Vitamin E pills raise prostate cancer risk, study suggests

By Rita Rubin, Special for USA TODAY
Updated 39m ago Comments 29

Vitamin E supplements significantly increased the risk of prostate cancer in healthy men even after they stopped taking them, scientists reported today.

Given the popularity of supplements containing vitamin E among people 60 and older, the researchers wrote, "the implications of our observations are substantial." Men in the study took 400 international units (IUs) a day.

MORE: Pros and cons of PSA screening test for prostate cancer

Consumers might wonder whether it's time to dispose of their supplements. The prostate cancer findings come a day after publication of a study that raised questions about the effects of common vitamin and mineral supplements in older women. That 19-year study of nearly 39,000 women linked supplement use to a higher risk of death. Participants decided on their own whether to take supplements, so factors leading to that decision, not the supplements themselves, could be to blame.

"I think many Americans view supplements as an insurance policy," says Lori Minasian, a co-author of the vitamin E and prostate cancer report and acting director of the Division of Cancer Prevention at the National Cancer Institute.

"We don't always exercise right, we don't always eat right. It's just easier to take a pill."

Unlike the older women study, Minasian's Selenium and Vitamin E Cancer Prevention Trial, or SELECT, randomly assigned participants to different treatments. About 35,000 U.S. and Canadian men were divided into four groups: vitamin E, selenium, vitamin E and selenium or a placebo. Each group included approximately 8,700 men. Black participants, who have a higher risk of prostate cancer, were 50 and older. The other men in the study were at least 55.

In September 2008, after the men had been taking their pills for 5½ years on average, researchers told them to stop a year earlier than planned. An interim analysis had shown that vitamin E wasn't going to reduce prostate cancer risk and might actually raise it, although that observation could have been due to chance.

Once the men stopped taking the pills, the researchers expected that the difference in prostate cancer risk between the men on vitamin E and those on the placebo would even out, Minasian says.

Instead, the gap between the men who'd taken vitamin E and those who hadn't continued to widen. By July of this year, 17% more prostate cancers, representing an additional 91 cases, had been reported in those who'd taken vitamin E than those who'd taken placebo pills, Minasian and her co-authors report in the Journal of the American Medical Association.

"We don't really understand what the optimal levels of most of the vitamins are," she says.

The authors say they don't have an explanation for their findings, which differ from other large randomized trials that examined the effect of vitamin E supplements on prostate cancer risk. Perhaps the men assigned to take vitamin E had higher levels to begin with, a question Minasian and her colleagues seek to answer by analyzing blood samples and toenail clippings taken from the men at the start of the study.

In addition, she says, the SELECT researchers are analyzing data to see whether vitamin E might reduce the risk of Alzheimer's disease, cataracts or macular degeneration, a leading cause of vision loss. Other research had shot down the idea that vitamin E supplements could reduce heart disease risk.

Neil Fleshner, the Love chair in prostate cancer prevention at Princess Margaret Hospital in Toronto, says he thinks the increased prostate cancer risk seen in SELECT was "just a statistical thing."

"I don't think it's cause and effect," says Fleshner, a urologist who was not involved in the study. "This is one study. There have been many other studies that have looked at this question and not shown that."

Fleshner says he used to take 800 units of vitamin E every day. "I truly believed that it would help prevent prostate cancer." He says he stopped taking the vitamin altogether when research a few years ago suggested large doses might increase risk of death.

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