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Antioxidant May Prevent Prostate Cancer

Study finds a protective effect in selenium

WEDNESDAY, May 5, 2004 (HealthDayNews) -- Men whose diets include high levels of selenium significantly reduce their risk of progressive prostate cancer, researchers report.

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."

More information

The National Institutes of Health can tell you about selenium, and the American Cancer Society explains prostate cancer.

SOURCES: Haojie Li, M.D., Ph.D., research fellow, Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston; Scott M. Lippman, M.D., chairman, department of clinical cancer prevention, and professor, cancer medicine and cancer prevention, University of Texas M.D. Anderson Cancer Center, Houston; May 5, 2004, Journal of the National Cancer Institute
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