What does selenium do?
Selenium activates an antioxidant enzyme called glutathione peroxidase, which may help protect the body from cancer. Yeast-derived forms of selenium have induced "apoptosis" (programmed cell death) in cancer cells in test tubes and in animals.1 2 3 A double-blind trial that included over 1,300 people found those given 200 mcg of yeast-based selenium per day for 4.5 years had a 50% drop in the cancer death rate compared with the placebo group.4 In that same study, however, selenium supplementation was associated with a significant increase in the risk of developing one type of skin cancer (squamous cell carcinoma).5 Another study found that men consuming the most dietary selenium (assessed indirectly by measuring toenail selenium levels) developed 65% fewer cases of advanced prostate cancer than did men with the lowest levels of selenium intake.6
Selenium is also essential for healthy immune functioning. Selenium supplementation has reduced the incidence of viral hepatitis in selenium-deficient populations, presumably by enhancing immune function.7 Even in a non-deficient population of elderly people, selenium supplementation has been found to stimulate the activity of white blood cells—primary components of the immune system.8 Selenium is also needed to activate thyroid hormones.
In a placebo-controlled study, supplementation with 200 mcg per day of selenium for three months reduced anti-thyroid antibody levels (indicating a reduction in disease activity) in people with autoimmune thyroiditis (inflammation of the thyroid gland).9
In a double-blind trial, selenium supplementation of infertile men improved the motility of sperm cells and increased the chance of conception.10
Where is selenium found?
Selenium has been used in connection with the following conditions
Who is likely to be deficient of selenium?
How much selenium is usually taken?
Are there any side effects or interactions with selenium?
Selenium enhances the antioxidant effect of vitamin E.
Are there any drug interactions?