ABSTRACT
The trace element selenium (Se) is an essential nutrient, but is toxic when consumed in excessive quantities. Selenosis or selenium toxicity signs in animals were described by Marco Polo in 1295 during his travels to China. The facile catalytic ability of selenium, rather than sulfur, accounts for selenocysteine’s inclusion into enzymes such as glutathione peroxidase, phospholipidhydroperoxide glutathione peroxidase, thioredoxin reductase and the deiiodinases. Evidence that the endemic cardiomyopathy in China called Keshan disease was linked to poor Se status, and was prevented by selenium supplementation, provided support for the nutritional essentiality of Se in humans. Selenium in nutritional supplements includes organic forms such as selenomethionine and Se-methylselenocysteine and inorganic forms such as sodium selenite and sodium selenite. Selenium status can be assessed using a variety of methods including measurement of Se in blood, plasma, serum, urine, red blood cells, platelets, hair and nails.
