Title: Selenium As An Antioxidant

Key words: selenium, antioxidant, Keshan disease, selenoproteins

Date: July 2000

Category: 3. Micronutrients

Type: Article

Author: Dr van Rhijn



Selenium As An Antioxidant

Potential Health Effects



Selenium has a number of biochemical metabolic functions in the body. Its antioxidant activity is thought to be due to it being a key component of three main functional selenoproteins, glutathione peroxidase, thioredoxin reductase and selenoprotein P.

What is the evidence for the involvement of selenium in the prevention of disease?

Antioxidant Mechanism

Selenium is an integral co-factor of the enzyme glutathione peroxidase (GSHPx)1,2 isoenzyme, which protects against oxidative damage in the body. This attribute accounts for the majority of selenium's health benefits. The mechanism by which this is achieved is by reduction of H2O2 lipid and free phospholipid hydroperoxides3 by using the GSH as the hydrogen donor. H202 + 2GSH ® 2H20 + GSSG. Research has shown that the most potent selenium compound, selenodiglutathione (SDG), a natural metabolite of selenite, does not induce oxidative stress. It is also part of thioredoxin reductase, which is a reducing enzyme (-S-S- bonds in proteins) with peroxidase activity and helps to regulate intracellular redox state. Selenoprotein P is an abundant extracellular selenoprotein that also possibly acts as an antioxidant defence system4. Selenoprotein W is a muscle protein containing selenocysteine. Selenium is an essential element of the glutathione synthase enzyme and a cofactor for the production of superoxide dismutase (SOD).

Health Effects

The enzyme iodothyronine 5’-deiodinase (IDI), required for converting thyroxin (T4) to the more metabolically active triiodothyronine (T3), is a selenium-containing protein5. Coexistence of iodine and selenium deficiency, as in Zaire, result in adverse effects on growth, development and neonatal survival. A lack of dietary selenium is associated with various clinical conditions, the best known of which is Keshan’s disease, a cardiomiopathy endemic in areas of China 6. Although supplementation and general dietary improvements have reduced the incidence of Keshan’s disease significantly7, research suggests the involvement of Vitamin E deficiency as well.

Experimental evidence suggests that Vitamin E and selenium may have a protective role in numerous viral infections8 (HIV9, 10, 11), and stimulation of the immune response. There is also strong epidemiological associative evidence of a protective role for selenium in degenerative conditions such as cancer (lung, bladder, stomach, breast, bowel and prostate). Selenium may act pharmacologically12 in a chemo-preventative role in cancer13 . Epidemiological evidence for its protective role in cardiovascular disease is equivocal14, 15. Low serum selenium may be a risk factor in pancreatitis16. Selenium may also be involved in conditions such as asthma, thrombosis, rheumatoid arthritis, ulcerative colitis and male fertility17.


Selenium is a major player in the antioxidant defence system against oxidative stress. It plays, therefore, a very important protective role in various degenerative conditions and serious viral infections.


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Additional reading: Vitamins Minerals and Health: Fact File No 3: 1997; National Dairy Council. London.