Dietary assessments in the European prospective study of diet and cancer (EPIC).

Biomarkers of nutrition intake were used to validate the dietary assessments proposed for use in the European prospective study of diet and cancer (EPIC). In the UK validation studies, the accuracy of several tested methods was assessed with weighed food records and biomarkers, 24 h urine nitrogen, potassium and plasma carotenoids and vitamin C. Correlations between dietary nitrogen intake from weighed food records and 24 h urine excretion were high (0.78-0.87). The correlations between nitrogen from estimated food diaries and urinary nitrogen were r = 0.60-0.70. Correlations with other methods were lower, but improved by energy adjustment, using residuals for those nutrients correlated with total energy, such as nitrogen and potassium, but not for nutrients not correlated with energy intake--for example, beta-carotene. Hence, the correlation between urinary nitrogen and unadjusted nitrogen from a food frequency questionnaire (FFQ) was 0.24 but improved with energy adjustment to 0.49. UK EPIC uses three methods (diary, improved FFQ and 24 h recall) to assess diet, with repeated measures from the food diary at 18 months and four years. Ninety-three percent of first food diaries are returned completed by participants. Results from 200 subjects randomly selected from the first 2,000 recruits suggest that differences between methods with improved FFQ design are less obvious than in the initial validation study. Results from the diary are more closely correlated with plasma carotenoids and vitamin C than other methods, although supplements of vitamin C are the main determinant of the magnitude of correlations. More detailed biomarker studies are in progress among EPIC participants.