Human Selenium Requirements

Human Selenium Requirements and Recommended Dietary Intakes All intake recommendations depend on the definitions used to derive them and the available scientific information. Accordingly, they are not to be considered final as they are periodically re-evaluated and revised. 

In terms of human dietary requirements, much of the wheat for breadmaking in the United States is produced in selenium-adequate sections of the country. Bread is generally a good source of dietary selenium, Selenomethionine decomposes lipid peroxides and inhibits in vivo lipid peroxidation in tissues of vitamin-E-deficient chicks. Selenocysdne catalyzes the decomposition of organic hydroperoxides. Selenoproteins show a high degree of inhibition of lipid peroxidation in livers of sheep, chickens, and rats, Thus, some forms of selenium exhibit in vivo antioxidant behavior,... 

Yang, G. and Xia, Y. 1995. Studies on human dietary requirements and safe range of dietary intakes of selenium in China and their application in the prevention of related endemic diseases. Biomed. Environ. Sci. 8, 187-201. 

Yang G, Ge K, Chen J, et al. 1988. Selenium-related endemic diseases and the daily selenium requirement of humans. In Bourne GH, ed. World review of nutrition and dietetics. Sociological and medical aspects. Vol. 55. Basel Karger, 98-152. 

Levander OA (1987) Dietary Selenium Requirements Minimal and Optimal Intake and Disadvantages in the Use of Supplements. 2nd Nordic Symposium on Trace Elements in Human Health and Disease, Odense. Abstract Mini-Symposium No. 12 and Round-Table Discussion on Mineral Supplementation. WHO Regional Office for Europe, Copenhagen. Environ Health 26 87-90. 

Most of the methods for the determination of selenium in human materials require some sample preparation or pretreatment. The biotransformation of selenium in man, which is characterized by a step-wise biochemical reduction, leading to the binding to or direct incorporation of the element into proteins, apparently involves the formation of intermediate volatile species. Dimethyl selenide as well as many other organic forms of selenium and its halides are relatively volatile. 

Many proteins, including many enzymes, contain hghtly bound metal ions. These may be inhmately involved in enzyme catalysis or may serve a purely structural role. The most common tightly bound metal ions found in metalloproteins include copper (Cu+ and Cu +), zinc (Zn +), iron (Fe + and Fe +), and manganese (Mn +). Other proteins may contain weakly bound metal ions that generally serve as modulators of enzyme activity. These include sodium (Na+), potassium (K+), calcium (Ca +), and magnesium (Mg +). There are also exotic cases for which enzymes may depend on nickel, selenium, molybdenum, or silicon for activity. These account for the very small requirements for these metals in the human diet. 

Lester et al. [24] have described a robotic system for the analysis of arsenic and selenium in human urine samples which demonstrates how robotics has been used to integrate sample preparations and instrument analysis of a biological matrix for trace elements. The robot is used to control the ashing, digestion, sample injection and operation of a hydride system and atomic absorption instrument, including the instrument calibration. The system, which routinely analyses both As and Se at ppb levels, is estimated to require only... 

Some very interesting examples of the effect of soils on the nutritional quality of plants are associated with selenium. The element has not been found to be required by plants, but it is required in very small amounts by warm-blooded animals and probably by humans. However, selenium in larger quantities can be very toxic to animals and humans. 

The unusual amino acid selenocysteine (a derivative of cysteine in which the sulfur atom is replaced by a selenium atom) is an essential component in a small number of proteins. These proteins occur in prokaryotes and eukaryotes ranging from E. coli to humans. In all cases, selenocysteine is incorporated into protein during translation in response to the codon UGA. This codon usually serves as a termination codon but occasionally, in some required but unknown context of bases, is used to specify selenocysteine instead. 

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