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1-800-228-0872 |
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1-800-228-0872 |
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T. J. Clark & Company Video Library and |
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Liquid Selenium |
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Selenium (Se) is an essential trace element that functions as a component of enzymes involved in antioxidant protection and thyroid hormone metabolism. In several intra- and extra-cellular glutathione
peroxidases, iodothyronine 5?-deiodinases, and in thioredoxin reductase, selenium is located at the active centers as the selenoamino acid, selenocysteine
(SeCYS). At least two other proteins of unknown function also contain
SeCYS. Although SeCYS is an important dietary form, it is not directly incorporated into these specific selenium-proteins; instead, a
co-translational process yields tRNA-bound SeCYS. In contrast, selenium as seleno-methionine is incorporated non-specifically into many proteins,
as it competes with methionine in general protein synthesis. Therefore, tissues often contain both specific, as well as the nonspecific, selenium-containing proteins when both SeCYS and selenomethionine are consumed, as found in many foods. Food sources: The most important sources in American diets are meats,
fish and grains. Brazil nuts can have relatively high selenium concentrations. Foods of low protein content, including most fruits and vegetables, provide little selenium. Food selenium is absorbed with efficiencies of 60-80%; the greatest factor affecting the utilization of food selenium is its chemical form. Toxicity: Selenium toxicity is characterized by dermatologic lesions; selenotic animals and humans develop brittle hair and nails/hooves. Sporadic cases of selenium-poisoning have been reported involving industrial or accidental exposures to selenium-compounds. In certain rural
Chinese communities chronic intakes of very high amounts (several milligrams per day) of selenium were linked to skin, hair and nail abnormalities which disappeared upon resuming regular selenium intakes.
Selenium has been identified as the cause of birth deformities in migratory
wildfowl in a wetland area (Kesterson Reservoir, CA) which receives selenium-enriched irrigation wastewater. This case involved the biological
amplification of selenium by aquatic plants which were important in the diet
of affected animals. The Reference Dose (RfD) set by the Environmental Protection Agency is 5 µg/kg body weight/day or 350 µg/day for a 70 kg
individual. This intake is regarded as having no significant risk of a deleterious effect over a lifetime of exposure.
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