Selenium, vitamin E, fiber, and the incidence of human cancer: an epidemiologic perspective.

It has been hypothesized that selenium, vitamin E, and fiber reduce the risk of specific human cancers. Evidence for a role of selenium is based primarily on animal studies, inverse geographic correlations between intake and site-specific cancer incidence, and an inverse association between serum selenium and subsequent risk of cancer. Certain geographic areas with high fiber intakes have lower rates of colon cancer and, in several case-control studies, consumption of fruits and vegetables has been associated with a lower risk of large bowel cancer. Suspicion that vitamin E might reduce the risk of human cancer is largely theoretical; a protective association has been observed in only 1 small study of breast cancer. The evidence that these 3 dietary factors reduce the risk of human cancer remains incomplete. Future epidemiologic investigations should simultaneously assess a wide variety of dietary factors to address potential confounding and interacting effects. Prospective study designs should be used whenever possible to avoid any influence of cancer on dietary intake or its measurement.