Perspectives in metal carcinogenesis. I. Selenium.

This review has focused primarily on the sources of exposure to selenium and its role as an antioxidant as well as its anticarcinogenic and antimutagenic properties. Selenium is an essential trace element and a constituent of glutathione peroxidase in human erythrocytes. Numerous studies with animals have demonstrated that it is a potent inhibitor of virally- and chemically-induced tumorigenesis when administered continuously in a variety of tumor systems (predominantly in the skin, liver, colon, and mammary gland). The mechanisms by which selenium inhibits tumorigenesis is not definitely known. Several epidemiological studies have demonstrated statistically significant inverse associations between human cancer mortalities in different populations. In these studies, the regional availabilities of selenium were measured via a variety of means, including blood selenium levels, the concentration of selenium in grains and forage crops or from calculated apparent selenium intake estimated from food consumption and consumption data. These animal and human studies demonstrating inverse associations between tumorigenesis and selenium levels have led to suggestions that selenium be considered a prophylactic agent in the chemoprevention of tumorigenesis. It would appear prudent to avoid the unnecessary supplementation of normal diets with selenium.