Why is selenium important in the body and why might it be used to treat cancer?

Answer 1

Selenium is an essential trace mineral that functions as an antioxidant nutrient, working primarily as a part of proteins—most notably, the enzyme glutathione peroxidase. Glutathione peroxidase and vitamin E work in tandem. Glutathione peroxidase prevents free-radical formation, thus blocking the damaging chain reaction before it begins; if free radicals do form, and a chain reaction starts, vitamin E halts it. Selenium-containing enzymes are necessary for the proper functioning of the iodine-containing thyroid hormones that regulate metabolism.
The question of whether selenium protects against the development of certain cancers, particularly prostate cancer, is under intense investigation. Adequate blood selenium seems protective against cancers of the prostate, colon, and other sites. Many questions remain unanswered regarding selenium status, intake, and cancer, however. For example, the range of selenium status and the levels of intakes most beneficial to reducing cancer risk have not been established. Given the potential for harm from excess selenium and the lack of conclusive evidence, recommending selenium supplements to prevent cancer would be premature.