Selenium is an essential element for humans, with a recommended daily intake of
about 1mg/kg of body weight for adults. Selenium compounds have been shown to
be genotoxic in in vitro systems with metabolic activation, but not in humans. There
was no evidence of teratogenic effects in monkeys. Long-term toxicity in rats is characterized
by depression of growth and liver pathology. In humans, the toxic effects of
long-term selenium exposure are manifested in nails, hair and liver. Data from China
indicate that clinical and biochemical signs occur at a daily intake above 0.8mg. Daily
intakes of Venezuelan children with clinical signs were estimated to be about 0.7mg
on the basis of their blood levels and the Chinese data on the relationship between
blood level and intake. Effects on synthesis of a liver protein were also seen in a small
group of patients with rheumatoid arthritis given selenium at a rate of 0.25mg/day
in addition to selenium from food. No clinical or biochemical signs of selenium toxicity
were reported in a group of 142 persons with a mean daily intake of 0.24mg
(maximum 0.72 mg) from food.