Associations of micronutrients with colon cancer risk in African Americans and whites: results from the North Carolina Colon Cancer Study.

African Americans have the highest incidence of colon cancer among United States racial/ethnic groups, but these disparities are largely unexplained. This report describes associations of micronutrients with colon cancer risk in African Americans and whites using data from a case-control study in North Carolina. Incident cases of histologically confirmed colon cancer, age 40-80 years (n = 613), and matched controls (n = 996) were interviewed in person to elicit information on potential colon cancer risk factors. A previously validated food frequency questionnaire adapted to include regional foods was used to assess diet over the year prior to diagnosis or interview date. Micronutrient exposure included food sources and dietary supplements. Multivariate logistic regression models estimated energy-adjusted and non-energy-adjusted odds ratios (ORs). African Americans reported lower mean micronutrient intakes than whites, primarily due to larger contributions from dietary supplements in whites. Controls generally reported higher micronutrient intakes than cases; however, these differences were only statistically significant for whites. In whites, high beta-carotene, vitamin C, and calcium intakes were associated with 40-60% reductions in colon cancer risk when contrasting highest to lowest quartiles in both energy-adjusted and non-energy-adjusted models, e.g., OR = 0.4 (95% confidence interval, 0.3-0.6) for the highest quartile of calcium in the energy-adjusted model. In African Americans, vitamins C and E were strongly inversely associated using both statistical approaches: high vitamin E intake was associated with a 70% reduced risk for colon cancer, and the OR comparing the highest to lowest quartiles of vitamin C was 0.5 (95% confidence interval, 0.3-0.8). Folate and lutein were not statistically significantly associated with colon cancer risk in either racial group. These results suggest that at high intakes, micronutrients commonly found in plant and other foods (in particular, beta-carotene, vitamin C, and calcium in whites and vitamins C and E in African Americans) exhibit independent associations consistent with 30-70% reductions in colon cancer risk.