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Selenium is a trace mineral required for the manufacture of vital enzymes, including glutathione peroxidase, the body's premier antioxidant enzyme. Present in all body tissues, selenium is most concentrated in the kidneys, liver, spleen, pancreas, and testes. Supplemental forms of selenium include inorganic salts, such as sodium selenite, and organic forms such as selenomethionine and selenium-rich yeast.
Good sources of selenium include wheat germ, Brazil nuts, whole grains, and seafood. The selenium content of food depends upon the selenium level of the soil in which it is grown; thus, food selenium content varies from region to region.
As a trace mineral, selenium is only required in small amounts. Although the U.S. National Research Council has calculated the RDA for selenium to be 70 and 55 mcg per day for adult men and women, respectively, many nutritionists recommend a daily intake of 50 to 200 mcg. Intake exceeding 1,000 mcg per day can result in toxicity. Symptoms of chronic selenium toxicity include emotional instability, nausea, a garlic odor in the breath and sweat, and in extreme cases, loss of hair and fingernails.