Selenium essential trace element

Elemental selenium has been said to be practically nontoxic and is considered to be an essential trace element however, hydrogen selenide and other selenium compounds are extremely toxic, and resemble arsenic in their physiological reactions. 

The bad guys, shown in pink in Figure 2.8, are toxic, often lethal, even in relatively small quantities. Several of the essential trace elements become toxic if their concentrations in the body increase. Selenium is a case in point. You need about 0.00005 g/day to maintain good health, but 0.001 g/day can be deadly. That s a good thing to keep in mind if you re taking selenium supplements. 

A current area of interest is the use of AB cements as devices for the controlled release of biologically active species (Allen et al, 1984). AB cements can be formulated to be degradable and to release bioactive elements when placed in appropriate environments. These elements can be incorporated into the cement matrix as either the cation or the anion cement former. Special copper/cobalt phosphates/selenates have been prepared which, when placed as boluses in the rumens of cattle and sheep, have the ability to decompose and release the essential trace elements copper, cobalt and selenium in a sustained fashion over many months (Chapter 6). Although practical examples are confined to phosphate cements, others are known which are based on a variety of anions polyacrylate (Chapter 5), oxychlorides and oxysulphates (Chapter 7) and a variety of organic chelating anions (Chapter 9). The number of cements available for this purpose is very great. 

Selenium is an essential trace element for optimal health but an excess is toxic. The British population is now reckoned to be selenium deficient because more European wheat is now used to make bread at the expense of North American wheat. The difference in the selenium content is caused by the difference in the selenium content of the soils. In geological terms, European soil is older and the selenium has washed out. 

Selenium is an essential trace element for both plants and animals, and it is a diet supplement in animal feed as well as for humans. 

The essential microelements are only required in trace amounts (see also p.2). This group includes iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), cobalt (Co), chromium (Cr), selenium (Se), and molybdenum (Mo). Fluorine (F) is not essential for life, but does promote healthy bones and teeth. It is still a matter of controversy whether vanadium, nickel, tin, boron, and silicon also belong to the essential trace elements. 

Toxicology. Selenium is an essential trace element that can be toxic in excessive amounts. Elemental selenium and selenium compounds as dusts, vapors, and fumes are irritants of the eyes, mucous membranes, and skin. Chronic exposure may cause central nervous system effects, gastrointestinal disturbances, and loss of hair and fingernails. 

In humans, the major pathway in the metabolism of the thyroid hormones consists of the removal of iodine or deiodination. Three deiodinase isoenzymes, encoded on three distinct genes, catalyze the reductive deiodination. All three enzymes contain the rare amino acid seleno-cysteine. The essential trace element selenium therefore plays an important role in thyroid hormone economy. 

Selenium is an essential trace element in the human body. This nutrient is an important part of antioxidant enzymes that protect cells against the effects of free radicals that are produced during normal oxygen metabolism. Selenium is also essential for normal functioning of immune system and thyroid gland. 

An enzyme cofactor can be either an inorganic ion (usually a metal cation) or a small organic molecule called a coenzyme. In fact, the requirement of many enzymes for metal-ion cofactors is the main reason behind our dietary need for trace minerals. Iron, zinc, copper, manganese, molybdenum, cobalt, nickel, and selenium are all essential trace elements that function as enzyme cofactors. A large number of different organic molecules also serve as coenzymes. Often, although not always, the coenzyme is a vitamin. Thiamine (vitamin Bj), for example, is a coenzyme required in the metabolism of carbohydrates. 

Some elements are essential to the composition or function of the body. Since the body is mostly water, hydrogen and oxygen are obviously essential elements. Carbon (C) is a component of all life molecules, including proteins, lipids, and carbohydrates. Nitrogen (N) is in all proteins. The other essential nonmetals are phosphorus (P), sulfur (S), chlorine (Cl), selenium (Se), fluorine (F), and iodine (I). The latter two are among the essential trace elements that are required in only small quantities, particularly as constituents of enzymes or as cofactors (nonprotein species essential for enzyme function). The metals present in macro amounts in the body are sodium (Na), potassium (K), and calcium (Ca). Essential trace elements are chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn), magnesium (Mg), molybdenum (Mo), nickel (Ni), and perhaps more elements that have not yet been established as essential. 

Several minerals and trace elements are vital to the human organism and must be ingested with daily food in sufficient amounts. Wine can contribute not only minerals containing potassium, calcium, and magnesium but also numerous essential trace elements, such as chromium, cobalt, iron, fluorine, copper, selenium, and zinc, among others. The contents found in wine are very low ranging from mg L 1 to igL, sometimes even lower. 

Selenium This metal is an essential trace element that functions as a component of enzymes involved in antioxidant protection and thyroid hormone metabolism. The existence of a number of selenoproteins has been demonstrated. In several intra- and extracellular glutathione peroxidases and iodothyronine... 

K. Yasumoto, K. Iwami, M. Yoshida, Nutritional efficiency and chemical form of selenium, an essential trace element, contained in soybean protein, Diazu Tanpakushitu Eiyo Kenkyuukai Kaishi (Nutr. Sci. Soy Protein Jpn.), 4 (1983), 35-40. 

Originally, nine of the trace elements were considered to be essential to humans cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, selenium, and zinc. Recently, chromium, silicon, and nickel have been added to this list (Reilly 1996). These are mostly metals some are metalloids. In addition to essential trace elements, several trace elements have no known essentiality and... 

Caution. All Chemicals in this reaction are highly reactive and poisonous. A good hood is essential for protection against vapors of HF, Se02F2, and HSeOFs. Though selenium is known to be an essential trace element for mammals, larger amounts attack the liver. 

Selenium is an essential trace element, being important in at least two critical enzymes, the antioxidant glutathione peroxidase (GPx), and type 1 iodothyronine deiodinase. GPx converts hydrogen peroxide to water, in the presence of reduced glutathione, while iodothyronine deiodinase catalyzes the conversion of thyroxine to triiodothyronine, the physiologically active hormone species. 

Use and exposure Selenium is an essential trace element for human health. However, acute and prolonged periods of exposure to high concentrations of selenium compounds cause adverse health effects in humans. The symptoms include garlicky breath irritation of eyes, skin, nose, and throat visual disturbances headache nausea vomiting chills fever weakness violent cough bitter metallic taste in the mouth nose bleeds dyspnea bronchial spasms bronchitis pulmonary edema gastrointestinal tract disturbance ... 

Selenium has been recognized as an essential trace element in the diets of man and animals for many years (1) Another strong indication of its essentiality is the fact that it is an essential component of the enzyme glutathione peroxidase (2) Recently, scientists from the People s Republic of China demonstrated that Keshan disease (a cardiomyopathy in children) was correlated with low dietary selenium Intakes ( ) and could largely be prevented with supplementation Similarly, poor selenium nutrition in patients receiving total parenteral nutrition has been linked to muscular discomfort (4) and cardiomyopathy ( ) ... 

In 1957 selenium was found to be an essential trace element [6].Since that time, the biological properties of selenium have been investigated, and in 1973 the first selenoenzyme,glutathione peroxidase, was discovered [7]. This has led to a growing interest in the enzymology and the bioorganic properties of selenium [8]. 

The uptake of trace metals from the soil by plants and animals can be studied with high sensitivity by radiotracer techniques. In these applications, it is important that the chemical form of the radiotracer is identical with that of the trace element to be studied. For example, in agriculture, the uptake of trace elements necessary for plant growth can be investigated. Essential trace elements, such as Se, are of special interest. By use of radioactively labelled selenium compounds the transfer of this element from soil to plants and animals can be measured. For the investigation of the transfer of radionuclides (radioecology), addition of tracers is, in general, not needed. 

Gastrointestinal absorption, and subsequent utilization and retention by the body, of essential trace elements such as zinc, copper, and selenium can also be enhanced or diminished by the presence or absence of other trace elements and chemicals in the diet (WHO, 1996). For example, cadmium and lead absorption is enhanced when dietetic intake of calcium, iron, and phosphate is low. Phytate, an organic phosphate that is abundant in diets high in unrefined grains, especially when accompanied by high dietetic calcium, helps suppress the uptake of potentially toxic elements such as lead and cadmium, but also inhibits the uptake of essential zinc (WHO, 1996). 

Selenium is an essential trace element. As an important constituent of glutathion peroxydase and thioredoxin reductase, it must be considered an extremely valuable antioxidant. The daily requirement of 75 gg is very often not achieved, especially by tumour patients, so that substitution is necessary. In addition, malignant diseases generally show a reduction in the serum value of selenium. Moreover, it intensifies the cytotoxicity of T lymphocytes and natural killer cells, leading to a corresponding effect on tumour cells. This effect can be enhanced through the stimulation of IFNy. The application of cytostatics thus becomes more favourable in every respect. A daily dose of 200 qg (-1,000 qg) selenium is recommended. Even in acute infections, i.v. administration of selenite has proved extremely useful, (s. p. 304)... 

It should be noted that in the majority of the above mentioned studies, metal-induced renal injury was considered as if exposure occurred to only one metal at a time. In reality it is clear that environmental and occupational exposure may involve several metals at the same time and in varying concentrations [34]. It has been shown that with combined exposure various metals may interact with each other and that one metal may alter the potential toxicity of another in either a beneficial or deleterious way. As an example, whilst arsenic has been shown to worsen cadmium-induced nephrotoxicity, data from experimental studies have shown that selenium may protect against the renal effects induced by cadmium [52]. Other studies have shown that the iron status may alter the toxic effects of aluminium at the level of the bone and the parathyroid gland [53,54], whilst in a recent increased lead accumulation was associated with disturbances in the concentration of a number of essential trace elements [55]. 

Selenium was discovered in 1817. It is an essential trace element at 0.1 ppm in diets. 

Selenium is an essential trace element and an integral component of heme oxidase. It appears to augment the antioxidant action of vitamin E to protect membrane lipids from oxidation. The exact mechanism of this interaction is not known however, selenium compounds are found in the selenium analogs of the sulfur-containing amino acids, such as cysteine and methionine. Se-cysteine is found in the active sites of the enzyme glutathione peroxidase, which acts to use glutathione to reduce organic hydroperoxides. 

Several of these metals are also considered essential trace elements and are discussed also in Chapter 30. Risk assessments for essentiality versus toxicity for chromium, copper, iodine, iron, manganese, molybdenum, selenium, and zinc have been performed by several U.S. governmental and private organizations. ... 

Although selenium compounds are notorious for being toxic and often have a particularly unpleasant smell, the element selenium has significant biological relevance Selenium is an essential trace element and some selenium-containing proteins, e.g., glutathione peroxidase, have been discovered. 

It is well established that selenium is an essential trace element and selenium dietary supplements are commonly available, especially in countries such as France and New Zealand, where soils are selenium deficient. The principal role of selenium in vivo is to prevent free-radical damage either through incorporation into radical scavengers, or indirectly through reduction of the byproducts of oxidative damage. 

Diets that are low in protein, zinc, selenium, vitamin Bg, and fat may collectively depress immune function. This type of diet may be associated with either a low-caloric-intake diet or low-fat, low-meat-products diet. Zinc is an essential trace element for many biological functions, including immune functions. Indeed, zinc is required for the biological activity of a thymic hormone, called thymulin in its zinc-bound form, and is important for the maturation and differentiation of T-cells. With advancing age, zinc, thymic functions, and peripheral immune efficiency show a progressive decline. Supplementing zinc in old age restores immune efficiency. 

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