Selenium may worsen prostate cancer

BOSTON, June 27 (UPI) -- Higher selenium levels in the blood may worsen prostate cancer in some men who have the disease, U.S. researchers said.

Researchers at Dana-Farber Cancer Institute in Boston and the University of California, San Francisco, said a higher risk of more-aggressive prostate cancer was seen in men with a certain genetic variant found in about 75 percent of the prostate cancer patients in the study.

In those subjects, having a high level of selenium in the blood was associated with a two-fold greater risk of poorer outcomes than among men with the lowest amounts of selenium.

In contrast, the 25 percent of men with a different variant of the same gene and who had high selenium levels were at 40 percent lower risk of aggressive disease.

The variants are slightly different forms of a gene that instructs cells to make manganese superoxide dismutase, an enzyme that protects the body against harmful oxygen compounds, the researchers said.

The findings suggest that "if you already have prostate cancer, it may be a bad thing to take selenium," senior author Dr. Philip Kantoff, director of Dana-Farber's Lank Center for Genitourinary Oncology, said in a statement.

Supplements of selenium have been sold and promoted as a means of preventing prostate cancer -- largely based on observational studies that found higher risk of prostate cancer incidence and mortality in areas of the country that are naturally low in selenium, Kantoff said.

The findings are published online ahead of print in the Journal of Clinical Oncology.