2. Epidemiology
• Epidemiology is defined as follows: It is
the study of the frequency, distribution and
determinants of health related phenomena
in human populations.
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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
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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
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•Many questions about diet and disease remain
unresolved.
•Nutritional epidemiology will enable us to
understand the relationship between diet and health
as well as diet and disease
•Our understanding of biologic mechanisms remains
incomplete to predict confidently the ultimate
consequences of eating a particular food or nutrient.
NUTRITIONAL EPIDEMIOLOGY
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– 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.
8. – 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.
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9. •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.
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Goals 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.
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Advantages of Nutritional Epidemiology
• 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 can be translated into
specific recommendations for changes in nutrient
intakes or food consumption patterns.
12. • Findings from nutritional epidemiology can have
direct implications for food processing and
technology
– 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.
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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 Epidemiology
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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.
Disadvantages of Nutritional Epidemiology
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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.
Disadvantages of Nutritional Epidemiology
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modern nutritional epidemiology
Major diseases throughout the world
• Heart disease
• Cancer
• Osteoporosis
• Cataracts
• Stroke
• Diabetes
• Neural tube defects
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1. Multiple determinants (factors) (multicausation)
diet, genetic, psychosocial,levels of physical activity;
2. Long latent periods
cumulative exposure over many years,
3. Not readily reversible
4. May result from excessive and/or insufficient
intake of dietary factors
Characteristics of modern nutrition-
related diseases
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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.
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• 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.
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• 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.
