ment (EAR) for selenium in adults. These included prevention of Keshan disease or various chronic diseases; concentration of selenium in blood, hair, and nails; concentration of selenoproteins in blood; and urinary excretion of the element.
Keshan disease, a cardiomyopathy that occurs almost exclusively in children, is the only human disease that is firmly linked to selenium deficiency (Keshan Disease Research Group, 1979). In addition to a low selenium intake, low blood and hair selenium concentrations are associated with Keshan disease. The disease occurs with varying frequency in areas of China where the population is severely selenium deficient (Ge et al., 1983). Based on these observations, the occurrence of Keshan disease in a population would indicate that the population is selenium deficient.
Although the forms of selenium in hair and nails have not been characterized, some correlations between dietary intake of the element and hair and nail concentrations of selenium have been demonstrated. However, the use of hair and nail selenium as markers of selenium status has been limited because factors such as the form of selenium fed, the methionine content of the diet, and the color of the hair affect the deposition of selenium in these tissues (Salbe and Levander, 1990). In addition, some shampoos in the United States and Canada contain selenium. Therefore, only well-controlled studies can make use of hair and nail selenium concentrations, and these markers are of little value in determining selenium requirements across population groups.
Several forms of selenium are present in blood and in metabolizing tissues; thus, they can be discussed together. Physiologically active forms include the selenoproteins and some as yet uncharacterized forms that are present in low abundance. These forms of selenium are under physiological regulation. Within a specific range of dietary selenium intakes, selenoprotein concentrations are a function of selenium intake. Above this range of intakes, selenoprotein concentrations become regulated only by genetic and environmental factors. This lack of selenium effect implies that the selenium