Type: Compound
Vitamin: B12
Name: Cyanocobalamin, Hydroxycobalamin, Methylcobalamin
RDA:3-6 µg
Importance- to Body:
Functions as coenzyme in all cells, particularly in gastrointestinal tract, nervous system, and bone marrow; in bone marrow, acts in synthesis of DNA; when absent, erythrocytes do not divide but continue to increase in size.
Distribution- in Body:
Most complex vitamin; contains cobalt; stable to heat; inactivated by light and strongly acidic or basic solutions; intrinsic factor required for transport across intestinal membrane; stored principally in liver; liver stores of 2000-3000 µg sufficient to provide for body needs for 3-5 years.
Excess Effects:
None listed
Deficiency Effects:
Most cases reflect impaired absorption rather than actual deficit
Pernicious Anemia, Pallor, Anorexia, Dyspnea, Weight Loss, Neurological Disturbances
Food Sources:
Not found in plant foods or butter
Liver, Meat, Poultry, Fish, Dairy, Eggs
Environmental/Geographic Sources:
None listed
Supplemental information:
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| Clinical data | |
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| Synonyms | vitamin B12, vitamin B-12 |
| AHFS/Drugs.com | Monograph |
| Routes of administration |
by mouth, sublingual, IV, IM, intranasal |
| ATC code | |
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| Pharmacokinetic data | |
| Bioavailability | Readily absorbed in distal half of the ileum |
| Protein binding | Very high to specific transcobalamins plasma proteins Binding of hydroxocobalamin is slightly higher than cyanocobalamin. |
| Metabolism | liver |
| Biological half-life | Approximately 6 days (400 days in the liver) |
| Excretion | kidney |
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| CAS Number | |
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| Chemical and physical data | |
| Formula | C63H88CoN14O14P |
| Molar mass | 1355.37 g/mol |
| 3D model (JSmol) | |
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Vitamin B12, also called cobalamin, is a water-soluble vitamin that has a key role in the normal functioning of the nervous system via the synthesis of myelin (myelinogenesis), and in the maturation of developing red blood cells in the bone marrow. It is involved in the metabolism of every cell of the human body: it is a cofactor in DNA synthesis, fatty acid metabolism, and amino acid metabolism.
No fungi, plants, or animals (including humans) are capable of synthesizing vitamin B12: only bacteria and archaea have the enzymes needed for its synthesis. Natural sources of B12 include shellfish and meat. Other sources are foods with the vitamin artificially added ("fortified"), intramuscular injection, and vitamin B12 tablets ("supplements") taken either orally or sublingually.
Vitamin B12 is one of eight B vitamins; it is the largest and most structurally complicated vitamin. It consists of a class of chemically related compounds (vitamers), all of which show pharmacological activity. It contains the biochemically rare element cobalt (chemical symbol Co) positioned in the center of a planar tetra-pyrrole ring called a corrin ring. The vitamer is produced by bacteria as hydroxocobalamin, but conversion among different forms of the vitamin occurs in the body after consumption. It is produced industrially via bacterial fermentation and also via total synthesis.
Vitamin B12 was discovered as a result of its relationship to the disease pernicious anemia, an autoimmune disease in which parietal cells of the lining of the stomach are destroyed: parietal cells are responsible for secreting both intrinsic factor and hydrochloric acid into the stomach. Because intrinsic factor is crucial for the normal absorption of B12, its lack in the presence of pernicious anemia causes a vitamin B12 deficiency. Many other subtler kinds of vitamin B12 deficiency and their biochemical effects have since been made clear. Due to impairment of vitamin B12 absorption during aging, people over age 60 are at risk of deficiency.