Tuesday, February 25, 2014

Selenium, Vitamin E Supplements May Double Prostate Cancer Risk

In the late 1990s and early 2000s, selenium and vitamin E were being touted as the potential cure for prostate cancer. In fact, the most influential study was conducted at the University of Arizona - SELECT (the Selenium and Vitamin E Cancer Prevention Trial) - just a few miles down the road from here. The SELECT study found no benefit by the time it ended in 2008, but over the following years, they found an increased risk in men who took only the vitamin E supplement (2011):
After an average of 7 years (5.5 years on supplements and 1.5 off supplements), there were 17 percent more cases of prostate cancer in men taking only vitamin E than in men taking only placebos.

Specifically, for every 1,000 men who took placebos there were 65 cases of prostate cancer over 7 years; for every 1,000 men who took vitamin E, there were 76 cases of prostate cancer.  This difference, an absolute increase of 11 cases per 1,000 men, was statistically significant and therefore is not likely due to chance.  These results were published in the Journal of the American Medical Association October 12, 2011 (see the paper Exit Disclaimer).
Now a new study is out showing that in men who take high dose vitamin E and selenium, there is a nearly two-found risks of developing prostate cancer. This new report seems to be using the same men who participated in the SELECT study.

Via Live Science:

Selenium, Vitamin E Supplements May Double Prostate Cancer Risk

By Bahar Gholipour, Staff Writer | February 21, 2014 

Selenium supplements are popular, but do they work?

Men who take selenium and vitamin E supplements may increase their risk of prostate cancer, researchers have found.

The new study examined about 1,700 men with prostate cancer and 3,100 healthy men. These men had previously participated in a large trial in 2001, in which they had been randomly assigned to take either high doses of vitamin E and selenium supplements, or a placebo. Researchers had measured the amount of selenium in the men's toenails before they started taking the supplements.

Now, the results showed that selenium supplements did not benefit men who had lower levels of the element at the start of the study, and nearly doubled the risk of prostate cancer in those who had higher levels of selenium (but still within ranges common among U.S. men).

In addition, vitamin E more than doubled the risk of the most aggressive type of prostate cancer, but only among men with low selenium levels at the beginning of the study. [5 Things You Should Know About Prostate Cancer]

"Men should avoid selenium or vitamin E supplementation at doses that exceed recommended dietary intakes," Dr. Eric Klein, chairman of the Glickman Urological and Kidney Institute at the Cleveland Clinic, and his colleagues wrote in their study, published today (Feb. 21) in the Journal of the National Cancer Institute.

The study is, in fact, a second look at a previous large, randomized trial, which aimed to investigate whether high doses of selenium and vitamin E supplements could lower a man's risk for prostate cancer, something that earlier studies had suggested.

However, that trial, which included 35,000 men, ended early with concerns that the treatments may do more harm than good. In fact, more users of vitamin E were getting prostate cancer than men who were on placebo. "Vitamins are not innocuous…they can be harmful," Klein told Live Science at the time in 2011.

The doses used in that trial were 200 micrograms of selenium and 400 international units of vitamin E. These doses are higher than most multivitamins, which contain about 50 micrograms of selenium and 30 to 200 international units of vitamin E.

Previous studies have suggested that the effects of nutrition supplements depend on how well-nourished a population is. Similarly, it is possible that the U.S. population is already getting adequately high levels of selenium through diet, and supplementing them with more selenium results in an unnaturally high amounts of the element, and has either no effect or increases cancer risk, the researchers said.

The findings also point to a complex interaction between selenium and vitamin E, the researchers said. The study showed that vitamin E increased the cancer risk in men who had low levels of selenium.

This was unexpected because both vitamin E and selenium have antioxidant roles and one could reasonably expect the opposite -- that supplemental vitamin E could compensate for an antioxidant deficit resulting from lower selenium, wrote Paul Frankel, a biostatistician at City of Hope Comprehensive Cancer Center, in an accompanying editorial.

It is unlikely that there will be another trial looking at these supplements and their role in preventing prostate cancer, the researchers said. Given the risks and lacking evidence of benefits for other diseases, men older than 55 should avoid supplementation with either vitamin E or selenium at doses that exceed recommended dietary intakes, the researchers said.

Email Bahar Gholipour or follow her @alterwired. Follow us @LiveScience, Facebook & Google+. Original article on Live Science.

No comments: