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Study participants received either selenium, vitamin E, both supplements or a placebo.
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SAN ANTONIO (Dec. 8, 2008) — A national study that involved 408 men at The University of Texas Health Science Center at San Antonio and Wilford Hall Medical Center concluded that two widely used health supplements do not prevent prostate cancer, despite promising results in two previous studies.

“If you’re taking vitamin E or selenium to prevent prostate cancer, you could better spend your money elsewhere, such as on a gym membership or a new pair of running shoes,” remarked one of the study’s authors, Ian M. Thompson, Jr., M.D., professor and chairman of urology. He directs the genitourinary clinic at the Cancer Therapy & Research Center (CTRC) at the UT Health Science Center.

Results published in JAMA
The Journal of the American Medical Association released the results Dec. 9 online and will publish the findings in its Jan. 7 issue. Until this study, vitamin E and selenium represented the best hope for prostate cancer prevention, apart from prescribed medication, Dr. Thompson said. He estimated that half of healthy men over 50 are taking either of these supplements or both to prevent prostate cancer.

Men randomly selected for one of four study groups
The Selenium and Vitamin E Cancer Prevention Trial, known as SELECT, enrolled more than 35,000 relatively healthy men in the U.S., Canada and Puerto Rico. They were randomly divided into four study groups to receive either selenium and a placebo, vitamin E and a placebo, both supplements or two placebos. Neither the patients nor their physicians knew what the men received.

Small increased risks of prostate cancer, diabetes shown
Leaders of the study, administered by the Southwest Oncology Group in San Antonio and Ann Arbor, Mich., told research sites to stop giving participants the supplements Oct. 23 in year seven of the 12-year trial at the recommendation of an oversight committee. The evidence “convincingly demonstrated no benefit from either study agent,” according to the article. Moreover, there were small increases in the risk of prostate cancer in men taking vitamin E and of diabetes in men taking selenium. Neither increase was statistically significant, but authors said the adverse effects were of some concern.

Ian Thompson, M.D., coordinated SELECT at the UT Health Science Center.

Why were selenium and vitamin E ineffective in SELECT? The authors cite a few possibilities. One is that SELECT was specifically designed to test the effectiveness of the two supplements, while previous studies were not. In those other smaller studies, the cancer prevention effect may have been due to chance. There also were differences between SELECT and previous trials in formulations, dosages and patient characteristics.

Finasteride shown to decrease prostate cancer risk
“If healthy men want to invest in prevention, they should ask their physicians about the drug finasteride,” Dr. Thompson says. “If men at risk for prostate cancer took finasteride, 50,000 men destined to be diagnosed in 2009 would not get this cancer.”

Prostate cancer is diagnosed in 200,000 U.S. men each year. Finasteride was found to reduce a man’s risk of prostate cancer by 25 percent in a large study, the National Cancer Institute's Prostate Cancer Prevention Trial, coordinated by Dr. Thompson.

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