Micronutrients and colorectal cancer

There are indications that several aspects of diet, including selected micronutrients, may influence colorectal carcinogenesis. Micronutrients of potential relevance may be subdivided into three major groups: 1) calcium and vitamin D, which bind bile acids and free fatty acids to form insoluble soaps, and hence inhibit intestinal cell proliferation; 2) ascorbic acid, dietary carotenoids and vitamin E, which act through an antioxidant effect; 3) folate, which may increase DNA methylation and the production of S-adenosylmethionine, the primary methyl donor in the body. The relationship between various micronutrients and colorectal cancer risk was considered on the basis of a case-control study conducted between January 1992 and June 1996 in Italy. Cases were 1953 incident, histologically confirmed colorectal cancers (1225 of the colon and 728 of the rectum), admitted to the major teaching and general hospitals in the study areas, and controls 4154 subjects with no history of cancer, admitted to hospitals in the same catchment areas for acute, non-neoplastic diseases unrelated to the digestive tract, and requiring no long-term modifications of the diet. Dietary habits were investigated using a validated food frequency questionnaire. For most micronutrients, the multivariate odds ratios (ORs) were below unity with increasing quintile of intake. The most consistent protective effects were for carotene, riboflavin and vitamin C (the ORs from the continuous model, with unit set as the difference between the upper cut-point of the fourth quintile and that of the first one, were 0.65, 0.73 and 0.80 respectively). Inverse relationships were observed also for calcium and vitamin D (ORs of 0.85 and 0.93 respectively). When the combined effect of calcium and vitamin D and selected antioxidants was considered, the OR reached 0.46 in subjects reporting high calcium/vitamin D and high antioxidant intake as compared to those reporting low intake of both groups of micronutrients. Most results were apparently stronger for colon cancer and among females. Thus, there is a protective effect of several micronutrients on colorectal cancer risk, and some indications for a stronger effect of selected antioxidants.