Vitamin B12

This article is about the family of vitamers. For individual forms, see hydroxocobalamin, cyanocobalamin, methylcobalamin, and adenosylcobalamin.

"B12" and "Cbl" redirect here. For other uses of B12, see B12 (disambiguation). For the musical group, see Carbon Based Lifeforms.

Vitamin B12
General skeletal formula of cobalamins
Stick model of cyanocobalamin (R = CN) based on the crystal structure[1]
Clinical data
Other namesVitamin B12, vitamin B-12, cobalamin
AHFS/Drugs.comMonograph
MedlinePlusa605007
License data
Routes of
administration		By mouth, sublingual, intravenous (IV), intramuscular (IM), intranasal
ATC code
Legal status
Legal status
  • UK: OTC
  • US: OTC
Pharmacokinetic data
BioavailabilityReadily absorbed in distal half of the ileum.
Protein bindingVery high to specific transcobalamins plasma proteins.
Binding of hydroxocobalamin is slightly higher than cyanocobalamin.
MetabolismLiver
Elimination half-lifeApproximately 6 days
(400 days in the liver).
ExcretionKidney
Identifiers
  • α-(5,6-Dimethylbenzimidazolyl)cobamidcyanide
CAS Number
PubChem CID
DrugBank
ChemSpider
UNII
KEGG
ChEMBL
Chemical and physical data
FormulaC63H88CoN14O14P
Molar mass1355.388 g·mol−1
3D model (JSmol)
  • NC(=O)C[C@@]8(C)[C@H](CCC(N)=O)C=2/N=C8/C(/C)=C1/[C@@H](CCC(N)=O)[C@](C)(CC(N)=O)[C@@](C)(N1[Co+]C#N)[C@@H]7/N=C(C(\C)=C3/N=C(/C=2)C(C)(C)[C@@H]3CCC(N)=O)[C@](C)(CCC(=O)NCC(C)OP([O-])(=O)O[C@@H]6[C@@H](CO)O[C@H](n5cnc4cc(C)c(C)cc45)[C@@H]6O)[C@H]7CC(N)=O
  • InChI=1S/C62H90N13O14P.CN.Co/c1-29-20-39-40(21-30(29)2)75(28-70-39)57-52(84)53(41(27-76)87-57)89-90(85,86)88-31(3)26-69-49(83)18-19-59(8)37(22-46(66)80)56-62(11)61(10,25-48(68)82)36(14-17-45(65)79)51(74-62)33(5)55-60(9,24-47(67)81)34(12-15-43(63)77)38(71-55)23-42-58(6,7)35(13-16-44(64)78)50(72–42)32(4)54(59)73–56;1–2;/h20-21,23,28,31,34-37,41,52-53,56-57,76,84H,12-19,22,24-27H2,1-11H3,(H15,63,64,65,66,67,68,69,71,72,73,74,77,78,79,80,81,82,83,85,86);;/q;;+2/p-2/t31?,34-,35-,36-,37+,41-,52-,53-,56-,57+,59-,60+,61+,62+;;/m1../s1 checkY
  • Key:RMRCNWBMXRMIRW-WYVZQNDMSA-L checkY

Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism.[2] It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, and in both fatty acid and amino acid metabolism.[3] It is important in the normal functioning of the nervous system via its role in the synthesis of myelin, and in the circulatory system in the maturation of red blood cells in the bone marrow.[2][4] Plants do not need cobalamin and carry out the reactions with enzymes that are not dependent on it.[5]

Vitamin B12 is the most chemically complex of all vitamins,[6] and for humans the only vitamin that must be sourced from animal-derived foods or supplements.[2][7] Only some archaea and bacteria can synthesize vitamin B12.[8] Vitamin B12 deficiency is a widespread condition that is particularly prevalent in populations with low consumption of animal foods. Such diets can be due to a variety of reasons, such as low socioeconomic status, ethical considerations, or lifestyle choices such as veganism.[9]

Foods containing vitamin B12 include meat, shellfish, liver, fish, poultry, eggs, and dairy products.[2] Many breakfast cereals are fortified with the vitamin.[2] Supplements and medications are available to treat and prevent vitamin B12 deficiency.[2] They are usually taken by mouth, but for the treatment of deficiency may also be given as an intramuscular injection.[2][6]

Vitamin B12 deficiencies have a greater effect on young children, pregnant and elderly people, and are more common in middle and lower developed countries due to malnutrition.[10] The most common cause of vitamin B12 deficiency in developed countries is impaired absorption due to a loss of gastric intrinsic factor (IF) which must be bound to a food-source of B12 in order for absorption to occur.[11] A second major cause is an age-related decline in stomach acid production (achlorhydria), because acid exposure frees protein-bound vitamin.[12] For the same reason, people on long-term antacid therapy, using proton-pump inhibitors,[13] H2 blockers or other antacids are at increased risk.[14]

The diets of vegetarians and vegans may not provide sufficient B12 unless a dietary supplement is taken.[2] A deficiency may be characterized by limb neuropathy or a blood disorder called pernicious anemia, a type of anemia in which red blood cells become abnormally large.[2] This can result in fatigue, decreased ability to think, lightheadedness, shortness of breath, frequent infections, poor appetite, numbness in the hands and feet, depression, memory loss, confusion, difficulty walking, blurred vision, irreversible nerve damage, and many others.[15] If left untreated in infants, deficiency may lead to neurological damage and anemia.[2] Folate levels in the individual may affect the course of pathological changes and symptomatology of vitamin B12 deficiency. Vitamin B12 deficiency in pregnant women is strongly associated with an increased risk of spontaneous abortion, congenital malformations such as neural tube defects, problems with brain development growth in the unborn child.[10]

Vitamin B12 was discovered as a result of pernicious anemia, an autoimmune disorder in which the blood has a lower than normal number of red blood cells, due to a deficiency of vitamin B12.[5][16] The ability to absorb the vitamin declines with age, especially in people over 60.[17]

  1. ^ Prieto T, Neuburger M, Spingler B, Zelder F (2016). "Inorganic Cyanide as Protecting Group in the Stereospecific Reconstitution of Vitamin B12 from an Artificial Green Secocorrinoid" (PDF). Org. Lett. 18 (20): 5292–5295. doi:10.1021/acs.orglett.6b02611. PMID 27726382.
  2. ^ a b c d e f g h i j Office of Dietary Supplements (6 April 2021). "Vitamin B12: Fact Sheet for Health Professionals". Bethesda, Maryland: US National Institutes of Health. Archived from the original on 2021-10-08. Retrieved 24 December 2021.
  3. ^ Yamada K (2013). "Cobalt: Its Role in Health and Disease". In Sigel A, Sigel H, Sigel RK (eds.). Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. Vol. 13. Springer. pp. 295–320. doi:10.1007/978-94-007-7500-8_9. ISBN 978-94-007-7499-5. PMID 24470095.
  4. ^ Cite error: The named reference Calderon2020 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Smith2019 was invoked but never defined (see the help page).
  6. ^ a b "Vitamin B12". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis, OR. 4 June 2015. Archived from the original on 29 October 2019. Retrieved 5 April 2019.
  7. ^ Vincenti A, Bertuzzo L, Limitone A, D'Antona G, Cena H (June 2021). "Perspective: Practical Approach to Preventing Subclinical B12 Deficiency in Elderly Population". Nutrients. 13 (6): 1913. doi:10.3390/nu13061913. PMC 8226782. PMID 34199569.
  8. ^ Watanabe F, Bito T (January 2018). "Vitamin B12 sources and microbial interaction". Exp Biol Med (Maywood). 243 (2): 148–158. doi:10.1177/1535370217746612. PMC 5788147. PMID 29216732.
  9. ^ Obeid R, Heil SG, Verhoeven MM, van den Heuvel EG, de Groot LC, Eussen SJ (2019). "Vitamin B12 Intake From Animal Foods, Biomarkers, and Health Aspects". Front Nutr. 6: 93. doi:10.3389/fnut.2019.00093. PMC 6611390. PMID 31316992.
  10. ^ a b Cite error: The named reference :0 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference PKIN2020VitB12 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference DRItext was invoked but never defined (see the help page).
  13. ^ Choudhury A, Jena A, Jearth V, Dutta AK, Makharia G, Dutta U, et al. (May 2023). "Vitamin B12 deficiency and use of proton pump inhibitors: a systematic review and meta-analysis". Expert Rev Gastroenterol Hepatol. 17 (5): 479–487. doi:10.1080/17474124.2023.2204229. PMID 37060552.
  14. ^ "Acid-Reflux Drugs Tied to Lower Levels of Vitamin B-12". WebMD. Archived from the original on 2018-07-23. Retrieved 2018-07-23.
  15. ^ "Vitamin B12 Deficiency Anemia". www.hopkinsmedicine.org. 8 August 2021. Retrieved 2022-02-16.
  16. ^ "Pernicious anemia: MedlinePlus Medical Encyclopedia". medlineplus.gov. Retrieved 2022-01-06.
  17. ^ Baik HW, Russell RM (2021-11-18). "Vitamin B12 deficiency in the elderly". Annual Review of Nutrition. 19: 357–377. doi:10.1146/annurev.nutr.19.1.357. PMID 10448529.