Selenium Deficiency in Humans

Pure selenium deficiency, without concurrent vitamin E deficiency, is not generally seen except in animals on experimental diets (113). In China, selenium deficiency in humans has been associated with Keshan disease, a cardiomyopathy seen in children and in women of child-bearing ages, and Kashin-Beck disease, an endemic osteoarthritis in adolescents (113). 

Selenium deficiency in humans occurs in the loessial region of the North China and Tibet Plateau of China (Liu, 1996). The arid and semi-arid soils in these areas of China contain low total Se in their parent materials. 

Selenium deficiency in animals is manifested by hepatic necrosis and a set of symptoms called white muscle disease. Very serious selenium deficiency in humans has been reported in China, in the Keshan region, where there is very low selenium content in the... 

Ishihara H, Kanda F, Matsushita T, Chihara K, Itoh K. White muscle disease in humans myopathy caused by selenium deficiency in anorexia nervosa under long term total parenteral nutrition. J Neurol Neurosurg Psychiatry 1999 67(6) 829-30. 

Selenium is an issue in the biology of one of the poxviruses, one of the largest viruses in existence, as well as in the biology of coxsackievirus, one of the smallest of viruses. In the case of MCV, a poxvirus, the virus s genome codes for the well-known selenoprotein glutathione peroxidase. Apparently, this enzyme protects the virus from the defense system of the host. In the case of coxsackievirus, selenium deficiency in the host, whether a mouse or human, provokes activation of the virus within the host cell, resulting in disease to the host (damage to the heart). 

This is documented by the discovery of essential functions for the "new trace elements in the past seven years (I) and by the increasing knowledge of marginal or pronoimced deficiencies in humans of such elements as iron (2), zinc (3), chromium (4), and perhaps copper (5) and selenium (6), Although some of these deficiencies occur only in special age and sex groups or under unusual conditions, their existence has aroused public and scientific concern for the exact definition of human trace element needs and for the assessment of trace element nutritional status. These two major challenges for human trace element research cannot be met without proper analytical support. I will attempt to describe the present status of trace element analysis as it relates to nutrition research and to point out some new concepts that might well influence the future direction of trace element analysis. 

The clinical relevance of selenium deficiency is more difficult to estabhsh than that of iodine deficiency. Moderate selenium deficiency is present in some regions of Europe, but it has not been associated with any cfinical condition in humans. Nonetheless, the degree of selenium deficiency in Finland was considered severe enough to implement a control program based on the supplementation of fertilizers with selenium (Aro et ai, 1995). New Zealand adopted the same strategy, because of the beneficial effects of selenium supplementation on the productivity of their animal industry. 

In animals, selenium deficiency is known to induce growth retardation in second-generation selenium-deficient rats (Ewan, 1976 Thompson et ai, 1995), but the mechanism involved remains unclear. Observations suggest that in humans, bone tissue is also affected by selenium deficiency. In healthy infants, a significant correlation has been observed between urinary levels of selenium and pyridin-ium cross-links of collagen, a marker of bone metabolism (Tsukahara et ai, 1996). This suggests a link between bone turnover and selenium status. The osteopenia observed in some phenylketonuric children may be related to their low selenium intake, but selenium-supplementation studies have not been performed so far to test this hypothesis. 

Evidence of Selenium Deficiencies. There is no hard evidence of human selenium deficiency in the United States. Nevertheless, a growing number of nutrition researchers believe that the well-documented and severe disorders which occur in all species of selenium-deficient farm animals show the need for closer examination of the circumstantial evidence for human deficiencies. Also, it is noteworthy that... 

There are areas (22) where selenium levels in the soil are very low these include regions of volcanic activity like that adjacent to the Cascade mountains in the Pacific Northwest states of the United States and the central north island of New Zealand. There, because the heat of emption volatilized the selenium, the residual soil parent material is virtually devoid of selenium. Other areas of low soil-selenium reflect leaching of selenium out of the top soil, as in the Canterbury plain on New Zealand s south island. Areas of selenium deficiency have negative implications for animal and human health. 

Selenium is a vital microelement for people. It has dual properties. Selenium is an essential nutrient at low concentration levels and it becomes toxic at higher concentration levels. Deficiency of selenium results in weakness and hard diseases. Selenium is a building material of many hormones and ferments it neutralizes free radicals, radioactive radicals in organism. The range of selenium safety concentration in food and water is very narrow. The daily normal amount of human consumption of selenium is 10-20 p.g, maximum safe concentration of selenium in water is 5-10 p.g/1. It becomes toxic at 20-30 p.g and bigger content in different objects. 

Water soluble Se in the North West region varied from 0.0002-0.0429 mg/kg. Water soluble Se accounted for 2.13-6.34% of the total Se in the soils of North China. Selenium is an essential element to animals and humans. When water soluble Se in soils is less than 0.003 mg/kg, Se deficiency in animal and human beings may occur. EDTA-extractable Se in the alkali desert soils of North China was in the range of 0.011-0.090 mg/kg this was about 5-11% of the total Se in the soils. Selenium deficiency was mostly found in the Loess Plateau and Tibet region. NH4OAc-cxtractable Ni in soils from Beijing was 0.29 mg/kg. 

Accordingly, the proposed selenium criteria shown in Table 31.5 for prevention of selenium deficiency and for protection of aquatic life, livestock, crops, and human health, should be viewed as guidelines, pending acquisition of additional, more definitive, data. 

Excess selenium intake can occur in both animals and humans living in areas with elevated selenium in the soil. Most grass and grains do not accumulate selenium, but when an animal consumes plants that do accumulate selenium (some up to 10,000 mg/kg) they can develop a condition called the blind staggers . Symptoms include depressed appetite, impaired vision, and staggering in circles and can ultimately lead to paralysis and death. Humans are susceptible to similar effects as well as additional neurological effects. Selenium deficiency results in heart disorders, skeletal muscle effects, and liver damage. 

Selenium deficiency has been identified in humans in a broad area of China, stretching from the northeast to the southwest. Two syndromes are evident Keshan disease, an endemic cardiomyopathy which affects children, and Kashin-Beck disease, an edemic osteoarthropathy (big-joint), also mainly involving children, which occurs in eastern Siberia and parts of China. As a result of these observations, a protective effect for selenium has been proposed, and various selenium-containing preparations have been applied to preserve animal and human health. 

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