Selenium rising … all over again


As some of our older readers will remember, there was a major Phase III clinical trial several years ago (the SELECT trial) designed to study whether taking regular selenium supplements could help to lower risk for a diagnosis of prostate cancer. It didn’t.

However, a newly published paper by Allen et al. in the Journal of the National Cancer Institute now claims to show that selenium levels in nail clippings do appear to be predictive of risk for prostate cancer, and selenium levels in nail clippings and in blood may be predictive for aggressive forms of prostate cancer.

Specifically, Allen and her collaborators used data from men participating in 15 different prospective studies to show that, based on data from actual prostate cancer patients and comparable but healthy “control” patients who did not have prostate cancer:

  • Men with a high level of selenium in the blood were
    • Not at less risk for diagnosis with any form of prostate cancer (odds ratio [OR] = 1.01)
    • At significantly less risk for diagnosis with advanced prostate cancer or prostate cancer-specific mortality (OR = 0.43), but
    • Not at less risk for diagnosis with non-aggressive forms of prostate cancer
  • Men with a high level of selenium in toenail and/or fingernail clippings were
    • At significantly less risk for diagnosis with any form of prostate cancer (OR = 0.29)
    • At significantly less risk for diagnosis with advanced prostate cancer or prostate cancer-specific mortality (OR = 0.18)
    • At significantly less risk for diagnosis with non-aggressive forms of prostate cancer (OR = 0.33)

The authors conclude that:

Nail, but not blood, selenium concentration is inversely associated with risk of total prostate cancer, possibly because nails are a more reliable marker of long-term selenium exposure. Both blood and nail selenium concentrations are associated with a reduced risk of aggressive disease, which warrants further investigation.

The authors also state that these findings do not conflict with the findings from the SELECT study.

If these data are accurate, and selenium levels in blood and nail clippings really are indicative of risk for aggressive forms of prostate cancer, this might offer us yet another way to evaluate the risk for aggressive prostate cancer in men prior to making decisions about treatment. What these data do not suggest, however, is that we should revisit the use of selenium supplements as an agent that could be used to prevent prostate cancer. It was clear from the SELECT study that the use of selenium supplements was associated with no evidence of clinical benefit in terms of a reduction in risk for prostate cancer, and that — conversely — there were suggestions that continuing treatment with selenium might be associated with an increased risk for type II diabetes.

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