In a major cancer prevention study, long-term supplementation with vitamin E or C did not reduce the risk of prostate or other cancers for nearly 15,000 male physicians.
In some observational studies, intake or blood levels of vitamins E and C have been associated with reduced risk of certain cancers. "However, definitive proof that vitamins E and C can reduce the risk of overall or site-specific cancers must rely on large-scale randomized trials," the authors write. "A number of trials have addressed the potential role of vitamins in the prevention of cancer; however, the results from these trials have not been consistent." Despite uncertainty about the long-term health effects or benefits, more than half of U.S. adults take vitamin supplements, and vitamins E and C are among the most popular individual supplements, according to background information in the article.
J. Michael Gaziano, M.D., M.P.H., of Brigham and Women's Hospital and VA Boston Healthcare System, Boston, and colleagues conducted the Physicians' Health Study II, a randomized, placebo-controlled trial to examine the effects of vitamin E and vitamin C on prostate cancer and total cancer. The study included 14,641 male physicians in the United States, age 50 years or older at the time of entering the trial, of whom 1,307 had a prior history of cancer. Participants were randomized to receive individual supplements of 400 IU of vitamin E every other day and 500 mg. of vitamin C daily.
During an average follow-up of 8.0 years, there were 1,943 confirmed total cancer cases and 1,008 prostate cancer cases. Compared with placebo, vitamin E had no effect on the incidence of prostate cancer or total cancer. The researchers also found no significant effect of vitamin C on total cancer or prostate cancer. Neither vitamin E nor vitamin C had a significant effect on site-specific cancers, including colorectal, lung, bladder and pancreatic. Stratification by various cancer risk factors demonstrated no significant modification of the effect of vitamin E on prostate cancer risk or either agent on total cancer risk.
"These data provide no support for the use of these supplements in the prevention of cancer in middle-aged and older men," the authors conclude.
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