Selenium is one of the essential trace elements needed by humans. It is indirectly responsible for keeping the body's supply of vitamin C, glutathione, and vitamin E intact.

The functions of Selenium in the body include protecting cell membranes from lipid peroxidation, slowing or preventing the biochemical aging process of tissue degeneration and hardening, stimulating antibody formation, protecting from toxicity, aiding in protein synthesis, reducing menopausal symptoms, and maintaining proper functioning of the thyroid gland.

It may also play a role in the prevention and or treatment of health conditions such as acne, multiplesclerosis, asthma and ovarian cysts. While it is widely available from many foods, mother's milk usually has several times more selenium than cow's milk. Animal foods such as liver, butter, most fish and lamb have adequate amounts. Many vegetables, whole grains, nuts and molasses are fairly good sources.

While dietary deficiency is the most common cause of selenium deficiency, the latter has also been reported in malnourished individuals and high-risk areas of Africa, Russia, New Zealand, and China. Although the occurrence of selenium toxicity is extremely rare, the few reported cases have been associated with industrial accidents and a manufacturing error that led to an excessively high dose of selenium in a supplement.