Vitamins and cancer

The prospect that high intake of certain vitamins may confer protection against cancer has drawn substantial attention during the last decades. This paper gives a concise update of the role of a number of promising vitamins in prevention of cancer. Vitamin A and its analogues have an important role in cellular processes related to carcinogenesis. However, blood vitamin A levels are under strict control and a high intake of preformed vitamin A does not seem to be relevant for cancer prevention. The antioxidant vitamins C and E and beta-carotene may also have other biological activities than free radical trapping that relate to their cancer preventive properties. Mechanisms include immune stimulation, inhibition of nitrosamine formation, enhancement of cell communication and an influence on metabolic activation of carcinogens. Epidemiological data for the antioxidant vitamins are promising, but cannot rule out that another factor or combination of factors in fruits and vegetables might be responsible for a protective effect. The B vitamin folic acid is one of these potential factors that is currently thought to have an influence on DNA methylation and thus on proto-oncogene expression. Folic acid seems to be promising and deserves further study. Vitamin D might be relevant in colon cancer development due to its close links with calcium metabolism that might influence cell proliferation. Overall, results are promising, but the first human intervention trials on (antioxidant) vitamins and human cancer have yielded somewhat disappointing results. At this moment the data seem insufficient to make recommendations for vitamin supplementation to prevent cancer. The results are certainly in line with the advice that a diet rich in fruits and vegetables will help reduce cancer risk. (C) 1997 Elsevier Science Ireland Ltd.