Selenium is a trace found in many natural sulphides (pyrite, sphalerite), and is an important ingredient of some rare minerals. The elemental form is in the lead chamber mud in the production of sulfuric acid. In the process, obtained as a by-product. Selenium was discovered 1817th Jons Jakob Bercelius (Jons Jacob Berzelius). Its name comes from the Greek word selene meaning moon. Essentiality of selenium for animal life discovered 1957th Schwartz and Folc (Schwarc, folzi) when the study on rats, a diet without vitamin E and selenium, found that small amounts of selenium (a trace) can prevent the occurrence of liver necrosis in animals tested.
The importance of selenium in the human body was observed in late seventies when the development of cardiomyopathy in young women and children in Kesan in China was associated with a lack of selenium in food / nutrition, and soil. That is why this disorder due to deficiency of selenium named Kešanska disease.
Mixed and balanced diet, daily intake of selenium is 70-100 mcg (micrograms). Rich natural sources include: meat, fish, cereals and dairy products. The content of selenium in vegetables / fruits depends on the land on which it grows. The amount of selenium in fruit and vegetables is usually less than 0.1 mg / g of edible parts. On the other hand the kešanskoj areas in China, maize, rice and soybeans contain about 0.005, 0.007 and 0.010 mg of selenium / g of edible parts. Given that the selenium in a group VI of the periodic system, it often happens that some plants do not differ from the sulfur and selenium replacing sulfur with selenium in sulfur-containing amino acids. Because amino acid substitution occurs and selenomethionine proteins in which the composition of inputs. Many plants selenomethionine is the main form that contains selenium.
The role of the body
The importance of selenium in health and disease comes from the role of selenium as an integral part of the antioxidant system of human organisms. So far in mammals was discovered and cloned 18 different selenium - enzymes and proteins. Selenium protects the body from the harmful effects of free radicals, it is an integral part of glutathione peroxidase, one of the most important and most abundant antioxidant enzyme systems of the body of Man. There are 4 glutathione peroxidase. Classical or glutathione peroxidase-1 (GPX1, EC 126.96.36.199) is the main depot of selenium in the body (> 50% of body reserves) and is found in all tissues.
The metabolism of thyroid hormones play an important role, and selenium. The enzyme jodtironin dejodinaza, which contains three atoms of selenium is needed for the synthesis and decomposition of T3, while the second enzyme with selenium tioredoksin reductase protects thyroid from the effects of hydrogen peroxide generated during the synthesis of thyroid hormones. Therefore, there should be an optimal intake of iodine and selenium because selenium deficiency may further exacerbate the deficit of iodine.
The recommended daily intake for adults
Defining and determining the recommended daily intake for adults who, by definition, should satisfy the needs of 97-98% of healthy people of all age and sex is not easy. Research shows that there are certain mechanisms in the body of a man who allows the maintenance of normal levels of selenium and balance despite large variations in daily intake. The recommended daily intake of selenium is defined by the amount of selenium required for maximum activity of the enzyme glutathione peroxidase in blood plasma.
The recommended daily intake of selenium for adults (in micrograms **)
SAFE ENTRY *
400 micrograms (0.4 milligrams)
* A safe daily intake of selenium is the amount that is not harmful to health
** 1000 micrograms = 1 milligram
Deficit and excess intake
Deficiency in humans is rare, occurring in the areas of land which does not contain selenium in people on restrictive diets and in patients on total pareneteralnoj diet. Areas poor in selenium: a broad belt of southwest to northeast China, N. Zealand, the central parts of the United States and in our river basin Timok, Morava, and Kolubara part of. Established clinical selenium deficiency in humans is extremely rare. Symptoms include change in color of nails, muscle weakness and cardiomyopathy (enlargement of Commerce and the increase in volume, followed by loss of elasticity of the muscle fibers and scarring).
Elemental selenium is toxic, but its compounds are that the biochemical / physiological effects similar to arsenic. Increased intake of selenium can cause toxicity. Selenium toxicity occurs when the daily intake of 4-5 mg. Narrow the line between therapeutic and toxic doses, so it is not above the recommended daily intake of 150 micrograms. Excessive intake can cause loss of hair, nails, teeth, fatigue, nausea, vomiting, metallic taste, peripheral neuropathy, etc..