A study from the Danish Cancer Society Research Centre of more than 27,000 men found no relationship between blood levels of selenium and prostate cancer. However, markers of severe prostate disease were higher in selenium-deficient men. In men with diagnosed prostate cancer, higher selenium levels reduced the overall risk of death from the disease. Taking selenium supplements, however, could be dangerous. Researchers from the National Cancer Institute in Bethesda, MD found that heavy vitamin use (greater than seven times per week) or taking specific supplements such as zinc, beta-carotene and selenium increased risk of the disease by 7% to 300%.