By Danielle Krol, M.D.
A new study might have men thinking twice about taking supplements.
The study, published today in the Journal of National Cancer Institute, links the micronutrients selenium and vitamin E to an increased risk of prostate cancer - a disease the supplements were once thought to prevent.
The finding is the latest to come out of the SELECT Trial, an ongoing study of more than 35,000 American men aged 55 and older. The trial started on the hunch that certain supplements might reduce the risk of prostate cancer. But initial results in 2008 suggested that selenium and vitamin E, taken alone or together, did not prevent prostate cancer. In fact vitamin E supplements appeared to raise the risk of the disease by 17 percent.
At the time, participants were instructed to stop taking these supplements but to keep checking in with the researchers. Now, more than five years later, it appears supplementing with high doses of selenium nearly doubled the risk of high-grade prostate cancer in some men. High doses of vitamin E more than doubled the risk of high-grade prostate cancer among other men in the study.
"High dose micronutrients were believed to reduce cancer risk, and our trial was started to prove that," said study author Alan Kristal, a professor of epidemiology at the Fred Hutchinson Cancer Research Center. "These micronutrients turn out to be toxic.
"What I would like people to understand is that we now know of no added benefits of taking these supplements in high amounts," Kristal added.
Dr. Durado Brooks, director of prostate and colorectal cancers at the American Cancer Society, said the new findings lend further weight to existing concerns about high-dose supplements.
"These findings confirm the impact of vitamin E and the increased number of men developing prostate cancer," said Brooks, who was not involved with the study. "This study further supports the notion that selenium and vitamin E are not protective against prostate cancer - but harmful."
Brooks added that the doses of selenium and vitamin E used in this study far exceed the dose found in most multivitamins - a fact that may offer comfort to men taking a daily pill that happens to contain selenium and vitamin E.
Prostate cancer is the second most-common cancer in men worldwide, and more than 2.6 million American men live with the disease, according to National Cancer Institute estimates. The NCI also predicts that there will be an estimated 233,000 new cases of prostate cancer diagnosed this year, as well as nearly 30,000 deaths.
Nearly half of U.S. adults take vitamins and other dietary supplements - a level that's been holding steady for much of the past decade. During the past few years, study after study has raised doubts about what, if any, good vitamins actually do. And given more recent evidence - including this study - it's becoming clear that they could even pose some real risks.
The U.S. Preventive Services Task Force (USPSTF) concluded in 2003 that there is insufficient evidence to recommend for or against the use of supplements in the prevention of cancer. Meanwhile, the researchers behind this new study, based on their findings, suggest that men over age 55 should avoid vitamin E, selenium or the antioxidant combinations of the two that exceed recommended dietary intake of 55 micrograms for selenium and 15 milligrams for vitamin E.
Ultimately, consumers will decide for themselves. The important thing to remember is that nutritional supplements - useful or not - are no substitute for regular medical care, a good diet and other important health habits.