Selenium is a component of an antioxidant enzyme called glutathione peroxidase. In the body, it teams up with vitamin E, another important antioxidant. There is mounting evidence that Selenium plays an important role in preventing several types of cancer, heart disease, cataracts, and fertility problems. Selenium also boosts immune systems, detoxifying certain poisons, as well as protecting newborns against sudden infant death syndrome (SDIS).