Selenium is required by the body for proper functioning of the Thyroid Gland and may help protect against free radical damage. Deficiency in selenium can lead to pain in the muscles and joints, unhealthy hair, and white spots on the fingernails. Due to acute selenium defficiency body's own immune system attacks the Thyroid Gland. Excessive selenium can lead to bad breath, diarrhea, and even hair loss.
In addition to food supplements rich in Zinc ,discussed earlier, Sunflower seeds are also rich in Selenium. For more details, DV (daily value) know about