Selenium is a mineral that is required in very low doses for the body to function normally. It is an antioxidant, meaning that it prevents oxygen from damaging cells. Although most people get enough selenium in their diet, selenium is included in many multivitamins and is sold as a supplement itself. Many people take selenium supplements to stay healthy. Some research suggests that selenium supplements can improve the way the body handles sugar and might prevent some complications of diabetes. However, other research suggests that selenium supplementation has no effect on diabetes or health.