Selenium is a trace element that acts as an important dietary mineral. Animals and humans require small amounts of selenium to help maintain proper health. Plants do not require selenium, though they contain the mineral if grown in selenium-rich soil. Selenium supports several metabolic functions and aids in the production of enzymes in the body that have antioxidant effects, helping to reduce the cell damage caused by chemicals called free radicals.
Foods
According to the National Institutes of Health, several different foods provide selenium in the diet. Plants that grow in selenium-rich soils are high in the nutrient. The highest source of dietary selenium is Brazil nuts, which have more than 500 mcg of selenium in a single 1-oz. serving. Other good sources include wheat products, particularly those made with whole wheat, rice and oats. Foods from animals that take in selenium in their diets also contain elevated amounts of selenium. These include shellfish, such as shrimp and crab meat, and fin fish like salmon, tuna and halibut. Meats such as beef, pork and chicken are also high in the nutrient.
Dietary Requirements
According to the Linus Pauling Institute, individuals at various stages of growth require different amounts of dietary selenium. Infants from 0 to 6 months should receive 15 mcg per day, while those from 7 to 12 months should have 20 mcg. Children require from 20 mcg to 40 mcg, depending on their age. Adolescents and adults require 55 mcg per day. Women who are pregnant or breastfeeding should take in 60 or 70 mcg of dietary selenium, respectively.
Function
Selenium is essential for the production of enzymes called selenoproteins that assist in antioxidant activities, thyroid gland function, the production of sperm and immune system function. The mineral also might play a role in preventing inflammatory reactions and cancer.
Deficiency
While deficiency of selenium can lead to limited production of selenium-based metabolic enzymes and might reduce the efficiency of iodine in the body, there is generally no specific illness that results from a selenium-deficient diet. In rare cases, typically in selenium-depleted diets in individuals receiving intravenous feeding without selenium supplementation, muscle weakness and wasting, and inflammation and damage to the heart can occur. These and other symptoms are also seen within the general population in certain areas in China and Russia, where selenium is particularly low in the soil and less available in the diet.
Toxicity
While selenium is an essential nutrient, the mineral is toxic at high levels. It is relatively difficult to ingest toxic levels of the mineral from diet alone. According to the Linus Pauling Institute, cases of selenium toxicity have occurred, however, in individuals taking selenium supplements over time. Symptoms of chronic selenium toxicity include brittle hair and nails, gastrointestinal problems, rashes, irritability, fatigue and neurological abnormalities.
HIV/AIDS
The interaction of selenium and the HIV virus causes depletion of the mineral within the body. Low levels of selenium in the bloodstream can act as a significant marker for identifying individuals with HIV/AIDS. Selenium supplementation also might help increase resistance to the HIV virus in infected persons by enhancing the activity of T cells within the immune system.
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