WASHINGTON — The government is stopping part of a major study of whether vitamin E and selenium prevent prostate cancer — because the supplements are not working and there is a hint of risk.
More than 35,000 men age 50 and older have been taking one or both supplements or dummy pills for several years as part of a study called the SELECT trial.
But the National Cancer Institute (NCI) announced Monday that they will be getting letters in the next few days telling them to stop: 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 does not prove that the supplements post risks, the NCI stressed: Neither blip was statistically significant, meaning they could have been coincidences.
Earlier, smaller studies had suggested the nutrients might help, but instead they have 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 did not 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 in the United States, 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.