Also known as Methylcobalamin, Cyanocobalamin
Water-soluble vitamin required for red blood cell formation, myelin synthesis, and DNA production; deficiency, common in older adults and vegans, causes fatigue and neurological symptoms that supplementation corrects.
Be careful if: pregnant, breastfeeding
Ask first if you take: diabetes medicines, including insulin, other medicines
Suspect a side effect? Report it to the MHRA Yellow Card scheme ↗
We link to relevant studies and leave interpretation to you and your healthcare professional.
The large figures are what the studies reported for each thing they measured. Open a card for every result.
Colour keyReported a benefitNo clear benefitUnclearPossible harmAmber is for highlights, such as where the most research is. It never means a result was good.
No figure given: Attention and calculation (reported a benefit); Visual-spatial ability (reported a benefit).
Every resultWhat sources report about side effects, who should be careful, and medicines to ask about first.
| Applies to | What sources say | Sources |
|---|---|---|
| pregnant | No pregnancy-specific caution found in the sources checked: the NHS B-vitamins page lists no pregnancy warning for B12 and advises that supplement doses of 2 mg a day or less are unlikely to cause harm; the NIH ODS fact sheet states B12 has no tolerable upper intake level. | Vitamin B (incl. B12 section) - NHS vitamins and minerals (page last reviewed 2020-08-03)Vitamin B12 (NIH ODS fact sheet, Health Professional edition; retrieved via Internet Archive snapshot 2026-10-12) |
| breastfeeding | No breastfeeding-specific caution found in the sources checked (NHS B-vitamins page and NIH ODS fact sheet list none). | Vitamin B (incl. B12 section) - NHS vitamins and minerals (page last reviewed 2020-08-03)Vitamin B12 (NIH ODS fact sheet, Health Professional edition; retrieved via Internet Archive snapshot 2026-10-12) |
| Severity | Medicine | Sources |
|---|---|---|
| listed | diabetes medicines, including insulin — Metformin may affect vitamin B12 levels (NIH ODS); long-term users may need B12 status checks agreed with a clinician. | Vitamin B12 (NIH ODS fact sheet, Health Professional edition; retrieved via Internet Archive snapshot 2026-10-12) |
| listed | other medicines — Gastric acid inhibitors (e.g. proton pump inhibitors) may affect vitamin B12 levels (NIH ODS). | Vitamin B12 (NIH ODS fact sheet, Health Professional edition; retrieved via Internet Archive snapshot 2026-10-12) |
Audited published research for Vitamin B12 by condition. Drill into a pair page for the full breakdown.
What this means: Bars count reported findings, not treatment effectiveness or certainty.
One study may report several findings or appear in more than one pairing. Counts do not show the size of an effect. Comparable numerical estimates are not established for this summary.
| Compound and condition | Findings (count) | Studies (count) | Reported results (finding counts) | How sure? |
|---|---|---|---|---|
| Cognitive Function | 3 | 2 | Benefit: 2; no benefit: 1; harm: 0; unclear: 0; not recorded / unrecognised: 0 | Not formally graded |
Where people report using it and what trials suggest
Common claims the trials do not support
Essential vitamin; supplementation clearly benefits deficient people (vegans, older adults, metformin/PPI users) and is wasted otherwise.
Evidence grades reflect study quality and consistency, not marketing claims.
Ordered by strength of evidence, then result direction.
01Differences in Ferritin, Vitamin D, and Vitamin B12 Between Fibromyalgia Patients and Healthy Individuals: A Systematic Review and Meta-AnalysisIsmail O, et al. · Musculoskeletal care · 2025PMID 39832803 ↗02Associations between Diet and Cognitive Function in Stroke Survivors: A Systematic Review and Meta-analysisAmanat S, et al. · Advances in nutrition (Bethesda, Md.) · 2025PMID 40355028 ↗03A Systematic Review of Symptoms of Pernicious AnemiaSeage CH, et al. · Food and nutrition bulletin · 2024PMID 38987871 ↗04B vitamins and prevention of cognitive decline and incident dementia: a systematic review and meta-analysisWang Z, et al. · Nutrition reviews · 2022PMID 34432056 ↗05Vitamin Supplementation and Dementia: A Systematic ReviewGil Martínez V, et al. · Nutrients · 2022PMID 35268010 ↗06Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-RegressionMarkun S, et al. · Nutrients · 2021PMID 33809274 ↗Reported results grouped by condition. Values and units are preserved as recorded; missing information is not estimated.
How to read this table
Reported direction, numerical results and study design are separate. Certainty has not been formally graded in this table.
| What was measured | Reported findings | Result and units | Reported sample and duration | Study / source |
|---|---|---|---|---|
| Cognitive function in people with dementia and low serum B12 | Vitamin B12 supplementation showed no significant benefit for cognitive function compared with placebo in people with dementia and low B12.No clear benefit | Not reported Recorded unit: Not reported | Sample (as reported): Not reported Follow-up: Not reported | Meta-analysis · 2003 Study detailsVitamin B12 for cognition. Meta-Analysis |
| attention and calculation | Vitamin B12 improved attention and calculation vs control in 115 patients over six months (p < 0.01). (p < 0.01)Benefit seen | Not reported Recorded unit: Not reported | Sample (as reported): 115 Follow-up: six months | Randomised trial · 2023 Study detailsVitamin B12 supplementation improves cognitive function in middle aged and elderly patients with cognitive impairment. Randomized Controlled Trial |
| visual-constructional ability | Vitamin B12 improved visual-constructional ability vs control in 115 patients over six months (p < 0.05). (p < 0.05)Benefit seen | Not reported Recorded unit: Not reported | Sample (as reported): 115 Follow-up: six months | Randomised trial · 2023 Study detailsVitamin B12 supplementation improves cognitive function in middle aged and elderly patients with cognitive impairment. Randomized Controlled Trial |
Associated conditions and community-reported outcomes, wrapped together on one page. Aggregates appear only once enough reports arrive.
How this compound is sold in the UK, and where our readers typically find it.
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