What is the function of SELENIUM ?

SELENIUM IMPORTANCE:
A major antioxidant nutrient, protects cell membranes and prevents free radical generation thereby decreasing the risk of cancer and disease of the heart and blood vessels.

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 glutathioine peroxidases and iodothyronine 5'-deiodinases, 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.

SELENIUM LIVER CANCER Medical surveys show that increased selenium intake decreases the risk of breast, colon, lung and prostate cancer. Selenium also preserves tissue elasticity; slows down the aging and hardening of tissues through oxidation; helps in the treatment and prevention of dandruff.SELENIUM LIVER CANCER

DEFICIENCY SYMPTOMS:R CANCER
May result in premature aging, heart disease, dandruff, loose skin. SELENIUM LIVER CANCER

Selenium deprivation reduces activities of the selenium-dependent peroxidases and deiodinases. The signs in animals depend upon vitamin E status and appear only when both nutrients are limiting. They vary according to species. For example, selenium- and vitamin E-deficient animals show myopathies of skeletal (e.g., sheep, cow, horse), cardiac (pig) or smooth (dog, cow) muscle; hepatic necrosis (rat, pig); increased capillary permeability (chicken); or pancreatic acinar degeneration (chicken). Characteristic signs of selenium deficiency have not been described in humans, but very low selenium status is a factor in the etiologies of a juvenile cardiomyopathy (Keshan Disease) and a chondrodystrophy (Kaschin-Beck Disease) that occur in selenium-deficient regions of China.SELENIUM LIVER CANCER

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 (Kesteron Reservoir, CA) which receives selenium-enriched irrigation wastewater. This case involved the biological amplification of selenium by aquatic plants which were important in the diets of affected animals.SELENIUM LIVER CANCER

Diet recommendations:SELENIUM LIVER CANCER
The Recommended Dietary Allowances are: 0-0.5 years, 10 µg; 0.5-1.0 years, 15 µg; 1-6 years, 20 µg; 7-10 years, 30 µg; males, 11-14 years, 40 µg; females, 11-14 years, 45 µg; males and females 15-18 years, 50 µg; adult males 70 µg; adult females, 55 µg; pregnant females, 65 µg; and lactating females, 75 µg. SELENIUM LIVER CANCER

U.S. RDA FOR SELENIUM
babies: birth to 6 months 6 months to 1 year	10 mcg per day 15 mcg per day
children: 1 to 6 years 7 to 10 years	20 mcg per day 30 mcg per day
men and boys: 11 to 14 years 15 to 18 years 19 to 51+ years	40 mcg per day 50 mcg per day 70 mcg per day
women and girls: 11 to 14 years 15 to 18 years 19 to 51+ years	45 mcg per day 50 mcg per day 55 mcg per day
pregnant women	65 mcg per day
nursing mothers	75 mcg per day

Food sources:
The most important sources in American diets are meats, fish and grains. Additionally, some foods such as Brazil nuts can have relatively high selenium concentrations. Foods of low protein content, including most fruits and vegetables, do not provide substantial amounts of selenium. Food selenium appears to be absorbed with efficiencies of 60-80%; the greatest factor affecting the utilization of food selenium is its chemical form.SELENIUM LIVER CANCER

Recent research: Anti-tumorigenic effects of high levels of selenium have been demonstrated in several animal models. The mechanism(s) of anti-tumorigenic effects of selenium and the possible role of selenium in affecting the risk of human cancer are not clear.

For further information:

Burk, R.F., ed. (1994) Selenium in Biology and Human Health. Springer-Verlag, New York, NY

Combs, G.F., Jr. (1994) Essentiality and toxicity of selenium: a critique of the Recommended Dietary Allowances and the Reference Dose. In: Risk Assessment of Essential Elements (Mertz, C., Abernathy, C. & Olin, S.S., eds.), pp. 167-183. International Life Sciences Institute Press, Washington, DC.

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