Recommended Nutrient Intakes for Vitamin and Minerals

Selenium

Functions

Selenium is a component of several selenoproteins. These include the following:

• Glutathione peroxidase
• Selenoprotein P
• Iodothyronine 5'-deiodinase
• Selenoprotein W
• 58, 56, and 14 kDa Se-binding protein

The roles of all these proteins are not known. Some of these enzymes seem to have antioxidant roles. Others may act as storage or transport proteins.

Selenium, through its role in the enzyme 5'-deiodinase, catalyses the conversion of thyroxine (T4) to its active metabolite, tiiodothyronine (see notes on Iodine). Therefore, selenium plays a key role in the metabolism of thyroid hormones, which are essential for growth and development.

Recommended Intakes

Table: Recommended Intakes for Selenium (mg/day)

Food Sources

Dietary intakes of selenium differ depending on geographical region and the level of selenium in the soils of these regions.

Fish and meat organs are the richest sources of selenium. Other good sources include meats, cereals and grains, and diary products, Brazil nuts are also a good source of selenium.

Deficiency

Pure selenium deficiency is rare. There appears to be an interaction between selenium and vitamin E in the aetiology of deficiency diseases in animals. Therefore selenium deficiency may only occur when a low selenium status is linked with an additional stress such as chemical exposure or increased oxidant stress due to vitamin E deficiency.

There are some selenium responsive diseases in humans. In low selenium areas in China there is an endemic cardiomyopathy called Keshan disease. This disease mainly effects children and women of childbearing age. Another disease that has been associated with selenium deficiency in China is Kashin-Beck disease, an endemic osteoarthritis that occurs during pre-adolescent or adolescent years.

Toxicity

The margin between adequate and toxic intakes of selenium is narrow. Over-exposure to selenium known as selenosis may occur from consuming foods from areas that are very high in selenium (seleniferous areas) e.g. Venezuela and some regions in China.

Long-term mega-dosing of selenium may also cause toxicity.

Some signs of selenium toxicity are loss of hair and nails, lesions of the skin, nervous system and teeth.