In this new study, researchers found high blood levels of selenium decreased
the risk of advanced prostate cancer. In addition, for men who had above-normal
levels of prostate-specific antigen (PSA) at the start of the study, high
selenium levels significantly reduced risk of all prostate cancer. PSA is a
protein that is found in all men, but it shows up in high levels in men with
prostate cancer or other prostate problems.
Selenium is an antioxidant that can be found in most plant foods and in some
meats and shellfish. Nuts, particularly Brazil nuts, are also a good source of
dietary selenium.
"We found a relationship between blood levels of selenium and the risk of
developing advanced prostate cancer over 13 years of follow-up," said lead
researcher Dr. Haojie Li, a research fellow at the Channing Laboratory of
Harvard Medical School.
Li and her colleagues collected data on 586 men diagnosed with prostate
cancer over a 13-year period and 577 normal subjects. All the men participated
in the Physicians Health Study, according to the report in the May 5 issue of
the Journal of the National Cancer Institute.
The protective effect of selenium was most pronounced in patients with
slightly abnormal PSA levels, Li said. However, among men who had normal PSA at
the beginning of the study there did not seem to be significant benefit from
selenium in preventing prostate cancer, she added.
Men with an elevated PSA can reduce their risk of progressive prostate cancer
by as much as 50 percent, Li said.
"Our interpretation of the findings is that higher levels of selenium may
slow prostate cancer tumor progression," Li explained. Elevated PSA indicates
that a tumor exists, and selenium seems to prevent the tumor from growing, she
said.
Li said this data is not sufficient to suggest that men take selenium
supplements to ward off prostate cancer. She added that a trial to test the
effects of selenium on prostate cancer prevention is under way.
This trial may show whether or not men should increase their selenium intake
to fight prostate cancer, she said.
"Right now, all we can say is that eating foods with higher levels of
selenium seems to be beneficial in terms of prostate cancer prevention," Li
said. But at this point, "we can't say that everyone with elevated PSA should be
taking selenium supplements."
Dr. Scott M. Lippman, chairman of the department of clinical cancer
prevention at the University of Texas M.D. Anderson Cancer Center, said this
study confirms findings from animal and cell studies showing that selenium
reduces the progression of prostate cancer.
There is some debate about the value of selenium in preventing prostate
cancer in men with normal PSA levels, said Lippman, co-author of an accompanying
editorial. But a study of selenium and skin cancer, "did find that selenium was
associated with a reduced risk of prostate cancer in men with normal PSA," he
added.
The data from the study by Li suggests selenium slows the progression of
prostate cancer in men who have cancer that cannot be detected. "Selenium may
slow the clinical expression of prostate cancer, which is equivalent to
prevention," Lippman said.
Lippman agreed it is too early to recommend taking selenium supplements. "I
would not recommend taking selenium supplements until the results of the ongoing
trials are known," he said. "All of the evidence we have to date [is]
encouraging, but not definitive."
