Brief and precise summary of Vitamin B12
Note
5 minutes
difficulty level Easy
Matthew Messer

Matthew Messer

Editor-in-chief

Vitamin B12, also known as cobalamin, is a water-soluble vitamin, which owes its name to its cobalt content. It plays an important role in the proper functioning of the central nervous system and partakes in methylation along with folate and other B vitamins. This process helps repair DNA errors and prevent inflammation. 

We store a fair amount of vitamin B12, so it may take years for a deficiency to develop, yet it is hard to notice and may even cause irreparable damage.  Deficiencies develop with the greatest likelihood in those following a plant-based diet, in older people, and those with digestive illnesses, but frequently taking gastric acid reducing medication can be problematic, too, as they inhibit the absorption of vitamin B12 from foods. (2) In the above cases, it is especially important to mind adequate supplementation. 

The advantage of supplements is that they do not require stomach acid or a substance produced in the stomach called IF in order to be absorbed, so even with digestive problems or acid reducers, they are effective in mitigating a deficiency. Even at high doses, vitamin B12 intake is safe. Long-term health effects are mainly associated with its deficiency, which can lead to anemia, fatigue, neurological damage, and birth defects. (2,4) 

What types are there?  

The known forms of vitamin B12 are methylcobalamin, adenosylcobalamin, cyanocobalamin, and hydroxycobalamin. Methylcobalamin, adenosylcobalamin, and hydroxycobalamin are forms found mainly in food, while cyanocobalamin is most commonly used in supplements. There is no significant difference in their absorption and utilization, all forms are broken down into cobalamin and reconverted to the active forms within our bodies. (5, 6) 

A common question about cyanocobalamin its whether its consumption can cause any issues, since it is, as the name suggests, related to cyanide? Although cyanide is indeed harmful, even with higher doses of vitamin B12 supplementation, one is taking in far less cyanide than a balanced diet already contains. Nevertheless, as there is no naturally occurring cyanocobalamin in our food, methylcobalamin is a more viable choice as a supplement. 

How much vitamin B12 do we need? 

The daily requirement for vitamin B12 intake was set at 2.4 mcg for adults and less on a body weight basis for children. Since our bodies can store on average 1 to 5 mg of vitamin B12, the required intake depends greatly on how much vitamin B12 we have consumed in the past, going back as far as several years. Children's needs are also affected by how much the mother consumed during her pregnancy because if the mother's B12 intake was low, there is a good chance that her child will develop a deficiency. (3) 

Mild deficiency of vitamin B12 is quite common, affecting around 25-40% of the population, and up to 70% among the elderly, as measured by blood levels. However, this method does not always give accurate results, so homocysteine and other biomarkers should also be checked for greater accuracy. (7,8)

How to ensure adequate levels of vitamin B12? 

The best sources of vitamin B12 are foods of animal origin, liver being a particularly good source. Dairy products, fish, and meats are all good sources of vitamin B12, however, the only plant foods that contain vitamin B12 are those that are fortified with it. Consequently, it is essential to consume a vitamin B12 supplement or foods fortified with vitamin B12 if following a plant-based diet. (3)  

There is a wide variation in the B12 content of capsule supplements, which usually contain 1-1000 mcg of vitamin B12. It is worth noting that the absorption of vitamin B12 decreases significantly with increasing dosage, but there is no difference in the utilization of the different forms. (5,6) In some specific diseases, vitamin B12 cannot be replaced by oral supplements because they are not utilized, but in such cases the injectable form is helpful. (3, 10) 

Health effects of vitamin B12 

Vitamin B12 deficiency causes serious health problems. One of these is anemia, which causes overly large, yet poorly developed red blood cells to form and significantly lowers their levels. The other type of anemia is autoimmune; substances needed to absorb vitamin B12 are not produced. If the deficiency persists over a long period of time, the nervous system is also damaged, which can lead to cognitive decline and even dementia. Vitamin B12 deficiency is not always associated with obvious symptoms, so it is important to keep in mind, should you develop symptoms. (2,4,7) 

Vitamin B12 is of particular importance during pregnancy for the above-mentioned reasons, because the mother's supply determines the vitamin B12 levels of the unborn child, and a lack of vitamin B12 significantly increases the incidence of birth defects and pregnancy complications. (20,21) 

Vitamin B12 deficiency can increase osteoporosis and various skin problems, but supplementation is effective in reducing the incidence of these problems. (22,23,25) 

As with folate, vitamin B12 deficiency increases homocysteine levels, which may increase the risk of dementia, Alzheimer's disease, and cardiovascular disease. (11, 12) However, despite reducing homocysteine, vitamin B12 supplementation did not significantly improve the risk of these diseases in people who are healthy and have no symptomatic B12 deficiency. (13,14,15,16)  

As with folate, vitamin B12 levels are often low in depressed individuals. (17) Several studies have examined the relationship between the two, and vitamin B12 levels predicted the occurrence of depression independently of folate and homocysteine. (18) In one study, moreover, antidepressant therapy was more effective in those with better vitamin B12 levels. (19)  

[The cover photo of the note shows clams. 100 grams contain 99 μg of vitamin B12, which is 20 times the recommended daily intake, but we don't have to worry, as the absorption of B12 is significantly reduced in the case of such high doses.]

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  2. Green R, Allen LH, Bjørke-Monsen AL, Brito A, Guéant JL, Miller JW, Molloy AM, Nexo E, Stabler S, Toh BH, Ueland PM, Yajnik C. Vitamin B12 deficiency. Nat Rev Dis Primers. 2017 Jun 29;3:17040. doi: 10.1038/nrdp.2017.40. Erratum in: Nat Rev Dis Primers. 2017 Jul 20;3:17054. PMID: 28660890. 

  3. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/#en5 

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  6. Paul C, Brady DM. Comparative Bioavailability and Utilization of Particular Forms of B12 Supplements With Potential to Mitigate B12-related Genetic Polymorphisms. Integr Med (Encinitas). 2017;16(1):42-49. 

  7. Carmel R. How I treat cobalamin (vitamin B12) deficiency. Blood. 2008 Sep 15;112(6):2214-21. doi: 10.1182/blood-2008-03-040253. Epub 2008 Jul 7. PMID: 18606874; PMCID: PMC2532799. 

  8. Pfisterer KJ, Sharratt MT, Heckman GG, Keller HH. Vitamin B12 status in older adults living in Ontario long-term care homes: prevalence and incidence of deficiency with supplementation as a protective factor. Appl Physiol Nutr Metab. 2016 Feb;41(2):219-22. doi: 10.1139/apnm-2015-0565. Epub 2016 Jan 19. PMID: 26781161. 

  9. Tillemans MP, Donders EM, Verweij SL, Van der Hoeven RT, Kalisvaart KJ. Effect of administration route on the pharmacokinetics of cobalamin in elderly patients: a randomized controlled trial. Curr Ther Res Clin Exp. 2014 Mar 20;76:21-5. doi: 10.1016/j.curtheres.2014.01.001. PMID: 25031664; PMCID: PMC3994916. 

  10. Wang H, Li L, Qin LL, Song Y, Vidal-Alaball J, Liu TH. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2018 Mar 15;3(3):CD004655. doi: 10.1002/14651858.CD004655.pub3. PMID: 29543316; PMCID: PMC6494183. 

  11. Seshadri S, Beiser A, Selhub J, Jacques PF, Rosenberg IH, D'Agostino RB, Wilson PW, Wolf PA. Plasma homocysteine as a risk factor for dementia and Alzheimer's disease. N Engl J Med. 2002 Feb 14;346(7):476-83. doi: 10.1056/NEJMoa011613. PMID: 11844848. 

  12. Chrysant SG, Chrysant GS. The current status of homocysteine as a risk factor for cardiovascular disease: a mini review. Expert Rev Cardiovasc Ther. 2018 Aug;16(8):559-565. doi: 10.1080/14779072.2018.1497974. Epub 2018 Jul 17. PMID: 29979619. 

  13. Martí-Carvajal AJ, Solà I, Lathyris D, Dayer M. Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev. 2017 Aug 17;8(8):CD006612. doi: 10.1002/14651858.CD006612.pub5. PMID: 28816346; PMCID: PMC6483699. 

  14. Rutjes AW, Denton DA, Di Nisio M, Chong LY, Abraham RP, Al-Assaf AS, Anderson JL, Malik MA, Vernooij RW, Martínez G, Tabet N, McCleery J. Vitamin and mineral supplementation for maintaining cognitive function in cognitively healthy people in mid and late life. Cochrane Database Syst Rev. 2018 Dec 17;12(12):CD011906. doi: 10.1002/14651858.CD011906.pub2. PMID: 30556597; PMCID: PMC6353240. 

  15. Dangour AD, Allen E, Clarke R, Elbourne D, Fletcher AE, Letley L, Richards M, Whyte K, Uauy R, Mills K. Effects of vitamin B-12 supplementation on neurologic and cognitive function in older people: a randomized controlled trial. Am J Clin Nutr. 2015 Sep;102(3):639-47. doi: 10.3945/ajcn.115.110775. Epub 2015 Jul 1. PMID: 26135351; PMCID: PMC4548176.  

  16. van der Zwaluw NL, Dhonukshe-Rutten RA, van Wijngaarden JP, Brouwer-Brolsma EM, van de Rest O, In 't Veld PH, Enneman AW, van Dijk SC, Ham AC, Swart KM, van der Velde N, van Schoor NM, van der Cammen TJ, Uitterlinden AG, Lips P, Kessels RP, de Groot LC. Results of 2-year vitamin B treatment on cognitive performance: secondary data from an RCT. Neurology. 2014 Dec 2;83(23):2158-66. doi: 10.1212/WNL.0000000000001050. Epub 2014 Nov 12. PMID: 25391305. 

  17. Coppen A, Bolander-Gouaille C. Treatment of depression: time to consider folic acid and vitamin B12. J Psychopharmacol. 2005 Jan;19(1):59-65. doi: 10.1177/0269881105048899. PMID: 15671130. 

  18. Penninx BW, Guralnik JM, Ferrucci L, Fried LP, Allen RH, Stabler SP. Vitamin B(12) deficiency and depression in physically disabled older women: epidemiologic evidence from the Women's Health and Aging Study. Am J Psychiatry. 2000 May;157(5):715-21. doi: 10.1176/appi.ajp.157.5.715. PMID: 10784463. 

  19. Hintikka J, Tolmunen T, Tanskanen A, Viinamäki H. High vitamin B12 level and good treatment outcome may be associated in major depressive disorder. BMC Psychiatry. 2003 Dec 2;3:17. doi: 10.1186/1471-244X-3-17. PMID: 14641930; PMCID: PMC317314. 

  20. Molloy AM, Kirke PN, Troendle JF, et al. Maternal vitamin B12 status and risk of neural tube defects in a population with high neural tube defect prevalence and no folic Acid fortification. Pediatrics. 2009;123(3):917-923. doi:10.1542/peds.2008-1173 

  21. Molloy AM, Kirke PN, Brody LC, Scott JM, Mills JL. Effects of folate and vitamin B12 deficiencies during pregnancy on fetal, infant, and child development. Food Nutr Bull. 2008 Jun;29(2 Suppl):S101-11; discussion S112-5. doi: 10.1177/15648265080292S114. PMID: 18709885. 

  22. Tucker KL, Hannan MT, Qiao N, Jacques PF, Selhub J, Cupples LA, Kiel DP. Low plasma vitamin B12 is associated with lower BMD: the Framingham Osteoporosis Study. J Bone Miner Res. 2005 Jan;20(1):152-8. doi: 10.1359/JBMR.041018. Epub 2004 Oct 25. PMID: 15619681. 

  23. Brescoll J, Daveluy S. A review of vitamin B12 in dermatology. Am J Clin Dermatol. 2015 Feb;16(1):27-33. doi: 10.1007/s40257-014-0107-3. PMID: 25559140. 

  24. Christen WG, Glynn RJ, Chew EY, Albert CM, Manson JE. Folic acid, pyridoxine, and cyanocobalamin combination treatment and age-related macular degeneration in women: the Women's Antioxidant and Folic Acid Cardiovascular Study. Arch Intern Med. 2009;169(4):335-341. doi:10.1001/archinternmed.2008.574 

  25. Kannan R, Ng MJ. Cutaneous lesions and vitamin B12 deficiency: an often-forgotten link. Can Fam Physician. 2008;54(4):529-532. 

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