WASHINGTON-Depending on the study, selenium either shows an associated reduced risk of prostate cancer, or it doesn't. Now, researchers in the Netherlands, where men typically have low selenium levels, reported that selenium is associated with a substantial decrease in the risk of advanced prostate cancer, particularly during later follow-up.
The trial, reported here at the American Association for Cancer Research Annual Meeting (Abstract 3613) is unique in that the researchers studied toenail selenium, which they say reflects longer exposure to selenium.
"Studies in the past have been conducted among men with moderate to high selenium levels, but it is important to study populations of men who have low to moderate levels of selenium, who would be expected to have a higher risk of prostate cancer," said the first author, Milan S. Geybels, a PhD candidate in Cancer Epidemiology at the CAPHRI School for Public Health of Maastricht University in the Netherlands.
Also, he said, studies in the past have used plasma or serum selenium, which reflect recent selenium intake versus long-term exposure.
Part of Netherlands Cohort Study of 58,279 Men
The new study was part of the Netherlands Cohort study of 58,279 men, age 55 to 69. The selenium study population included 898 men identified as having advanced prostate cancer (Stages III/IV) during a 17-year follow-up, and 1,203 men in a subcohort. Toenail clippings were submitted by participants in the study by mail when they returned the questionnaires to enroll.
The average toenail selenium concentration in the subcohort was 0.549 [mu]g/g. Men who developed advanced prostate cancer had lower concentrations, averaging 0.527 [mu]g/g. Those with the highest amount of toenail selenium had a 59 percent reduction in the risk of developing advanced prostate cancer.
"We specifically evaluated advanced prostate cancer because that is associated with a poor prognosis and therefore clinically relevant," he said.
The researchers noted that a recent meta-analysis did show higher selenium levels associated with a reduced risk of prostate cancer (Hurst et al: Am J Clin Nutr 2012;96:111-122), while the large SELECT (Selenium and Vitamin E Cancer Prevention Trial) showed no such effect (Klein et al: JAMA 2011;306:1549-1556).
"If our results can be confirmed, a prevention trial of selenium and prostate cancer in a low-selenium population may be justified," Geybels said.
Important Biological Functions
Selenium exerts important biological functions through its presence in selenoproteins, he explained, and genetic variation in the major selenoproteins glutathione peroxidase 1 (GPX1) and selenoprotein P (SEPP1) has been associated with the risk of prostate cancer.
Interestingly, in the new study toenail selenium was associated with a reduced risk of advanced prostate cancer among smokers and former smokers, but not among never smokers; and the association was slightly more pronounced for men diagnosed at eight or more years of follow-up.
In the next analysis, Geybels said, this same population will be studied to analyze the association of common variation in GPX1 and SEPP1 with advanced prostate cancer.