A new study says that people who are already suffering from prostate cancer must avoid selenium as it worsens their condition.
Researchers at Dana-Farber Cancer Institute the University of California, San Francisco, have observed a higher risk of more-aggressive prostate cancer in men with SOD2 genetic variant, found in about 75 percent of the prostate cancer patients in the study.
In such men, having a high level of selenium in the blood was linked with a two-fold greater risk of poorer outcomes than men with the lowest amounts of selenium.
On the other hand, 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 (SOD2)-an enzyme that protects the body against harmful oxygen compounds.
Senior author Dr. Philip Kantoff, director of Dana-Farber's Lank Center for Genitourinary Oncology, says that the findings of the study suggest that for those who already have prostate cancer, it may be a bad thing to take selenium.
The unexpected results are the first to raise concern about this potentially harmful consequence of taking supplemental selenium.
Kantoff said: "These findings are interesting particularly in light of the recent negative results from the SELECT prevention study, which asked if selenium could protect against prostate cancer."
The new study reveals the strong interaction between selenium and SOD2 to influence the biology of prostate cancer-a finding that has earlier been shown.
The authors said that the current research demonstrated that variations in the make up of the SOD2 gene dramatically alter the effects of selenium on the risk of aggressive prostate cancer.
Selenium is a mineral found widely in rocks and dirt and small amounts of selenium are essential for health.
The study has been published in the Journal of Clinical Oncology.