Potential hazards of selenium as a chemopreventive agent.

Clinical and metabolic features of the trace element selenium and the full spectrum of its animal and human toxicity have been reviewed. The difficulties in coming to an easy understanding of the biologic properties of selenium stem from its multiple forms and complex metabolic and biochemical pathways. It is suggested that chemoprevention trials focus on the efficacy of organic and inorganic prototype forms such as selenomethionine and the selenite ion. While some appreciation of the toxic potential of these two prototype forms can be predicted from existing information, additional formal toxicology will be necessary, particularly for selenomethionine.