Cyanocobalamin, also known as Cobalamin or vitamin B12, is a chemical compound that is needed for nerve cells and red blood cells, and to make DNA. It is a water-soluble organometallic compound with a trivalent cobalt ion bound inside a corrin ring.


History as a treatment for anemia

Vitamin B12 deficiency is the cause of several forms of anemia. The treatment for this disease was first devised by William Murphy who bled dogs to make them anemic and then fed them various substances to see what (if anything) would make them healthy again. He discovered that ingesting large amounts of liver seemed to cure the disease. George Minot and George Whipple then set about to chemically isolate the curative substance and ultimately were able to isolate vitamin B12 from the liver. For this, all three shared the 1934 Nobel Prize in Medicine.

The chemical structure of the molecule was determined by Dorothy Crowfoot Hodgkin and her team in 1956, based on crystallographic data.


Vitamin B12 is mostly absorbed in the terminal ileum. The production of intrinsic factor in the stomach is vital to absorption of this vitamin. Megaloblastic anemia can result from inadequate intake of vitamin B12, inadequate production of intrinsic factor (pernicious anemia), disorders of the terminal ileum resulting in malabsorption, or by competition for available B12 (such as fish tapeworms or bacteria present in blind loop syndrome). Neurological signs of B12 deficiency, which can occur without accompanying hematologic abnormalities, include demyelination and irreversible nerve cell death. Symptoms include numbness or tingling of the extremities and an ataxic gait.

The American Psychiatric Association's American Journal of Psychiatry has published studies showing a relationship between depression levels and deficient vitamin B12 blood levels in elderly people in 2000 [1] ( and 2002 [2] (

Inadequate intake can be overcome with oral B12 supplements or modification of diet. However, the (not uncommon) lack of intrinsic factor, leading to inadequate absorption, is typically unresponsive to oral supplementation. In such cases intramuscular injection of ~1mg of methylcobalimin about monthly can overcome the consequent pernicious anemia. The Shillings test can determine whether symptoms of B12 deficiency are caused by lack of intrinsic factor.


In nature, B12 is solely produced by bacteria found in animals (including humans), so that dirt could actually be considered a natural source of B12. While vegetarians usually get enough B12 through dairy products or eggs, it can sometimes be lacking in those following vegan diet who do not make an effort to find B12 enriched foodstuffs, like enriched cereals, soy-based products or yeast extract. Claimed sources of B12 that have been shown through direct studies of vegans to be inadequate include spirulina (an algae), nori (a seaweed), barley grass, and human gut bacteria. Several studies of vegans on raw food diets show that raw food offers no special protection against B12 deficiency either.


Vitamin B12 is used in the body in two forms: Methylcobalamin and 5-deoxyadenosyl cobalamin.

The enzyme methionine synthase needs methylcobalamin as a cofactor. This enzyme is involved in the conversion of the amino acid homocysteine into methionine. Methionine in turn is required for DNA methylation.

5-Deoxyadenosyl cobalamin is a cofactor needed by the enzyme that converts L-methylmalonyl-CoA to succinyl-CoA. This conversion is an important step in the extraction of energy from proteins and fats. Furthermore, succinyl CoA is necessary for the production of hemoglobin, the substances that carries oxygen in red blood cells.

External links

de:Cobalamin es:Cianocobalamina fa:ویتامین ب١٢ fr:Vitamine B12 it:Cobalamina lb:Cobalamin lt:Kobalaminas ms:Vitamin B12 nl:Cobalamine ja:シアノコバラミン pl:Witamina B12 fi:B12-vitamiini


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