Effects of the intake of selected vitamins and minerals on cancer prevention.

This paper provides an overview of our knowledge on the involvement in cancer of vitamins A, C and E and of calcium, selenium and zinc. This work is a background for studies on dietary magnesium's effects on cancer. Consumption of vitamin A and its dietary precursors has been associated with reduced cancer at several sites in human and animal studies. Carcinogenesis studies using several models of cancer have been conducted on the influence of vitamin A deficiency, vitamin A excess and supplementation of vitamin A analogues. Vitamins C and E are effective in the prevention of N-nitroso compound (nitrosamine) formation. Vitamin C is effective in aqueous and vitamin E is effective in non-aqueous media. Both of these vitamins also have inhibited carcinogenesis by preformed carcinogens at several sites, but enhancement has been observed at some sites when excess vitamin treatment was studied. The potential role of calcium in the prevention of colon cancer is being pursed. Few experimental studies have been conducted but data support an effect of calcium on colonic epithelial proliferation. Epidemiological and especially experimental results suggest an inhibition of cancer by dietary selenium. In animal studies, selenium supplementation has been particularly effective in inhibiting colon and mammary carcinogenesis, but enhanced carcinogenesis was observed in some studies on skin, liver and pancreas cancer. Data suggest that zinc deficiency may be a factor in esophageal cancer; however, studies on tumor growth have demonstrated retarded tumor growth in zinc-deficient animals.