Vitamin used in animal cell metabolism
- "B12" and "Cbl" redirect here. For other uses of B12, see B12 . For the musical group, see Carbon Based Lifeforms.
Vitamin B12, also known as cobalamin or extrinsic factor, is a water-soluble vitamin involved in metabolism. One of eight B vitamins, it serves as a vital cofactor in DNA synthesis and both fatty acid and amino acid metabolism. It plays an essential role in the nervous system by supporting myelin synthesis and is critical for the maturation of red blood cells in the bone marrow. While animals require B12, plants do not, relying instead on alternative enzymatic pathways.
Vitamin B12 is the most chemically complex of all vitamins, and is synthesized exclusively by certain archaea and bacteria. Natural food sources include meat, shellfish, liver, fish, poultry, eggs, and dairy products. It is also added to many breakfast cereals through food fortification and is available in dietary supplement and pharmaceutical forms. Supplements are commonly taken orally but may be administered via intramuscular injection to treat deficiencies.
In healthy adults, vitamin B12 deficiency is not common, mainly because body stores of the vitamin are substantial and turnover is slow, with relatively low dietary requirements. The most common cause in developed countries is impaired absorption due to loss of gastric intrinsic factor (IF), required for absorption. A related cause is reduced stomach acid production with age or from long-term use of proton-pump inhibitors, H2 blockers, or other antacids. Elderly people due to impaired intestinal absorption, children, premenopausal women, and pregnant women, whose diets are low in animal foods, are at increased risk.
Deficiency is especially harmful in pregnancy, childhood, and older adults. It can lead to neuropathy, megaloblastic anemia, and pernicious anemia, causing symptoms such as fatigue, paresthesia, depression, cognitive decline, ataxia, and even irreversible nerve damage. In infants, untreated deficiency may result in neurological impairment and anemia. Maternal deficiency increases the risk of miscarriage, neural tube defects, and developmental delays in offspring. Folate levels may modify the presentation of symptoms and disease course.