Akademik

Vitamin B12

A vitamin important for the normal formation of red blood cells and the health of the nerve tissues. Undetected and untreated vitamin B12 deficiency can lead to anemia and permanent nerve and brain damage. Pernicious anemia is a blood disorder caused by inadequate vitamin B12 in the blood. Patients who have this disorder do not produce the protein substance in the stomach that allows the body to absorb vitamin B12. This substance is called intrinsic factor (IF). Pernicious anemia is simply treated with injections of vitamin B12. The vitamin B12 has to be administered by injection because people with PA do not have IF (or an effective form of IF) and so cannot absorb vitamin B12 taken by mouth. Pernicious anemia has also been called Addison’s anemia, addisonian anemia, Biermer’s anemia. Patients with Crohn’s disease involving the small intestine (Crohn’s ileitis) or who have undergone small intestine resection may not be able to absorb vitamin B12. Strict vegetarians who consume no animal products can develop B12 deficiency since there is a lack of B12 in vegetables. The recommended daily allowances of vitamin B12 in the United States are 2mcg for infants, 3 mcg for children under 4 years old, 6mcg for children over 4 years old and adults, and 8 mcg for pregnant women. It is recommended for adults to take one multivitamin daily. One multivitamin a day is safe and inexpensive. The multivitamin should contain 400 micrograms of folic acid, approximately 2-3 mg of vitamin B6, 6-9 micrograms of vitamin of B12, and 400 IU of vitamin D. The folic acid and the other B vitamins can help lower homocysteine. The vitamin D is one of the important factors in preventing osteoporosis. High blood homocysteine levels have been found to be a risk factor for atherosclerosis and heart disease. Most doctors will treat homocysteine levels higher than 9-10umol/liter. A doctor experienced in treating coronary heart disease should supervise the treatment of hyperhomocysteinemia. Treatment involves high doses of the B vitamins (1-5 mg/day of folic acid, 10mg/day of B6, and 0.4 mg/day of B12). ALL vitamin supplements, with the exception of vitamin B12 supplement, are chemically synthesized. This means that they are produced by combining separate chemical elements in a factory. Vitamin B12 is biosynthesized, which means that it is made by using bacterial enzymes. Also called cobalamin.

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vitamin B₁₂ -'bē-'twelv n

1) a complex cobalt-containing compound C₆₃H₈₈CoN₁₄O₁₄P that occurs esp. in liver, is essential to normal blood formation, neural function, and growth, and is used esp. in treating pernicious and related anemias and in animal feed as a growth factor called also cyanocobalamin

2) any of several compounds similar to vitamin B₁₂ in action but having different chemistry

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a vitamin of the B complex. The form of vitamin B₁₂ with coenzyme activity is 5-deoxyadenosyl cobalamin, which is necessary for the synthesis of nucleic acids, the maintenance of myelin in the nervous system, and the proper functioning of folic acid, another B vitamin. The vitamin can be absorbed only in the presence of intrinsic factor, a protein secreted in the stomach. A deficiency of vitamin B₁₂ affects nearly all the body tissues, particularly those containing rapidly dividing cells. The most serious effects of a deficiency are pernicious anaemia and degeneration of the nervous system. Vitamin B₁₂ is manufactured only by certain microorganisms and is contained only in foods of animal origin. Good sources are liver, fish, and eggs. The daily recommended adult intake is 3-4 µg.

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cyanocobalamin (q.v.) by chemical definition, but generally any substituted cobalamin (def. 2) derivative with similar biological activity; it is a water-soluble hematopoietic vitamin occurring in meats and animal products. To be absorbed by the intestine, it must combine with intrinsic factor, and its metabolism is interconnected with that of folic acid. The vitamin is necessary for the growth and replication of all body cells and the functioning of the nervous system, being required for purine and pyrimidine (and hence DNA, protein, and nucleoprotein) synthesis, methylation reactions, hematopoiesis, and myelin synthesis; at least some of these effects are mediated through its role in folic acid metabolism. Deficiency of the vitamin causes pernicious anemia and other forms of megaloblastic anemia, and neurologic lesions. See also adenosylcobalamin, cobalamin, hydroxocobalamin, and methylcobalamin.

Medical dictionary. 2011.