Effect of copper and zinc status on susceptibility to cadmium intoxication. Environ. Health Perspect

The effects of dietary cadmium on copper and zinc metabolism in animals are described. Emphasis is given to situations involving chronic exposure to low levels of cadmium, to the identification of population groups most at risk, and to the protective effect of dietary supplementation with copper and zinc. The mechanism of the interaction between the metals and the involvement of metailothionein are discussed. It is now widely recognized that the toxicity of metals cannot be considered without due regard being given to dietary composition and the nutri-tional state of the animal. Increased cadmium intake can cause alterations in the metabolism of copper and zinc in experimental animals and, conversely, the development of certain symptoms of cadmium toxicity may, on occasion, be prevented by dietary copper and zinc supplementation. For example, elevated cadmium intakes in rats, chicks and mice have resulted in increased mortality, poor growth, and anemia (1, 2). The growth rate was restored by zinc supplementation and the mortality and anemia reduced by increasing the copper intake. Supplementation with copper also prevented the degeneration of aortic elastin, presumably by re-storing the activity of the copper-dependent enzyme lysyl oxidase. Clinical signs of zinc deficiency have been reported in poultry (3) fed on high cadmium diets, but were absent in animals in which the zinc intake had been increased. The widespread occurrence of competitive an-tagonisms between metals has been explained in terms of their isomorphous replacement at particu-lar sites in biological systems. This concept was of considerable value in furthering our understanding of the multiplicity of trace metal interactions, but it did not explain all facets of trace metal imbalance. One difficulty was that the antagonistic effect of a metal was, on occasion, associated with increased concentrations of the agonist in tissues exhibiting signs of pathological change, rather than with th