Selenium

USE: Selenium is a trace mineral that is essential to good health but required only in small amounts. Selenium is required by the body for proper functioning of the thyroid gland, and may help protect against free radical damage and cancer. A deficiency in selenium can lead to pain in the muscles and joints, unhealthy hair, and white spots on the fingernails. In long term cases it may even lead to Hashimoto's disease, a condition in which the body's own immune system attacks the thyroid.
Selenium enhances vitamin E function in the body, increases energy and stamina by balancing the adrenal glands and is also thought to reduce the risk of cancer of the prostate, breast, colon, rectum and lung.
SOURCE: Good sources include seafood, meats, grains and nuts (especially Brazil nuts).