Selenium is a mineral found mostly in plants, with selenium content varying according to soil composition at the place where the plant was grown. Soils in the U.S. are relatively rich in selenium, and selenium deficiency is therefore quite rare. Areas including China are naturally poorer in selenium content. Your body requires only small quantities of selenium for healthy functioning, and the hazards of selenium are associated with overly heavy consumption of selenium-containing foods or supplements.
Selenium Function
Your body uses selenium to make vital antioxidant enzymes known as selenoproteins. The antioxidant effects of selenoproteins include protecting against cellular damage and regulating the functioning of your thyroid. Antioxidant enzymes may protect against heart disease and cancer, according to the Office of Dietary Supplements. Food sources of selenium include Brazil nuts, tuna, cod, beef and turkey meat. Selenium is also available in commercial dietary supplements.
Recommended Daily Intake
For most healthy adults, 55mcg of selenium is a sufficient daily intake. Pregnant women require 60mcg of selenium daily, increasing to 70mcg daily while breastfeeding. Children between the ages of 1 and 3 years require only 20mcg daily; this rises to 30mcg for 4- to 8-year-olds and 40mcg for 9- to 13-year-olds. For a healthy adult over the age of 14, a tolerable upper daily intake level of selenium is 400mcg. Doses above this maximum level are considered potentially hazardous.
Selenosis Hazard
If you develop high levels of selenium in your blood, you run an increased risk of the condition selenosis. A blood concentration of more than 100mcg of selenium per deciliter of blood is considered a high level. Selenosis causes a range of symptoms including mild damage to nerves, tiredness, irritability, hair loss and blotchy white nails. An odor of garlic on your breath and an upset stomach are also common symptoms of selenosis.
Selenium Toxicity
Selenium toxicity is an unusual occurrence. In 2008, errors in the manufacturing process for certain selenium supplements led to an outbreak of selenium poisoning among consumers who purchased these supplements. A 2010 report in the journal "Archives of Internal Medicine" indicated a liquid selenium supplement had been accidentally manufactured with 200 times more selenium than was declared on the product label. Consumers taking the supplement ingested nearly 442,000mcg of selenium daily, leading to over 200 cases of selenium toxicity. Symptoms of selenium toxicity include diarrhea, joint pain, hair loss, fatigue, nausea and loss or discoloration of the fingernails.
References
- Office of Dietary Supplements: Selenium Fact Sheet
- "Canadian Journal of Veterinary Research"; The Two Faces of Selenium-Deficiency and Toxicity are Similar in Animals and Man; L.D. Koller, J.H. Exon ; July 1986
- "Archives of Internal Medicine"; Acute Selenium Toxicity Associated with a Dietary Supplement.; J.K. MacFarquhar, et al.; February 2010
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