updated 10/28/2008 9:45:58 AM ET 2008-10-28T13:45:58

The government is stopping part of a major study of whether vitamin E and selenium prevent prostate cancer — because the supplements aren't working and there's a hint of risk.

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More than 35,000 men age 50 and older have been taking one or both supplements or dummy pills as part of a study called the SELECT trial.

But the National Cancer Institute announced Monday that they will be getting letters in the next few days telling them to quit the pills. An early review of the data shows neither supplement, taken alone or together, is preventing prostate cancer.

Of more concern, slightly more users of vitamin E alone were getting prostate cancer — and slightly more selenium-only users were getting diabetes, the NCI said.

That doesn't prove there is a risk from the supplements, the NCI stressed: Neither blip was statistically significant, meaning it could be a coincidence.

Earlier smaller studies had suggested the nutrients might help, but instead they've become the latest failures in a quest to find cancer-preventing dietary supplements.

Researchers will continue to track the men's health for another three years, including previously scheduled blood tests. As with most well-designed studies, the participants didn't know which nutrients they'd been assigned to take, or if they were in the placebo group. If they ask now, doctors will tell them. But researchers say the study's results will be more accurate if most of the men wait to find that out until the follow-up health tracking is complete.

The study's active phase had been scheduled to run through 2011, so the latest-enrolling participants could take the supplements for seven years. Average use now is five years.

Prostate cancer is the most common cancer in American men. More than 186,000 cases will be diagnosed this year, and prostate cancer will claim 28,660 lives.

Some research shows that a drug already used for an enlarged prostate, finasteride, can help prevent prostate cancer as well, but side effects limit its use.

Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.


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