A major study on whether vitamin E and selenium prevent prostate cancer has been stopped because the supplements are not effective and also because there is a suspicion of a risk.
The study, the 'SELECT' trial, conducted by the National Cancer Institute (NCI), has been stopped by government health experts after an early review of the data showed neither supplement, taken alone or together, prevents prostate cancer.
The NCI says that more of a concern, was that slightly more users of vitamin E alone were getting prostate cancer and slightly more selenium-only users were getting diabetes.
The study involved more than 35,000 men age 50 and older who have been taking one or both supplements or dummy pills; earlier research had suggested that the nutrients might help, but they have instead failed.
The NCI says the trial did not prove there is a risk from the supplements, as neither statistic was statistically significant, and could be merely a coincidence.
Meanwhile the researchers will continue to track the men's health for another three years, including previously scheduled blood tests.
As with most studies, the participants were unaware which nutrients they had been assigned to take, or if they were in the placebo group - doctors are now obliged to tell them if they ask.
Dr. Eric Klein of the Cleveland Clinic in Ohio, who worked on the study, says the study's results will be more accurate if most of the men wait to find that out when the follow-up health tracking is complete - the study's active phase had been scheduled to run through to 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 amongst American men and more than 186,000 cases are expected to be diagnosed this year - prostate cancer will claim as many as 28,660 lives.
Other research has shown that a drug already used for an enlarged prostate, finasteride, can help prevent prostate cancer as well, but side effects limit its use.