Selenium is a mineral that works as a cofactor for many enzymes and proteins; increasing antioxidant and antiviral activity, promoting thyroid hormone and insulin function, and regulating cell growth. Selenium works as a cofactor for glutathione peroxidase and is needed for the conversion of thyroxine (T4) to the active thyroid hormone triiodothyronine (T3) benefiting thyroid function.
Selenium may be beneficial in the treatment of burns, heart disease, thyroid disorders, cancer, Down syndrome, hepatitis, lymphedema, and alcoholism.
Low selenium levels have been associated with depression, anxiety, confusion, and hostility.
Symptoms of deficiency include hair loss, infertility, anemia, and pancreatic atrophy. Severe selenium deficiency due to a long-term selenium-free diet has been shown to cause cardiomyopathy, muscle pain and weakness, and elevated liver enzymes.
Food sources of selenium include meat, fish, whole grains, legumes, Brazil nuts, and certain other nuts, garlic, mushrooms, and asparagus. Selenium found in plants is usually found as selenomethionine, whereas selenium from animal sources is usually found as selenocysteine. The amount of selenium in plants is determined by the soil it is grown in.
Once selenium is absorbed it is distributed throughout the body with the highest concentration found in the thyroid gland.
The RDA for selenium in adults is 55 mcg/day. The Food and Nutrition Board of the Institute of Medicine set the no-observed-adverse-effect level for selenium at 800 mcg/day for adults, but to be safe in the case of sensitive individuals the Tolerable Upper Intake Level recommendation is 400 mcg/day.
Alcohol consumption has been shown to decrease selenium levels.
Selenium blood levels can be tested. However, serum selenium levels do not correlate with tissue levels or selenium intake.
Selenium is excreted in the urine and feces. Selenium balance is maintained by the kidneys.
Adverse effects of selenium that can occur with excessive intake include hair loss, brittleness or loss of nails, white spots on nails, dermatitis, depression, and neurological abnormalities. Toxicity and even death have been reported in people consuming 3,200 mcg/day or more of selenium.
Vitamin C supplementation as low as 600mg/day has been shown to significantly increase the absorption of certain forms of selenium.
Vitamin E works closely with selenium, so a deficiency in Vitamin E can increase symptoms of selenium deficiency.
Selenium can be found in supplements as selenomethionine, sodium selenite, and sodium selenate. Selenomethionine has been shown to increase tissue levels to a greater amount, but it is unknown if it has a greater activity than the other forms of selenium.
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