Increased exposure to selenium was associated with a significantly reduced risk of advanced prostate cancer, according to the results of a large, prospective cohort study of men in the Netherlands.
The results of the study, conducted in men with low to moderate selenium levels, "suggest that selenium may prevent advanced, clinically relevant, prostate cancer," noted Milan Geybels, M.Sc., at the annual meeting of the American Association for Cancer Research. And since there is little evidence on risk factors that can modify prostate cancer risk, "any compound that would prevent the incidence of advanced, clinically relevant prostate cancer would have a substantial impact on public health," Mr. Geybels said in an interview.
The men were enrolled in the Netherlands Cohort Study, a study of diet and cancer in 58,279 men between the ages of 55 and 69 years at entry. Over 17 years, 898 men were diagnosed with advanced prostate cancer and were compared with 1,203 men also in the study. Using the concentration of selenium in the men’s toenails, an indication of long-term exposure, the investigators determined that the risk of advanced prostate cancer was significantly reduced as selenium levels increased. The risk for advanced prostate cancer was more than 60% lower in men with the highest levels of toenail selenium, when compared with those with the lowest levels, and the association was "more pronounced" among the men diagnosed later in the follow-up period, noted Mr. Geybels, a doctoral candidate in cancer epidemiology at Maastricht University, the Netherlands.
Previous prospective studies on the possible link between selenium and prostate cancer risk have produced conflicting results. Many of the studies included men with moderate to high selenium levels. Also, they did not exclusively study advanced prostate cancer, and "almost exclusively" used blood levels of selenium, which reflect recent exposure, he noted.
SELECT (Selenium and Vitamin E Cancer Prevention Trial) found no relationship between selenium supplementation and prostate cancer risk. However, "a possible explanation for the null finding is that selenium intake among SELECT participants was adequate ... [so], further selenium supplementation had no effect on prostate cancer incidence," he said.
The intake of selenium varies worldwide as a result of variations in soil content and the related variability in the selenium content in foods; in the Netherlands, low selenium is common.
The results need to be replicated in more prospective studies, and if confirmed, "A prevention trial of selenium and advanced prostate cancer in a low selenium population may be justified," said Mr. Geybels. Whether levels higher than those detected in the men in the study are associated with a further reduction in risk is unknown.
He and his coauthors had no disclosures to report.