269 CHS 1 Nutritional Epidemiology What is it How is it important

1.  269 CHS (# 1) Nutritional EpidemiologyWhat is it?How is it important? Reference: Nutrition Epidemiology by Walter Willet

2. INTRODUCTION Many of the major questions about diet and disease remain unresolved. Nutritional epidemiology will enable us to understand the relationship between diet and long term health and disease A basic premise is that our understanding of biologic mechanisms remains far too incomplete to predict confidently the ultimate consequences of eating a particular food or nutrient. Thus, the epidemiologic studies directly relating intake of dietary components to risk of death or disease among humans play a critical complementary role to laboratory investigation.

3. What is Nutritional epidemiology? Concept: diet influences occurrence of diseases Relatively new: the basic method used for > 200 years to identify essential nutrients Nutritional epidemiology is a relatively new discipline which combines the knowledge compiled by nutritionists during this century with the methodology developed by epidemiologists to study the determinants of diseases with multiple etiologies and long latent periods. ?Example? Observations that fresh fruits and vegetables could cure scurvy by Lind in 1753.

4. Goals of nutritional epidemiology The most basic is monitoring the food consumption, nutrient intake and nutritional status of a population. To generate new hypotheses about diet and disease, to produce evidence that supports or refutes existing hypotheses and to assess the strength of diet-disease associations. The overall goal is to contribute to the prevention of disease and the improvement of public health.

5. Objectives of nutritional epidemiology COURSE Understanding the complex relationships between diet and the major diseases (as cancer and atherosclerosis) Having an overview of research strategies in nutritional epidemiology Indentifying methods of dietary assessment using data on food intake, biochemical indicators of diet, and measures of body size and composition. Discussing the analysis, presentation, and interpretation of data from epidemiologic studies of diet

6. Advantages of Nutritional Epidemiology The key advantage is its direct relevance to human health. Epidemiologists study real life. They do not need to extrapolate from animal models or in vitro systems. The results of their work are often used to calculate direct estimates of risk, which can then be translated into specific recommendations for changes in nutrient intakes or food consumption patterns. Findings from nutritional epidemiology can even have direct implications for food processing and technology

7. For example, recent epidemiological studies associating high intakes of trans fatty acids (found in margarine and other processed vegetable fats) with increased risks of coronary heart disease will probably prompt margarine manufacturers to seek out ways to reformulate their products to reduce their trans fatty acid content.

8. 1-The most important one is the potential for many kinds of bias. Bias is defined as systematic error, resulting in over- or underestimation of the strength of an association between an exposure and an outcome. Studies in nutritional epidemiology must be designed and executed with great care to minimize bias. Disadvantages of Nutritional Epidemiology

9. 2-The 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 the 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 � cigarette smoking.

10. 3-The apparent simplicity and �real life� relevance of epidemiological findings may also be a disadvantage in some circumstances because they encourage the misuse and over-interpretation of data. This is especially true when preliminary or unconfirmed findings come to the attention of the news media and the general public. For example, the reports of an association between margarine intake and cardiovascular disease may have prompted some consumers to switch back to butter, even though most experts believe that this course of action would not be beneficial to cardiovascular health.

11. Nutrition problems in the past Typical deficiency syndromes Protein energy malnutrition Iron deficiency anemia Goiter High frequency among those with very low intake Short latent periods Can be reversed within days or weeks

12. Contemporary nutritional epidemiology Major diseases throughout the world Heart disease Cancer Osteoporosis Cataracts Stroke Diabetes Congenital malformations

13. Characteristics Multiple determinants (causes) diet, genetic, occupational, psychosocial, and infectious factors; levels of physical activity; behavioral characteristics Long latent periods cumulative exposure over many years, or relatively short exposure occurring many years before diagnosis Occur with relatively low frequency despite a substantial cumulative lifetime risk Conditions not readily reversible May result from excessive and/or insufficient intake of dietary factors Why is it hard to study contemporary nutrition-related disease?

14. For example, coronary heart disease has a wide variety of recognized risk factors including age, gender, menopausal status in women, family history, body weight, blood pressure, blood cholesterol and diabetes. Other factors, such as the degree of oxidation of blood lipoproteins and levels of the amino acid homocysteine, may also be involved. Many of these risk factors and suspected risk factors are influenced by multiple aspects of diet.

15. For example, Intakes of several types of fatty acids influence blood cholesterol levels and Intakes of three different B vitamins influence homocysteine levels. Some risk factors exert their effects over long periods of time (usually by influencing the progression of atherosclerosis). Others, however, may exert their effects very quickly (by influencing the likelihood of blood clotting). The more that scientists learn about the nature of coronary heart disease, the more complex the causes seem to be.

16. So, scientists do not fully understand the reasons for differences in coronary heart disease rates at different times and places.

17. The complex nature of diet has posed an unusually difficult challenge to nutritional epidemiology: Diet represents an unusually complex set of exposures that are strongly intercorrelated, cannot be characterized as present or absent Continuous variables often with a rather limited range of variation

18. Individuals rarely make clear changes in their diet at identifiable points in time; typically eating patterns evolve over periods of years Individuals are generally not aware of the content of the foods that they eat ?consumption of nutrients is usually determined indirectly based on the reported use of foods or on the level of biochemical measurements

19. A major difficulty of nutritional epidemiology lies in the extremely complex nature of diet. To understand this complexity, it is helpful to compare diet with another exposure that also influences the risk of many of the same diseases � cigarette smoking.

20. In contrast, one cannot learn much by asking people, "Do you eat?" Everyone eats. 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.

21. 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 because filtering removes the components that may have cholesterol-raising effects.

22. An epidemiologist who is studying tobacco can obtain a great deal of useful information simply by asking people, "Do you smoke?" By collecting a few additional pieces of information � the number of cigarettes smoked per day, the types or brands of cigarettes smoked, the age at which the person began (or stopped) smoking and any changes that may have occurred in the pattern of cigarette use � the researcher can obtain a clear, reasonably accurate picture of an individual's smoking history.

23. Limitation in nutritional epidemiology research: -Lack of practical methods to measure diet for large number of subjects -Dietary assessment methods must be: Reasonably accurate Relatively inexpensive -Diets of persons within one country are too homogeneous to detect relationships with disease.

24. Epidemiologic Approaches to Diet and Disease Sources of the concepts, hypotheses, and techniques of nutritional epidemiology: -Biochemistry -Cell culture methods -Experiments in laboratory animals -Metabolic and biochemical studies among human subjects Findings from in vitro studies and animal experiments cannot be extrapolated directly to humans The basic science areas provide critical direction for information that can aid in the interpretation of the epidemiologic findings: New methods for measuring genetic and environmental exposures that can be applied in epidemiologic studies In vitro (Latin: within the glass) refers to the technique of performing a given experiment in a controlled environment outside of a living organism; for example in a test tube. In vitro (Latin: within the glass) refers to the technique of performing a given experiment in a controlled environment outside of a living organism; for example in a test tube.