Selenium is a nutritionally essential trace element for humans. The National Research Council’s Recommended Dietary Allowance for selenium in adults ranges from 55 to 75 mcg per day depending on age and gender. Selenium is a cofactor to about 10 selenoproteins in the body; the most important of these appears to be glutathione peroxidase (GPX). GPX uses glutathione to reduce hydrogen peroxide and thus protect cells and plasma against free radical injury. GPX activity depends on an adequate supply of dietary selenium. Selenium and vitamin E appear to have synergistic effects, since some signs of vitamin E deficiency in animals can be alleviated by dietary selenium. Dietary selenium is generally well absorbed and utilized in the body. The richest food sources of selenium are seafood and organ meats, followed by muscle meats, cereals and grains, and dairy products. Fruits and vegetables are typically low in selenium, and low selenium status has been reported in vegetarians.