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Vitamin B-12, also known as cobalamin, cyanocobalamin, and hydroxycyanocobalamin, is a water-soluble vitamin in the B-complex vitamin group. The B vitamins are used by the body as coenzymes. They are essential for maintaining the skin, hair, liver, and good muscle tone in the gastrointestinal tract. The B vitamins also help metabolize carbohydrates, proteins and fats. Vitamin B-12 was discovered as a result of attempts to treat anemia. In 1926, scientists discovered that eating liver once a day could reverse anemia. By the late 1940s, cobalamin was isolated as the active ingredient in the liver that effectively controlled the anemia.
Cobalamin is found in foods such as beef, swiss and blue cheese, clams, eggs, liver, and milk. It is not found in vegetables. Vegans, strict vegetarians who avoid dairy products, are at high risk of becoming cobalamin deficient.
Cobalamin is involved in forming nucleoproteins and red blood cells, and in the functioning of the nervous system. It is involved in cell activity, DNA replication, and the production of the mood-affecting substance called SAMe (S-adenosyl-L-methionine).
On average, dietary intakes of cobalamin are sufficient. In cases of elevated homocysteine levels, doctors usually prescribe cobalamin supplementation through injection, tablet, or capsule form. Cobalamin is also often available as a constituent of multivitamin/mineral preparations. The RDA recommendation of vitamin B-12 for adults is 2 mcg per day. The therapeutic range varies from between 100 to 1,000 mcg. There is a very low incidence of vitamin B-12 toxicity, even in intakes of up to 1,000 mcg per day.