We examined the validity of energy and 16 nutrient intake measurements from a self-administered food frequency questionnaire (FFQ) used in the 5-year follow-up survey of the JPHC study using 28-or 14-day dietary records (DR) as the gold standard. The median (range) correlation coefficients between 16 nutrients measured by FFQ and DR were 0.52 (0.31-0.81) for men and 0.41 (0.22-0.56) for women. The median (range) for energy-adjusted correlation coefficients was 0.40 (0.22-0.82) for men and 0.39 (0.15-0.48) for women. With further adjustment for area, it was 0.41 and 0.35, respectively. The mean percentage of classification into the same categories between the two methods was 33% in men and 30% in women. Only 2% of subjects were classified into the extreme opposite categories. In conclusion, the results suggest that the FFQ can be used in the JPHC Study Cohort I to rank individuals according to the intakes for most of the nutrients examined.J Epidemiol 2003;1 3(Suppl):S51 -S56.Key words: validity, nutrient, food frequency questionnaire, dietary record.The dietary assessment method is an important issue in prospective epidemiological study on diet and chronic diseases such as cancer and cardiovascular diseases. Considering the long time course of chronic disease development and the mechanistic role of nutrients in diet, the average nutrient intake over one year should be assessed using an appropriate tool. The causative association between nutrient intake and chronic diseases is neither dichotomous (yes or no) nor always linear. The optimal level should be quantitatively explored, so a quantitative assessment of nutrient intake is needed.Although the long-term dietary record (DR), e.g., 365 days, may be one of most accurate methods for estimating nutrient intake over a given year, it is not appropriate when applied to a large population. A semiquantitative food frequency questionnaire (FFQ), which can estimate the usual level of nutrient intake, was developed and validated in the United States and is now a standard tool in nutritional epidemiology.1 We have developed a FFQ for use in the 5-year follow-up survey of the JPHC study, which was based on data obtained from a 3-day DR survey in the same area of the JPHC Study Cohort I.2Here, we examined the validity of energy and 16 nutrient intakes assessed with the FFQ using a 28-or 14-day dietary record (DR).
MATERIALS AND METHODSThe study design and subject characteristics have been reported elsewhere in this Supplement.3 The subjects included in the analysis were 102 men and 113 women who completed 28-day DRs in Iwate, Akita, and Okinawa, and 14-day DRs in Okinawa, and answered the FFQ after the completion of their DRs. The survey method using dietary records and the method for computing nutrient intakes from FFQ have been described elsewhere in this Supplement.4.5 We compared the mean intakes and computed Spearman rank correlation coefficients for energy and 15 nutrients, for which food composition tables are available in the published Standard Tables of Food Compos...