Selenium
Function
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 and Excretion
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.
Clinical Conditions
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.
Recommended Intake
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.
Food Sources
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.
Figure 4.1: Selenium Content of Selected Foods
Supplementation
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.
