Evidence for arsenic essentiality.

Although numerous studies with rats, hamsters, minipigs, goats and chicks have indicated that arsenic is an essential nutrient, the physiological role of arsenic is open to conjecture. Recent studies have suggested that arsenic has a physiological role that affects the formation of various metabolites of methionine metabolism including taurine and the polyamines. The concentration of plasma taurine is decreased in arsenic-deprived rats and hamsters. The hepatic concentration of polyamines and the specific activity of an enzyme necessary for the synthesis of spermidine and spermine, S-adenosylmethionine decarboxylase, are also decreased in arsenic-deprived rats. Thus, evidence has been obtained which indicates that arsenic is of physiological importance, especially when methionine metabolism is stressed (e.g. pregnancy, lactation, methionine deficiency, vitamin B6 deprivation). Any possible nutritional requirement by humans can be estimated only by using data from animal studies. The arsenic requirement for growing chicks and rats has been suggested to be near 25 ng g(-1) diet. Thus, a possible human requirement is 12 μg day(-1). The reported arsenic content of diets from various parts of the world indicates that the average intake of arsenic is in the range of 12-40 μg. Fish, grain and cereal products contribute most arsenic to the diet.