Selenium body content

While less is known about the selenium content of the various human tissues and body fluids, the results appear to reflect dietary intake [49]. The total body content of North Americans, as estimated fixirn autopsy, ranged from 13 to 20 mg [58], whereas for New Zealanders the range was only 3-6 mg [59]. The order is in agreement with Se in the body tissues. In China, a wide range of Se intakes is reflected in the wide range of Se levels in blood, tissue, and urine. 

It is well known that the toxicity of many elements depends on the physicochemical forms they assume. So, for instance, determining the total content of a certain element in a sample is definitely not sufficient to measure its toxicity. Selenium is a case in point in small amounts this element is essential to human health. But the transition from the necessary amount (about 70pg of selenium per day for an adult) to a toxic dose (about 800 pg of selenium per day) is relatively easy. In rats, moreover, the fatal dose of Se(IV) compounds is 3.2 mg kg 1 of body mass, whereas for dimethyl selenide it is 1600 mg kg 1 of body mass. Nonorganic selenium compounds [Se(IV) and Se(VI)] are believed to be the most toxic ones, whereas in the environment selenium occurs most commonly bound to amino acids (selenomethionine and selenocysteine). The least toxic forms seem to be the volatile methyl compounds of selenium, which are metabolites of a detoxication process. 

Previous dietary treatment with selenium (1 ppm) decreased the hepatic content of malonic aldehyde of the fiver of rats fed CCI4 (2.5 ml/kg body weight) to nearly the normal values (Bene-DETTi et al. 1974). 

In an adequately supplied adult male human subject, the total body selenium content is on the order of 30-60 mg, of which one-third is found in the skeleton and two-thirds in the soft tissues. A substantial fraction of kidney selenium is retained even when selenium at other sites is severely depleted during deficiency, and renal selenium is more constant between human populations than selenium in other tissues or body fluids. Regulation of selenoprotein synthesis at the transcription level appears to ensure a hierarchy of preservation of individual selenoproteins at critical sites. The cytosolic glutathione peroxidase (GPx I) and selenoprotein P can donate selenium to other sites whenever overall depletion occurs. Selenium crosses the placenta readily, and breast milk selenium concentration is responsive to changes in maternal selenium intake. In the United States, breast milk Se concentrations are generally in the range of 0.19-0.25 pmol/1, but colostrum has levels that are two or three times higher than those of mature breast milk. 

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