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📰Read the full Cobalamin evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ Neurological symptoms (paresthesias, gait ataxia) can precede anemia by months or years — check B12 even with normal MCV [3]
⚠ Every vegan patient — confirm B12 supplementation status; deficiency is inevitable without it [2]
⚠ Metformin users with peripheral neuropathy — check B12 before attributing symptoms solely to diabetes [7]
⚠ Elderly patient on chronic PPI with macrocytosis — assess B12 status [9]
⚠ Nitrous oxide exposure (recreational or surgical) in a marginally deficient patient — can precipitate acute neurological crisis [3]
🥗 Food first — build your daily 2.4 mcg
Check the foods you regularly eat — the bar fills toward your daily target.
Clams, cooked (85 g)84.1 mcg
Beef liver, cooked (85 g)70.7 mcg
Nutritional yeast, fortified (15 g)8.3 mcg
Trout, cooked (85 g)5.4 mcg
Salmon, cooked (85 g)4.8 mcg
Beef, cooked (85 g)2.1 mcg
Milk (240 mL)1.1 mcg
Egg, cooked (1 large)0.6 mcg
Check your regular foods above
☑ Risk checker
Vegan diet without supplementation (no plant B12 sources) [2]
Pernicious anemia (autoimmune anti-IF/anti-parietal cell antibodies) [4]
Age >60 years (atrophic gastritis, reduced acid/pepsin) [9]
Long-term metformin therapy [7]
Chronic PPI or H2 blocker use [9]
Gastrectomy or ileal resection [3]
Crohn disease affecting the terminal ileum [2]
Chronic alcoholism [2]
Select factors
🔬 Lab interpreter
Recommended test
Serum cobalamin (B12)
Serum cobalamin (B12)
Reference range / target
>221 pmol/L (300 pg/mL) preferred; <148 pmol/L (200 pg/mL) = deficient
>221 pmol/L (300 pg/mL) preferred; <148 pmol/L (200 pg/mL) = deficient
When to test
At baseline if risk factors or symptoms; repeat 2–3 months after starting treatment [2].
At baseline if risk factors or symptoms; repeat 2–3 months after starting treatment [2].
Can be normal despite tissue deficiency (false normal in liver disease, myeloproliferative disorders). If borderline, check MMA [2].
Full lab monitoring ↓⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
B12 deficiency causes irreversible neurological damage (subacute combined degeneration) that can occur WITHOUT anemia — never wait for hematological signs before treating. Vegans require mandatory supplementation. Metformin and PPI use are underrecognized risk factors in diabetes and elderly populations [3] [4] [7].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: Specific dosage data under clinical review
👦 Pediatric: See guidance
Infants 0–6 months: 0.4 µg/day AI; children 1–3 years: 0.9 µg/day; 4–8 years: 1.2 µg/day [1]. Infants of B12-deficient mothers (especially vegans) can develop severe deficiency within months,
🏃 Athletes: Standard dose
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Consult specialist
Dose adjustment may be needed in renal impairment.
🌱 Vegan: Specific dosage data under clinical review
How to take
🍽 Timing: Can be taken at any time. Sublingual forms bypass GI absorption — useful in malabsorption states, though evidence of superiority over oral swallowed tablets is mixed [2].
💊 With food: No specific requirement. Crystalline B12 from supplements does not require acid-pepsin release and is better absorbed than food-bound B12 in elderly [9].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['Cyanocobalamin', 'common', 'Synthetic form most commonly used in supplements and fortification. Must be converted to active forms (methyl- and adenosylcobalamin). Stable and inexpensive. Contains a cyanide moiety released upon conversion (trace amounts, clinically insignificant) [1].'] | Standard | Check label | |
| ['Methylcobalamin', 'preferred', 'Bioactive form — the coenzyme for methionine synthase. Does not require conversion. Commonly marketed for neurological conditions. Less stable than cyanocobalamin (light-sensitive) [2].'] | Standard | Check label | |
| ['Hydroxocobalamin', '', 'Used for intramuscular injection. Longer retention time than cyanocobalamin. Also used as cyanide antidote (Cyanokit). Preferred IM form in many countries [4].'] | Standard | Check label | |
| ['Adenosylcobalamin', '', 'Mitochondrial coenzyme form for methylmalonyl-CoA mutase. Available in some supplements. Less commonly used than methylcobalamin [1].'] | Standard | Check label |
3 Common questions
Can vegans get B12 from any plant sources? ▼
How is pernicious anemia diagnosed? ▼
Pernicious anemia is diagnosed by: low serum B12, elevated MMA, megaloblastic anemia, and positive anti-intrinsic factor antibodies (highly specific, ~50% sensitive) or anti-parietal cell antibodies (less specific, ~80% sensitive) [4]. The Schilling test is no longer routinely available. Patients require lifelong B12 replacement (IM or high-dose oral) [4].
Can oral B12 work for pernicious anemia? ▼
Yes — at high doses (1,000–2,000 µg/day), approximately 1% of oral B12 is absorbed by passive diffusion, bypassing intrinsic factor [4]. Multiple studies show equivalence between high-dose oral and intramuscular B12 for maintaining serum levels. However, adherence may be better with monthly IM injections [4].
Does metformin cause B12 deficiency? ▼
Long-term metformin use reduces B12 absorption by 10–30%, likely by altering calcium-dependent ileal membrane uptake [7]. The ADA recommends periodic B12 monitoring in patients on metformin, particularly those with anemia or peripheral neuropathy. Supplementation is straightforward and effective [7].
4 Clinical evidence
Strong
Treatment and prevention of megaloblastic (pernicious) anemia [4]. Prevention and treatment of subacute combined degeneration of the spinal cord (posterior and lateral column demyelination) [3]. Reduction of elevated homocysteine and methylmalonic acid [2]. Essential supplementation for vegans — no plant-based food contains bioavailable B12 [2]. HIGH
Moderate
Cognitive function in deficient elderly: B12 supplementation improves cognitive scores in individuals with documented deficiency and elevated MMA [6]. Peripheral neuropathy improvement: early treatment of B12-deficient neuropathy can reverse symptoms if initiated before irreversible axonal damage [3]. Diabetic neuropathy: metformin-induced B12 depletion contributes to neuropathy; supplementation may improve symptoms [7]. MODERATE
Insufficient
Cancer prevention: no consistent evidence [2]. Cardiovascular disease prevention through homocysteine lowering: B12 + folate reduces homocysteine but major trials (HOPE-2, VITATOPS) showed mixed cardiovascular results [2]. Enhancement of energy or athletic performance in B12-replete individuals: no evidence of benefit [1]. LOW
5 Safety, toxicity & adverse events
Absolute contraindications
✕ Known hypersensitivity to cobalt or cobalamin (rare)
Relative
⚠ Leber's hereditary optic neuropathy — avoid the cyanocobalamin form (may accelerate vision loss); use hydroxocobalamin
⚠ Polycythemia vera — may further raise red-cell mass
⚠ Undiagnosed macrocytic anemia — do not self-treat without excluding concurrent folate deficiency
🚩 Red flags
● Gait ataxia + posterior column signs (vibration/position sense loss) — subacute combined degeneration. Treat urgently with B12 [3]
● Vegan infant with failure to thrive and developmental regression — check B12 status immediately [8]
● Megaloblastic anemia treated with folic acid alone showing neurological deterioration — B12 deficiency was masked [1]
● Metformin user with unexplained peripheral neuropathy — check serum B12 and MMA [7]
● Post-nitrous oxide exposure with acute paresthesias or confusion — acute B12 inactivation [3]
6 Interactions
Drug interactions
Metformin Major
Mechanism: Metformin alters calcium-dependent ileal membrane uptake of the IF-B12 complex, reducing absorption by 10–30%. [7]
Effect: Serum B12 decline over years; 5–30% develop biochemical deficiency. May contribute to neuropathy mistakenly attributed to diabetes. [7]
Action: Monitor serum B12 annually in all metformin users. Supplement if deficient. Calcium supplementation may partially reverse the effect [7].
Proton pump inhibitors (chronic >2 years) Moderate
Mechanism: PPIs suppress gastric acid, preventing acid-pepsin release of protein-bound B12 from food. Crystalline B12 (supplements) is not affected. [9]
Effect: Food-bound B12 malabsorption. Serum B12 declines over years of use. [9]
Action: Monitor B12 periodically in chronic PPI users, especially elderly. Crystalline B12 supplements bypass this interaction [9].
Nitrous oxide (N2O) Major
Mechanism: N2O irreversibly oxidizes the cobalt atom of B12, permanently inactivating methionine synthase. [3]
Effect: Acute precipitation of subacute combined degeneration in borderline-deficient patients. Can occur after a single prolonged exposure. [3]
Action: Check B12 status before elective surgery if risk factors present. Absolute contraindication to recreational N2O use in deficient patients [3].
Colchicine Moderate
Mechanism: Disrupts ileal mucosal cell function, impairing B12 absorption. [2]
Effect: Reduced B12 absorption with chronic use. [2]
Action: Monitor B12 levels during prolonged colchicine therapy [2].
Supplement synergies
Folate · 400–800 µg DFE/day
B12 is required to release active tetrahydrofolate from the 5-MTHF methyl trap. Without B12, folate cycle stalls. Co-supplementation ensures both pathways function [2].
B12 is required to release active tetrahydrofolate from the 5-MTHF methyl trap. Without B12, folate cycle stalls. Co-supplementation ensures both pathways function [2].
Iron · As per deficiency protocol
B12 deficiency causes megaloblastic ineffective erythropoiesis. Iron may be needed concurrently if iron-deficient or if recovering from pancytopenia [2].
B12 deficiency causes megaloblastic ineffective erythropoiesis. Iron may be needed concurrently if iron-deficient or if recovering from pancytopenia [2].
Vitamin D · 600–2,000 IU/day
Both deficiencies are common in elderly and vegan populations. Co-supplementation addresses the two most common nutrient gaps in these groups [2].
Both deficiencies are common in elderly and vegan populations. Co-supplementation addresses the two most common nutrient gaps in these groups [2].
7 Regulatory
United States (FDA): Classified as a dietary supplement. No mandatory fortification but voluntarily added to many products. Injectable B12 (cyanocobalamin, hydroxocobalamin) is prescription in some jurisdictions. No UL established (low toxicity) [1].
European Union (EFSA): Authorized health claims for energy metabolism, nervous system function, homocysteine metabolism, psychological function, red blood cell formation, immune function, and reduction of fatigue [10]. No UL established.
Japan (MHLW): Eligible for Foods with Function Claims. Recommended intake: 2.4 µg/day. Methylcobalamin widely available as OTC pharmaceutical for neuropathy.
South Korea (MFDS): Registered health functional food ingredient. Approved claims: energy metabolism and blood cell formation.
8 US supplement products
19
on-market products containing Cobalamin (NIH DSLD)
Brands carrying Cobalamin (1)
Click a brand to see its Cobalamin products.
9 Cite this page
Vancouver: Pkhakadze G. Cobalamin — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Aug 15]. Available from: https://supplement.ge/ingredients/cobalamin/
APA 7th: Pkhakadze, G. (2026). Cobalamin — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/cobalamin/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: February 2027
References: 10 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Cobalamin — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/cobalamin/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG