Selenium is an essential trace mineral necessary as a co-factor in the glutathione peroxidase enzyme. It is also a co-factor in the deiodination of thyroxine (T4) to triiodotyrosine (T3).
Selenium is an essential trace mineral found in Brazil nuts (544 mcg per ounce) sunflower seeds, fish and poultry products , onions and grains. Plants do not require selenium and therefore the content of plant sources varies with the soil content. Brazil nuts are grown in selenium rich soil in Brazil. Selenium content of the body is estimated to be 3-6mg in individuals living in low selenium areas and 13 mg in those living in high selenium areas. It is found mainly in the liver and kidneys.
What does selenium do?
The major importance of selenium lies in its place in 25 selenium dependent enzymes called selenoproteins. 5 important selenoproteins are
1) Cellular glutathione peroxidase
2) Extracellular glutathione peroxidase
3) Phospholipid hydroperoxide glutathione peroxidase
4) Gastrointestinal glutathione peroxidase
5) Olfactory glutathione peroxidase
- Selenium contributes to the protection of cells from oxidative stress and the protection of DNA, proteins and lipids from oxidative damage. All the selenoproteins above are antioxidant enzymes which are able to reduce the damaging reactive oxygen species to harmless water and alcohols
- Selenium contributes to normal spermatogenesis. The phospholipid hydroperoxide glutathione peroxidase protects the sperm mitochondrial capsule from oxidative damage and is then involved in the formation of a structural protein required by the mature sperm. Another selenoprotein ( selenoprotein V) exists only in the testes and is also involved in spermatogenesis
- Selenium contributes to normal thyroid function. Selenium is required for 3 different selenium dependent iodotyronine deiodinase enzymes. Thyroxn (T4) is converted to Triiodotyronine (T3) by one or more of these selenium dependent enzymes. These three enzymes can both activate and inactivate thyroid hormones
- Selenium contributes to the normal function of the immune system. It appears to regulate the expression of cytokines, cell signalling molecules which are in charge of the immune response. Selenium deficiency is associated with impaired immune function.
- Selenium contributes to the maintenance of normal hair and nails. Selenium deficiency can lead to weak hair and nails. Hair and nails are primarily composed of proteins and these proteins are dependent on seleno proteins for their healthy production. Hair follicles and nail beds are renewing structures composed of cells called keratinocytes and seloproteins are essential for normal keratinocyte function
Selenium compounds are also important to kill a fungus which can live on the scalp that can cause dry shedding skin fragments (dandruff)
Although selenium is an essential, important mineral, care should be taken not to exceed one capsule a day. Although the mechanism of toxicity is uncertain it may be due to excess selenium inhibiting dehydrogenase enzymes
Vitamins E, B6 and copper have all been shown to be synergistic to selenium and
Vitamin A, C and K antagonistic