[Antioxidant minerals and vitamins. Role in cancer prevention]

Cancer is a disease of the genome and free-radicals can damage genomic DNA, hence the interest in the potential protective antioxidant effect of vitamin and minerals. Indeed, the findings of most retrospective studies suggest that diets rich in fruits and vegetables have a protective effect against cancer. Prospective randomized trials have however given controversial results. Beta-carotene, the precursor of vitamin A has been shown to induce regression of precancerous lesions and 13-cis retinoic acid has a preventive effect on the development of a second cancer in patients with epidermoid cancer of the buccal cavity, the pharynx or the larynx although no effect has been observed on the primary cancer. Current research also suggests vitamin C has a potential anticancer effect, particularly for cancer of the stomach, the rectum and the cervix. For vitamin E, epidemiological data give less conclusive results. Several prospective studies suggest the absence of any correlation between vitamin E intake and general risk of cancer. A Chinese trial has shown a decreased incidence of oesophageal and gastric carcinoma while a Finnish trial revealed increased incidence of cancer among smokers treated by beta-carotene and vitamin E. Selenium and zinc intake, based on geographical correlations, has also been suggested to affect cancer incidence, but the results of prospective studies are conflicting. For example in 10 such trials analyzing blood selenium levels and risk of cancer, 4 have demonstrated a significant correlation. Further research is needed but is hindered by the absence of an adequate animal model and the difficulty in conducting large clinical trials. Nevertheless, positive data collected to date must be validated to determine the real effect of dietary preventive measures in the fight against cancer.