Selenium levels in tissue and prostate cancer risk


According to a paper presented yesterday by Geybels et al. at the ongoing annual meeting of the American Association for Cancer Research in Washington, DC, among almost 60,000 men aged 55 to 69 at the beginning of the study, the men with the highest levels of selenium in their toenail clippings were 60 percent less likely to develop advanced prostate cancer.

A full report on this presentation can be found on the HealthDay web site. We should point out immediately that it would be entirely wrong to conclude from this report that taking selenium supplements could reduce the short-term risk for prostate cancer. Indeed, the results from the Prostate Cancer Prevention Trial in some 18,000 men has already shown that this is absolutely not the case.

The issue of the association between selenium levels in tissue and risk for prostate cancer is complex. As the HealthDay report is careful to note, the new study by Geybels and her colleagues looked only at men who were deficient in selenium and tracked only cases of advanced prostate cancer, which is linked with a poor long-term prognosis. The levels of selenium in toenail clippings is associated with long-term selenium intake. The data on which the Prostate Cancer Prevention Trial was based, as the research team is careful to point out, was based on blood levels of selenium among men who started out with relatively normal levels of selenium in their blood.

A host of factors affect the development of selenium levels in toenail clippings over time, including many dietary and environmental factors (because different regions have different selenium levels in soil and therefore in the plants grown on that soil and in the animals that graze on those plants). The original idea for the Prostate Cancer Prevention Trial was, in fact, based on a much earlier finding that men who had low levels of selenium were at higher risk for prostate cancer, so from that perspective the finding reported by Geybels et al. is not exactly new.

Is it possible that we could show that increasing the selenium in the diets of men with normally low levels of selenium could lower their risk for progressive prostate cancer? Yes, it is. What we don’t have a clue about, however, is how long it might take to conduct such a study. For starters, at what age does a man need to ensure that he has “normal” levels of selenium in his toenail clippings (or his blood) to prevent later onset of advanced prostate cancer — when he is 15 or 55?

There is no evidence at this time that even men with low blood levels of selenium would benefit from selenium supplements, and there is good evidence that excessive selenium intake can be toxic, can result in skin problems, and may increase risk for diabetes. On the other hand, increasing one’s selenium intake from dietary sources is probably not a problem. The Office of Dietary Supplements at the National Institutes of Health offers a fact sheet on dietary sources of selenium and the recommended normal levels of selenium intake.

7 Responses

  1. As a previous article on this web site showed, there appears to be a strong link between genetic makeup and the value of selenium.

    Unfortunately, the genetic test for the alleles involved appears to not be available.

  2. The study Doug refers to is now some 3+ years old. I am not aware of any follow-up study related to this issue or any other study confirming the data originally presented by Penney et al.

  3. I am re-posting a comment I made last July, when another research paper on selenium was reported; it is still pertinent when considering whether to take selenium supplements:

    “I am reminded of June Chan’s 2009 research (http://jco.ascopubs.org/content/27/22/3577.short) 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”

  4. Does anyone know where to get this genotyping test done?

    I e-mailed Kantoff (one of the authors of the study) and he didn’t know where to get it.

  5. My guess would be that Rick D. might be able to put you in touch with June Chan.

  6. Yup … Try June Chan at this e-mail address.

  7. Thanks. I e-mailed her.

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