Vitamin B12 – Obtained from liver, milk, eggs, fish, oysters, and clams: used chiefly in the treatment of pernicious anemia and sprue, and as a growth factor for hogs, dogs, and chickens.

Cyanocobalamin, commonly known as vitamin B12, is a compound that is metabolized to a vitamin in the B complex. Vitamin B12 is important for the normal functioning of the brain and nervous system and for the formation of blood. It is involved in the metabolism of every cell of the body, especially affecting the DNA synthesis and regulation but also fatty acid synthesis and energy production. Its effects are still not completely known.

The name vitamin B12 is used in two different ways.

• In a broad sense it refers to a group of cobalt-containing compounds known as cobalamins - cyanocobalamin (an artifact formed as a result of the use of cyanide in the purification procedures), hydroxocobalamin and the two coenzyme forms of B12, methylcobalamin (MeB12) and5-deoxyadenosylcobalamin (adenosylcobalamin – AdoB12).

• In a more specific way, the term B12 is used to refer to only one of these forms, cyanocobalamin, which is the principal B12 form used for foods and in nutritional supplements. This use is being contested because research indicates that it may not be able to correct B12 deficiency in the brain effectively. Being an unnatural form of B12 it is misleading to equate it with the vitamin especially if it is not a fully effective supplement.

Pseudo-B12 refers to B12-like substances which are found in certain organisms, including spirulina and other algae; however, these substances do not have B12 biological activity for humans.

The human physiology of vitamin B12 is complex, and therefore is prone to mishaps leading to vitamin B12 deficiency. The vitamin enters the digestive tract bound to proteins, known as salivary R-binders. Stomach proteolysis of these proteins requires an acid pH, and also requires proper pancreatic release of proteolytic enzymes. The vitamin B12 then attaches to gastric intrinsic factor, which is generated by the gastric parietal cells. The conjugated vitamin B12-intrinsic factor complex can then be absorbed by the terminal ileum of the small bowel. Absorption of vitamin B12 therefore requires an intact and functioning stomach, exocrine pancreas, intrinsic factor, and small bowel. Problems with any one of these organs makes a vitamin B12 deficiency possible.

B12 deficiency is the cause of several forms of anemia. The treatment for this disease was first devised by William Murphy who devised experiments on anemia in dogs due to blood loss 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 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervous system.

B12 can be supplemented in healthy subjects by oral pill; sublingual pill, liquid, or strip; or by injection. B12 is available singly or in combination with other supplements.

Vitamin B12 is naturally found in foods of animal origin including meat, especially liver and shellfish, and milk products. Eggs are usually mentioned as a good source; however they also contain a factor that blocks absorption. Fortified breakfast cereals are a particularly valuable source of vitamin B12 for vegetarians and vegans.

Cyanocobalamin is converted to its active forms, first hydroxocobalamin and then methylcobalamin and adenosylcobalamin in the liver. A 2003 study found no significant difference in absorption for serum levels from oral vs sublingual delivery of 500 micrograms of cobalamin. Injection is useful and usually necessary in cases where digestive absorption is impaired. Oral absorption is complex and requires specific intestinal transport proteins (intrinsic factor) produced in the stomach. In any case the absorption is saturated and is rate limited.

Interestingly, certain insects such as termites have been found to contain B12.

Cyanocobalamin is also sometimes added to beverages including Diet Coke Plus and many energy drinks, in some cases with over 80 times the recommended intake.

Vitamin B12 supplements should be avoided in people sensitive or allergic to cobalamin, cobalt, or any other product ingredients.As part of a well-balanced diet that is low in saturated fat and cholesterol, folic acid, vitamin B6 and vitamin B12 may reduce the risk of vascular disease.*

*The FDA has evaluated the above claim and found that, while it is known that diets low in saturated fat and cholesterol reduce the risk of heart disease and other vascular diseases, the evidence in support of the above claim is inconclusive.

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