Biomarkers in nutritional epidemiology.

OBJECTIVE: To illustrate biomarkers of diet that can be used to validate estimates of dietary intake in the study of gene-environment interactions in complex diseases.
DESIGN: Prospective cohort studies, studies of biomarkers where diet is carefully controlled.
SETTING: Free-living individuals, volunteers in metabolic suites.
SUBJECTS: Male and female human volunteers.
RESULTS: Recent studies using biomarkers have demonstrated substantial differences in the extent of measurement error from those derived by comparison with other methods of dietary assessment. The interaction between nutritional and genetic factors has so far largely gone uninvestigated, but can be studied in epidemiological trials that include collections of biological material. Large sample sizes are required to study interactions, and these are made larger in the presence of measurement errors.
CONCLUSIONS: Diet is of key importance in affecting the risk of most chronic diseases in man. Nutritional epidemiology provides the only direct approach to the quantification of risks. The introduction of biomarkers to calibrate the measurement error in dietary reports, and as additional measures of exposure, is a significant development in the effort to improve estimates of the magnitude of the contribution of diet in affecting individual disease risk within populations. The extent of measurement error has important implications for correction for regression dilution and for sample size. The collection of biological samples to improve and validate estimates of exposure, enhance the pursuit of scientific hypotheses, and enable gene-nutrient interactions to be studied, should become the routine in nutritional epidemiology.