Men who took 400 international units of vitamin E daily had more prostate cancers compared to men who took a placebo, according to an updated review of data from the Selenium and Vitamin E Cancer Prevention Trial (SELECT).
The findings showed per 1,000 men, there were 76 prostate cancers in men who took only vitamin E supplements, versus 65 in men on placebo over a seven-year period, or 11 more cases of prostate cancer per 1,000 men. This represents a 17 percent increase in prostate cancers relative to those who took a placebo. The results of this update appeared Oct. 12 in the Journal of the American Medical Association.
"Based on these results and the results of large cardiovascular studies using vitamin E, there is no reason for men in the general population to take the dose of vitamin E used in SELECT as the supplements have shown no benefit and some very real risks," said Dr. Eric Klein, study co-chair at the Cleveland Clinic. "For now, men who were part of SELECT should continue to see their primary care physician or urologist and bring these results to their attention for further consideration."
The Public Health Sciences Division's Phyllis Goodman and Drs. Cathy Tangen and Gary Goodman (whose primary appointment is at the Swedish Cancer Institute) analyzed the data for this study.
SWOG, an international network of research institutions, carried out SELECT at more than 400 clinical sites in the United States, Puerto Rico and Canada. The Hutchinson Center directed data analysis for the massive international effort.
Poor results stop trial in 2008
The National Cancer Institute-funded study began in 2001 and included over 35,000 men. It was started because earlier research had suggested that selenium or vitamin E might reduce the risk of developing prostate cancer. However, based on an independent safety monitoring review in 2008, participants were told to stop taking their study supplements because it had become clear that the trial would never produce the 25 percent reduction in prostate cancer the study was designed to show with the use of these supplements. In 2010, the study sites were closed and over half of the participants consented to have their health monitored via mail questionnaires. Now, because of this latest finding, researchers are encouraging all participants to consider taking part in long-term study follow-up so investigators can continue to track outcomes.
"SELECT has definitively shown a lack of benefit from vitamin E and selenium supplements in the prevention of prostate cancer and has shown there is the potential for harm," said Dr. Lori Minasian, study co-author and acting director of NCI's Division of Cancer Prevention. "Nevertheless, this type of research has been critically important to understanding the potential benefits and risks from supplements."
Prostate cancer is the second most common type of cancer in men in the United States. The current lifetime risk of prostate cancer for American men is 16 percent. In 2011, there will be an estimated 240,890 new cases of prostate cancer and 33,720 deaths from this disease in the United States.
[Adapted from a National Institutes of Health news release]