Comparing biological measurements of vitamin C, folate, alpha-tocopherol and carotene with 24-hour dietary recall information in nonhispanic blacks and whites

PURPOSE: To assess intake of several vitamins in preparation for a large co hort study investigating the effect of diet on risk of colon and prostate c ancer. METHODS: The dietary intake of several vitamins were assessed using eight d ifferent 24-hour recalls and a 200-item food frequency questionnaire (FFQ) from each subject. Participants also attended a clinic where blood was draw n and body composition, weight, height, and blood pressure were measured. A total of 97 black and 96 nonhispanic white subjects participated. The leve ls of alpha-tocopherol, carotene, folate, and vitamin C in the blood were c orrelated with the dietary intakes as measured by both 24-hour recalls and FFQ. RESULTS: Correlations between blood levels and energy-adjusted dietary inta ke assessed by 24-hour recalls (with supplements) were as follows: carotene (adjusted for serum cholesterol): 0.47 and 0.55 in black and white subject s, respectively; alpha-tocopherol (adjusted for serum cholesterol): 0.61 (b lacks) and 0.50 (whites); vitamin C: 0.22 (blacks) and 0.17 (whites); folat e: 0.54 (blacks) and 0.55 (whites). Correlations between blood levels and F FQ indices were smaller in magnitude: 0.34 and 0.28 for carotene in black a nd white subjects, respectively, 0.37 and 0.56 for alpha-tocopherol (adjust ed for serum cholesterol), 0.20 and 0.03 for vitamin C and 0.24 and 0.32 fo r folate. CONCLUSIONS: The correlations observed were generally of modest to moderate size and were similar to or larger than those reported by others. This is despite variations in absorption, metabolism, and excretion of the vitamins and suggests that both the 24-hour recalls and the FFQ contain valid infor mation. (C) 2001 Elsevier Science Inc. All rights reserved.