II. Physiology

  1. B12 dependent reactions in humans
    1. Methylmalonic acid converted to succinyl-CoA
    2. Homocysteine converted to methionine
    3. 5-Methyltetrahydrofolate converted to tetrahydrofolate
      1. Required for DNA synthesis and RBC production
  2. Normal B12 absorption pathway
    1. Requires ingestion (animal source or fortified cereal) as cannot be synthesized in humans
    2. Acidic Stomach environment breaks down food-bound B12
      1. Insufficient acid decreases B12 absorption
      2. Proton Pump Inhibitors suppress B12 absorption
    3. Intrinsic factor (IF) binds B12 in duodenum
      1. Intrinsic factor produced in Stomach parietal cells
      2. Pernicious Anemia is autoimmune parietal cell death
      3. Insufficient IF results in decreased B12 absorption
    4. Vitamin B12 absorption via 2 pathways
      1. Primary B12 absorption
        1. Vitamin B12 with intrinsic factor absorbed in ileum
        2. Absorbed Vitamin B12 binds Transcobalamin II
      2. Alternate B12 absorption
        1. Pathway independent of intrinsic factor and ileum
        2. Absorption of up to 1% of large oral B12 dose
        3. Allows for oral B12 supplementation
    5. Vitamin B12 storage
      1. Vitamin B12 is stored in the liver
      2. Large hepatic stores may delay B12 Vitamin Deficiency presentation more than 5 years

IV. Sources: Animal sources only

  1. Liver
  2. Muscle Meats
  3. Fish
  4. Eggs
  5. Dairy products
  6. Vitamin B12 fortified foods (Cereals)

V. Doses

  1. See Vitamin B12 Supplementation
  2. Recommended daily allowance: 2.4 mcg/day
  3. Elderly:
    1. B12 Fortified foods (Cereals)
    2. Daily dietary supplement up to Vitamin B12 1000 mcg orlly daily

VI. References

  1. Babior in Wilson (1991) Harrisons, McGraw, p. 1523-9
  2. Oh (2003) Am Fam Physician 67(5):979-86 [PubMed]

Images: Related links to external sites (from Bing)

Related Studies (from Trip Database) Open in New Window

Cost: Medications

cyanocobalamin (on 8/17/2016 at Medicaid.Gov Survey of pharmacy drug pricing)
CYANOCOBALAMIN 1,000 MCG/ML Generic $6.83 per ml

Ontology: Vitamin B 12 (C0042845)

Definition (NCI_NCI-GLOSS) A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Cyanocobalamin helps make red blood cells, DNA, RNA, energy, and tissues, and keeps nerve cells healthy. It is found in liver, meat, eggs, poultry, shellfish, milk, and milk products. Cyanocobalamin is water-soluble (can dissolve in water) and must be taken in every day. Not enough cyanocobalamin can cause certain types of anemia (a condition in which the number of red blood cells is below normal) and neurologic disorders. It is being studied with folate in the prevention and treatment of some types of cancer.
Definition (NCI_CRCH) Cobalt-containing water soluble vitamin that is a coenzyme in the metabolism of fatty acids of odd-chain length and in methyl transfer. (DRI)
Definition (NCI_NCI-GLOSS) A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Vitamin B12 helps make red blood cells, DNA, RNA, energy, and tissues, and keeps nerve cells healthy. It is found in liver, meat, eggs, poultry, shellfish, milk, and milk products. Vitamin B12 is water-soluble (can dissolve in water) and must be taken in every day. Not enough vitamin B12 can cause certain types of anemia (a condition in which the number of red blood cells is below normal) and neurologic disorders. It is being studied with folate in the prevention and treatment of some types of cancer.
Definition (NCI) A cobalt-containing coordination compound generated by intestinal microbes, and a natural water-soluble vitamin of the B-complex family that must combine with Intrinsic Factor for absorption by the intestine. Cyanocobalamin is necessary for hematopoiesis, neural metabolism, DNA and RNA production, and carbohydrate, fat, and protein metabolism. B12 improves iron functions in the metabolic cycle and assists folic acid in choline synthesis. B12 metabolism is interconnected with that of folic acid. Vitamin B12 deficiency causes pernicious anemia, megaloblastic anemia, and neurologic lesions.
Definition (CSP) cyanocobalamin or cobalamin derivative with similar biological activity; a water soluble hematopoietic vitamin, absorbed in the intestine after combination with intrinsic factor.
Definition (MSH) A cobalt-containing coordination compound produced by intestinal micro-organisms and found also in soil and water. Higher plants do not concentrate vitamin B 12 from the soil and so are a poor source of the substance as compared with animal tissues. INTRINSIC FACTOR is important for the assimilation of vitamin B 12.
Definition (PDQ) An essential nutrient and natural water-soluble vitamin of the B-complex family that must combine with an intrinsic factor for absorption by the intestine, Vitamin B12 (cyanocobalamin) is necessary for hematopoiesis, neural metabolism, DNA and RNA production, and carbohydrate, fat, and protein metabolism. B12 improves iron functions in the metabolic cycle and assists folic acid in choline synthesis. B12 metabolism is interconnected with that of folic acid. Vitamin B12 deficiency causes pernicious anemia, megaloblastic anemia, and neurologic lesions. Check for "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=530928&idtype=1" active clinical trials or "http://www.cancer.gov/Search/ClinicalTrialsLink.aspx?id=530928&idtype=1&closed=1" closed clinical trials using this agent. ("http://nciterms.nci.nih.gov:80/NCIBrowser/ConceptReport.jsp?dictionary=NCI_Thesaurus&code=C939" NCI Thesaurus)
Concepts Pharmacologic Substance (T121) , Organic Chemical (T109) , Vitamin (T127)
MSH D014805
SnomedCT 81064004, 11611006, 30010009, 259664005, 327706007, 419382002
LNC LP15262-6, LP31689-0, LP32549-5
English B 12, Vitamin, B12, Vitamin, Cyanocobalamin, Vitamin B 12, Vitamin B12, vitamin B12, Vitamin B12 preparation, Vitamin B12 (substance) [Ambiguous], Vitamin B12 preparation (product), Vitamin B12 preparation (substance), Vitamin B<sub>12</sub> (substance) [Ambiguous], Vitamin B<sub>12</sub> preparation (product), Vitamin B<sub>12</sub> preparation (substance), Vitamin B<sub>12</sub> preparation, cyanocobalamin, Vitamin B-12, vitamin B12 compound, VITAMIN B A 12, B12 - Vitamin B12, B12 - Cyanocobalamin, cyanocobalamin (medication), vitamin B12 (medication), vitamins cyanocobalamin, Cobalamin, Cobalamin (1+), CYANOCOBALAMIN, Vitamin B 12 [Chemical/Ingredient], vitamin B 12, vit b12, b 12 vitamin, Vitamin B<sub>12</sub>, Vitamin B12 (substance), Vitamin B>12<, Vitamin B>12< (substance), Vitamin B<sub>12</sub> (substance), COBALAMIN, B12 - Cyanocobalamin prep, Cyanocobalamin preparation, Cyanocobalamin product, Vitamin B>12< preparation, Cyanocobalamin preparation (product), Vitamin B>12< preparation (product), Cyanocobalamin preparation (substance), Vitamin B>12< (substance) [Ambiguous], Vitamin B>12< preparation (substance), VIT B12, Vitamin-B12, B12 Vitamin, CYANOCOBALMIN, Cyanocobalamin (substance)
Spanish cianocobalamina, cianocobalamina (sustancia), vitamina B12 (concepto no activo), vitamina B<sub>12</sub> (concepto no activo), preparado de vitamina B<sub>12</sub> (sustancia), preparado de vitamina B12 (sustancia), preparado con vitamina B>12< (producto), preparado con vitamina B<sub>12</sub> (producto), vitamina B>12< (producto), vitamina B12, preparado con vitamina B12 (producto), vitamina B12 (producto), vitamina B>12<, cianocobalamina (producto), cobalamina, preparado con cianocobalamina (producto), vitamina B<sub>12</sub>, vitamina B<sub>12</sub> (producto), preparado con cianocobalamina, preparado con vitamina B<sub>12</sub>, preparado con vitamina B12, preparado con vitamina B>12<, vitamina B12 (sustancia), vitamina B<sub>12</sub> (sustancia), vitamina B>12< (sustancia), B12 - cianocobalamina, Vitamina B12, preparado de cianocobalamina (sustancia), preparado de vitamina B>12< (sustancia), vitamina B>12< (concepto no activo), Cianocobalamina, Vitamina B 12
German Zyanocobalamin, Cyanokobalamin, Zyanokobalamin, VITAMIN B A 12, Cyanocobalamin, Vitamin B12
Swedish Vitamin B12
Czech vitamin B 12
Finnish Syanokobalamiini
Italian Cianocobalamina, Vitamina B12
Russian TSIANOKOBALAMIN, VITAMIN B12, KOBALAMIN, ВИТАМИН B12, КОБАЛАМИН, ЦИАНОКОБАЛАМИН
Japanese ビタミンB12, シアノコバラミン, コバラミン
Polish Cyjanokobalamina, Kobalamina, Witamina B12
Norwegian Not Translated[Vitamin B 12]
Portuguese Vitamina B12, Cianocobalamina, Vitamina B 12
French Cyanocobalamine, Vitamine B12