cent of all adults reported use of supplements containing selenium (Moss et al., 1989).

The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects in almost all individuals. Although members of the general population should be advised not to exceed the UL for selenium routinely, intake above the UL may be appropriate for investigation within well-controlled clinical trials. In light of evaluating possible benefits to health, clinical trials of doses above the UL should not be discouraged, as long as subjects participating in these trials have signed informed consent documents regarding possible toxicity and as long as these trials employ appropriate safety monitoring of trial subjects. Also, the UL is not meant to apply to individuals who are receiving selenium under medical supervision.

The Tolerable Upper Intake Level (UL) for selenium pertains to selenium intake from food and supplements. As discussed earlier, drinking water does not contain nutritionally significant amounts of selenium. The data on chronic selenosis, acute toxicity, and biochemical indicators of toxicity are reviewed.

Chronic Selenosis. Chronic toxicity of selenium has been studied in animals and has been observed in humans. The limited data available in humans suggest that chronic toxicities from inorganic and organic forms have similar clinical features but differ in rapidity of onset and relationship to tissue selenium concentrations.

The most frequently reported features of selenosis (chronic toxicity) are hair and nail brittleness and loss (Yang et al., 1983). Other reported signs include gastrointestinal disturbances, skin rash, garlic breath odor (caused by selenium compounds), fatigue, irritability, and nervous system abnormalities (CDC, 1984; Helzlsouer et al., 1985; Jensen et al., 1984; Yang et al., 1983; G.-Q. Yang et al., 1989a).

The high prevalence of selenosis in Enshi, South China, provided an opportunity to study approximately 380 people with high selenium intakes (Yang and Zhou, 1994; G.-Q. Yang et al., 1989a, 1989b). Toxic effects occurred with increasing frequency in people with a