Selenium is a trace mineral. It is a very important antioxidant, essential for the enzyme glutathione peroxidase. It works in synergy with vitamin E. As an antioxidant, selenium protects the immune system, preventing the formation of free radicals. It also aids (especially when combined with vitamin E) in the production of antibodies and helps to maintain a healthy heart.

Selenium increases the number of antibodies for resistance to disease. It increases the levels of the antioxidant enzyme glutathione peroxidase, which helps to reduce lipoperoxidation. Selenium may improve energy levels and help in the process of aging by attacking free radicals. It is important for ailments related to the heart and high blood pressure, and it decreases platelet aggregation.

Some research in the 1970s showed that selenium protects against radiation. It is needed for pancreatic function and tissue elasticity. It is essential for reproduction; some studies show that selenium deficiency results in infertility. Male sperm cells contain high amounts of selenium. Considerable amounts are lost during sexual intercourse; for this reason, selenium necessity is higher in men than women.