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Selenium
Description:
Selenium is an essential nutrient for many species, including humans. Deficiencies of this element are very apparent in animals, with symptoms ranging from muscular dystrophy in lambs, to the destruction of liver tissue in pigs.
Selenium is an important constituent of the enzyme glutathione peroxidase, which is responsible for destroying lipid-damaging peroxides. In this role, selenium complements the anti-oxidizing function of vitamin E.
The enzyme glutathione peroxidase is contained within white blood cells and blood platelets, and has importance in the immune system and blood clotting mechanisms of the body.
Selenium may also be important in the regulation of serum cholesterol levels, although this effect has not been conclusively proven experimentally.
Selenium serves to prevent the incidence of mercury poisoning by affecting the body’s metabolism of the potential toxin.
Method of Action:
Selenium is an important constituent of the enzyme glutathione peroxidase. This enzyme acts to destroy peroxides, thereby protecting cells and membranes against oxidative damage. Vitamin E and selenium tend to enhance the effect of one another in that vitamin E works to prevent the formation of peroxides, and glutathione peroxide acts to destroy.
Glutathione peroxidase is also a constituent of blood platelets and white blood cells, making it an important part of the body’s immune system and blood clotting mechanism.
Absorption of selenium is dependent upon the solubility of the ingested compound and upon the dietary ratio of selenium to sulfur. The availability of selenium for absorption is dependent upon many different factors, among which are the nature of the food source (i.e., seafood is high in selenium, but the selenium is poorly absorbed) and the method of food processing.
Once absorbed, selenium interacts with the sulfur-containing amino acids (e.g., cysteine and methionine) to form the enzyme glutathione peroxidase, and for incorporation into various proteins, such as hemoglobin and myoglobin.
Excesses of selenium are secreted in the urine, and the selenium-containing molecule dimethyl selenide is excreted during respiration. This molecule gives breath a garlic odor characteristic of selenium toxicity.
Properties & Uses:
Selenium supplementation has been useful in the treatment of a certain congestive heart disease found primarily in Chinese children. Selenium has also been used to eliminate skeletal muscle pain in some people. Selenium, in conjunction with vitamin E, may be useful in the prevention of heart disease.
Selenium supplements have been used in the treatment of anemia and growth problems which would not respond to other kinds of treatment.
Selenium moderates the symptoms of mercury toxicity and may be useful in instances of subacute mercury poisoning.
Adequate selenium intake has been statistically linked to a lower incidence of cancer mortality, but the conclusive evidence regarding selenium’s relation to cancer development is not available.
Toxicity Levels:
Consequences of Deficiency
Selenium deficiency has not been conclusively linked to any specific set of symptoms in humans, although monkeys and other animals have serious physiological manifestations of deficiency. Symptoms in animals include muscle pain, red blood cell fragility, pancreas degeneration, growth retardation, and cataract formation. The link between animal and human symptoms of deficiency have not been conclusively established, but there is strong evidence indicating the same deficiencies in humans.
As a side note, children with kwashiorkor have unusually low selenium stores and, therefore, selenium deficiency may occur concomitantly with abnormal protein metabolism.
Selenium deficiencies have been statistically linked to a higher incidence of cancer mortality, but the conclusivity of this relationship has not been settled to everyone’s satisfaction.
Deficiencies of selenium may contribute to the excessive buildup of fats and other lipids in the liver, producing fatty liver syndrome.
Some of the recent literature indicates all the items in the following section as selenium deficiency problems in humans.
Recommended Dietary Allowances:
RDA for adults 50 to 200 mcg.
RDA for children 6+ 50 to 200 mcg.
RDA for children 4 to 6 30 to 120 mcg.
RDA for children 1 to 3 20 to 80 mcg.
RDA for infants 0.5 to 1 20 to 60 mcg.
RDA for infants 0 to 0.5 10 to 40 mcg.
Food Sources:
Beef
Beef kidney
Liver
Brewer’s yeast
Brown rice
Cereals
Eggs
Fish
Garlic
Milk
Nuts
Poultry
Whole wheat bread
Deficiency Symptoms:
Muscular discomfort Cardiomyopathy
Certain forms of arthritis Poor prostaglandin synthesis
High blood pressure Reduced male sex potency
Cataracts Poor skin and hair growth
Cardiac dysfunction Anemia
• Premature aging due to lack of selenium as an antioxidant
• Inadequate detoxification of heavy metal poisoning
• Increased vulnerability to cancer
• Decreased production of the selenium containing enzyme glutathione peroxidase,resulting in:
• Poor antibody production by white blood cells
• Poor blood clotting mechanism
• Lowered ability to destroy "free radicals"