Selenium, Vitamins E and C Won't Prevent Prostate Cancer
TUESDAY Dec. 9, 2008 -- Selenium, vitamin E and vitamin C won't prevent men from getting prostate cancer.
In findings that were released early because of the public health implications, the results of two large randomized, controlled clinical trials showed the supplements failed to provide a cancer-prevention benefit, despite past findings that seemed to indicate great promise -- particularly for selenium. Both studies were expected to be published in the Jan. 7 print issue of the Journal of the American Medical Association.
"Our results showed no evidence of benefit from selenium and vitamin E on prostate cancer and other cancers," said the lead author of one of the studies, Dr. Scott Lippman, a professor of medicine in the division of cancer medicine at M.D. Anderson Cancer Center, in Houston.
Lippman's study, known as the SELECT trial, included more than 35,000 men. Black men included in the study were all over 50, and men from other races were all over 55. (Blacks have a higher risk of developing prostate cancer than do men of other races, according to the American Cancer Society.)
The men were randomly assigned to one of four groups: selenium; vitamin E; selenium and vitamin E; or a placebo. The average follow-up time was more than five years.
The researchers found no statistically significant difference between the groups, and the trial was ended early, because there was no convincing evidence of efficacy.
The second study, done by Harvard researchers, included almost 15,000 male physicians over 50 who were randomly assigned to receive vitamin E, vitamin C, or a placebo. The average follow-up time for this trial was eight years.
Again, no statistically significant benefits were found from either vitamin C or E when it came to preventing prostate and other cancers.
These studies are just the latest in a long list of recent research that's been discounting the use of individual vitamins and supplements for chemoprevention. Other recent studies have suggested that vitamins, B, C, D, E, folic acid and calcium taken alone, or in various combinations, aren't effective for cancer prevention.
"Single-agent interventions, even in combinations, may be an ineffective approach to primary prevention in average-risk populations," wrote Dr. Peter Gann, the author of an accompanying editorial in the same issue of the journal.
Andrew Shao, vice president of scientific and regulatory affairs for the Center for Responsible Nutrition in Washington, D.C., said he thought researchers need to "redefine our expectations for nutrients. They're not magic bullets, though they do have tangible effects."
Shao said studies that look at vitamins and cancer prevention tend to treat vitamins the same way they would a targeted pharmaceutical agent. But, he said, "the whole body is affected by nutrients, while pharmaceuticals are highly specialized and targeted to specific cells."
"It would be a mistake to look at one trial that answers a very specific question and say these nutrients don't work at all," said Shao.
Lippman, however, said he doesn't recommend the use of supplements for cancer prevention. "There's no evidence to support taking these," he said.
To learn more about prostate cancer prevention, visit the American Cancer Society.
Posted: December 2008