Selenium and Vitamin E Do Not Help Prostate Cancer

The results of two large clinical trials show the supplements selenium and Vitamin E failed to provide a cancer-prevention benefit, despite encouraging past findings. 

"Our results showed no evidence of benefit from selenium and vitamin E on prostate cancer and other cancers," says the lead author of one of the studies, Dr. Scott Lippman, at M.D. Anderson Cancer Center.

Initial, independent review of study data from the Selenium and Vitamin E Cancer Prevention Trial (SELECT), shows that selenium and vitamin E supplements, taken either alone or together, did not prevent prostate cancer.

Study Participants Learn of Findings

The data also showed two concerning trends among the more than 35,000 men involved in the study.

There was a small, statistically insignificant increase in the number of prostate cancer cases among the men age 50 and older taking only vitamin E. For those men age 50 and older taking only selenium, there was a small increase in the number of cases of adult onset diabetes. Again, the increase was statistically insignificant.

Because this is an early analysis of the data from the study, neither of these findings proves an increased risk from the supplements, and both may be due to chance.

SELECT participants are receiving letters explaining the study review and telling them to stop taking their study supplements.

Participants will continue to have their health monitored by the study staff to detect prostate cancer. Measures will include routine digital rectal exams and blood tests for PSA (prostate specific antigen).

Researchers intend to follow the participants for about three years to determine the long-term effects of taking either of the supplements or a placebo (inactive substance).

The collected blood samples will undergo extensive molecular analyses so researchers can gain a better understanding of prostate cancer, other cancers, and diseases of male aging. This data collection is a vital part of the study.

Neither the men nor their physicians know which supplements or placebos the participants have been taking. Upon request, though, the men will be informed about which supplement, if any, they have received.

"SELECT was always designed as a study that would answer more than a single question about prostate cancer," says Dr. Eric Klein, a study co-chair for SELECT and a physician at the Cleveland Clinic.

"As we continue to monitor the health of these 35,000 men, this information may help us understand why two nutrients that showed strong initial evidence to be able to prevent prostate cancer did not do so," he explains.

SELECT was undertaken to substantiate earlier, separate findings from studies in which prostate cancer was not the primary outcome.

In 2001, men were recruited to participate in SELECT, based on earlier study findings. Four groups were formed, and more than 8,000 men were randomly assigned to each one.

One group took both selenium and vitamin E; one took selenium and a vitamin E placebo; one took vitamin E and a selenium placebo; and the final group received placebos of both supplements.

The researchers note that in 2003, while SELECT was recruiting men, a different SWOG-sponsored study reported that the drug finasteride reduced the incidence of prostate cancer by 25 percent.

When this was discovered, men on SELECT were informed and allowed to take finasteride if they wished.  Finasteride has not yet been approved by the US Food and Drug Administration for prostate cancer prevention.

Nutrients Not Always Magic Bullets

Except for skin cancer, prostate cancer is the most common type of cancer for men in the US. In 2008, there will be an estimated 186,000 new cases of prostate cancer and nearly 29,000 deaths from this disease in the US.

"Finding methods to prevent and treat prostate cancer remains a priority for the NCI, and with the aid of new molecular diagnostic tools and applications, we hope to continue to make headway in reducing deaths and new cases of this disease," says NCI Director Dr. John E. Niederhuber.

"The science of cancer prevention is also leading toward individualized, molecular prevention, in which we will calculate risk and design preventive steps based on an individual's genome," he says.

Dr. Andrew Shao, vice president of scientific and regulatory affairs for the Center for Responsible Nutrition in Washington, DC, says researchers need to "redefine our expectations for nutrients. They're not magic bullets, though they do have tangible effects."

Always consult your physician for more information.