Vitamin supplements and cancer risk: the epidemiologic evidence

Abstract

This report reviews published epidemiologic research on theassociations of vitamin and mineral supplementation with cancer risk.Although the literature on nutrition and cancer is vast, few reports to datehave addressed supplemental nutrients directly (seven clinical trials, 16cohort, and 36 case-control studies). These studies offer insight intoeffects of nutrients that are distinguishable from effects of otherbiologically active compounds in foods. Randomized clinical trials have notshown significant protective effects of β-carotene, but have foundprotective effects of: α-tocopherol against prostate cancer; mixturesof retinol/zinc and β-carotene/α-tocopherol/ selenium againststomach cancer; and selenium against total, lung, and prostate cancers.Cohort studies provide little evidence that vitamin supplements areassociated with cancer. Case-control studies have reported an inverseassociation between bladder cancer and vitamin C; oral/pharyngeal cancer andseveral supplemental vitamins; and several cancers and vitamin E. Arandomized clinical trial, a cohort study, and a case-control study have allfound inverse associations between colon cancer and vitamin E. Overall, thereis modest evidence for protective effects of nutrients from supplementsagainst several cancers. Future studies of supplement use and cancer appearwarranted; however, methodologic problems that impair ability to assesssupplement use and statistical modeling of the relation between cancer riskand supplement use need attention.