It is often available in single or multivitamin supplements. Selenium is needed to activate a number of hormones produced by the thyroid gland. Selenium also plays a vital role in the functioning of the immune system. Studies have found that selenium supplementation stimulates the activity of white blood cells. It also enhances the effect of vitamin E, one of three vitamins that act as antioxidants.
Brazil nuts are the best source of selenium.
Yeast, whole grains, garlic and seafood are also good sources. Some vegetables may contain considerable amounts of selenium depending on the content of selenium in the soil. While most people do not consume enough selenium on a daily basis, severe deficiency is rare. Soils in some areas are selenium deficient, and people who eat foods grown primarily on selenium-poor soils can be at greater risk for deficiency. The most notable condition caused by selenium deficiency is Keshan disease, which causes an abnormality of the heart muscle.