Selenium is involved in a number of important bodily functions. Selenium is a component of the antioxidant enzyme glutathone peroxidase that transfers reducing agents from glutathione to hydrogen peroxide or lipid peroxide. Along with vitamin E, this process protects cells and membranes against oxidative damage. Selenium also protects against mercury, cadmium, and silver toxicity.
Absorption of selenium depends on the availability of the form in which it is ingested and also on the ratio of dietary selenium to sulfur. Selenium is primarily excreted in the urine. Very high intake of selenium can cause excretion through exhalation.
A deficiency in dietary selenium has been associated with a disorder called Keshan disease, which is characterized by cardiomyopathy. Intervention studies in China have showed that selenium supplementation reduced the incidence of the disease, although it did not reverse the cardiac damage that had already occurred. Selenium deficiency has been shown to be associated with another disease in China called Kashin-Beck disease. It is characterized by osteoarthritis and results in dwarfism and joint deformities.
Recently updated recommendations for selenium intake are: 55 mcg for adults and adolescents, 20-40 mcg for infants and children, 60 mcg for pregnant women, and 70 mcg for lactating women.
The amount of selenium in foods vary according to the soil content. Generally good sources include organ meats, seafood, legumes, other meats, whole grains, and dairy products.
Selenium is used as an antioxidant supplement. An instance of selenium toxicity occurred when a manufacturing error resulted in a dosage 100 times greater than that which was listed on the label. Symptoms included nausea, diarrhea, fatigue, neuropathy, hair loss, and changes in fingernails.