Se is an essential nutrient that provides antioxidant protection in concert with vitamin E. Several selenoproteins have been identified, but only one, SeGSHpx, has a known function, that of neutralizing toxic hydroperoxides. Plasma Se concentration, being responsive to changes in Se intake, is the most practical and widely used measure of nutritional Se status. The plasma Se concentrations of the majority of healthy infants and children fall within the range of 50 to 150 µg/L. Although SeGSHpx activity measures the metabolically functional form of Se, the lack of a standardized analytical method has limited its usefulness as an index of nutritional Se status. Se deficiency was first observed in animals, but it is now recognized to occur in humans. Two human diseases associated with severe nutritional Se deficiency have been reported from China: a juvenile cardiomyopathy named Keshan disease and a chondrodystrophy named Kaschin-Beck disease. Long-term TPN, which provides negligible amounts of intrinsic Se, has been demonstrated in some cases to result in biochemical and clinical impairment. Although there are no consistent signs and symptoms characteristic of TPN-associated Se deficiency, in addition to the low blood selenium levels, some patients will experience leg muscle pain and altered serum transaminase and creatine kinase activities. These manifestations of Se deficiency usually take years to develop.
Recent information about the amount of dietary Se needed to maximize plasma SeGSHpx activity in adult men has allowed for better estimates of the Se requirement for humans. Recommended daily dietary allowances published recently by the National Academy of Sciences have been revised for infants and children in this paper by making appropriate adjustments for the protein requirements of these age-groups. These recommended intakes for Se can generally be met by consuming adequate amounts of cereals, meat, eggs, dairy products, human milk, and infant formula, which are good sources of highly available Se and are of low risk of providing excess amounts of Se. Suboptimal Se intakes by pregnant women may predispose their infants to low Se status at birth, which in turn may affect the infants' ability to maintain adequate Se status during the first few months of life. In those situations where protein intake is restricted, such as in phenylketonuria and maple syrup urine disease, Se-supplemented formulas should be used. The most critical situation for Se supplementation is in pediatric patients receiving long-term TPN therapy. When supplementing with Se, consideration must be given to the amount and form of Se to be used; with long-term TPN therapy, plasma Se levels should be monitored.
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