Selenium and cancer: a review.

The essential trace element selenium retards the growth of certain chemically induced tumors in animals. The addition of subtoxic amounts of this element in form of selenite to the supply water lowers the incidence of spontaneous mammary tumors in female C3H mice significantly without affecting the health and life-span of the animals. Arsenic, a selenium antagonist, administered in form of arsenite in the supply water, also lowers the tumor incidence at dosage levels of 10 ppm, but those animals which develop spontaneous mammary tumors under these conditions demonstrate dramatically enhanced tumor growth rates. The results of initial epidemiological studies suggest that the human cancer mortality is lower in areas providing an adequate dietary intake of selenium as estimated from the selenium content in grains and forage crops in various regions of the United States, or the dietary selenium intakes as calculated from food consumption data in various countries.