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Selenium (Se) is a part of the enzyme glutathione peroxidase, which metabolizes hydroperoxides formed from polyunsaturated fatty acids. Selenium is also a part of the enzymes that deiodinate thyroid hormones. Generally, selenium acts as an antioxidant that works with vitamin E. Some epidemiologic studies associate low selenium levels with cancer. In children with Down syndrome, selenium supplements help prevent bacterial infections. Plasma levels vary from 8 to 25 μg/dL, depending on selenium intake. Diagnosis is usually clinical; sometimes blood glutathione peroxidase is measured.
Deficiency:
Deficiency is rare, even in New Zealand and Finland, where selenium intake is 30 to 50 μg/day, compared with 100 to 250 μg/day in the US and Canada. In certain areas of China, where intake averages 10 to 15 μg/day, selenium deficiency predisposes patients to Keshan disease, an endemic viral cardiomyopathy affecting primarily children and young women. This cardiomyopathy can be prevented but not cured by sodium selenite supplements of 50 μg/day po. Patients receiving long-term TPN have developed selenium deficiency with muscle pain and tenderness that responded to a selenomethionine supplement. In Siberian Russia and China, growing children with selenium deficiency may develop chronic osteoarthropathy (Kashin-Beck disease). Selenium deficiency may contribute synergistically with iodine deficiency to the development of goiter and hypothyroidism. Diagnosis is made by measuring selenium levels in RBCs or hair and glutathione peroxidase activity. Measuring serum selenium is less useful. Treatment consists of sodium selenite 100 μg/day po.
Toxicity:
At high doses (> 900 μg/day), selenium produces toxicity. Manifestations include hair loss, abnormal nails, dermatitis, peripheral neuropathy, nausea, diarrhea, fatigue, irritability, and a garlic odor of the breath. The plasma levels may be > 100 μg/dL (> 1.27 µmol/L); however, no sensitive or specific biochemical tests for selenium are available.
Last full review/revision November 2005
Content last modified November 2005
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