By Amanda Gardner
The authors of the study said the mineral -- found in foods such as Brazil nuts, in supplements and in foods grown in selenium-rich soil -- might one day offer a way to reduce prostate cancer risk in men.
"There is very little evidence on modifiable prostate cancer risk factors," said study author Milan Geybels. "Any compound that would prevent the incidence of advanced prostate cancer would have a substantial impact on public health."
Geybels, who is a doctoral candidate in cancer epidemiology at Maastricht University in Maastricht, the Netherlands, was scheduled to present the findings Tuesday at the annual meeting of the American Association of Cancer Research, in Washington, D.C. Data and conclusions presented at medical meetings typically are considered preliminary until published in a peer-reviewed journal.
Still, the findings should not be construed as an endorsement of selenium supplements, experts warned.
"At this point, I wouldn't recommend that all men run out and buy a bottle of selenium to take," said Dr. Elise Cook, an associate professor of clinical cancer prevention at the M.D. Anderson Cancer Center in Houston.
Too much selenium can be toxic, resulting in skin problems, and may even be associated with an increased risk of diabetes, Cook said. Getting selenium from dietary sources, however, shouldn't be a problem.
Cancer researchers have been interested in the supposed benefits of selenium on prostate cancer for years, until results from a large trial several years ago showed that selenium, taken either alone or with vitamin E, did not prevent prostate cancer.
"Before that, selenium supplements had been flying off the shelves," said Dr. Alexander Kutikov, an associate professor of urologic oncology at Fox Chase Cancer Center in Philadelphia. "Enthusiasm [for selenium] was really dampened by that trial."
But that study looked at men with normal selenium levels when they entered the trial, and it did not focus on a specific type of prostate cancer. This latest study looked only at men who were deficient in selenium and tracked only cases of advanced prostate cancer, which is linked with a poor prognosis.
Among a group of almost 60,000 men aged 55 to 69 at the beginning of the study, the researchers found that men with the highest selenium levels, as measured in toenail clippings, had more than a 60 percent reduced risk for advanced prostate cancer.
Selenium levels in toenail clippings indicate long-term selenium intake, the researchers noted. The large trial from several years ago measured blood levels of the mineral, which reflects only recent exposure.
Still, the study is "hypothesis-generating at best," Kutikov said. Although the findings suggested an association between selenium levels and advanced prostate cancer risk, they did not prove a cause-and-effect link.
Geybels said the results could point the way to another trial assessing risk for advanced prostate cancer in men with low selenium levels.