Brewer's yeast and wheat germ, both regarded as "health foods," usually contain high concentrations of selenium. Animal sources such as liver, butter, most fish, and lamb have adequate amounts. Many vegetables, whole grains, nuts, and molasses are fairly good selenium foods. Brazil nuts have high amounts; barley, oats, whole wheat, and brown rice are also good sources; and shellfish such as scallops, lobster, shrimp, clams, crab, and oysters are all rich in selenium. Garlic and onions, mushroom, broccoli, tomatoes, radishes, and Swiss chard may be good selenium sources if the soil in which they are grown contains it. Therefore, if we want to make sure we get adequate amounts of selenium and other minerals, it is best to eat a varied diet of wholesome foods.
Functions: Selenium has a variety of functions, and research is revealing new information. Its main role is as an antioxidant in the enzyme selenium-glutathione peroxidase. Selenium is part of a nutritional antioxidant system that protects cell membranes and intracellular structural membranes from lipid peroxidation. It is actually the selenocysteine complex that is incorporated into glutathione peroxidase (GP), an enzyme that helps prevent cellular degeneration from the common peroxidase free radicals, such as hydrogen peroxide. (Selenomethionine can be supplemented to generate the organically complexed and active selenocysteine.) GP also aids red blood cell metabolism and has been shown to prevent chromosome damage in tissue cultures. Solidification of tissue membranes may occur through the oxidation of fatty acids. As an antioxidant, then, selenium in the form of selenocysteine prevents or slows the biochemical aging process of tissue degeneration and hardening-that is, loss of youthful elasticity. This protection of the tissues and cell membranes is enhanced by vitamin E. The antioxidant effect may also benefit the cardiovascular system and protect against cancer. We need adequate daily amounts of selenium for the maintenance of these antioxidant functions and for selenium's other cellular functions as well.
Selenium also appears to help stimulate antibody formation in response to vaccines. This immunostimulating effect is also enhanced by vitamin E; the presence of these two nutrients can increase antibody formation by 20-30 times, as shown by research.
Selenium is thought to offer protection against cardiovascular disease, possibly by its antioxidant function but possibly by another, as yet, unknown mechanism. Epidemiological studies show an increased incidence of strokes and other cardiovascular problems in many low-selenium areas.
Selenium is also being found to have an anticarcinogenic effect; its blood or tissue levels may correlate more closely with cancer risk than those of any other substance. Public health research shows this relationship in many cases; good selenium levels correlate with low cancer rates and low levels with increased cancer rates. I do not yet know exactly how this works other than possibly through the antioxidant function. Perhaps selenium decreases cell division or helps cell repair, or perhaps it protects against mutagenic changes in the first place.
Selenium also seems to protect us from the toxic effects of heavy metals and other substances. People with adequate selenium intake have fewer adverse effects from cigarette smoking, alcohol, oxidized fats, and mercury and cadmium toxicity. Aside from the likely antioxidant influence, the specific mechanism by which selenium affords this protection is not known, though the effect is confirmed by some research.