Major Use of Selenium

Selenium is one of several essential trace minerals required for good health. In the U.S., plant foods grown in soils rich in selenium provide enough of the mineral to the general population to ensure a rarity of deficiency. The same foods, grown in different regions of the world, can contain vastly different amounts of selenium due to differing levels in the soil.

Selenoproteins

The main function of selenium is to combine with proteins to make selenoproteins. Selenoproteins act as antioxidant enzymes, protecting the body from free radicals that are created through oxidation. Free radicals cause cellular damage and may contribute to a host of conditions and diseases, including heart disease and cancers. Selenoproteins also play a role in proper thyroid and immune-system functions.

Making Selenoproteins

Selenocysteine is created after the digestive system breaks proteins from the diet into its individual amino acids. Selenocysteine is a genetically coded amino acid, serving as a stop codon. Stop codons signal amino-acid chains, which will become proteins, to stop growing, releasing the protein to perform its intended function in the body. Selenoproteins are formed when the amino acid selenocysteine -- often called the 21st amino acid -- combines with selenium from the diet in a very specific spot in the amino-acid chain.

Recommended Intake, Deficiency and Toxicity

The Institute of Medicine recommends adult men and women get 55 mcg of selenium per day. Pregnant women need 60 mcg, and breastfeeding women need 70 mcg for optimum health. Selenium deficiency is rare in the general U.S. population but is more common in countries with nutrient-depleted soils, such as China and Russia, or in people with nutrient-absorption diseases, such as Crohn's disease. Deficiency can weaken the immune system, making the body more susceptible to illness, as well as lead to heart disease or hypothyroidism. Low levels of selenium have been linked to a shorter lifespan in patients with AIDS or human immunodeficiency virus. Selenium toxicity is also rare in the U.S. and is usually a result of manufacturing error or industrial accidents. The upper limit for selenium for adults is 400 mcg per day.

Sources

Selenium is found in most plant-based foods. Brazil nuts are one of the best sources, with up to 780 percent of your daily recommended intake in a 1-oz. serving. Brazil nuts should be eaten only occasionally to avoid possible selenium toxicity. Whole grains including wheat, rice and oats grown in selenium-rich soils are additional good sources of the mineral. Livestock fed on selenium-rich plant foods contain high amounts in the muscles. Beef, turkey and chicken can provide between 30 and 50 percent of your daily requirement. Seafood like tuna and cod supply 45 to 95 percent of your daily requirement.