(CBS/AP) Think vitamin pills will keep you healthy?
Actually, a new study suggests that high doses of vitamin E can slightly elevate men's risk for prostate cancer - and researchers called the finding another reminder that people should be careful about using vitamins and other supplements.
"People tend to think of vitamins as innocuous substances, almost like chicken soup - take a little and it can't hurt," said lead author Dr. Eric Klein of the Cleveland Clinic. "If you have normal levels, the vitamin is probably of no benefit, and if you take too much, you can be harmed".
The study showed that men randomly assigned to take a 400-unit capsule of vitamin E every day for about five years were 17 percent more likely to get prostate cancer than those given dummy pills. That dose, common in over-the-counter supplements, is almost 20 times higher than the recommended adult amount, which is about 23 units daily.
The results mean for every 1,000 men who took vitamin E, there were 11 additional cases of prostate cancer, compared with men given dummy pills.
About 160 of every 1,000 U.S. men will develop prostate cancer at some point. The risk increases as men age, and detection can be tricky since symptoms such as frequent urination can also be caused by harmless conditions. Treatment is also complex since some slow-growing prostate tumors are not deadly but some procedures, including surgery, can cause erectile dysfunction and urinary incontinence.
About 13 percent of American men take vitamin E, according to a supplement trade group. What's the study's take-away message for these men?
Dr. Otis Brawley, chief medical officer for the American Cancer Society, says they should stop taking large doses and talk to their doctors about risks and benefits of prostate cancer screening. Smaller doses, typically found in multivitamins, are probably fine, said Brawley, who was not involved in the research.
Brawley noted that the study echoes previous thinking on beta-carotene, which once was thought to guard against cancer but more recently has been linked with increased risk for lung cancer, especially in smokers.
"There should be a global warning that ... excessive use of vitamins has not been proven to be beneficial and may be the opposite," Brawley said.
Experts generally agree that foods are the best sources for vitamins. Vitamin E is found in foods such as nuts, seeds and vegetable oils.
The new research - published in the Journal of the American Medical Association - involved more than 35,000 healthy men aged 50 and older, from the U.S., Canada and Puerto Rico.
The researchers said it was unclear how vitamin E would harm the prostate.
The Prostate Cancer Foundation has more on prostate cancer.