VITAMIN SUPPLEMENTS AND CANCER RISK - THE EPIDEMIOLOGIC EVIDENCE

This report reviews published epidemiologic research on the associatio ns of vitamin and mineral supplementation with cancer risk. Although t he literature on nutrition and cancer is vast, few reports to date hav e addressed supplemental nutrients directly (seven clinical trials, 16 cohort, and 36 case-control studies). These studies offer insight int o effects of nutrients that are distinguishable from effects of other biologically active compounds in foods. Randomized clinical trials hav e not shown significant protective effects of beta-carotene, but have found protective effects of: alpha-tocopherol against prostate cancer; mixtures of retinol/zinc and beta-carotene/alpha-tocopherol/selenium against stomach cancer; and selenium against total, lung, and prostate cancers. Cohort studies provide little evidence that vitamin suppleme nts are associated with cancer. Case-control studies have reported an inverse association between bladder cancer and vitamin C; oral/pharyng eal cancer and several supplemental vitamins; and several cancers and vitamin E. A randomized clinical trial, a cohort study, and a case-con trol study have all found inverse associations between colon cancer an d vitamin E. Overall, there is modest evidence for protective effects of nutrients from supplements against several cancers. Future studies of supplement use and cancer appear warranted; however, methodologic p roblems that impair ability to assess supplement use and statistical m odeling of the relation between cancer risk and supplement use need at tention.