Effects of selenium antagonists on cancer susceptibility: new aspects of chronic heavy metal toxicity.

Uptake, transport, metabolism and physiological activity of selenium are influenced by interactions with a variety of heavy metals. With elements exhibiting especially high affinities for selenium, significant interactions may occur at concentrations close to the no-effect threshold levels. At low dietary Se intakes, this may produce states of latent Se deficiency as well as increased susceptibility to cancer development. In experiments with MMTV-infected female mice, exposures to low levels of the Se-antagonistic elements As, Pb and Cd in the drinking water abolish the cancer-protecting effects of Se. At higher exposure levels, these elements may act as inhibitors or promotors of malignant transformation and tumor growth. These findings are of potential importance to human health as the contaminant levels of Se-antagonistic elements in foods and in the environment result in exposures which often significantly exceed the dietary Se intakes.