Original Research Communications-methods Validation of a dietary questionnaire with plasma carotenoid and a-tocopherol levels13

ABSTRACT We assessed the validity ofa self-administered semiquantitative food frequency questionnaire by comparing carotene and vitamin E intake scores derived from this form with plasma carotenoid and es-tocopherol levels among a group of 59 men and women. The simple correlation between carotene intake and plasma carotenoid was 0.29 (p = 0.02) and the partial correlation was 0.35 (p = 0.005) after adjustment for age, sex, total caloric intake, and plasma cholesterol and triglycerides. The simple correlation between vitamin E intake and plasma a-tocopherol was 0. 12 (p = 0. 19). However, adjustment for total caloric intake and plasma lipids each substantially increased this association so that the partial correlation adjusting simultane-ously for caloric intake, plasma lipids, age, and sex was 0.34 (p = 0.006). As expected on the basis of previous randomized trials, the correlation between preformed vitamin A intake and plasma retinol was weak and not statistically significant. These data support the utility of self-administered food frequency questionnaires for use in epidemiological studies. In addition, they illustrate the importance ofadjusting blood a-tocopherol levels for lipid concentrations when the former are used as surrogates for vitamin E intake. Am J Cliii Nutr 1983:38:631-639. KEY WORDS Diet, questionnaire, carotene, vitamin E, bloo