Category: Natural chemicals
Introduction and description
Selenium is a chemical element with symbol Se. It is a nonmetal. Although it is toxic in large doses, selenium is an essential micronutrient for animals.
In plants, it occurs as a 'bystander mineral', sometimes in toxic proportions in forage. Some plants may accumulate selenium as a defense against being eaten by animals, but certain species of plants are considered indicators of high selenium content of the soil, since they require high levels of selenium to thrive. The main selenium indicator plants are Astragalus species (including some locoweeds), prince's plume (Stanleya sp.), woody asters (Xylorhiza sp.), and false goldenweed (Oonopsis sp.).
The human body's content of selenium is believed to be in the 13–20 milligram range. The biological function of Selenium in the human body are as follows:
- Antioxidant - In humans, selenium is a trace element nutrient that functions as cofactor for reduction of antioxidant enzymes. One family of selenium-containing molecules (the glutathione peroxidases) destroy peroxide and repair damaged peroxidized cell membranes, using glutathione.
Peroxides are chemicals that have a bleaching effect on organic substances and therefore are added to some detergents and hair colorants. Other large-scale applications include medicine and chemical industry, where peroxides are used in various synthesis reactions or occur as intermediate products. Thus selenium has a role in repairing damage if you are exposed to this toxin.
- Thyroid regulation - Selenium also plays a role in the functioning of the thyroid gland and in every cell that uses thyroid hormone, by participating as a cofactor for the three of the four known types of thyroid hormone deiodinases, which activate and then deactivate various thyroid hormones and their metabolites.
Selenium may inhibit Hashimoto's disease, in which the body's own thyroid cells are attacked as alien. A reduction of 21% on TPO antibodies was reported with the dietary intake of 0.2 mg of selenium.
- Reproduction system and fertility - there appears to be some connection between selenium and fertility - or at least the viability of sperm, for example
Low sperm production and poor sperm quality are consistent features of Se-deficient animals. The pivotal link between Se, sperm quality and male fertility is GPX4 since the enzyme is essential to allow the production of the correct architecture of the midpiece of spermatozoa. Se also has insulin-mimetic properties, an effect that is probably brought about by stimulating the tyrosine kinases involved in the insulin signalling cascade. Furthermore, in the diabetic rat, Se not only restores glycaemic control but it also prevents or alleviates the adverse effects that diabetes has on cardiac, renal and platelet function. PMID: 15749805
The additional paragraph at the end indicates a possible role in other hormone and endocrine systems as well
- Chelation - Increased dietary selenium intakes reduce the effects of mercury toxicity and it is now recognized that the molecular mechanism of mercury toxicity involves irreversible inhibition of selenoenzymes that are required to prevent and reverse oxidative damage in brain and endocrine tissues
- Anti-fungal agent - The substance loosely called selenium sulfide (approximate formula SeS2) is the active ingredient in some anti-dandruff shampoos. The selenium compound kills the scalp fungus Malassezia, which causes shedding of dry skin fragments. The ingredient is also used in body lotions to treat Tinea versicolor due to infection by a different species of Malassezia fungus.
Illnesses and diseases of Selenium imbalance
It is possible to be both deficient in Selenium and also to overdose. Overdosing causes Selenosis. See Selenium imbalance.
Dietary selenium comes from:
Fish and shellfish – particularly tuna, crab and lobster, as well as mackerel, smoked salmon, pickled herring, canned sardines, blue mussels, swordfish. Marine fishes and vertebrate thyroid glands have the highest concentration of selenium and iodine.
Nuts – brazil nuts are the richest dietary source, but other nuts also contain selenium
Eggs – the white contains more thna the yolk
Cereals – principally wheat, but also barley malt
Offal – particularly kidney and also liver
Seeds – particularly sunflower seeds, but also sesame seeds
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