Two concepts are often currently applied to selenium in adult men in the United States: • Intake is generally enough to maximize blood glutathione peroxidase activities. • In such men, selenium supplementation does not reduce risk of prostate cancer. In contrast to these concepts, 30 healthy middle-aged men were studied to test the following hypothesis: 6-week supplementation of 200 μg of selenium as glycinate can raise activities of 2 blood selenium enzymes and lower a marker of prostate cancer risk. The hypothesis was confirmed, in that selenium supplementation raised activities for erythrocyte and plasma glutathione peroxidase as well as lowered values for plasma prostate-specific antigen. The enzyme activity increases were not extremely large, but based on a chicken study, changes in blood glutathione peroxidase activities can reflect bigger changes in the prostate. Placebo treatment did not duplicate the selenium effects in 30 other men. In conclusion, this study suggests that US middle-aged men may not typically consume optimal amounts of selenium.
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