An essential mineral that is a component of a key antioxidant enzyme, glutathione reductase, in tissue respiration. Deficiency of selenium causes Keshan disease, a fatal form of cardiomyopathy (disease of the heart muscle) first observed in Keshan province in China and since found elsewhere. According to the National Academy of Sciences, the Recommended Dietary Allowances of selenium are 70 milligrams per day for men and 55 milligrams per day for women. Food sources of selenium include seafoods, some meats such as kidney and liver, and some grains and seeds. Too much selenium may cause reversible changes in the hair (balding) and nails, garlic odor to the breath, intestinal distress, weakness and slower mentation (slowed mental functioning).
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A metallic element chemically similar to sulfur, atomic no. 34, atomic wt. 78.96; an essential trace element toxic in large quantities; required for glutathione peroxidase and a few other enzymes; 75Se (half-life equal to 119.78 days) is used in scintography of the pancreas and parathyroid glands. [G. selene, moon]
- s. sulfide a mixture of crystalline s. monosulfide and solid solutions of s. and sulfur in an amorphous form, containing 52–55.5% Se; used in the treatment of seborrhea of the scalp or dandruff; it is applied to the scalp as a suspension.

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se·le·ni·um sə-'lē-nē-əm n a nonmetallic element that resembles sulfur and tellurium chemically, causes poisoning in range animals when ingested by eating some plants growing in soils in which it occurs in quantity, and occurs in allotropic forms of which a gray stable form varies in electrical conductivity with the intensity of its illumination and is used in electronic devices symbol Se see ELEMENT (table)

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a trace element that is an essential component of the enzyme glutathione peroxidase, which catalyses the oxidation of glutathione by hydrogen peroxide. It thus has important antioxidant properties. Dietary deficiency of selenium results in cardiomyopathy. Symbol: Se.

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se·le·ni·um (Se) (sə-leґne-əm) [Gr. selēnē moon] a nonmetallic element resembling sulfur; atomic number, 34; atomic weight, 78.96. It is an essential mineral, being a constituent of the enzyme glutathione peroxidase, and believed to be closely associated with vitamin E in its functions. Selenium occurs in toxic levels in certain plants growing in soil with high concentrations of it, causing selenium poisoning (q.v.) in grazing animals. Dietary deficiency, occurring where the soil has a low sodium content, results in cardiomyopathy (see Keshan disease, under disease).

Medical dictionary. 2011.

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