Selenium and Methylselenocysteine
Selenium is an essential trace mineral that is essential for life. It is also a toxic metal when consumed in excess. Selenium is required to activate various key enzymes, including the antioxidant glutathione peroxidase, the metabolic enzyme thioredoxin reductase, and the thyroid-hormone-activating enzyme iodothyronine deiodinase. Food sources of selenium include brazil nuts, yeast, whole grains and seafood. Selenium content of food is dependent on selenium content in the soil and both are highly variable.
Selenium: The Anticancer Mineral
Epidemological studies recognized a connection between cancer incidence and low levels of selenium in the blood as early as 1969. Researchers noted that breast cancer rates were low in areas where selenium levels in the soil and food were high and high in areas where selenium levels were low. The same correlation was found between death rates and selenium levels. Similar correlations were subsequently found in animal studies.
Helps in treatment and prevention of dandruff. Necessary for healthy hair and nails. May also increase the elastic youthfulness of the skin and be helpful in removing age spots. When ingested in the natural algae form of selenomethionine, skin cancer incidence from ultraviolet light may also be reduced.
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 5н-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.
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. 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.
Deficiencies: Selenium deprivation reduces activities of the selenium-dependent enzymes. 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 (Kashin-Beck Disease) that occur in selenium-deficient regions of China. May result in premature aging, heart disease, dandruff, loose skin.
Diet recommendations: The Recommended Dietary Allowances are in µg/day: 0-0.5 yrs, 10; 0.5-1.0 yrs, 15; 1-6 yrs, 20; 7-10 yrs, 30; males 11-14 yrs, 40; females 11-14 yrs, 45; males and females 15-18 yrs, 50; adult males, 70; adult females, 55; pregnancy, 65; and lactation, 75.
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