Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood.
It is one of the eight B vitamins. It is normally involved in the metabolism of every cell of the human body, especially affecting DNA synthesis and regulation, but also fatty acid synthesis and energy production.
It is the largest and most structurally complicated vitamin and can be produced industrially only through bacterial fermentation-synthesis.
Vitamin B12 consists of a class of chemically related compounds (vitamers), all of which have
vitamin activity. It contains the biochemically rare element cobalt.
Biosynthesis of the basic structure of the vitamin is accomplished only by bacteria, but conversion between different forms of the vitamin can be accomplished in the human body.
A common synthetic form of the vitamin, cyanocobalamin, does not occur in nature, but is used in many pharmaceuticals and supplements, and as a food additive, because of its stability and lower cost.
In the body it is converted to the physiological forms, methylcobalamin and adenosylcobalamin, leaving behind the cyanide, albeit in minimal concentration.
More recently, hydroxocobalamin, methylcobalamin, and adenosylcobalamin can also be found in more expensive pharmacological products and food supplements. The extra utility of these is currently debated
Vitamin B12 was discovered from its relationship to the disease pernicious anemia, which is an autoimmune disease in which parietal cells of the stomach
responsible for secreting intrinsic factor are destroyed.
Intrinsic factor is crucial for the normal absorption of B12, so a lack of intrinsic factor, as seen in pernicious anemia, causes a vitamin B~12 deficiency.
Many other subtler kinds of vitamin B12 ~deficiency and their biochemical effects have since been elucidated.[1]