Selenium is a trace mineral incorporated into proteins, to form selenoproteins. Selenoproteins are antioxident enzymes that help prevent cellular damage from free radicals (free radicals are natural products of oxygen metabolism that are thought to contribute to the development of chronic diseases such as cancer). Selenium also plays a role in thyroid regulation and in the immune system. Selenium can be found in brazil nuts, other nuts, seafood, meat, poultry as well as other less potent sources.