vitamin B12


vitamin B12

      a complex water-soluble organic compound that is essential to a number of microorganisms and animals, including humans. vitamin B12 aids in the development of red blood cells in higher animals. The vitamin, which is unique in that it contains a metallic ion, cobalt, has a complex chemical structure as shown:

      Vitamin B12 occurs in several forms, called cobalamins; cyanocobalamin is the principal one used in vitamin supplements and pharmaceuticals. Vitamin B12 was first isolated in 1948 by American chemist Karl Folkers and British chemist Baron Alexander Todd.

       vitaminsVitamin B12 is involved in cellular metabolism in two active coenzyme forms—methylcobalamin and 5-deoxyadenosylcobalamin. Vitamin B12 cooperates with folic acid (folate) in the synthesis of deoxyribonucleic acid ( DNA). A deficiency of either compound leads to disordered production of DNA and, hence, to the impaired production of red blood cells. Vitamin B12 also has a separate biochemical role, unrelated to folic acid, in the synthesis of fatty acids in the myelin sheath that surrounds nerve cells. (See table of the vitamins (vitamins).)

      Vitamin B12 is synthesized by microorganisms that occur in the rumen (the first stomach chamber) of cows and sheep. From the rumen it is transferred to the muscle and other tissues, which other animals and humans eat. Good dietary sources of vitamin B12 are eggs, meat, and dairy products. Several kinds of bacteria unable to make the substance require minute amounts for growth.

      In humans a lack of the vitamin results in defective formation of the papillae (small projections) of the tongue, giving an appearance of abnormal smoothness. A deficiency of vitamin B12 often causes defective function of the intestine, resulting in indigestion and sometimes constipation or diarrhea. A very serious effect is degeneration of certain motor and sensory tracts of the spinal cord; if the degeneration continues for some time, treatment with vitamin B12 may not correct it. Initial numbness and tingling of fingers or toes may, without treatment, progress to instability of gait or paralysis.

      Because vitamin B12 is found in animal but not vegetable foods, strict vegetarians (vegetarianism) (vegans) who do not eat dairy products, meats, fish, eggs, or vitamin B12-fortified foods may develop a deficiency if they do not receive supplements of the vitamin. Deficiency may also result from competition for vitamin B12 by the broad tapeworm or by intestinal bacteria growing in cul-de-sacs or above partial obstructions in the digestive tract. Additional nutritional deficiencies, such as those of folic acid or iron, are likely to develop in such cases, as in primary intestinal diseases such as celiac disease, tropical sprue, or regional enteritis, all of which affect the absorptive capacity of the small bowel. pernicious anemia, a disease characterized by the impaired production of red blood cells, is caused by the lack of intrinsic factor, a substance that is normally produced by the stomach and binds with vitamin B12, allowing it to be absorbed and used by the body; treatment involves the administration of intramuscular injections of the vitamin.

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Universalium. 2010.

Look at other dictionaries:

  • Vitamin B12 — Systematic (IUPAC) name α (5,6 dimethylbenzimidazolyl)coba …   Wikipedia

  • vitamin B12 — n. a B vitamin that is used to treat pernicious anemia. Syn: cobalamin, cyanocobalamin. [WordNet 1.5] …   The Collaborative International Dictionary of English

  • vitamin B12 — vitamin B12. См. витамин В12. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • vitamin B12 — cobalamin (см.). (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Vitamin B12 — ⇒ Cobalamin …   Deutsch wörterbuch der biologie

  • Vitamin B12 — Strukturformel Coenzym B12 (=AdoCbl): R = 5 Desoxyadenosyl Cyanocobalamin (=Vitamin B12): R = –C≡N Hydroxycobalamin (=Vitamin B12a): R = OH Methylcobalamin (=MeCbl oder MeB12): R = –CH3 …   Deutsch Wikipedia

  • 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… …   Medical dictionary

  • vitamin B12 — cyanocobalamin 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… …   The new mediacal dictionary

  • vitamin B12 — noun a B vitamin that is used to treat pernicious anemia • Syn: ↑cobalamin, ↑cyanocobalamin, ↑antipernicious anemia factor • Hypernyms: ↑B complex vitamin, ↑B complex, ↑vitamin B complex, ↑vitamin B …   Useful english dictionary

  • vitamin B12 — A vitamin that is needed to make red blood cells and DNA (the genetic material in cells) and to keep nerve cells healthy. It is found in eggs, meat, poultry, shellfish, milk, and milk products. Vitamin B12, along with folate, may be given to help …   English dictionary of cancer terms


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