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Posted October 30, 2008

Possible Risk Rather than Benefit Found in Trial of Vitamin E and Selenium for Prostate Cancer

On October 27, 2008 the National Cancer Institute (NCI) announced that men in the Selenium and Vitamin E Cancer Prevention Trial (SELECT) are being told to stop taking their supplements. An early analysis conducted by the SELECT data monitoring committee in September 2008 concluded that selenium and vitamin E, taken individually or together for an average of five years, failed to prevent prostate cancer, and, that selenium and vitamin E are unlikely to significantly reduce the risk of developing prostate cancer. In addition, the review found that there were slightly more cases of prostate cancer in men taking only vitamin E and slightly more cases of diabetes in men taking only selenium.

The amount of selenium (provided as l-selenomethionine) was 200 micrograms (µg or mcg) daily. Since the start of SELECT, four studies have been published looking at the effect of selenium on blood glucose and risk of diabetes: two studies suggested that higher levels of selenium taken from supplements or received naturally were associated with an increased risk of diabetes. One study showed no association.

The amount of vitamin E (provided as dl-alpha-tocopherol acetate) was 400 milligrams (mg), which is equivalent to 400 International Units (IU) per day. This dose of vitamin E can thin the blood somewhat. Men with uncontrolled high blood pressure were not eligible to take part in SELECT because taking this much vitamin E might have increased their risk of stroke.

Between 2001 and 2004, SELECT enrolled more than 35,000 men in the US, Puerto Rico, and Canada to study the effects of selenium and vitamin E supplements on prostate cancer, adult onset diabetes, and other diseases common among aging men. Participants in SELECT are being informed of the initial findings and told to stop taking their study supplements. They will continue to have their health monitored by study staff for about three more years, after which, all of the study information will be fully analyzed.