Perceptual and Motor Skills, 2011, 113, 2, 677-685. © Perceptual and Motor Skills 2011

DOI 10.2466/02.09.13.15.16.PMS.113.5.677-685 ISSN 0031-5125

VItaMIN D aND ExEcutIVE FuNctION: a PrElIMINary rEPOrt1, 2

aNIta l. HaNSEN

Department of Psychosocial Science University of Bergen

Centre for Research and Education in Forensic Psychiatry

Haukeland University Hospital

lISbEtH DaHl

National Institute of Nutrition and Seafood Research

lENE bakkE

Faculty of Education Bergen University College

JulIaN F. tHayEr

Department of Psycho logy The Ohio State University

Mannheim Institute of Public Health, Social and Preventive Medicine

Mannheim Medical Faculty Heidelberg University

Summary.—the aim of this study was to investigate the relationship between vitamin D levels and cognition, both executive and nonexecutive functions, in men incarcerated in a Norwegian prison. Participants were divided into high vitamin D and low vitamin D groups based on established criteria (high level ≥ 50 nmol/L; low level < 50 nmol/L). The mean vitamin D concentration was 69 (SD = 12) and 38 (SD = 9) nmol/L in the high-level group (n = 14) and the low level group (n = 11), re-spectively. Results revealed that the high vitamin D group had significantly more correct responses than the low vitamin D group on the executive function task. there was no difference between the groups on the nonexecutive function task. The reac-tion time data indicated that the high levels of correct responses in the high vitamin D group on the executive function tasks were not due to a speed-accuracy trade-off.

Impulsive and antisocial behaviors as well as other mental disorders (e.g., anxiety and depression) are overrepresented among the incarcerat-ed (Tiihonen, 1993). Interestingly, Gesch, Hammond, Hampson, Eves, and Crowder (2002) argued that the incarcerated are characterized by inad-equacy of nutrients and demonstrated that supplementing the diet with vitamin and mineral capsules caused a reduction in antisocial behavior. However, little is known about the possible mechanisms of this effect. Mechanisms involved in behaviour and self-regulation or psychological functioning are cognitive processes such as executive and nonexecutive

1address correspondence to anita l. Hansen, Department of Psychosocial Science, univer-sity of Bergen, Christiesgt. 12, Bergen, Norway or e-mail (anita.hansen@psysp.uib.no).2the present study was supported by grants from the Program board of Nutrition, univer-sity of bergen, Norway, and a Humboldt Senior research award to JFt. the authors wish to thank all participants for their cooperation and also livar Frøyland and leif Waage for their cooperation in the research process.

a. l. HaNSEN, ET al.678

functions (Thayer, Hansen, Saus-Rose, & Johnsen, 2009). Thus, investigat-ing the relationship between specific nutrients and cognitive subprocesses in inmates might help to illuminate further the mechanisms responsible for the beneficial effects of nutrients on psychological functioning.

McCann and Ames (2008) argued that vitamin D is important for brain development and functions as well as for maintenance of mental activity throughout the lifespan. Vitamin D, obtained from the diet, di-etary supplements, or synthesized in the skin during sunlight exposure, has long been recognized for its importance in maintaining bone health (Holick, 2007). Levels of 25-hydroxyvitamin D [25(OH)D] are typically measured to establish the vitamin D status of an individual. In Norway, a level of vitamin D above 50 nmol/L is considered sufficient, while levels in the range of 25–50 nmol/l and 12.5–24 nmol/l indicate mild and mod-erate vitamin D deficiency, respectively. A level of vitamin D below 12.5 nmol/L is defined as serious vitamin D deficiency (The Norwegian Coun-cil of Nutrition, 2006).

Vitamin D receptors are located in the human cortex and hippocam-pus, which are key areas for cognition (Kalueff & Tuohimaa, 2007). In an observational study, Wilkins, Sheline, Roe, Birge, and Morris (2006) re-ported that low levels of vitamin D were associated with poorer cognitive test performance on the Short blessed test, an orientation-memory and concentration test of cognitive impairments. In addition, vitamin D de-ficiency was associated with mood disorders among Alzheimer patients. Other studies have also revealed a positive correlation between vitamin D levels and scores on cognitive tests like the Mini-Mental State Exami-nation (MMSE; e.g., Przybelski & Binkley, 2007). Surprisingly, Dumville, Miles, Porthouse, Cockayne, Saxon, and King (2006) did not find any im-provement in mental health after vitamin D supplementation in elderly women. However, they argued that their negative findings might be due to the use of an inappropriate measure of psychological functioning, in this case the Short Form Health Survey (SF–12), which is a questionnaire to assess subjective psychological well-being.

Experimental performance tasks, measuring different cognitive sub-processes, e.g., executive versus nonexecutive functions, may be alterna-tive measurement tools that might provide useful information about basic neurocognitive processes involved in behavioral and psychiatric condi-tions (Fertuck, Lenzenweger, Clarkin, Hoermann, & Stanley, 2006). Exec-utive functions, located in the prefrontal cortex area of the brain (luria, 1980), are responsible for goal-directed behavior, planning, reasoning, problem solving, and decision making (Shimamura, 2000). These psy-chological operations require working memory, sustained attention, be-havioural inhibition, and general mental flexibility (Thayer & Brosschot, 2005). Thayer and Lane (2000) emphasized that selective attention and the

VItaMIN D aND ExEcutIVE FuNctION 679

ability to sustain and shift attention are important components of self-reg-ulation and adaptability. In contrast to executive functioning, nonexecu-tive functioning is needed when task demands require a passive atten-tion toward the event. thus, nonexecutive functioning is activated when cognitive processes are driven automatically or reflexively by stimulation (Cowan, 1988, 1995; Posner & Raichle, 1999).

by using experimental performance tasks such as n-back tasks (i.e., 0-back and 2-back), it is possible to get a measure of different cognitive subprocesses, because they change systematically in mental load (Schoofs, Preuß, & Wolf, 2008). During performance of n-back tasks, fMrI studies have shown that performance of these tasks causes activity in a network of spatially distributed cortical areas in a load-dependent manner. Inter-estingly, bilateral activation in the medial frontal gyrus, superior frontal sulcus, and intraparietal sulcus was found during performance of a 2-back task compared to a 0-back task (carlson, Martinkauppi, rämä, Salli, kor-venoja, & Aronen, 1998). A limitation of many psychological studies is the use of instruments that do not give information about basic underlying mechanisms involved in psychological functioning. therefore, the aim of the present study was to investigate the level of vitamin D in relation to both executive and nonexecutive functions using experimental perfor-mance tasks.

MethodParticipants

Twenty-five male volunteers with a mean age of 35 yr. (range 20–60) serving sentences of 1 to 12 yr. for a variety of crimes, including property, violent, and drug offences, in a Norwegian prison were compliant with the study protocol. the participants did not receive any reward for par-ticipation. before the start of the experiment, the participants signed an informed consent statement and were informed about their rights to with-draw from the study at any time. It was emphasized that participation was voluntary and anonymous and that their participation or failure to participate would have no impact on their status within the correctional system. The study protocol was sanctioned by the National Committee for research Ethics and the Norwegian Social Science Data Services. apparatus and Stimuli

In order to measure nonexecutive and executive functions, a comput-erized version of an n-back task, both a 0-back and a 2-back task, using the E-prime system (Psychology Software Tools, Inc., Pittsburgh, PA) was used. Both tasks consisted of a continuous flow of letters. For the 0-back task, participants were instructed to respond to letters that appeared on the screen. they were told to press the “1” key on a keypad as quickly as

a. l. HaNSEN, ET al.680

they could every time they saw the letter “h.” If a letter other than “h” ap-peared, they were told to press “2” as quickly as possible. For the 2-back task, participants had to detect letters that matched the one presented two trials/targets previously. the 2-back task adds a more complex element of memory since individuals must keep in mind the last two letters that were seen on the screen. This task requires focused attention and complex manipulation of new information while retaining something in working memory (Shimamura, 2000). Thus, the 2-back task can be regarded as an executive function task, while the 0-back can be regarded as a nonexecu-tive function task, because this task only requires a simple element of re-action (Posner & Raichle, 1999). For each task condition, 40 stimuli were presented in a randomized order. The stimuli on the screen disappeared when a response was given. the number of correct responses and reaction times were recorded by the computer. the n-back test is widely used and is regarded as the “gold standard” of measurement of cognitive processes (Kane & Engle, 2002). Procedure

all participants were tested individually and were assigned to one of two groups based on vitamin D level, measured as 25(OH)D (The Nor-wegian Council of Nutrition, 2006). Participants with 25(OH)D levels ≥ 50 nmol/L were assigned into the High vitamin D level group (n = 14), and participants with levels < 50 nmol/L were assigned into the Low vita-min D level group (n = 11). Thus, the mean vitamin D concentration was 69 nmol/l (SD = 12) and 38 nmol/L (SD = 9) in the High vitamin D group (n = 14) and the Low vitamin D group (n = 11), respectively. It is well-estab-lished that vitamin D varies throughout the year in response to seasonal changes in sunlight exposure, and in the absence of sufficient sun expo-sure for dermal synthesis, dietary vitamin D intake becomes important (cashman, Hill, lucey, taylor, Seamans, Muldowny, et al., 2008). The test performance and the blood samples in the present study were collected during November and December.

blood samples were drawn from nonfasting participants, and serum vitamin D was determined by a radioimmunoassay (RIA) method [Gam-ma-b 25-Hydroxy Vitamin D rIa, Immunodiagnostic System limited (IDS), Tyne & Wear, UK]. Assays were performed at a routine laboratory at Haukeland University Hospital, Bergen, Norway. The assay coefficient of variation (CV) was 8.5% for low control material (M = 58.5 nmol/L) and 10.5% for high control material (M = 115 nmol/L). The laboratory reference range of 25(OH)D was 50 to 113 nmol/L. Design and Statistics

Spearman rank order correlations were used to investigate the rela-tionship between individual vitamin D level, performance on the cogni-

VItaMIN D aND ExEcutIVE FuNctION 681

tive tasks (accuracy and reaction time to the 0-back and 2-back), and age. To examine the differences between the high and low vitamin D groups on age and the performance data, the kolmogorov-Smirnov test was used. In order to examine the magnitude of the differences between the means, the effect size was calculated as Cohen’s d (1992).

ResultsMeans and standard deviations for age, vitamin D, and cognitive per-

formance data on the 0- and 2-back tasks are presented in table 1. corre-tablE 1

Means, Score Range, and Standard Deviations of Age, Vitamin D Level, Measured as 25(OH)D (nmol/L), and Number of Correct

Responses and Reaction Time on the 0- and 2-back Tasks

Variable Valid N M SD range

age, yr. 25 34.64 9.38 20.00–60.00Vitamin D 25 56.12 18.77 21.00–96.002-back # correct 25 33.28 7.47 5.00–40.000-back # correct 25 38.44 1.23 36.00–40.00reaction time 2-back, sec. 25 958.61 380.86 270.89–1,884.60reaction time 0-back, sec. 25 635.70 132.76 428.97–954.70

lations between the vitamin D level, age, and performance data are pre-sented in Table 2. Interestingly, a statistically significant relationship was found between the level of vitamin D and accuracy performance on the 2-back task (r = .48, p < .02). Furthermore, there was a statistically signifi-cant relationship between accuracy and reaction time on the easiest task, the 0-back (r = .38, p < .04). Additionally, there was a statistically signifi-cant relationship between age and reaction time on the 0-back task (r = .59, p < .001), but not between age and reaction time on the 2-back test (r =.19, p < .31). There was no statistically significant difference between the groups in age (Table 3).

tablE 2Correlations Between Vitamin D Measured as 25(OH)D (nmol/L),

Age, and Performance With 95% Confidence Intervals

Vitamin D accuracy reaction time

2-back 0-back 2-back 0-back

Vitamin D .48* .11 .02 −.0795%CI .10, .75

age −.13 −.05 .07 .19 .59†95%CI .21, .80

accuracy 2-back .230-back .38*95%CI −.01, .71

*p < .05. †p < .001.

a. l. HaNSEN, ET al.682

When looking at accuracy data for the two groups, the kolmogorov-Smirnov test showed that the high vitamin D group (M = 36.00, SD = 3.84) had statistically significantly more correct responses than the low vitamin D group (M = 29.82, SD = 9.55; p < .05; Cohen’s d = 0.85). For the 0-back task, there were no significant differences between the groups (see Table 3).

Interestingly, examination of the reaction time on the 2-back task re-vealed that there was no statistically significant difference between the groups. Additionally, there was no statistically significant difference be-tween the groups in reaction time on the 0-back task. thus, even if the High vitamin D group had better accuracy than the Low vitamin D group on the 2-back task, this was not due to more time spent on the task. there-fore, there was no evidence of a speed-accuracy trade-off.

Discussionusing experimental performance tasks measuring both executive and

nonexecutive functions, the current results show that vitamin D level may play an important role for executive functioning. this is supported by both the accuracy and the reaction time data. thus, the good performance in the High vitamin D group was not due to a speed-accuracy trade-off. this was further supported by the lack of a positive relationship between accuracy and reaction time on the 2-back task.

the current results are in line with Wilkins, et al. (2006), who found an association between vitamin D deficiency and worse performance on the Short Blessed Test, and with Przybelski and Binkley (2007), who reported a relationship between vitamin D concentration and scores on the Mini-Mental State Examination in older adults. by using experimental perfor-mance tasks measuring both nonexecutive and executive functioning in-

tablE 3Means and Standard Deviations of Age and Performance Data For the

High (n = 14) and Low (n = 11) Vitamin D Groups With Comparisons

Variable High Vitamin D low Vitamin D kolmogorov-Smirnov p

Cohen’sdM SD M SD

age 31.57 7.19 38.55 10.69  > .10 −0.77*2-back no. correct 36.00 3.84 29.81 9.55  < .05 0.850-back no. correct 38.57 1.02 38.27 1.49  > .10 0.23reaction time 2-back 950.54 334.28 968.88 450.19  > .10 0.05reaction time 0-back 600.25 110.33 680.83 149.93  > .10 −0.61*Based on the effect size of .85 and a total number of 25 participants (Low vitamin D group = 11 and High vitamin D = 14) and a two-tailed test (p < .05), the power in this study was only 0.52. In order to achieve a higher power (0.99), based on a p value of .05 (two-tailed test) and a large effect size of .85, this will require a total sample size of 116. Thus, the effect sizes for some of the nonsignificant effects in this study were moderate (age and reaction time), but the power was low.

VItaMIN D aND ExEcutIVE FuNctION 683

volved in self-regulation and behavior, the present study supports and extends previous investigations (cf. Dumville, et al. 2006).

as vitamin D is thought to play a key role in many important biologi-cal processes in the brain (Kalueff & Tuohimaa, 2007; McCann & Ames, 2008), there might be a number of possible explanations for the positive relationship between vitamin D and executive functions. Heart rate vari-ability, which is associated with parasympathetic influences on cardiac function, is an underlying physiological mechanism that has shown to be an important index of prefrontal functioning (thayer, et al., 2009). In a se-ries of studies concerning heart rate variability and cognition, there was a significant relationship between high heart rate variability and good per-formance on the 2-back task (see thayer, et al., 2009, for a review). Thus, both vitamin D and heart rate variability could be of importance for better executive functioning. Interestingly, Stumpf and Privette (1989) found that vitamin D is a key factor in the regulation of serotonin, which again is im-portant for the regulation of heart rate variability (Hibbeln, Ferguson, & Blasbalg, 2006). However, larger intervention studies are needed in order to understand a possible beneficial effect of vitamin D.

the present study suggests some very interesting relationships, al-though there are several limitations. among these are the small sample size, lack of data on IQ, and no women in the sample. Thus, other under-lying variables might be responsible for the significant relationship be-tween vitamin D and executive function found in this study. However, based on the association between intake of nutrients and a reduction in antisocial behavior (Gesch, et al., 2002) together with the findings showing that antisocial behavior is characterized by impaired executive functions (Morgan & Lilienfeld, 2000), the results from the unique sample used in this study may have some important implications with regard to future investigation. Executive functions are regarded as responsible for basic human behavior and improvement of memory and cognitive processes. these mechanisms are relevant for the elderly, school children, for people working in complex environments and operational settings, as well as for those with psychiatric and antisocial problems.

there are few dietary sources of vitamin D, and during the winter season, sunlight supplies negligible amounts of vitamin D at Norway’s de-gree of latitude (Holick, 2007). Therefore, regular intake of dietary sources of vitamin D such as fatty fish (> 8% fat), e.g., salmon, mackerel, and her-ring, or supplements will help satisfy the requirement for adequate vi-tamin D intake. More knowledge about the relationship between mech-anisms involved in psychological functioning and nutrients might have implications for interventions to improve adaptation in the incarcerated with impulsive and behavior problems.

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accepted September 29, 2011.