Antioxidant vitamins in the prevention of cancer

Cancer is a leading cause of morbidity and mortality in the United States a nd other developed countries. In searching for preventive strategies agains t this disease, researchers have postulated that antioxidant vitamins may p lay a role in preventing cancer since several plausible biological mechanis ms exist. This article reviews the epidemiological evidence for a role of a ntioxidant vitamins (in particular, beta-carotene, vitamin E, and vitamin C ) in the development of cancer. Observational studies provide fairly consis tent data fur an inverse association between high intake of antioxidant vit amins, especially beta-carotene and vitamin C, and cancer risk. However, ra ndomized trials generally have not supported the hypothesis. Several explan ations for these inconsistent findings are possible. These include: 1) conf ounding by other healthy dietary and nondietary habits in observational stu dies: 2) the protective role of a combination of many different nutrients p resent in fruits and vegetables, rather than the single nutrient or combina tion of two nutrients that most trials have tested; 3) inadequate duration of follow-up in most randomized trials; and 3) heterogeneity of the populat ions studied. Reliable epidemiological evidence regarding whether antioxida nt vitamins play a role in preventing cancer will have to come from both ob servational studies and randomized trials since these different study desig ns each have unique strengths and limitations. Based on the available evide nce, it seems prudent to advocate a diet rich in fruits and vegetables, rat her than the consumption of specific antioxidant vitamin supplements, in or der to decrease the risk of developing cancer.