Epidemiology Setting the Scene

The risk of developing a disease can be increased by exposure to a disease-promoting factor or decreased by a protective factor. In terms of antioxidants, high risk is generally assumed to be associated with low intakes, plasma levels, or tissue concentrations of antioxidants. Epidemiological studies often express results in terms of the relative risk (RR) of mortality or disease. The RR is generally given as the mean and 95% confidence interval (CI). In general, an RR of 0.80 indicates an average reduction in risk of 20%; however, RR values must be interpreted with caution and the CI must be considered. If the CI spans 1.0, the RR is not statistically significant, regardless of its magnitude.

Different approaches are used in observational epidemiology. Cross-cultural studies compare standardized mortality rates (from all causes or from a specific disease) or disease prevalence and the factor of interest ('exposure variable') in different populations within or between countries. These can be regarded as 'snapshot' observational surveys. Case-control studies compare the factor of interest in people who have a disease (the cases) with that in those who do not (the controls). Prospective trials are longitudinal studies of apparently disease-free subjects whose health is monitored over years or decades; the exposure variable of interest is compared, retrospectively, between those who develop the disease of interest and those who do not.

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