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Vitamin B12

Also known as Cobalamin, B12

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Linked references: 5 identified
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Evidence recency: 1998–2020
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Government reference1
Study type could not be determined4

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Classified references

Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B(6), Folate, Vitamin B(12), Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academies Press; 1998.
Government reference · Population basis: unknown · Directness: not assessed
Carmel R. Cobalamin (vitamin B12). In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:369-89.
Study type could not be determined · Population basis: unknown · Directness: not assessed
Allen LH. Vitamin B12. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:812-20.
Study type could not be determined · Population basis: unknown · Directness: not assessed
Allen LH. Vitamin B-12. Adv Nutr 2012;3:54-5. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Stabler SP. Vitamin B12. In: Marriott BP, Birt DF, Stallings VA, Yates AA, eds. Present Knowledge in Nutrition. 11th ed. Washington, DC: Elsevier; 2020:257-71.
Study type could not be determined · Population basis: unknown · Directness: not assessed

Read imported source wording

Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. Because vitamin B12 contains the mineral cobalt, compounds with vitamin B12 activity are collectively called cobalamins [1]. Methylcobalamin and 5-deoxyadenosylcobalamin are the metabolically active forms of vitamin B12. However, two others forms, hydroxycobalamin and cyanocobalamin, become biologically active after they are converted to methylcobalamin or 5-deoxyadenosylcobalamin [1-3].

Vitamin B12 is required for the development, myelination, and function of the central nervous system; healthy red blood cell formation; and DNA synthesis [1,4,5]. Vitamin B12 functions as a cofactor for two enzymes, methionine synthase and L-methylmalonyl-CoA mutase [1-3,5]. Methionine synthase catalyzes the conversion of homocysteine to the essential amino acid methionine [1,2]. Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 different substrates, including DNA, RNA, proteins, and lipids [3,5]. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the metabolism of propionate, a short-chain fatty acid [2].

Vitamin B12 is bound to protein in food and must be released before it is absorbed [5]. The process starts in the mouth when food is mixed with saliva. The freed vitamin B12 then binds with haptocorrin, a cobalamin-binding protein in the saliva. More vitamin B12 is released from its food matrix by the activity of hydrochloric acid and gastric protease in the stomach, where it then binds to haptocorrin [1]. In the duodenum, digestive enzymes free the vitamin B12 from haptocorrin, and this freed vitamin B12 combines with intrinsic factor, a transport and delivery binding protein secreted by the stomach’s parietal cells. The resulting complex is absorbed in the distal ileum by receptor-mediated endocytosis [1,5]. If vitamin B12 is added to fortified foods and dietary supplements, it is already in free form and therefore does not require the separation step.

Where did MEDucated get this?

Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements. Government health-professional reference material imported without MEDucated medical review.

Source section: Introduction
ODS revision: July 2, 2025
Retrieved: 2026-08-10T22:07:05.257Z
Source fingerprint: a488ce5e4f73cbe7a517bfad2bc6c15f8da92daa99709eca8b3c56aadea00ae8
Cited reference numbers: 1, 2, 3, 4, 5

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Evidence source: NIH ODS evidence synthesis
Linked references: 1 identified
Human evidence: Human evidence not identified in the frozen metadata
Randomized trials: Randomized trials not identified in the frozen metadata
Reviews and meta-analyses: Systematic reviews or meta-analyses not identified in the frozen metadata
Evidence recency: 1998–1998
Source-described consistency: Not characterized in these source blocks
MEDucated evidence rating: Not assigned

Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

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Government reference1

Source-described limitations

No explicit limitation phrase was identified in these imported source blocks.

Classified references

Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B(6), Folate, Vitamin B(12), Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academies Press; 1998.
Government reference · Population basis: unknown · Directness: not assessed

Vitamin B12 does not have a tolerable upper intake level because it is generally considered to be safe, even at high doses.

UL reference intake

The FNB did not establish a UL for vitamin B12 because of its low potential for toxicity [1]. Even at large doses, vitamin B12 is generally considered to be safe because the body does not store excess amounts.

UL reference intake

Where did MEDucated get this?

Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements. Government health-professional reference material imported without MEDucated medical review.

Source section: Health Risks from Excessive Vitamin B12
ODS revision: July 2, 2025
Retrieved: 2026-08-10T22:07:05.257Z
Source fingerprint: a488ce5e4f73cbe7a517bfad2bc6c15f8da92daa99709eca8b3c56aadea00ae8
Cited reference numbers: 1

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Evidence source: NIH ODS evidence synthesis
Linked references: 3 identified
Human evidence: Human evidence not identified in the frozen metadata
Randomized trials: Randomized trials not identified in the frozen metadata
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Evidence recency: 2013–2018
Source-described consistency: Not characterized in these source blocks
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Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

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Meta-analysis1
Study type could not be determined2

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Classified references

Jung SB, Nagaraja V, Kapur A, Eslick GD. Association between vitamin B12 deficiency and long-term use of acid-lowering agents: A systematic review and meta-analysis. Intern Med J 2015;45:409-16. [PubMed abstract]
Meta-analysis · Population basis: unknown · Directness: not assessed
Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA 2013;310:2435-42. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Miller JW. Proton pump inhibitors, H2-receptor antagonists, metformin, and vitamin B-12 deficiency: Clinical implications. Adv Nutr 2018;9:511S-8S. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed

Vitamin B12 supplements may interact with medications, and some medications, including gastric acid inhibitors and metformin, may affect vitamin B12 levels.

Vitamin B12 supplements have the potential to interact with certain medications. In addition, several types of medications might adversely affect vitamin B12 levels. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin B12 status with their health care providers.

Gastric acid inhibitors include proton pump inhibitors, such as omeprazole (Prilosec) and lansoprazole (Prevacid), and histamine 2-receptor antagonists, such as cimetidine (Tagamet) and ranitidine (Zantac). These drugs are used to treat gastroesophageal reflux disease and peptic ulcer disease. They can interfere with vitamin B12 absorption from food by slowing the release of gastric acid into the stomach and thereby lead to vitamin B12 deficiency [101-103].

Metformin, an antihyperglycemic agent used as first-line treatment for prediabetes and diabetes, might reduce the absorption of vitamin B12 and significantly reduce serum vitamin B12 concentrations [103].

Where did MEDucated get this?

Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements. Government health-professional reference material imported without MEDucated medical review.

Source section: Interactions with Medications
ODS revision: July 2, 2025
Retrieved: 2026-08-10T22:07:05.257Z
Source fingerprint: a488ce5e4f73cbe7a517bfad2bc6c15f8da92daa99709eca8b3c56aadea00ae8
Cited reference numbers: 101, 102, 103

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No overall rating assigned

Evidence source: NIH ODS evidence synthesis
Linked references: 7 identified
Human evidence: Human evidence not identified in the frozen metadata
Randomized trials: Randomized trial identified
Reviews and meta-analyses: Systematic reviews or meta-analyses not identified in the frozen metadata
Evidence recency: 1998–2021
Source-described consistency: Not characterized in these source blocks
MEDucated evidence rating: Not assigned

Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

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Evidence types identified

Government reference1
Study type could not be determined5
Randomized controlled trial1

Source-described limitations

No explicit limitation phrase was identified in these imported source blocks.

Classified references

Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B(6), Folate, Vitamin B(12), Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academies Press; 1998.
Government reference · Population basis: unknown · Directness: not assessed
Allen LH. Vitamin B12. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:812-20.
Study type could not be determined · Population basis: unknown · Directness: not assessed
Office of Dietary Supplements, National Institutes of Health. Dietary Supplement Label Database. 2021.
Study type could not be determined · Population basis: unknown · Directness: not assessed
Paul C, Brady DM. Comparative bioavailability and utilization of particular forms of B(12) Supplements with potential to mitigate B(12)-related genetic polymorphisms. Integr Med 2017;16:42-9. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Carmel R. How I treat cobalamin (vitamin B12) deficiency. Blood 2008;112:2214-21. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Yazaki Y, Chow G, Mattie M. A single-center, double-blinded, randomized controlled study to evaluate the relative efficacy of sublingual and oral vitamin B-complex administration in reducing total serum homocysteine levels. J Altern Complement Med 2006;12:881-5. [PubMed abstract]
Randomized controlled trial · Population basis: unknown · Directness: not assessed
Sharabi A, Cohen E, Sulkes J, Garty M. Replacement therapy for vitamin B12 deficiency: Comparison between the sublingual and oral route. Br J Clin Pharmacol 2003;56:635-8. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed

Read imported source wording

Vitamin B12 is present in many dietary supplements, often as cyanocobalamin, but other forms may also be used. Supplements that only contain vitamin B12 typically have the highest doses of the vitamin, while multivitamin/mineral supplements and supplements that combine vitamin B12 with other B-complex vitamins usually contain lower doses.

Vitamin B12 is available in multivitamin/mineral supplements, in supplements containing other B-complex vitamins, and in supplements containing only vitamin B12. Multivitamin/mineral supplements typically contain vitamin B12 at doses ranging from 5 to 25 mcg [23]. Vitamin B12 levels are higher, generally 50 to 500 mcg, in supplements containing vitamin B12 with other B-complex vitamins and even higher, typically 500 to 1,000 mcg, in supplements containing only vitamin B12.

Source intake rangeSource-described amount

The most common form of vitamin B12 in dietary supplements is cyanocobalamin [1,3,23,24]. Other forms of vitamin B12 in supplements are adenosylcobalamin, methylcobalamin, and hydroxycobalamin [23].

No evidence indicates that absorption rates of vitamin B12 in supplements vary by form of the vitamin. These rates are about 50% at doses (less than 1–2 mcg) that do not exceed the cobalamin-binding capacity of intrinsic factor and are substantially lower at doses well above 1 to 2 mcg [24,25]. For example, absorption is only about 2% at doses of 500 mcg and 1.3% at doses of 1,000 mcg [25].

Source intake rangeSource-described amount

In addition to oral dietary supplements, vitamin B12 is available in sublingual preparations as tablets or lozenges [23]. Evidence suggests no difference in efficacy between oral and sublingual forms [26,27].

Where did MEDucated get this?

Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements. Government health-professional reference material imported without MEDucated medical review.

Source section: Dietary supplements
ODS revision: July 2, 2025
Retrieved: 2026-08-10T22:07:05.257Z
Source fingerprint: a488ce5e4f73cbe7a517bfad2bc6c15f8da92daa99709eca8b3c56aadea00ae8
Cited reference numbers: 23, 1, 3, 24, 25, 26, 27

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Evidence source: NIH ODS evidence synthesis
Linked references: 1 identified
Human evidence: Human evidence not identified in the frozen metadata
Randomized trials: Randomized trials not identified in the frozen metadata
Reviews and meta-analyses: Systematic reviews or meta-analyses not identified in the frozen metadata
Evidence recency: 1998–1998
Source-described consistency: Not characterized in these source blocks
MEDucated evidence rating: Not assigned

Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

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Evidence types identified

Government reference1

Source-described limitations

No explicit limitation phrase was identified in these imported source blocks.

Classified references

Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B(6), Folate, Vitamin B(12), Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academies Press; 1998.
Government reference · Population basis: unknown · Directness: not assessed

Read imported source wording

The Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine has established Recommended Dietary Allowances and Adequate Intakes for vitamin B12. These values range from 2.4 to 2.8 mcg for adults and from 0.4 to 2.8 mcg for infants, children, and adolescents, depending on age.

RDA reference intakeAI reference intakeSource intake rangeSource-described amount

Intake recommendations for vitamin B12 and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine [1]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and sex, include the following:

Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals
Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA
Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals
Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects

RDA reference intakeAI reference intakeUL reference intake

Table 1 lists the current RDAs for vitamin B12 [1]. For adults, the main criterion that the FNB used to establish the RDAs was the amount needed to maintain a healthy hematological status and serum vitamin B12 levels. For infants age 0 to 12 months, the FNB established an AI that is equivalent to the mean intake of vitamin B12 in healthy, breastfed infants.

AI reference intake

Table 1: Recommended Dietary Allowances (RDAs) for Vitamin B12 in Micrograms (mcg)[1]
Age	Male	Female	Pregnancy	Lactation
Birth to 6 months*	0.4 mcg	0.4 mcg
7–12 months*	0.5 mcg	0.5 mcg
1–3 years	0.9 mcg	0.9 mcg
4–8 years	1.2 mcg	1.2 mcg
9–13 years	1.8 mcg	1.8 mcg
14–18 years	2.4 mcg	2.4 mcg	2.6 mcg	2.8 mcg
19+ years	2.4 mcg	2.4 mcg	2.6 mcg	2.8 mcg
* Adequate Intake (AI)

RDA reference intakeAI reference intakeSource-described amount

Where did MEDucated get this?

Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements. Government health-professional reference material imported without MEDucated medical review.

Source section: Recommended Intakes
ODS revision: July 2, 2025
Retrieved: 2026-08-10T22:07:05.257Z
Source fingerprint: a488ce5e4f73cbe7a517bfad2bc6c15f8da92daa99709eca8b3c56aadea00ae8
Cited reference numbers: 1

Inspect the official NIH ODS source

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Imported NIH ODS source content is available for this topic. MEDucated has preserved the source wording and has not converted it into personalized guidance.

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Evidence source: NIH ODS evidence synthesis
Linked references: 21 identified
Human evidence: Human evidence identified
Randomized trials: Randomized trial identified
Reviews and meta-analyses: Systematic review or meta-analysis identified
Evidence recency: 1998–2019
Source-described consistency: Not characterized in these source blocks
MEDucated evidence rating: Not assigned

Reference counts describe frozen source associations; a larger count does not establish stronger evidence.

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Evidence types identified

Government reference1
Study type could not be determined15
Meta-analysis1
Randomized controlled trial1
Narrative review2
Systematic review1

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No explicit limitation phrase was identified in these imported source blocks.

Classified references

Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B(6), Folate, Vitamin B(12), Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academies Press; 1998.
Government reference · Population basis: unknown · Directness: not assessed
Carmel R. Cobalamin (vitamin B12). In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:369-89.
Study type could not be determined · Population basis: unknown · Directness: not assessed
Allen LH. Vitamin B12. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:812-20.
Study type could not be determined · Population basis: unknown · Directness: not assessed
Allen LH, Miller JW, de Groot L, Rosenberg IH, Smith AD, Refsum H, et al. Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review. J Nutr 2018;148:1995S-2027S. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Green R, Allen LH, Bjorke-Monsen AL, Brito A, Gueant JL, Miller JW, et al. Vitamin B12 deficiency. Nat Rev Dis Primers 2017;3:17040. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Wong CW. Vitamin B12 deficiency in the elderly: Is it worth screening? Hong Kong Med J 2015;21:155-64. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
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;41:219-22. [PubMed abstract]
Study type could not be determined · Population basis: human · Directness: not assessed
Cavalcoli F, Zilli A, Conte D, Massironi S. Micronutrient deficiencies in patients with chronic atrophic autoimmune gastritis: A review. World J Gastroenterol 2017;23:563-72. [PubMed abstract]
Study type could not be determined · Population basis: human · Directness: not assessed
Weck MN, Stegmaier C, Rothenbacher D, Brenner H. Epidemiology of chronic atrophic gastritis: Population-based study among 9444 older adults from Germany. Aliment Pharmacol Ther 2007;26:879-87. [PubMed abstract]
Study type could not be determined · Population basis: human · Directness: not assessed
Kalkan Ç, Karakaya F, Tüzün A, Gençtürk ZB, Soykan I. Factors related to low serum vitamin B12 levels in elderly patients with non-atrophic gastritis in contrast to patients with normal vitamin B12 levels. Geriatr Gerontol Int 2016;16:686-92. [PubMed abstract]
Study type could not be determined · Population basis: human · Directness: not assessed
Rojas Hernandez CM, Oo TH. Advances in mechanisms, diagnosis, and treatment of pernicious anemia. Discov Med 2015;19:159-68. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Ao M, Tsuji H, Shide K, Kosaka Y, Noda A, Inagaki N, et al. High prevalence of vitamin B-12 insufficiency in patients with Crohn's disease. Asia Pac J Clin Nutr 2017;26:1076-81. [PubMed abstract]
Study type could not be determined · Population basis: human · Directness: not assessed
Bledsoe AC, King KS, Larson JJ, Snyder M, Absah I, Choung RS, et al. Micronutrient deficiencies Are common in contemporary celiac disease despite lack of overt malabsorption symptoms. Mayo Clin Proc 2019;94:1253-60. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Ward MG, Kariyawasam VC, Mogan SB, Patel KV, Pantelidou M, Sobczyńska-Malefora A, et al. Prevalence and risk factors for functional vitamin B12 deficiency in patients with Crohn's disease. Inflamm Bowel Dis 2015;21:2839-47. [PubMed abstract]
Study type could not be determined · Population basis: human · Directness: not assessed
Pan Y, Liu Y, Guo H, Jabir MS, Liu X, Cui W, et al. Associations between folate and vitamin B12 levels and inflammatory bowel disease: A meta-analysis. Nutrients 2017;9:382. [PubMed abstract]
Meta-analysis · Population basis: unknown · Directness: not assessed
Gomollón F, Gargallo CJ, Muñoz JF, Vicente R, Lue A, Mir A, et al. Oral cyanocobalamin is effective in the treatment of vitamin B12 deficiency in Crohn's disease. Nutrients 2017;9:308. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Dogan K, Aarts EO, Koehestanie P, Betzel B, Ploeger N, de Boer H, et al. Optimization of vitamin suppletion after Roux-en-Y gastric bypass surgery can lower postoperative deficiencies: a randomized controlled trial. Medicine (Baltimore) 2014;93:e169. [PubMed abstract]
Randomized controlled trial · Population basis: unknown · Directness: not assessed
Kornerup LS, Hvas CL, Abild CB, Richelsen B, Nexo E. Early changes in vitamin B12 uptake and biomarker status following Roux-en-Y gastric bypass and sleeve gastrectomy. Clin Nutr 2019;38:906-11. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Pawlak R, Lester SE, Babatunde T. The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: A review of literature. Eur J Clin Nutr 2014;68:541-8. [PubMed abstract]
Narrative review · Population basis: unknown · Directness: not assessed
Dror DK, Allen LH. Vitamin B-12 in human milk: A systematic review. Adv Nutr 2018;9:358s-66s. [PubMed abstract]
Systematic review · Population basis: human · Directness: not assessed
Piccoli GB, Clari R, Vigotti FN, Leone F, Attini R, Cabiddu G, et al. Vegan-vegetarian diets in pregnancy: Danger or panacea? A systematic narrative review. Bjog 2015;122:623-33. [PubMed abstract]
Narrative review · Population basis: unknown · Directness: not assessed

Read imported source wording

Certain groups of people are more likely than others to be vitamin B12 deficient. These include older adults, people with pernicious anemia or gastrointestinal disorders, and those who have had gastrointestinal surgery. Other groups that are at risk of vitamin B12 deficiency include people who follow vegetarian diets and the infants of women who follow vegan diets.

The following groups are among those most likely to be vitamin B12 deficient.

Depending on the definition used, between 3% and 43% of community-dwelling older adults, especially those with atrophic gastritis, have vitamin B12 deficiency based on serum vitamin B12 levels [43,44]. The deficiency rate at a cutoff of less than 211 pg/mL (156 pmol/L) at admission to a long-term care facility, according to one study, was 14%, and 38% of these older adults had levels lower than 407 pg/mL (300 pmol/L) [44].

Conditions associated with vitamin B12 inadequacy include pernicious anemia, present in about 15% to 25% of older adults with vitamin B12 deficiency [45]. Atrophic gastritis, an autoimmune condition affecting 2% of the general population but 8% to 9% of adults age 65 and older, decreases production of intrinsic factor and secretion of hydrochloric acid in the stomach and thus decreases absorption of vitamin B12 [45,46]. A third condition associated with vitamin B12 deficiency in older adults is Helicobacter pylori infection, possibly because this bacterium causes inflammation that leads to malabsorption of vitamin B12 from food [47].

Pernicious anemia is an irreversible autoimmune disease that affects the gastric mucosa and results in gastric atrophy [1,48]. This disease leads to attacks on parietal cells in the stomach, resulting in failure to produce intrinsic factor and malabsorption of dietary vitamin B12, recycled biliary vitamin B12, and free vitamin B12 [1,6,11].Therefore, without treatment, pernicious anemia causes vitamin B12 deficiency, even in the presence of adequate vitamin B12 intakes.

Pernicious anemia is the most common cause of clinically evident vitamin B12 deficiency around the world [11,48]. The incidence of pernicious anemia in the United States is an estimated 151 per 100,000, and this condition is more common in women and in people of European ancestry [48].

Individuals with stomach and small intestine disorders, such as celiac disease and Crohn’s disease, may be unable to absorb enough vitamin B12 from food to maintain healthy body stores [2,3,49]. However, although rates of vitamin B12 deficiency are higher in people with celiac disease than other people [50], the evidence for whether rates of vitamin B12 deficiency are higher in people with Crohn’s disease is mixed [49,51,52]. Vitamin B12 deficiency in people with Crohn’s disease is typically treated with intramuscular cobalamin injections, but high doses of oral cyanocobalamin therapy (e.g., 1,000 mcg/day) might be equally effective [53].

Source-described amount

Surgical procedures in the gastrointestinal tract, such as for weight loss or to remove all or part of the stomach, can cause a complete or partial loss of cells that secrete hydrochloric acid and cells that secrete intrinsic factor [54,55]. Thus, these procedures reduce the amount of vitamin B12, particularly food-bound vitamin B12, that the body absorbs [54,55]. High doses (1,000 mcg/day) of oral methylcobalamin supplements appear to be as effective as hydroxycobalamin injections in normalizing vitamin B12 values in patients who have undergone Roux-en-Y gastric bypass surgery [55].

Source-described amount

Vegans who consume no animal products and vegetarians who consume some animal products (e.g., dairy products, eggs, or both) but not meat have a higher risk of developing vitamin B12 deficiency because natural food sources of vitamin B12 are limited to animal foods [3,57]. Consumption of foods fortified with vitamin B12 (such as fortified nutritional yeasts) as well as vitamin B12 supplements can substantially reduce the risk of deficiency [57].

Exclusively breastfed infants of women who consume no animal products might have very limited reserves of vitamin B12 and can develop vitamin B12 deficiency, sometimes very early in life [58]. The infant’s deficiency can be severe, especially if the mother’s deficiency is severe or caused by pernicious anemia; sometimes, the mother’s own deficiency is clinically mild and not recognized. Undetected and untreated vitamin B12 deficiency in infants can result in neurological damage, failure to thrive, developmental delays, and anemia [2,58,59]. The reasons include the small amounts of vitamin B12 in the breast milk of vegan mothers as well as the limited amounts of vitamin B12 crossing the placenta in these women during fetal development.

Where did MEDucated get this?

Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements. Government health-professional reference material imported without MEDucated medical review.

Source section: Groups at Risk of Vitamin B12 Inadequacy
ODS revision: July 2, 2025
Retrieved: 2026-08-10T22:07:05.257Z
Source fingerprint: a488ce5e4f73cbe7a517bfad2bc6c15f8da92daa99709eca8b3c56aadea00ae8
Cited reference numbers: 43, 44, 45, 46, 47, 1, 6, 11, 48, 2, 3, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59

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Classified references

Carmel R. Cobalamin (vitamin B12). In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:369-89.
Study type could not be determined · Population basis: unknown · Directness: not assessed
Allen LH, Miller JW, de Groot L, Rosenberg IH, Smith AD, Refsum H, et al. Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review. J Nutr 2018;148:1995S-2027S. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Langan RC, Goodbred AJ. Vitamin B12 deficiency: Recognition and management. Am Fam Physician 2017;96:384-9. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Maruvada P, Stover PJ, Mason JB, Bailey RL, Davis CD, Field MS, et al. Knowledge gaps in understanding the metabolic and clinical effects of excess folates/folic acid: A summary, and perspectives, from an NIH workshop. Am J Clin Nutr 2020;112:1390-403 [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Hannibal L, Lysne V, Bjørke-Monsen A-L, Behringer S, Grünert SC, Spiekerkoetter U, et al. Biomarkers and algorithms for the diagnosis of vitamin B12 deficiency. Front Mol Biosci 2016;3:27. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Mineva EM, Sternberg MR, Zhang M, Aoki Y, Storandt R, Bailey RL, et al. Age-specific reference ranges are needed to interpret serum methylmalonic acid concentrations in the US population. Am J Clin Nutr 2019;110:158-68. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed
Green R, Allen LH, Bjorke-Monsen AL, Brito A, Gueant JL, Miller JW, et al. Vitamin B12 deficiency. Nat Rev Dis Primers 2017;3:17040. [PubMed abstract]
Study type could not be determined · Population basis: unknown · Directness: not assessed

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Serum or plasma vitamin B12 levels are typically used to assess a person’s vitamin B12 status, with values lower than 200 or 250 pg/mL generally being considered subnormal. The most sensitive marker of vitamin B12 status is a vitamin B12-associated metabolite called methylmalonic acid, and serum levels of this metabolite can be used to confirm a diagnosis of vitamin B12 deficiency if a patient’s serum vitamin B12 level is between 150 and 399 pg/mL.

Vitamin B12 status is typically assessed by measurements of serum or plasma vitamin B12 levels. The cutoff between normal vitamin B12 levels and deficiency varies by method and laboratory, but most laboratories define subnormal serum or plasma values as those lower than 200 or 250 picograms per milliliter (pg/mL) (148 or 185 picomols per liter [pmol/L]) [2]. Levels of serum methylmalonic acid (MMA), a vitamin B12-associated metabolite, are the most sensitive markers of vitamin B12 status, and an MMA level greater than 0.271 micromol/L suggests vitamin B12 deficiency [6-8]. However, MMA levels also rise with renal insufficiency and tend to be higher in older adults [6,9,10]. Another marker is total plasma homocysteine levels, which rise quickly as vitamin B12 status declines; a serum homocysteine level higher than 15 micromol/L, for example, suggests vitamin B12 deficiency [11]. However, this indicator has poor specificity because it is influenced by other factors, such as low folate levels and, especially, by declines in kidney function [6]. Experts suggest that if a patient’s serum vitamin B12 level is between 150 to 399 pg/mL (111 to 294 pmol/L), the patient’s serum MMA levels should be checked to help confirm a diagnosis of vitamin B12 deficiency [7,9].

Where did MEDucated get this?

Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements. Government health-professional reference material imported without MEDucated medical review.

Source section: Assessing Vitamin B12 Status
ODS revision: July 2, 2025
Retrieved: 2026-08-10T22:07:05.257Z
Source fingerprint: a488ce5e4f73cbe7a517bfad2bc6c15f8da92daa99709eca8b3c56aadea00ae8
Cited reference numbers: 2, 6, 7, 8, 9, 10, 11

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Fixture ID: fixture:supplement:vitamin-b12:ods-evidence-preview
Fixture revision: source-revision:nih-ods:vitamin-b12-health-professional:2026-08-10.a488ce5e4f73
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Vitamin B12 — Fact Sheet for Health Professionals

NIH Office of Dietary Supplements

Fixture ID: fixture:supplement:vitamin-b12:ods-evidence-preview
Fixture revision: source-revision:nih-ods:vitamin-b12-health-professional:2026-08-10.a488ce5e4f73
Content classification: source backed demonstration
Medical review: not medically reviewed
Evidence classification: government reference
External source metadata: Available in source inspection