CHS 269_Lecture (1)1 Nutritional epidemiology (CHS 269) Lecture NO (1)

CHS 269_Lecture (1)1

Nutritional epidemiology

(CHS 269)

Lecture NO (1)

Epidemiology• Epidemiology is defined as follows: It is

the study of the frequency, distribution and determinants of health related phenomena in human populations.



NUTRITION• Science of food, nutrients and other substances

therein, • the processes by which the organism ingests

food, digests, absorbs nutrients, transports, utilizes and excretes waste or undigested substances

– And their action, interaction and balance in relation to health and disease


Nutritional epidemiology

The study of the nutritional determinants of disease in

human populations.


Nutrition in Epidemiology

• In the field of Epidemiology , nutrition can be defined as:– The way in which the human body reacts with

diet– The extent to which the diet influences levels of

health


• Many questions about diet and disease remain Many questions about diet and disease remain unresolved.unresolved.

• Nutritional epidemiology will enable us to Nutritional epidemiology will enable us to understand the relationship between diet and understand the relationship between diet and healthhealth as well as diet and as well as diet and diseasedisease

• Our understanding of biologic mechanisms remains Our understanding of biologic mechanisms remains incomplete to predict confidently the ultimate incomplete to predict confidently the ultimate consequences of eating a particular food or nutrient.consequences of eating a particular food or nutrient.

NUTRITIONAL EPIDEMIOLOGY


– Low intake of fruits and vegetables has been shown to be related to increased risk of cardiovascular disease.

– Replacing saturated and trans fats with unsaturated fats can play an important role in the prevention of coronary heart disease and type 2 diabetes.

– Many diseases—as cataracts, neural-tube

defects, and macular degeneration—that were not thought to be nutritionally related have been found to have important dietary determinants.

Nutritional epidemiology has contributed to understanding the etiology of many diseases.

– In the early 1990s, epidemiological studies established that women could substantially reduce their risk of bearing a child with a neural tube birth defect by increasing their intake of the B vitamin folic acid.

– Medical organizations in many nations have recommended increased intakes of folic acid for women of childbearing potential

– Government agencies in several countries are planning to fortify staple foods with folic acid.


•Nonetheless, much more needs to be learned regarding other diet and disease relations,

•Furthermore, new products are constantly being introduced into the food supply requiring continued epidemiologic attention.



Goals of nutritional epidemiologyGoals of nutritional epidemiology

• Monitoring food consumption, nutrient intake and nutritional status of a population.

• Generating new hypotheses about diet and disease, to:– produce evidence that supports or refutes existing hypotheses – assess the strength of diet-disease associations.

• Contributing to prevention of disease and improvement of public health.


Advantages of Nutritional EpidemiologyAdvantages of Nutritional Epidemiology• Its direct relevance to human health. Its direct relevance to human health.

– Epidemiologists study real life. Epidemiologists study real life. – They do not need to extrapolate from animal They do not need to extrapolate from animal

models or in vitro systems. models or in vitro systems. – The results of their work can be translated into The results of their work can be translated into

specific recommendations for changes in nutrient specific recommendations for changes in nutrient intakes or food consumption patterns.intakes or food consumption patterns.

• Findings from nutritional epidemiology can have Findings from nutritional epidemiology can have direct implications for food processing and direct implications for food processing and technologytechnology– Epidemiological studies showed that there is

an associating between high intakes of trans fatty acids (found in margarine and other processed vegetable fats) with increased risks of coronary heart disease

– This will probably prompt margarine manufacturers to seek out ways to reformulate their products to reduce their trans fatty acid content.



1.The potential for many kinds of bias.– Bias is defined as systematic error, resulting in

over- or underestimation of the strength of association between exposure and outcome.

Disadvantages of Nutritional EpidemiologyDisadvantages of Nutritional Epidemiology


2.Difficulty in determining whether observed associations are causal.

• If the association between a factor and a disease is not causal, efforts to modify exposure to that factor will not reduce disease risk.

• For example, • even though drinking of alcohol is associated with lung cancer risk,

efforts to discourage alcohol consumption would not be likely to reduce the lung cancer death rate,

• because the relationship is not causal.

• Instead, it reflects the association of both alcohol intake and lung cancer with a third factor which is cigarette smoking.



3.The apparent simplicity and “real life” relevance of epidemiological findings.

• This is especially true when preliminary or unconfirmed findings come to the attention of the news media and the general public.

• For example, • reports of an association between margarine intake and

cardiovascular disease have prompted some consumers to switch back to butter,

• most experts believe that this action would not be beneficial to cardiovascular health.



modern nutritional epidemiologymodern nutritional epidemiology

Major diseases throughout the worldMajor diseases throughout the world• Heart diseaseHeart disease• CancerCancer• OsteoporosisOsteoporosis• CataractsCataracts• StrokeStroke• DiabetesDiabetes• Neural tube defects Neural tube defects


1.1. Multiple determinants (factors) Multiple determinants (factors) (multicausation) (multicausation)

diet, genetic, psychosocial,levels of physical activity; diet, genetic, psychosocial,levels of physical activity;

2.2. Long latent periodsLong latent periodscumulative exposure over many years, cumulative exposure over many years,

3.3. Not readily reversibleNot readily reversible

4.4. May result fromMay result from excessive and/or insufficient excessive and/or insufficient intakeintake of dietary factors of dietary factors

Characteristics of modern nutrition-Characteristics of modern nutrition-related diseasesrelated diseases


Difficulties facing nutritional epidemiology

Extremely complex nature of diet.• To understand this complexity, it is helpful to

compare diet with another exposure such as cigarette smoking.


• An epidemiologist who is studying tobacco can obtain useful information simply by asking people, "Do you smoke?"

• By collecting a few additional pieces of information such as:-– number of cigarettes smoked per day,

– types or brands of cigarettes smoked,

– age at which the person began (or stopped) smoking

• the researcher can obtain a clear, reasonably accurate picture of an individual's smoking history.

• In contrast, one cannot learn much by asking people, "Do you eat?"

• In contrast, everyone eats and everyone is exposed, to varying degrees, to most dietary factors.


• Eating patterns often evolve slowly over periods of years and people may not remember when their habits changed.

• The foods that people eat consist of complex mixtures of compounds, with substantial differences even among seemingly similar products.

• People who eat more of one type of food must eat less of other types of foods, thus creating a complex set of inter- correlations among dietary components.

• Eating habits may be correlated with other factors that influence disease risk, such as ethnic background, socioeconomic status and tobacco use.

• Even the method of preparation of foods may be important. – For example, – boiled coffee may raise blood cholesterol levels; – filtered coffee does not raise blood cholesterol because filtering

removes the components that may have cholesterol-raising effects.

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CHS 269_Lecture (1)1 Nutritional epidemiology (CHS 269) Lecture NO (1)