Selenium is mineral that is found in soil and occurs naturally in certain foods (such as whole grains, Brazil nuts, sunflower seeds, and seafood). Selenium is not produced in the body, but it is needed for proper thyroid and immune system function. Selenium is used to treat or prevent selenium deficiency. Selenium has been used in alternative medicine as an aid to treat Hashimoto's thyroiditis (an autoimmune disorder of the thyroid), and to treat high cholesterol. Not all uses for selenium have been approved by the FDA. Selenium should not be used in place of medication prescribed for you by your doctor. Selenium may also be used for purposes not listed in this product guide.