VALIDATION OF DIETARY ASSESSMENT METHODS IN THE UK ARM OF EPIC USING WEIGHED RECORDS, AND 24-HOUR URINARY NITROGEN AND POTASSIUM AND SERUM VITAMIN-C AND CAROTENOIDS AS BIOMARKERS

Background. In the UK EPIC validation studies, the accuracy of several methods was assessed by comparison with 16-day weighed records and th e biomarkers, 24-hour urine nitrogen (N) and potassium (K), plasma car otenoids and plasma vitamin C. Methods. Comparisons between methods we re made on 156 women, studied over 1 year at 3-monthly intervals at ho me. On each of four occasions, volunteers completed 4 days of weighed records and provided two 24-hour urine collections and a fasting blood sample. Results. In comparison with the 16 days of weighed records, a food frequency questionnaire (FFQ) yielded higher values mainly due t o greater reported consumption of milk and of vegetables, A 24-hour re call was as good as the FFQ in placing individuals in the distribution of habitual diet from weighed records. Results obtained from a 7-day estimated record were closest to those obtained from the weighed recor d. Correlations between 24-hour urine excretion and dietary N intake f rom weighed records were high (0.78-0.87) as were those with estimated food diaries (0.60-0.70). Correlations between urine N and the FFQ an d 24-hour recall were lower (0.10 to 0.27), but improved by energy adj ustment using residuals for N and K which are correlated with total en ergy intake. Comparisons between dietary estimates and urinary K and s erum carotenoids and vitamin C showed broadly similar results. Limited biomarker information amongst 200 UK EPIC participants supported the findings of the validation study. Conclusions. UK EPIC uses three meth ods (the 7-day diary, an improved FFQ, and the 24-hour recall) to asse ss diet. 93% of first food diaries are returned completed by participa nts. Repeated diaries are the main dietary assessment method for neste d case-control analyses.