; Basow & Rubin, 1999; Bremberg, 2006;

Friberg et al., 2012; Hagquist, 2009; Skolverket, 2010). Unfortunately,

the present thesis only provides exploratory data concerning gender dif-

44

ferences without being able to explain conclusively the reasons for their

occurrence; however, a number of possible causes are shortly mentioned.

Previous research provides several possible explanations for stress-

related gender differences. One possible explanation is that gender differ-

ences could be caused by differences in stress exposure, which implies

that adolescent girls experience more or other stressors than boys and

thus perceive more stress symptoms (Rudolph, 2002). Another explana-

tion, which suggests biological differences, is based upon the assumption

that the gender differences found could be due to differences in stress

reactivity. In other words, there are differences in physiological predispo-

sitions, in which case women would have a higher vulnerability, which is

a lower threshold for releasing the stress reaction when confronted with

certain stressors, compared to men (Rudolph, 2002; Stroud et al., 2002).

Research indicates that this might occur in connection with events which

have negative interpersonal consequences (Stroud et al., 2002; Troisi,

2001). A third explanation emphasizes differences in socialization pro-

cesses which may also account for differences both when it comes to the

cognitive appraisal of the situation as stressful and concerning the way of

dealing with stressors (Renstig & Sandmark, 2005). In fact, girls have

been shown to be more exposed to interpersonal stress (Murberg & Bru,

2004; Rudolph, 2002; Stroud, et al., 2002) and to be more sensitive to

others’ reactions over their successes and failures (Liu & Kaplan, 1999;

Thomson, 1998). Furthermore, Wiklund et al. (2010) found that girls tend

to adapt to and live up to the needs and expectations of others. In another

study, girls tended to use more passive, avoidant coping strategies com-

pared to boys, based on the misconception that active coping implies a

heightened risk for failure and that therefore the avoidance of dealing

with the stressor spares them from disappointment (Liu & Kaplan, 1999).

Yet another explanation is that they are more mature at this period of life

than boys and thus experience life as more serious and demanding

(Murberg & Bru, 2004). Gender differences in stress perception could

also be due to differences in affiliate relationship patterns, as indicated by

Feingold (1994). While women put more emphasis on interpersonal rela-

tionships, men tend to focus more on personal autonomy. The “cost of

caring hypothesis” suggests that women and men are equally vulnerable

to self-focused events, but women react stronger to events involving oth-

ers (Troisi, 2001).

However, based on the results of the present thesis, reliable explana-

tions of the gender differences found cannot be provided. Future research

will hopefully be able to produce more conclusive findings on gender

differences in regard to chronic stress perceptions and responses among

adolescents and whether they are related to physiological dispositions,

socialization or both.

45

Limitations and methodological considerations

Several limitations may have influenced the results of the included stud-

ies and therefore ought to be considered in the following section.

The first limitation relates to the samples used and the generalizability

of the findings. Although the distribution of the sexes was relatively bal-

anced in all samples, one should be cautious in generalizing the results to

all high school students. The samples were drawn from only one geo-

graphic area, i.e., Stockholm, and thus represent a limited range of com-

munity and school environments. Moreover, since the investigations only

involved students from high-ranking high schools, further research would

be needed among adolescents from less elite high schools or with other

socio-economic backgrounds in order to draw conclusions for all Swedish

adolescents. However, the proportion of the students reporting stress

symptoms as well as the proportion of females who did so is similar to

the results of nation-wide surveys (Ahrén, 2010; Bremberg, 2006;

Socialstyrelsen, 2009).

Furthermore, it is worth mentioning that, in the present thesis, only

students who had chosen an academic educational high school track were

investigated. Typically, adolescents who choose an academic high school

track are confronted with higher academic demands and expectations.

Due to the greater competition it can be more difficult for them to main-

tain their position as excellent students, compared to high school students

from less demanding educational programs. Thus, the prevalence and

consequences of chronic stress may very well differ between high school

students who attend an academic educational track and those who attend

a vocational educational track, as indicated by Samela-Aro and

Tynkkynen’s (2012) findings on school burnout.

Another limitation concerns the fact that all of the instruments for

measuring stress and stress-related factors were based on self-report ques-

tionnaires. Self-reports may be affected by perceptual and cognitive bias-

es (e.g., mood and social desirability). Moreover, studies among adoles-

cents that are only based on self-report instruments can be especially

problematic, because the respondents’ personality and identity develop-

ment are still not complete, which may contribute to more fluctuating

self-perceptions (Kroger, 2006; Marcia 2006). In future investigations,

the use of more objective measures such as physiological indicators of

stress (e.g., saliva cortisol and heart rate variability) and sleep parameters

would be preferable. Yet, to develop sufficiently sensitive methods of

capturing reliable associations between physiological indicators of stress

and self-reported well-being and stress is still a challenge and thus a topic

for future research.

46

Study I had a cross-sectional design, which does not permit drawing

any conclusions on causal relationships among the investigated variables

or on the direction of the relation regarding chronic stress development.

More longitudinal studies on this topic are therefore warranted in order to

disentangle the potential predictive relationships between variables.

In Study II and Study III, access to baseline measures of academic

achievement among the investigated participants would have been desir-

able. However, it seems safe to assume that all of the participating stu-

dents had at least sufficiently good grades from primary school since they

had met the requirements needed for entering elite high schools. Moreo-

ver, in Study II access to some of the participant’s entrance grades per-

mitted analyses that revealed no significant initial differences between the

stress groups.

Based on the findings in the present thesis, 15% of the adolescents suf-

fered from chronic stress (Study II). It cannot be shown for certain, that

these students will end up developing stress-related diseases, such as

clinical burnout, in the long run. Conducting follow-up measurements at

some point or otherwise gathering a more objective confirmation of the

impact of their chronic stress after high school could have provided use-

ful information on the risks for subsequent stress-related health problems

and diminished career prospects.

Another limitation concerns the fact that although data were clustered

by school, this was not taken into account in substantive analyses

throughout the studies, which may have led to less precise estimates. An

approach to account for this clustering could have been through the use of

structural equation modeling (SEM), but the results would probably not

have changed the main conclusions of the thesis. The suboptimal ap-

proach of treating missing data by list-wise deletion instead of more ap-

propriate strategies (e.g., estimation depending on how data were miss-

ing) has to be mentioned as yet another limitation.

The fact that some of the scales, such as the PBS scale and the SMBQ,

have not been previously applied to such young respondents may also be

limiting in that there does not exist any previous information on the basic

measurement properties with which to draw comparisons. Moreover, a

recent study on the internal construct validity of the SMBQ among

healthy and burnout adults led to the conclusion that a revised 18-item

version of the SMBQ would correspond better with modern measurement

standards (Lundgren-Nilsson et al., 2012). Nonetheless, in the present

studies the reliabilities of the SMBQ measurements were tested and

found to be satisfactory (Cronbachs α ≥ 0.80).

However, for some scales the reliability was low. For example, in

Study II the Cronbach’s α for the control index was 0.30. Therefore, it

was decided to refrain from applying the construct in the subsequent sta-

47

tistical analyses of the study. A possible reason for the low reliability of

the applied scale could be that questions about perceived control were

formulated in a very general and abstract way and thus did not match

with the situation of adolescent high school students (e.g., I constantly

need to learn new things in order to deal with my life.). However, in pre-

vious studies, perceived control has been successfully measured among

adolescents by using more appropriately formulated items (Gillander-

Gådin & Hammarström, 2000; Modin et al., 2011), and this should be

continued in future research.

Finally, the number of variables was rather limited. Unfortunately, a

number of potentially relevant variables fell outside the scope of the pre-

sent investigation, such as stressful life events, extra work, school con-

text, physical illness, peer rejection, cognitive deficits, and family-related

issues, which could have had some influence on the present results.

The attempt of the present thesis was to investigate stress in an other-

wise healthy population of adolescent high school students. Thus, more

severe psychiatric diagnoses, such as anxiety disorders or major depres-

sion, were not taken into account as potential explanatory or confounding

factors when analyzing the data, which can be considered a limitation.

However, the data analysis in Study II and III was limited to participants

with available final high school grades. Maybe it is therefore legitimate to

make the conclusion that the fact that they had completed high school

suggested that they did not suffer from any severe psychiatric conditions.

Despite the limitations, the studies also have strengths, such as the rel-

atively large sample sizes, high response rates, and use of objective

measures of academic achievement based on final grades. Also, the pro-

spective design of Study II and Study III contributed to the strength of the

conclusions.

Implications for future research

As stated in the beginning of the present thesis, an exhaustive investiga-

tion of a broad and complex research topic like chronic stress in a hetero-

geneous and complex population like adolescents would be impossible to

accomplish within the scope of one thesis. However, an attempt was

made to provide some novel and exciting insights which may inspire

other researchers to dig into and further this very important research area.

Experiencing the symptoms of social jetlag on a weekly basis, as oc-

curred among the adolescents of this thesis, will eventually drain a person

of the energy that is needed for overall functioning, health, and well-

being. While social jetlag may be a fairly new concept, its prevalence and

48

potential negative impact provide reason to dedicate more attention to it

in the future within the research area of chronic stress among adolescents.

The fact that sufficient recovery has been shown to be essential for pre-

venting adults from clinical burnout, as indicated by Söderström (2012),

also highlights the importance of further research on regenerative pro-

cesses, such as sleep and recovery among adolescents. Not only sleep but

other regenerative activities, such as contemplation, relaxation, and par-

ticipation in cultural or physical activities, may be helpful in restoring the

body’s energy and thus deserve consideration in future research attempts

within this area.

It was shown that chronic stress was associated with academic

achievement at the end of high school. For future research, it would be

interesting to separately investigate the relative contribution of each of

the three chronic stress/burnout dimensions to adolescents’ academic

achievement, i.e., emotional exhaustion, physical exhaustion, and cogni-

tive difficulties. One might expect that cognitive difficulties and/or phys-

ical exhaustion might contribute most to the impairment of school per-

formance. Hypotheses on this could be formulated and tested. The out-

comes of the present thesis may also be useful for developing, estimating,

and testing theories and hypotheses about the causes and effects of chron-

ic stress.

The present thesis indicates that high perceived demands are associat-

ed with an increased risk for chronic stress. Providing a more exhaustive

picture of both the origins of these demands, in terms of inner versus

external demands, as well as of the domains within which these demands

are perceived and their relative importance (like academic demands,

physical appearance, social demands, economic demands etc.) would be

an interesting task for future research. Moreover, the definition of social

support was limited to supportive relationships in school only. Therefore,

more thorough measurements of the impact of different aspects of social

support on chronic stress perceptions would be of value.

The question of whether chronic stress may not only have importance

for academic achievement but also increase the risk for negative health

problems, such as clinical burnout later in life, remains. In order to pro-

vide an answer to this crucial question, longitudinal research is needed.

Following the same individuals over the course of several years, for ex-

ample, through high school and into adulthood, may provide an answer to

that question.

Future research could further build upon the findings of this thesis

through a qualitative research approach. An investigation of the factors

that serve to protect individuals from experiencing chronic stress in high

school would be interesting. Interviews of stress-resilient adolescents

could provide useful information for chronic stress prevention. Moreover,

49

it would be valuable to see if self-esteem might moderate stress reactivity

or coping strategies. To investigate the importance of other personality

aspects, such as perfectionism or obsessive–compulsive personality dis-

order, would also be of interest when examining chronic stress among

adolescents.

The focus in the present thesis was exclusively on individual charac-

teristics. Yet, the context within which individuals behave, study, and live

certainly also influences their well-being. For instance, previous studies

have taken the school setting into account when studying adolescent

stress and psychosomatic health and found that having a positive school

climate promoted health and decreased the risk for stress-related health

problems (Modin et al., 2011; Modin & Östberg, 2009; Salmela-Aro et

al., 2008). Other contextual factors which probably play a crucial role for

adolescents’ stress perception include the family context and the socio-

economic context. It remains for future research to take such factors into

consideration when investigating chronic stress among adolescents.

In short, hopefully, research on chronic stress among adolescents is to

be continued. When it comes to chronic stress prevention among adoles-

cents, more scientifically satisfactory research attempts are called for, as

indicated below.

Practical implications – preventing chronic stress

among adolescents

The results of the present thesis indicate that there is a critical need to

develop effective practical interventions for minimizing chronic stress

among adolescents.

Several attempts to decrease stress among adolescents have been made

(deAnda, 1998; Frydenberg et al., 2004; Harraldsson et al., 2008;

Hampel, Meier, & Kuemmel, 2008; Yahav & Cohen, 2008). School is a

natural setting for attempting to promote the health of as many adoles-

cents as possible (Haraldsson, et al., 2008; Kimber, Sandell, & Bremberg,

2008). It both provides good accessibility to adolescents and is appropri-

ate because the stressors and demands perceived by students most often

concern school-related issues (deAnda et al., 2000). In their meta-analysis

on nineteen stress interventions in classroom settings, Kraag, Zeegers,

Kok, Hosman, and Huijer-Abu-Saad (2006) came to the conclusion that

school programs targeting stress management or coping skills were effec-

tive.

Yet, SBU’s (2010) review on programs which aim at preventing young

people from experiencing stress and mental ill-health found that the ef-

50

fectiveness of these programs could not be backed by more than limited

scientific evidence. The systematic development, implementation, and

evaluation of stress treatment programs by means of randomized con-

trolled trials with systematic follow-up measurements are rare.

An attempt to develop a chronic stress prevention program was made

by researchers from the Stress Research Institute within the project

“Stress prevention in high school” in 2009–10 (Perski et al., 2010). In the

course of this project, a stress prevention program among high school

students who suffered from severe stress symptoms as indicated by the

SMBQ was developed and pilot-tested by my colleague Giorgio Grossi

and me. The program was designed as a group intervention. The compo-

nents of the program were based on the then available findings from the

present thesis in combination with insights from clinical psychological

work with adult burnout patients and current relevant treatment findings

and manuals (Grossi, 2008; Hayes, Strohsal, & Wilson, 1999; Livheim,

2004; Makower, 2008; Söderström, 2007). Due to the fairly high dropout

rates among the participating high school students, it has been problemat-

ic to scientifically evaluate the program’s treatment effects. The program

is still in development and more research is needed in order to confirm its

effectiveness. In the following section, some reflections on chronic stress

prevention based on the findings of the present thesis and the experiences

from the intervention pilot-project are provided.

The program was developed based on the theory and several treatment

elements from Cognitive Behavioral Therapy (CBT) and Acceptance and

Commitment Therapy (ACT). It consisted of elements such as

psychoeducation about stress and sleep, values work and committed ac-

tion, mindfulness, assertiveness training, and positive diary to enhance

self-esteem, just to name a few.

The inclusion of psychoeducation aimed to provide the participants

with knowledge about stress in general and training in recognizing indi-

vidual stress-evoking situations, stress-evoking thoughts and feelings,

physiological stress reactions, stress behaviors (i.e., adequate vs. inade-

quate coping strategies), and stress symptoms (Grossi, 2008).

ACT provides a promising approach for equipping individuals with a

broader and more flexible behavior repertoire even when facing challeng-

ing unforeseen events and high perceived demands, which was a main

purpose of the prevention program (Hayes et al., 1999; Livheim, 2004).

Hence, participants were asked to define their personal values, commit to

them, and try to live up to them despite any perceived barriers they may

have.

Because of the stress buffering effect of social support, the participants

were also provided with assertiveness training. Through this, apart from

having learned how to adequately deal on their own with aversive feel-

51

ings and thoughts that arise from perceived demands, the participants

became more skilled in how to mobilize social support by communicating

their needs, worries, and feelings of vulnerability to their social network.

They were taught that it is not only okay to show vulnerability and ask

for help, but that is also necessary and appropriate to do so in the face of

insuperable barriers and challenges. Indeed, in order to do so, a secure

social network that consists of accessible adults and supportive relation-

ships is needed.

In addition, it can be helpful to focus on the present moment and envi-

sion situations more objectively in order to see future events and chal-

lenging situations, such as academic exams, in a more neutral light rather

than as unmanageable threats and potential catastrophes. Therefore,

mindfulness training, which has been found to have a positive impact on

performance (Shao & Skarlicki, 2009), was incorporated into the inter-

vention. Besides, the students were given the opportunity to learn some

body-consciousness and breathing techniques, which have been found to

be useful in the treatment of adult clinical burnout patients (Ristiniemi).

To increase adolescents’ global self-esteem and to help them maintain

their sense of self-worth even when difficulties in life arise (Rosenberg,

1972) was identified as an important aspect in chronic stress prevention.

Self-esteem is indicative of individuals’ self-efficacy, which, according to

Bandura (1997, 2000), provides people with awareness about their own

capability of mastering certain situations. Therefore, focusing on increas-

ing adolescents’ self-efficacy, by giving them the tools to help them real-

ize that they are capable of successfully and autonomously solving prob-

lems or difficulties, may boost their self-esteem and help them to appraise

demands as less threatening or more manageable. Baumeister et al.

(2003) recommend reinforcing socially desirable behaviors and promot-

ing self-improvement to boost self-esteem. In other words, adolescents

have to be given the opportunity to experience that they can master chal-

lenges, which increases their self-efficacy and self-esteem. Within the

program, the participants were invited to use a CBT-based method, called

positive diary, developed by Makower (2008).

Finally, my colleague and I were especially surprised by the partici-

pants’ astonishment when they learned about the importance of sleep and

sufficient recovery in order to prevent stress, stay healthy, and perform

well in school. In the course of the program, the participants learned

about sleep in general, the importance of adequate sleeping routines, and

how to promote their sleep (Grossi, 2008; Söderström, 2007). Undoubt-

edly, adequate and regular sleep timing is an important factor when it

comes to chronic stress prevention among adolescents. However, to simp-

ly increase adolescents’ awareness of the importance of regular and suffi-

cient sleep and recovery is probably not enough. In previous research,

52

particularly late chronotypes found it difficult to implement earlier and

regular bed and rise times (Digdon, 2010; Zimmermann, 2011). Also, the

present outcomes that social jetlag was associated with severe stress

symptoms and worse academic achievement emphasize the importance of

finding effective methods to promote behavior changes that support suffi-

cient recovery and regular sleep. Other alternatives for accommodating

adolescents’ circadian rhythms and thereby counteracting the risk for

social jetlag and associated chronic stress may be to delay school start

times or to add more flexibility to the organization of the school curricu-

lum (Hsu, Gau, Shang, Chiu, & Lee, 2012; Mecacci & Rocchetti, 1998;

Owens, Belon, & Modd, 2010; Wolfson & Carskadon, 2003).

All in all, it is difficult to develop a group intervention program which

fits the individual needs and circumstances of all participants. Yet, hope-

fully, the findings of the present thesis will turn out to be applicable in

providing chronically stressed adolescents with some useful insights and

practical skills for coping better with their stress. To demonstrate this

remains a mission for future research.

53

Concluding remarks

Serious stress symptoms were reported by more than 30% of the investi-

gated sixteen-year-old high school students. Besides the negative conse-

quences chronic stress among adolescents might have on health in the

long run, it plays a more immediate role, for example, in academic

achievement, which has a direct impact on a young person’s future

chances of being accepted into a quality line of education. Moreover,

academic achievement is both associated with chronic stress and social

jetlag, which refers to the effects of major shifts in bedtimes between

school days and weekends. Global self-esteem, perceived demands,

sleep/recovery, and social support are considered to be the most relevant

factors in understanding adolescents’ chronic stress. Thus, their im-

provement should be seen as an essential aim in chronic stress prevention

programs for adolescents.

54

References

Ahrén, J.C. (2010). Skolan och ungdomars psychosociala hälsa [School and adolescents’ psychosocial health]. Stockholm: Socialdepartementet, [Minis-try of Health and Social Affairs], Research report, SOU 2010:80.

Aldwin, C.M. (2007). Stress, coping and development. An integrative perspec-tive. (2nd ed.) Guilford Press.

deAnda, D. (1998). The evaluation of a stress management program for middle school adolescents. Child and Adolescent Social Work Journal, 15 (1), 73-84.

deAnda, D., Baroni, S., Boskin, L., Buchwald, L., Morgan, J., Ow, J., Siegel Gold, J., & Weiss, R. (2000). Stress, stressors and coping among high school students. Children and Youth Services Review, 22 (6), 441-463.

Arnett, J.J. (1999). Adolescent storm and stress, reconsidered. American Psychologist, 54 (5), 317-326.

Arnsten, A.F. (2009). Stress signaling pathways that impair prefrontal structure and function. Nature Reviews Neuroscience, 10 (6), 410-422.

Armon, G., Shirom, A., Shapira, I., & Melamed, S. (2008). On the nature of burnout-insomnia relationships: A prospective study of employed adults. Journal of Psychosomatic Research, 65 (1), 5-12.

Auger, R.R., Burgess, H.J., Dierkhising, R.A., Sharma, R.G., & Slocumb, N.L. (2011). Light exposure among adolescents with delayed sleep phase disor-der: a prospective cohort study. Chronobiology International, 28 (10), 911-920.

Avison, R., & McAlpine, D.D. (1992). Gender differences in symptoms of de-pression among adolescents. Journal of Health and Social Behavior, 33 (2), 77-96.

Bandura, A. (1997). Self-efficacy. The exercise of control. New York: Freeman and Company, Inc.

Bandura, A. (2000). Self-efficacy. In A.E. Kazdin (Ed.), Encyclopedia of psy-chology 7 (pp. 212-213). Washington, DC, US: American Psychological As-sociation.

Basow, S.A., & Rubin, L.R. (1999). Gender influences on adolescent develop-ment. In N.G. Johnson, M.C. Roberts & J. Worell (Eds.), Beyond appear-ance: A new look at adolescent girls (p25-52). Washington DC: APA.

Baumeister, R.F., Campbell, J.D., Krueger, J.I., & Vohs, K.D. (2003). Does high self-esteem cause better performance, interpersonal success, happiness, or healthier lifestyles? Psychological science in the public interest, 4 (1), 1-44.

Beebe, D.W., Rose, D., & Amin, R. (2010). Attention, learning, and arousal of experimentally sleep-restricted adolescents in a simulated classroom. Jour-nal of Adolescent Health, 47, 523-525.

55

Besoluk, S., Önder, I., & Deveci, I. (2011). Morning-evening preferences and academic achievement of university students. Chronobiology International, 28 (2), 118-125.

Bernert, R., Merrill, K., Braithwaite, S., VanOrden, K., & Joiner, T. (2007). Family life stress and insomnia symptoms in a prospective evaluation of young adults. Journal of Family Psychology, 21(1), 58-66.

Birndorf, S., Ryan, S., Auinger, P., & Aten, M. (2005). High self-esteem among adolescents: Longitudinal trends, sex differences, and protective factors. Journal of Adolescent Health, 37, 194-201.

Blom, V. (2011). Striving for self-esteem: Conceptualization and role in burn-out. Doctoral thesis, Department of Psychology, Stockholm University.

Blom, V. (2012). Contingent self-esteem, stressors and burnout in working women and men. Work: A Journal of Prevention, Assessment and Rehabili-tation, 43 (2), 123-131.

Brandalize, M., Felden Pereira, R., Leite, N., Lorenzi Filho, G., & Mazzilli Louzada, F. (2011). Effect of morning school schedule on sleep and anthro-pometric variables in adolescents: a follow-up study. Chronobiology International, 28 (9), 779-785.

Bremberg, S. (2006). Ungdomar, stress och psykisk ohälsa – Analyser och förslag till åtgärder [Adolescents, stress, and mental health – Analyses and proposals for action]. Stockholm: Socialdepartementet [Ministry of Health and Social Affairs], Research report, SOU 2006:77.

Brolin-Låftman, S., & Modin, B. (2012). School-performance indicators and subjective health complaints: are there gender differences? Sociology of Health and Illness, 34 (4), 608-625.

Brolin-Låftman, S., & Östberg, V. (2006). The pros and cons of social relations: an analysis of adolescents’ health complaints. Social Science & Medicine, 63 (3), 611-623.

Buboltz, W.C., Brown, F., & Soper, B. (2001). Sleep habits and patterns of col-lege students: a preliminary study. Journal of American college health, 50 (3),131-135.

Butler, G. (1993). Definitions of stress. Occasional Paper Series RCGP, 61, 1-5. Butler, R.J., & Gasson, S.L. (2005). Self esteem/Self concept scales for children

and adolescents: A review. Child and Adolescent Mental Health, 10 (4), 190-201.

Byrne, D.G., Davenport, S.C., & Mazanov, J. (2007). Profiles of adolescent stress: The development of the adolescent stress questionnaire (ASQ). Jour-nal of Adolescence, 30, 393-416.

Campbell, J. D., & Lavallee, L. F. (1993). Who am I? The role of self-concept confusion in understanding the behavior of people with low self-esteem. In R.F. Baumeister (Ed.), Self-esteem: The puzzle of low self-regard (pp. 1 – 20). NY: Plenum.

Cannon, W.B. (1922). Bodily changes in pain, hunger, fear and rage. An ac-count of recent researches into the function of emotional excitement. New York and London D. Appleton and Company.

Chapman, P.L., & Mullis, R.L. (1999). Adolescent coping and self-esteem. Child study journal 29 (1), 69-78.

Cherniss, C. (1980). Staff Burnout. Job stress in the human services. Sage Publi-cations, Beverly Hills, London.

56

Crocker, J., & Wolfe, C.T. (2001). Contingencies of self-worth. Psychological Review, 108 (3), 593-623.

Crocker, J. (2002). The costs of seeking self-esteem. Journal of Social Issues, 58(3), 597-615.

Curcio, G., Ferrara, M., & DeGennaro, L. (2006). Sleep loss, learning capacity and academic performance. Sleep Medicine Reviews, 10, 323-337.

Dagys, N., McGlinchey, E.L., Talbot, L.S., Kaplan, K.A., Dahl, R.E., & Harvey, A.G. (2012). Double trouble? The effects of sleep deprivation and chronotype on adolescent affect. Journal of Child Psychology and Psychia-try, 53 (6), 660-667.

Dahl, R.E., & Lewin, D.S. (2002). Pathways to adolescent health: sleep regula-tion and behavior. Journal of Adolescent Health, 31, 175-184.

Dalman, C., & Wicks, S. (2006). Vilka grupper söker vård inom psykiatrin? En uppföljningsstudie av psykiatrisk vård och beroende vård i Stockholms län 1998-2005 [Who is seeking psychiatric care? A follow-up study on psychiat-ric care and care of addicts in Stockholm between 1998 and 2005]. Research report (nr. 6). Centrum för folkhälsa SLL [Center for public health], Stockholm.

Dedovic, K., Wadiwalla, M., Engert, V., & Pruessner, J.C. (2009). The role of sex and gender socialisation in stress reactivity. Developmental Psychology, 45 (1), 45-55.

Digdon, N. (2010). Circadian preference and college students’ beliefs about sleep education. Chronobiology International, 27 (2), 297-317.

Dumont, M., & Provost, M.A. (1998). Resilience in adolescents: Protective role of social support, coping strategies, self-esteem, and social activities on ex-perience of stress and depression. Journal of Youth and Adolescence, 28 (3), 343-363.

Eccles, J., Brown, B.V., & Templeton, J. (2008). A development framework for selecting indicators of well-being during the adolescent and young adult years. In Brown B.V. (Ed.), Key indicators of child and youth well-being (pp.197-236). Lawrence Erlbaum Associates, New York.

Ekstedt, M. (2005). Burnout and Sleep. Doctoral thesis, Department of Public Health Sciences, Karolinska Institute.

Ekstedt, M., Söderström, M., Åkerstedt, T., Nilsson, J., & Sondergaard, H.P., & Perski, A. (2006). Disturbed sleep and fatigue in occupational burnout. Scandinavian Journal of Work Environment and Health, 32 (2), 121-131.

Feingold, A. (1994). Gender differences in personality: a meta-analysis. Psycho-logical Bulletin, 116, 429-456.

Folkow, B. (1997). Physiological aspects of the “defence” and “defeat” reac-tions. Acta Physiologica Scandinavica Supplementum, 640, 34-37.

Freudenberger, H.J. (1974). Staff burn-out. Journal of Social Issues, 30, 159-165.

Friberg, P., Hagquist, C., & Osika, W. (2012). Self-perceived psychosomatic health in Swedish children, adolescents and young adults: an internet-based survey over time. BMJ Open; 2:e000681.

Frydenberg, E. (2002). Adolescent coping. Advances in Theory, Research and Practice. Taylor & Francis.

57

Frydenberg, E., Lewis, R., Bugalski, K., Cotta, A., McCarthy, C., & Luscombe-Smith, N., et al. (2004). Prevention is better than cure: Coping skills training for adolescents at school. Educational Psychology in Practice, 20, 117-134.

Fuligni, A., & Hardway, C. (2006). Daily variation in adolescents’ sleep, activi-ties, and psychological well-being. Journal of Research on Adolescence, 16 (3), 353-378.

Gillander-Gådin, K., & Hammarström, A. (2000). School-related health - a cross-sectional study among young boys and girls. International Journal of Health Services, 30 (4), 797-820.

Gomes, A.A., Tavares, J., & deAzevedo, M.H. (2011). Sleep and academic per-formance in undergraduates: a multi-measure, multi-predictor approach. Chronobiology International, 28 (9), 786-801.

Grossi, G. (2008). Hantera din stress med kognitiv beteendeterapi [Coping with stress through CBT]. Viva.

Grossi, G., Perski, A., Evengård, B., Blomkvist, V., & Orth-Gomér, K. (2003). Physiological correlates of burnout among women. Journal of Psychosomat-ic Research, 55, 309-316.

Gustafsson, J.-E., Allodi, M., Alin-Åkerman, B., Eriksson, C., Eriksson, L., & Fischbein, S., et al. (2010), School, Learning and Mental Health. A systemat-ic review. Health committee, The Royal Swedish Academy of Sciences.

Hagquist, C. (2009). Psychosomatic health problems among adolescents in Swe-den – are the time trends gender related? European Journal of Public Health, 19 (3), 331-336.

Hagquist, C. (2010). Discrepant trends in mental health complaints among younger and older adolescents in Sweden: An analysis of WHO data 1985-2005. Journal of Adolescent Health, 46, 258-264.

Hallsten, L., Bellaagh, K., & Gustafsson, K. (2002). Utbränning i Sverige – en populationsstudie [Burnout in Sweden – a population study]. Arbete och Hälsa, Arbetslivsinstitutet [National Institute of Working Life], (Nr. 2002:6).

Hallsten, L., Josephson, M., & Torgén, M. (2005). Performance-based self-esteem: A driving force in burnout processes and its assessment. Arbete och Hälsa. Arbetslivsinstitutet [National Institute of Working Life], Nr.2005:4.

Hallsten, L., Voss, M., Stark, S., Josephson, M., & Vingård, E. (2011). Job burn-out and job wornout as risk factors for long-term sickness absence. Work, 38, 181-192.

Hampel, P., Meier, M., & Kuemmel, U. (2008). School-based stress management training for adolescents: longitudinal results from experimental study. Jour-nal of Youth and Adolescence, 37, 1009-1024.

Hankin, B.L., Mermelstein, R., & Roesch, L. (2007). Sex differences in adoles-cent depression: Stress exposure and reactivity models. Child Development, 78 (1), 279-295.

Haraldsson, K.S. (2010). Buffra stress i riktning mot välbefinnande. Interventionsstudier och utforskande studier med fokus på unga flickor [Buffering stress for well-being. Intervention studies and explorative studies focusing on adolescent girls]. Doctoral thesis, University of Gothenburg, Sahlgrenska Academy.

Haraldsson, K.S., Lindgren, E-C.M., Fridlund, B.G., Baigi, A.M., Lydell, M.C., & Marklud, B.R. (2008). Evaluation of a school-based health promotion

58

program for adolescents aged 12-15 years with focus on well-being related to stress. Public Health, 122, 25-33.

Harter, S. (1993). Causes and consequences of low self-esteem in children and adolescents. In R.F. Baumeister (Ed.), Self-esteem. The puzzle of low self-regard (pp. 87-116). NY: Plenum.

Hayes, S.C., Strohsal, K.D., & Wilson, K.G. (1999). Acceptance and Commit-ment Therapy. An experiential approach to behavior change. The Guliford Press. New York London.

Hjern, A., Alfven, G., & Östberg, V. (2007). School stressors, psychological complaints and psychosomatic pain. Acta Paediatrica, 97, 112-117.

Howell, A.J., Jahrig, J.C., & Powell, R.A. (2004). Sleep quality, sleep propensity and academic performance. Perceptual and Motor Skills, 99 (2), 525-535.

Hsu, C-Y., Gau, S.S-F., Shang, C-Y., Chiu, Y-N., & Lee, M-B. (2012). Associa-tions between chronotypes, psychopathology, and personality among college students. Chronobiology International, 29 (4), 491-501.

Huan, V.S., Lay-See, Y., Ang, R.P., & Wan-Har, C. (2008). The impact of ado-lescent concerns on their academic stress. Educational Review, 60 (2), 169-178.

Ipsiroglu, O.S., Fatemi, A., Werner, I., Paditz, E., & Schwarz, B. (2002). Self-reported organic and nonorganic sleep problems in schoolchildren aged 11 to 15 years in Vienna. Journal of Adolescent Health, 31, 436-422.

Johnson, M. (1997). On the dynamics of Self-Esteem. Empirical validation of Basic self-esteem and Earning self-esteem. Doctoral thesis, Department of Psychology, Stockholm University.

Johnson, M., & Forsman, L. (1995). Competence strivings and self-esteem: an experimental study. Personality and Individual Differences, 19 (4), 417-430.

Jonsdottir, I.H., Nordlund, A., Ellbin, S., Ljung, T., Gilse, K., Währborg, P., & Wallin, A. (2012). Cognitive impairment in patients with stress-related ex-haustion. Stress, 1-10.

KFA, Karolinska Folkhälsoakademi (2009). Barnen i folkhälsorapporterna. Hur mår barn och unga vuxna i Stockholms län? [Children in public health re-ports. How well are children and adolescents in Stockholm?] Research report, 2009:02, Karolinska Institutet.

Kaplan, D.S., Liu, R.X., & Kaplan, H.B. (2005). School related stress in early adolescence and academic performance three years later: the conditional in-fluence of self-expectations. Social Psychology of Education, 8, 3-17.

Karasek, R., & Theorell, T. (1990). Healthy work: stress, productivity, and the reconstruction of working life. New York, NY: Basic Books.

Kecklund, G. & Åkerstedt, T. (1992). The psychometric properties of the Karolinska Sleep Questionnaire. Journal of Sleep Research, 1 (suppl 1), 113.

Kelly, W.E., Kelly, K.E., & Clanton, R.C. (2001). The relationship between sleep length and grade-point average among college students. College Stu-dent Journal, 35 (1), 84-87.

Kernis, M.H. (2006). Self-esteem, issues and answers. A sourcebook of current perspectives. New York: Psychology Press.

Keski-Rahkonen, A., Kaprio, J., Rissanen, A., Virkkunen, M., & Rose, R.J. (2003). Breakfast skipping and health-compromising behaviors in adoles-cents and adults. European Journal of Clinical Nutrition, 57, 842-853.

59

Kimber B., Sandell R., & Bremberg S. (2008). Social and emotional training in Swedish classrooms for the promotion of mental health: results from an ef-fectiveness study in Sweden. Health Promotion International, 23, 134-143.

Kivimäki, M., & Kalimo, R. (1996). Self-esteem and the occupational stress process: testing two alternative models in a sample of blue-collar workers. Journal of Occupational Health Psychology, 1 (2), 187-196.

Kling, K.C., Shibley-Hyde, J., Showers, C.J., & Buswell, B.N. (1999). Gender Differences in Self-Esteem: A Meta-Analysis. Psychological Bulletin, 125 (4), 470-500.

Kraag, G., Zeegers, M.P., Kok, G., Hosman, C., & Huijer Abu-Saad, H. (2006). School programs targeting stress management in children and adolescents: A meta-analysis. Journal of School Psychology, 44, 339-472.

Kroger, J. (2006). Identitetsutvecklingen i de tidiga vuxenåren [Identity development in early adulthood]. In A. Frisén & P. Hwang (Eds.), Ungdomar och Identitet [Adolescents and identity]. Blåvita Serien, Natur och Kultur.

KVH, Kungliga Vetenskapsakademiens Hälsoutskott [The Royal Swedish Academy of Science] (2010). Barns och ungdomars psykiska hälsa i Sverige. En systematisk litteraturöversikt med tonvikt på förändring över tid [Children’s and adolescents’ mental health in Sweden. A systematic review of the literature with a focus on change over time]. Research report.

Langstedt, E., Asplund, K., & Gillander-Gådin, K. (2009). Understanding ado-lescent mental health: The influence of social processes, doing gender and gendered power relations. Sociology of Health and Illness, 31(7), 962-978.

Lazarus, R.S. (1993). From psychological stress to the emotions: A history of changing outlooks. Annual Review of Psychology, 44, 1-21.

Lazarus, R.S. (1999). Stress and emotion. A new synthesis. Springer Publishing Company Inc.

Lazarus, R.S., & Folkman, S. (1984). Stress, appraisal, and coping. New York: Springer.

Levi, L. (2005). Stress – en översikt. Internationella och folkhälsoperspektiv [Stress – an overview. An international and public health perspective]. In R. Ekman & B. Arnetz (Eds.), Stress. Molekylerna-individen-Organisationen– Samhället [Stress. Molecules – the individual – the organization – society] (pp. 56-71). Liber: Stockholm.

Lidwall, U. (2010). Långtidssjukskrivna. Beskrivande statistik 1999-2009: kön, ålder, arbetsmarknadsstatus, sjukskrivningslängd, och diagnospanorama [Individuals on long-term sickleave. Descriptive statistics 1999-2009: sex, age, working status, duration of sickness absence, and medical diagnoses]. Socialförsäkringsrapport [Social insurance report] 2010:11. Stockholm, Försäkringskassan.

Lien, L. (2006). Is breakfast consumption related to mental distress and academ-ic performance in adolescents? Public health Nutrition, 10 (4), 422-428.

Lindblom, K.M., Linton, S.J., Fedeli, C., & Bryngelsson, I-L. (2006). Burnout in the working population: Relations to psychosocial work factors. Internation-al Journal of Behavioral Medicine, 13(1),51-59.

Liston, C., McEwen, B.S., & Casey, B.J. (2008). Psychosocial stress reversibly disrupts prefrontal processing and attentional control. PNAS, Proceedings of the National Academy of Sciences, 103(3), 912-917.

60

Liu, X., & Kaplan, H.B. (1999). Explaining gender differences in symptoms of subjective distress in young adolescents. Stress Medicine, 15, 41-51.

Livheim, F. (2004). Acceptance and Commitment Therapy i skolan – att hantera stress. En randomiserad, kontrollerad studie [Acceptance and Commitment Therapy in school – coping with stress. An RCT study]. Psychological mas-ter thesis, Uppsala University.

Locke, E.A., McClear, K., & Knight D. (1996). Self-esteem and work. Interna-tional Review of Industrial/Organizational Psychology, 11, 1-32.

Lund, H.G., Reider, B.D., Whiting, A.B., & Prichard, J.R. (2010). Sleep patterns and predictors of disturbed sleep in a large population of college students. Journal of Adolescent Health, 46, 124-132.

Lundberg, U. (2005). Stress hormones in health and illness: The roles of work and gender. Psychoneuroendocrinology, 30 (10), 1017-1021.

Lundgren-Nilsson, Å., Jonsdottir, I.H., Pallant, J., & Ahlborg, G. (2012). Internal construct validity of the Shirom-Melamed Burnout Questionnaire (SMBQ). Public Health, 12, 1-8.

Lupien, S.J., McEwen, B.S., Gunnar, M.R., & Heim, C. (2009). Effects of stress throughout the lifespan on the brain, behavior and cognition. Nature Reviews Neuroscience, 10, 434-445.

Major, B., Barr, L., Zubek, J., & Babey, S.H. (1999). Gender and self-esteem: A meta-analysis. In W.B. Swann, J.H. Langlois, & L.A. Gilbert (Eds.), Sexism and stereotypes in modern society: The gender science of Janet Taylor Spence (pp. 223–253). Washington, DC: American Psychological Associa-tion.

Makower, I. (2008). Att bygga upp självkänslan med hjälp av KBT [Building upp self-esteem through CBT]. Psykisk Hälsa, 2 (28), 22-34.

Marcia, J. (2006). Jagidentitet och objektrelationer [Identity and object relations]. In A. Frisén & P. Hwang (Eds.), Ungdomar och Identitet [Adolescents and identity]. Blåvita Serien, Natur och Kultur.

Marin, M-F., Lord, C., Andrews, J., Juster, R-P., Sindi, S., Arsenault-Lapierre, G., et al. (2011). Chronic stress, cognitive functioning and mental health. Neurobiology of Learning and Memory, 96, 583-595.

Marsh, H.W., & Hau, K-T., (2003). Big-Fish-Little-Pond Effect on academic self-concept. A cross-cultural (26-country) test of the negative effects of ac-ademically selective schools. American Psychologist, 58 (5), 364-376.

Maslach, C. (2001). What have we learned about burnout and health? Psycholo-gy and Health, 16 (5), 607-611.

Maslach, C., & Jackson, S.E. (1981). The measurement of experienced burnout. Journal of Occupational Behaviour, 2, 99-113.

Maslach, C., & Leiter, M.P. (1997). The truth about burnout. San Fransico: Jossey-Bass.

Maslach, C., Schaufeli, W.B., & Leiter, M.P. (2001). Job burnout. Annual Re-view of Psychology, 52, 397-422.

McEwen, B.S., & Stellar, E. (1993). Stress and the Individual: Mechanisms leading to disease. Archives of Internal Medicine, 153 (18), 2093-2101.

McEwen, B.S. (2006). Protective and damaging effects of stress mediators: cen-tral role of the brain. Dialogues Clinical Neuroscience, 8 (4), 367-381.

Mecacci, L., & Rocchetti, G. (1998). Morning and evening types: stress-related personality aspects. Personality and Individual Differences, 25, 537-542.

61

Meijer, A.M., Habekothe, H.T., & Van Den Wittenboer, G.L. (2000). Time in bed, quality of sleep and school functioning of children. Journal of Sleep Re-search, 9, 145–153.

Melamed, S., Kushnir, T., & Shirom, A. (1992). Burnout and Risk Factors for Cardiovascular Diseases. Behavioral medicine, 18, 53-60.

Melamed, S., Shirom, A., Toker, S., Berliner, S., & Shapira, I. (2006). Burnout and Risk of Cardiovascular Disease: Evidence, Possible Causal Paths, and Promising Research Directions. Psychological Bulletin, 132 (3), 327-353.

Modin, B., & Östberg, V. (2009). School climate and psychosomatic health: a multilevel analysis. School Effectiveness and School Improvement: An In-ternational Journal of Research, Policy and Practice, 20 (4), 433-455.

Modin, B., Östberg, V., Toivanen, S., & Sundell, K. (2011). Psychosocial work-ing conditions, school sense of coherence and subjective health complaints. A multilevel analysis of ninth grade pupils in the Stockholm area. Journal of Adolescence, 34 (1), 129-139.

Moksnes, U.K., Moljord, I.E., Espnes, G.A., & Byrne, D.G. (2010). The associa-tion between stress and emotional states in adolescents: The role of gender and self-esteem. Personality and Individual Differences, 49, 430-435.

Mortimer, J.T., Zimmer-Gembeck M.J., Holmes M., & Shanahan, M.J. (2002). The process of occupational decision making: Patterns during the transition to adulthood. Journal of Vocational Behavior, 61, 439-65.

Murberg, T.A., & Bru, E. (2004). School-related stress and psychosomatic symp-toms among Norwegian adolescents. School Psychology International, 25 (3), 317-332.

Nabkasorn, C., Miyai, N., Sootmongkol, A., Junprasert, S., Yamamoto, H., Arita, M., & Miyashita, K. (2005). Effects of physical exercise on depres-sion, neuroendocrine stress hormones and physiological fitness in adolescent females with depressive symptoms. European Journal of Public Health, 16 (2), 179-184.

Ollfors, M., & Andersson, S.I. (2007). Ability of stress, sense of control, and self-theories to predict Swedish high school students’ final grades. Educa-tional Research and Evaluation, 13 (2), 143-169.

Östberg, V. (2001). Hälsa och välbefinnande [Health and well-being]. In: Barns och ungdomars välfärd [Children’s and adolescents’ welfare]. Stockholm: Socialdepartementet, [Ministry of Health and Social Affairs], Research re-port, SOU 2001:55.

Owens, J.A., Belon, K., & Moss, P. (2010). Impact of delaying school start time on adolescent sleep, mood, and behavior. Archives of Pediatrics and Adoles-cent Medicine, 164 (7), 608-614.

Perski, A. (2006). Ur balans. Bonnier Fakta. Perski, A., Schraml, K., Grossi, G., Makower, I., & Ivarsson, M. (2010).

Intervention mot stress i gymnasiet. En slutrapport avseende projektet FP308 för Länsförsäkringars Forskningsfond. Research report, Stress Research Institute, Stockholm University.

Pilcher, J.J., Ginter, D.R., & Sadowsky, B. (1997). Sleep quality versus sleep quantity: relationships between sleep and measures of health, well-being and sleepiness in college students. Journal of Psychosomatic Research, 42 (6), 583-596.

62

Pines, A.M., & Aronson, E. (1988). Career burnout: causes and cures. New York. Free Press.

Pines, A.M., & Keinan, G. (2005). Stress and burnout: The significant differ-ence. Personality and Individual Differences, 39, 625-635.

Pyszczynski, T., Greenberg, J., Solomon, S., Arndt, J., & Schimel, J. (2004). Why do people need self-esteem? A theoretical and empirical review. Psy-chological Bulletin, 130 (3), 435-468.

Rabe-Hesketh, S., & Skrondal, A. (2008). Multilevel and longitudinal modeling using Stata. Stata Press.

Randler, C. (2011). Age and gender differences in morningness-eveningness during adolescence. Journal of Genetic Psychology, 172 (3), 302-308.

Rector, N.A., & Roger, D. (1997). The stress buffering effects of self-esteem. Personality and Individual Differences, 23(5), 799-808.

Renstig, M., & Sandmark, H. (2005). Kvinnors sjukskrivning – riskfaktorer för långtidssjukskrivning bland kvinnliga högre tjänstemän [Women’s sickness absence – risk factors for long-term sickness absence among female white-collar workers in high positions]. Research report, Department of Public Health Sciences, Karolinska Institute.

Rhee, H., Holditch-Davis, D., & Miles, M.S. (2005). Patterns of physical symp-toms and relationships with psychosocial factors in adolescents. Psychoso-matic Medicine, 67, 1006-1012.

Ristiniemi, H. Grounding and breathing exercises. For information: www.stressmottagning.nu

Roberts, R.E., Roberts, C.R., & Duong, H.T. (2009). Sleepless in adolescence: Prospective data on sleep deprivation, health and functioning. Journal of Adolescence, 32, 1045-1057.

Robins R.W., & Trzesniewski, K.H. (2005). Self-esteem development across the lifespan. Current Directions in Psychological Science, 14 (3), 158-162.

Roenneberg, T., Wirz-Justice, A., & Merrow, M. (2003). Life between clocks: Daily temporal patterns of human chronotypes. Journal of Biological Rhythms, 18 (1), 80-90.

Rosenberg, M. (1972). Society and the adolescent self image. Princeton, NJ University Press.

Rosenberg, M., Schooler, C., & Schoenbach, C. (1989). Self-esteem and adoles-cent problems: Modeling reciprocal effects. American Sociological Review, 54 (6), 1004-1018.

Ruble, D.N., Greulich, F., Pomerantz, E., & Gochberg, B. (1993). The role of gender-related processes in the development of sex differences in self-evaluation and depression. Journal of Affective Disorders, 29, 97-128.

Rudolph, K.D. (2002). Gender Differences in Emotional Responses to Interper-sonal Stress during Adolescence. Journal of Adolescent Health, 30, 3-13.

Sagatun, A., Sogaard, A.J., Bjertness, E., Selmer, R., & Heyerdahl, S. (2007). The association between weekly hours of physical activity and mental health: A three-year follow-up study of 15-16-year-old students in the city of Oslo, Norway. BMC Public Health, 7, 155-164.

Salmela-Aro, K., Kiuru, N., Pietikäinen, M., & Jokela, J. (2008). Does school matter? The role of school context in adolescents’ school related burnout. European Psychologist, 13 (1), 12-23.

63

Salmela-Aro, K., & Nurmi, J.E., (2007). Self-esteem during university studies predicts career characteristics 10 years later. Journal of Vocational Behav-ior, 70, 463-477.

Salmela-Aro, K., & Tynkkynen, L. (2012). Gendered pathways in school burn-out among adolescents. Journal of Adolescence, 35, 929-939.

Sapolsky, R.M. (2004). Why zebras don’t get ulcer: the acclaimed guide to stress, stress-related diseases and coping. (3rd

edition). Henry Holt and

Company. Sapolsky, R.M., Romero, L.M., & Munck, A.U., (2000). How do Glucocorti-

coids influence stress responses? Integrating permissive, suppressive, stimu-latory, and preparative actions. Endocrine Reviews, 21 (1), 55-89.

Saxvig, I.W., Pallesen, S., Wilhelmsen-Langeland, A., Molde, H., & Bjorvatn, B. (2012). Prevalence and correlates of delayed sleep phase in high school stu-dents. Sleep medicine, 13, 193-199.

SBU, Statens beredning för medicinsk utvärdering [Swedish Council on Health Technology Assessment] (2010). Methods to prevent mental ill-health in children. A systematic review. Research report, 202.

SCB, Statistiska centralbyrån [Statistics Sweden] (2007). Barns hälsa [Chil-dren’s health]. Living Conditions Report, 115.

SCB, Statistiska centralbyrån [Statistics Sweden] (2011). Barns sociala relationer [Children’s social relationships]. Living Conditions Report, 119.

SCB, Statistiska centralbyrån [Statistics Sweden] (2012). Barns upplevelser i skolan [Children’s experiences from school]. Living Conditions Report, 125.

Schaufeli, W.B., Leiter, M.P. & Maslach, C. (2009). Burnout: 35 years of re-search and practice. Career Development International, 14 (3), 204-220.

Schmidt, J.A., & Padilla, B. (2003). Self-esteem and family-challenge: An inter-vention of their effects on achievement. Journal of Youth and Adolescence, 32 (1), 37-46.

Schütz, A. (2003). Psychologie des Selbstwertgefühls. Von Selbstakzeptanz bis Arroganz. [Psychology on self-esteem. From self-acceptance to arrogance] (2nd ed). Kohlhammer.

Seiffge-Krenke, I. (2000). Causal links between stressful events, coping style, and adolescent symptomatology. Journal of Adolescence, 23, 675-691.

Seiffge-Krenke, I., Aunola, K., & Nurmi, J-E., (2009). Changes in stress percep-tion and coping during adolescence: the role of situational and personal fac-tors. Child Development, 80 (1), 259-279.

Selye, H. (1936). A syndrome produced by nocuous agents. Nature, 138, 32. Selye, H. (1978). The stress of life. (2nd ed). New York: McGraw Hill. SFI, Statens folkhälsoinstitut [Swedish National Institute of Public Health]

(2011). Svenska skolbarns hälsovanor 2009/10 [The health-related habits of Swedish school children 2009/10]. Research report, 2011:27.

Shao, R., & Skarlicki, D.P. (2009). The Role of Mindfulness in Predicting Indi-vidual Performance. Canadian Journal of Behavioral Science, 41 (4), 195-201.

Shirom, A. (2003). Job-related burn out. In J.C. Quick & L.E. Tetrick (Eds.), Handbook of occupational health psychology (pp. 245-265). Washington, DC: American Psychological Association.

64

Shirom, A., & Melamed, S. (2006). A comparison of the Construct Validity of Two Burnout Measures in Two Groups of Professionals. International Jour-nal of Stress Management, 13 (2), 176-200.

Shirom, A., Melamed, S., Toker, S., Berliner, S., & Shapira, I. (2005). Burnout and health review: Current knowledge and future research directions. In G.P. Hodgkinson, & J.K. Ford (Eds.), International review of industrial and or-ganizational psychology (Vol. 20, pp. 269–309). Chichester, UK: Wiley.

Skolverket [The Swedish National Agency for Education] (2010). Attityder till skolan 2009. Elevernas och lärarnas attityder till skolan [Attitudes towards school 2009. Pupils’ and teachers’ attitudes towards school]. Research re-port, 334.

Socialstyrelsen [The National Board of Health and Welfare] (2003). Utmattningssyndrom. Stressrelaterad psykisk ohälsa [Exhaustion syndrome. Stress-related mental illness]. Research report.

Socialstyrelsen [The National Board of Health and Welfare] (2009). Folkhälsorapport [Public Health report]. Research report.

Söderström, M. (2007). Sov bättre med kognitiv beteendeterapi [Sleeping better through CBT]. Viva.

Söderström, M. (2012). Burnout – a matter of impaired recovery. Doctoral the-sis, Department of Public Health Sciences, Karolinska Institute.

Söderström, M., Ekstedt, M., Åkerstedt, T., Nilsson, J., & Axelsson, J. (2004). Sleep and Sleepiness in Young Individuals with High Burnout Scores. Sleep: Journal of Sleep and Sleep Disorders Research, 27 (7), 1369-1377.

Sonnenschein, M., Sorbi, M.J., Van Doornen, L.J.P., Schaufeli, W.B., & Maas, C.J.M. (2007). Evidence that impaired sleep recovery may complicate burn-out improvement independently of depressive mood. Journal of Psychoso-matic Research, 62, 487-494.

Spencer, S.J., Josephs, RA, & Steele, C.M. (1993). Low self-esteem. The uphill struggle for self-integrity. In R. F. Baumeister (Ed.), Self-esteem: The puzzle of low self-regard (pp. 21-36). NY: Plenum.

Sterling, P., & Eyer, J. (1988). Allostasis: A new paradigm to explain arousal pathology. In S. Fisher & J. Reason (Eds.), Handbook of life stress, cogni-tion and health (pp.631-651). John Wiley and Sons Ldt.

Stinson, D.A., Logel, C., Zanna, M.P., Holmes, J.G., Cameron, J., Wood, J.V., & Spencer, S.J. (2008). The cost of lower self-esteem: Testing a self- and so-cial-bonds model of health. Journal of Personality and Social Psychology, 94 (3), 412-428.

Stroud, L.R., Salovey, P., & Epel, E.S. (2002). Sex differences in stress respons-es: social rejection versus achievement stress. Society of Biological Psychia-try, 52, 318-327.

Sundblad, G.B., Jansson, A., Saartok, T., Renström, P., & Engström, L.M. (2008). Self-rated pain and perceived health in relation to stress and physical activity among school-students: A 3-year follow-up. Pain, 136 (3), 239-249.

Tarafodi, R.W., & Swann, W.B. (1995). Self-Liking and Self-Competence as Dimensions of Global Self-Esteem: Initial Validation of a Measure. Journal of Personality Assessment, 65 (2), 322-342.

Taylor, D.J., Clay, K.C., Bramoweth, A.D., Sethi, K., & Roane, B.M. (2011). Circadian Phase Preference in College Students: Relationships with psycho-

65

logical functioning and academics. Chronobiology International, 28 (6), 541-547.

Theorell, T. (1996). The demand-control-support model for studying health in relation to work environment – an interactive model. In: K. Orth-Gomer & N. Schneiderman (Eds.), Behavioral medicine approaches to cardiovascular disease prevention (pp. 69-85). New Jersey: Lawrence Erlbaum Associates.

Theorell, T. (2004). Stressmekanismer och sjukskrivning [Stress mechanisms and sickness absence]. In C. Hogstedt, M. Bjurvald, S. Marklund, E. Palmer and T. Theorell (Eds.), Den höga sjukfrånvaron – sanning och konsekvens [High sickness absence rates – truth and consequences]. Research report, R 2004:15, SFI Statens folkhälsoinstitut [Swedish National Institute of Public Health].

Thomson, H. (1998). Anpassningens pris. Kvinnors liv i vård och vardag [The cost of adaptation. The work lives and everyday lives of women who work in health care]. Förlagshuset Gothia AB, Stockholm.

Thoreson, C.E., & Eagleston, J.R. (1983). Chronic stress in children and adoles-cents. Theory into Practice, 22 (1), 48-56.

Troisi, A. (2001). Gender differences in vulnerability to social stress. A Darwini-an perspective. Physiology & Behavior, 73, 443-449.

Vispoel, W.P., Boo, J., & Bleiler, T. (2001). Computerized and paper-and-pencil versions of the Rosenberg self-esteem scale: a comparison of psychometric features and respondent preferences. Educational and Psychological Meas-urement, 61 (3), 461-474.

Walker, M.P. (2008). Cognitive consequences of sleep and sleep loss. Sleep Medicine, 9 (1), 29-34.

Weber, A., & Jaekel-Reinhard, A. (2000). Burnout syndrome: a disease of mod-ern societies? Occupational Medicine, 50 (7), 512-517.

Wiklund, M., Bengs, C., Malmgren-Olsson, E-B., & Öhman, A. (2010). Young women facing multiple and intersecting stressors of modernity, gender or-ders and youth. Social Science & Medicine, 71, 1567-1575.

Wiles, N.J., Jones, G.T., Haase, A.M., Lawlor, D.A., Macfarlane, G., & Lewis, G. (2008). Physical activity and emotional problems amongst adolescents: a longitudinal study. Social Psychiatry and Psychiatric Epidemiology, 43, 765–772.

Wittmann, M., Dinich, J., Merrow, M., & Roenneberg, T. (2006). Social jetlag: Misalignment of biological and social time. Chronobiology International, 23 (1&2), 497-509.

Wolfson, A.R., & Carskadon, M.A. (2003). Understanding adolescents’ sleep patterns and school performance: a critical appraisal. Sleep Medicine Re-view, 7 (6), 491-506.

World Values Survey (2005/08). Available: www.worldvaluessurvey.org Yahav, R., & Cohen, M. (2008). Evaluation of a Cognitive-Behavioral Interven-

tion for Adolescents. International Journal of Stress Management, 15 (2), 173-188.

Yeung, W-F., Chung, K-F., & Cy Chan, T. (2008). Sleep-wake habits, excessive daytime sleepiness and academic performance among medical students in Hong Kong. Biological Rhythm Research, 39 (4), 369-377.

Zimmermann, L.K. (2011). Chronotype and the transition to college life. Chron-obiology International, 28 (10), 904-910.