Does Selenium Prevent Prostate Cancer?

Jodi H. Walker, PharmD

Disclosures

May 27, 2010

Question:

Should men take selenium daily for prostate cancer prevention?

Response from Jodi H. Walker, PharmD
Adjunct Faculty, Albany College of Pharmacy, Albany, New York; Clinical Pharmacy Coordinator, VA Medical Center, Bath, New York

Selenium is an important trace element that has surfaced in the past decade as a debatable treatment option for prevention of prostate cancer. Selenium is found naturally in such foods as nuts, whole grain wheat (cereals), and some meats and seafood.[1] The Recommended Daily Allowance for selenium is 55 μg/day,[1] which most Americans receive through their usual diet.[2] Taken orally, selenium accumulates in the prostate gland.[3]

The antitumor effects associated with selenium are thought to involve correcting nutritional deficiencies that are uncommon among Americans.[4] The exact mechanism by which selenium may inhibit the development of cancer is unknown, but it is believed that the antioxidant properties of selenium may help repair DNA, inhibit cell invasion, and cause stimulation of the signaling of transforming growth factor beta.[5]

The cancer preventive effects of selenium have been studied. SELECT (Effect of Selenium and Vitamin E on Risk of Prostate Cancer and Other Cancers: The Selenium and Vitamin E Cancer Prevention Trial) evaluated whether selenium (L-selenomethionine), vitamin E, or a combination of selenium and vitamin E had any benefit in preventing prostate cancer.[6]

Over 35,000 men from more than 400 sites throughout the United States, Canada, and Puerto Rico were randomly assigned to 1 of 4 groups: selenium 200 μg/day, vitamin E, selenium and vitamin E, or placebo. All participants were 55 years or older, except for African American men, who were 50 years or older. Inclusion criteria were current prostate-specific antigen serum levels 4 ng/mL or less, no history of prostate cancer, and negative results on digital rectal examination. Patients were evaluated for a median of 5.46 years.

SELECT did not demonstrate any benefit of selenium compared with placebo for prostate cancer prevention. Prostate cancer was detected in 4.56% and 4.43% of the selenium and placebo groups, respectively. Secondary endpoints found an increase in the prevalence of diabetes mellitus in the selenium group vs placebo, but this was not statistically significant. Although the trial was scheduled to run through 2012, the Data and Safety Monitoring Committee cut the trial short because no correlation between taking selenium and prevention of prostate cancer was found. Although the trial has ended, participants will continue to be followed until 2015.[6]

Clinical trials have shown that selenium supplementation may be beneficial for a small group of people,[7,8] but it has not been found effective for the majority of the patient population. Antioxidants can also be counterproductive in individuals who are already diagnosed with prostate cancer.[9] Taking into consideration the side effects associated with antioxidants and the risk for drug-drug interactions, other options at this point prove to be more beneficial for prostate cancer prevention.

The author thanks Brian Bohunicky, pharmacy student from The Albany College of Pharmacy, for his contribution in researching and compiling this response.

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