Back to the question of whether selenium levels affect prostate cancer risk

A newly published review and meta-analysis in The American Journal of Clinical Nutrition has suggested that biological levels of selenium that fall outside a relatively narrow “normal” range may well be associated with increased risk for prostate cancer. However, we wish to emphasize the authors’ clear staement that they do not believe that there is any evidence in support of the use of selenium supplements. Rather, they make the point that a good diet may be a more important fact in assuring “normal” biological levels of selenium. Specifically, one of the authors has been quoted by Reuters (see below) as staing that, “we recommend that selenium [be] provided by foods rich in selenium, not supplements.”

Hurst et al. set out to re-examine the evidence for any relationships between selenium intake, selenium status, and prostate cancer risk. To do this they conducted a systematic review and meta-analysis of randomized controlled trials, case-control studies, and prospective cohort studies published through September 2010. Studies appropriate for review and assessment needed to include reported measurements of selenium intake or status (plasma, serum, or toenail selenium), assessments of prostate cancer cases (number of events), and the relative risk for prostate cancer in the adult population.

Here are the core findings of this review and meta-analysis:

  • 12 appropriate studies with a total of 13,254 participants and 5,007 cases of prostate cancer were identified and included.
  • The risk for a diagnosis of prostate cancer decreased with increasing plasma/serum selenium levels of up to 170 ng/ml.
  • Three high-quality studies included in the meta-analysis of selenium levels in samples of toenail cuttings and cancer risk indicated a reduction in prostate cancer risk (estimated RR: 0.29) with a toenail selenium concentration between 0.85 and 0.94 μg/g.

The authors are also clear that this study is only hypothesis generating and cannot currently be used to make accurate determination about “the right” levels of selenium in serum or other biological specimens to minimize risk for prostate cancer.

Additonal commentary about this study can be found on the web site. In an e-mail to Reuters, the senior author of the study apparently stated their finding that:

  • A plasma/serum selenium concentration of 135 ng/ml is associated with
    • A 15 percent reduction in total prostate cancer risk
    • A 40 percent reduction in risk for advanced prostate cancer

As indicated above, there is clearly more work necessary to establish whether data of this type is truly definitive of risk for localized and advanced forms of prostate cancer over a man’s lifetime (as opposed to at a specific point in time)

3 Responses

  1. Core findings above, abstract, and Reuters only cover evidence for decreased risk.

    It appears that the suggestion for “increased risk” outside a range yet to be determined is purely speculative, at this point. The only evidence cited in the meta study indicated decreased risk, including that provocative 40% decrease in advanced prostate cancer.

    I’m curious whether the complete paper addresses the research by the group in the Boston area on selenium, SNIPs and prostate cancer. Dr. Elizabeth Platz summarized (in PMID: 20424133) recent research by the group as follows: “… Selenium may prevent poorer-prognosis prostate cancer and its progression to bony metastases and death, but only in men with genetic backgrounds that influence the requirement for selenium. These inferences point toward how to reconcile inconsistent prostate cancer risk results from the two randomized trials of selenium conducted to date.”

    I suspect I am not alone in continuing to take selenium for a challenging case of prostate cancer. My case was challenging 12.5 years ago and continues to evidence a doubling time of 3 to 4 months when not held in check. My recent Na18F PET/CT bone scan and Feraheme USPIO lymph node scan were both negative. Of course, it’s impossible to know what role selenium has played for me, but I am unwilling to “change horses” in mid-stream.

  2. I am reminded of June Chan’s 2009 research that suggests genotyping is required to determine whether selenium is an appropriate supplement for men with prostate cancer; with one particular gene type, selenium can reduce risk while it can promote risk with another.

  3. Thanks, Rick.

    I reviewed a couple of recent selenium/genotype studies – the 2009 Chan study that you mentioned, and the 2010 Penney study. My take-away lessons are that the impact of selenium on prostate cancer risk remains puzzling at this time, though it appears that patient genotypes play important roles, and that research progress is encouraging.

    While the Chan study found the impact you mentioned with higher selenium levels for patients with SNPs involving the antioxidant enzyme manganese superoxide dismutase (MnSOD or SOD2) gene, the Penney study found decreased risk of PCa mortality for men with the G allele for “a recently discovered selenoprotein, 15-kDa selenoprotein (SEP15) [which] is highly expressed in the prostate” and was possessed by about two thirds of study participants.

    The same collaborative research group looked at both genes (though with different protocols/study populations), and it would be interesting to see an analysis or fresh study of selenium level versus risk of aggressive prostate cancer that combined both genes, i.e. men with both the AA genotype for SOD2 (Chan) and the G allele for SEP 15 (Penney) (both associated with decreased risk), similar combinations of the alleles for higher risk for both genes, and mixes.

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