Associations between dietary methods and biomarkers, and between fruits and vegetables and risk of ischaemic heart disease, in the EPIC Norfolk Cohort Study

Background Methods for assessing diet are prone to measurement error, which may be substantial in large cohort investigations. Biomarkers can be used as objective measures with which to compare estimates of nutritional exposure using different methods Methods Cross sectional comparisons in 12 474 men and women of regression between biomarkers for vitamin C, sodium, potassium, fibre, carbohydrate, fat and phytoestrogens with intakes derived from food diaries and food frequency questionnaires (FFQ), and odds ratios for risk of ischaemic heart disease (IHD) by dietary and plasma vitamin C. Results There were strong (P < 0.001) associations between biomarkers and intakes as assessed by food diary. Coefficients were markedly attenuated for data obtained from the FFQ, especially so for vitamin C, potassium and phytoestrogens (Z P < 0.05). Risk of IHD was associated with plasma vitamin C (P < 0.001) and intake of vitamin C and fruit and vegetables assessed by food diary (P < quintile trends 0.001, 0.001) but not by the FFQ (P quintile trends 0.923, 0.186). Conclusions Nutritional data that reflect the findings from biomarkers reduce measurement error and will thus improve statistical power in studies of gene nutrient interactions in cohort studies.