Named after the Greek god of the moon Selene (Greek: σελήνη: Selene), the trace element selenium (chemical symbol Se) belongs to the group of chalcogens (“ore creators”) and it was discovered by the Swedish chemist Jöns Jakob Berzelius (1779-1848) in 1817. In the inanimate natural world, selenium is mostly found as an alloy of sulphurous ores, known as metal selenides. Of biomedical significance are the following selenium forms:
- inorganic selenate (SeO42-) and selenite (SeO32-) are found in water, seafood and selenium-containing preparations.
- Organic bound selenocysteine (SeCys) and selenomethionine (SeMet). In plant-based foots, selenomethione is most common; foods of animal origin contain predominantly selenocysteine.
Functions of selenium
An adult body's overall stores fluctuates between 10 and 15 mg and is ubiquitously spread throughout the human body. The tissues in the thyroid, cortex, pancreas and liver exhibit particularly high concentrations. Selenium is a component of around 25 selenoproteins in the tissues. It therefore plays a range of essential roles in the body:
- Antioxidant protection. As a constituent of glutathione peroxidases, selenium is an important component of the antioxidant defence system of the cells. Glutathione peroxidase eliminates hydrogen peroxide (H2O2) and lipid peroxides which arise in greater quantities under oxidative stress. Selenium therefore plays a part in protecting the cells against oxidative stress.
- Thyroid function. The selenium dependent thyroxine/deiodinases are of essential significance for the thyroid where they catalyse the splitting off of iodine from the hormone thyroxin. This explains the function of selenium for the homoeostasis of the thyroid hormones. Selenium thus makes a contribution to normal thyroid function.
- Thioredoxin reductases are enzymes which are involved in the RNA synthesis and play a role in the formation of disulphide bridges as part of protein folding. In this way, selenium has an influence on cell growth and differentiation and contributes to normal formation of sperm cells.
- Function of hair and nails. Selenium contributes to the maintenance of normal hair and nails.
- Immune defence. The activity of cells in the immune system are dependent on selenium. The trace element thus contributes to normal functioning of the body's defence system.
- The selenium supply is subject to major fluctuations around the world. In European countries like Germany, an average intake of around 40 µg per day is achieved; the intake is significantly higher in the USA (134 µg per day). Germany is therefore a typical selenium deficiency area; for large parts of the population, the supply of selenium is unsatisfactory.
- The metabolic behaviour of selenomethionine and selenite exhibits clear differences. A large proportion of the absorbed selenomethionine is incorporated in body proteins in an unspecific way and is therefore not available for specific selenium functions (formation of glutathione peroxidase etc.). Selenomethionine also bypasses the selenium homoeostasis and accumulates in the tissue in an uncontrolled fashion. This unwanted effects do not arise with selenite.
- The following applies for the bioavailability of selenium forms: Selenite > selenocysteine > selenomethionine.
Information on production technology
- Trace elements such as selenium, which are contained in products in very minimal concentrations are pre-thinned in an initial galenic process step in order to achieve an exact concentration in the end product.
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