To Prevent Prostate Cancer, SELECT Something Besides Selenium

A new analysis of data from the federally-funded SELECT (Selenium & Vitamin E Cancer Prevention Trial) study appears to deliver the death-blow to the idea that supplementation with selenium and vitamin E can reduce the risk of prostate cancer.

The study, which was funded by the National Cancer Institute as been the subject of considerable debate. It began in 2001, and enrolled more than 35,000 men over age 50 at 400 sites in the US, Puerto Rico and Canada. The objective was to assess whether the trace mineral, selenium, at a daily dose of 200 mcg alone or in combination with d-alpha tocopherol (vitamin E) in dose ranges of 400-660 IU.

In 2008, the NCI opted to stop the study after preliminary analysis showed no cancer-sparing benefit from either of the supplements compared with placebo, but a statistically significant 17% increase in risk of prostate cancer among the men taking the vitamin E. The men taking selenium alone also showed a slight increase in cancer risk, but the difference was not statistically significant.

Critics of the trial–and its cessation–held that by using d-alpha-tocopherol alone, SELECT unfairly vilifies “vitamin E” which in nature represents a composite of 8 different tocopherols and tocotrienols. For some, the initial data set also left open questions about the impact of selenium: was it truly contributing to a rise in cancer, or was this a statistical artifact.

A new analysis by Dr. Alan Kristal and colleagues at the Fred Hutchinson Cancer Research Center, Seattle, WA, indicates that–unfortunately–it’s the former scenario.

Dr. Kristal and his team looked at the impact of selenium supplementation stratified by baseline selenium levels. In other words, they were looking to see if men with the lowest baseline levels showed a decreased cancer risk after years of supplementation. This would corroborate the initial rationale for selenium supplementation based on earlier population-based studies indicating an association between seleniumd eficiency and higher prostate cancer risk.

The data showed no benefit in terms of reducing cancer risk in deficient men, and it actually increased the risk in men with the highest baseline selenium levels.

The researchers used toenail selenium content in clippings taken prior to starting the trial as the basic indicator of selenium levels. Selenium supplementation alone or in combination with vitamin E had no effect on prostate cancer rates in thise under the 60th percentile for baseline selenium, but provoked a 91% increased risk of high-grade prostate cancer in those in the highest baseline selinium quintile. The data were just published in the Journal of the National Cancer Institute.

Older men with high baseline selenium levels were particularly susceptible to the amplyfing effect of the supplementation.

The SELECT data also seem to put to rest the notion that low selenium is a risk factor for prostate cancer. Dr. Kristal’s team found no difference in prostate cancer risk between men in the lowest versus highest quintiles.

Based on these findings, Dr. Kristal concludes that “Men should avoid selenium or vitamin E at doses that exxceed recommended dietary intakes.”

The US Preventive Services Task Force is expected to make a final statement about the new SELECT findings shortly.

END

 

 

 

 
Subscribe to Holistic Primary Care