You need selenium in small amounts for making the enzymes and proteins your body needs. These enzymes provide an antioxidant effect, and help with immune function and thyroid function. Selenium deficiency is rare in the United States, but still does occur under certain conditions, so if you are at risk for this deficiency, get your selenium levels tested.
Selenium deficiency doesn't necessarily cause obvious symptoms. However, selenium deficiency affects your immune system, and may make you more likely to become ill. Signs of selenium deficiency include fatigue, muscle weakness, muscle wasting and heart problems. Chronic low levels of selenium, such as those in areas where the soil is deficient in the mineral, can lead to forms of selenium deficiency that affect the bones and joints and cause heart problems or mental retardation, according to the Office of Dietary Supplements.
People who live in areas where there is very little selenium in the soil have a higher risk of becoming deficient in selenium, as are people who are chronically ill and fed by total parenteral nutrition. If you have had surgery to remove part of your intestine, or you have a severe gastrointestinal illness, you are also more likely to become deficient in selenium, according to the Linus Pauling Institute.
Selenium supplementation usually restores selenium levels to normal. However, toxicity can occur with doses above 400 micrograms per day for adults, or with smaller supplemental selenium doses over long periods of time. Discuss selenium supplements with your doctor before taking them to ensure they are necessary and that you take the proper amount.
Getting sufficient selenium may decrease your risk for a number of illnesses, including viral infections, cancer and heart disease. Selenium supplementation may also help relieve rheumatoid arthritis symptoms and help with the treatment of HIV and AIDS, according to the Office of Dietary Supplements. However, more studies are necessary to determine the effectiveness of selenium for preventing and treating these conditions.