Supplement

Vitamin B12

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.

2linked conditions

19linked studies

On this pageEvidence Availability Outcomes & conditions →

Evidence

What the research actually shows

We link to relevant studies and leave interpretation to you and your healthcare professional.

Evidence analytics

Where the evidence is concentrated

Number of audited published findings for Vitamin B12 by condition. Drill into a pair page for the full breakdown.

Putative uses

Where people report using it and what trials suggest

Strong evidenceDeficiency correction / pernicious anaemia
Strong evidencePrevention in vegans & high-risk meds users

Where the evidence is negative

Common claims the trials do not support

No energy, cognition, or weight-loss benefit when replete.
Stroke/CVD prevention trials null.
High-dose oral for pernicious anaemia works for many but some still need injections.

Essential vitamin; supplementation clearly benefits deficient people (vegans, older adults, metformin/PPI users) and is wasted otherwise.

Safety notes: Water-soluble and non-toxic at supplement doses. Masks folate deficiency at very high doses.

Evidence grades reflect study quality and consistency, not marketing claims.

19studies referenced

14journals

1973–2026publication range

01Effects of B vitamins and magnesium on fatigue, disease activity and quality of life in inflammatory bowel diseaseRamezani E, et al. · Scientific reports · 2026PMID 42010310 ↗02Electroacupuncture frequency for chemotherapy-induced neuropathy in breast cancer: a randomized controlled trialShen Q, et al. · The oncologist · 2025PMID 40828899 ↗03l-Carnitine and Alpha-Lipoic Acid Fail to Improve Anaerobic and Aerobic Performance in Trained Cyclists Despite a Reduction in Blood Lactate Concentrationde Rozas A, et al. · Nutrients · 2025PMID 40647331 ↗04Differences 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 ↗05Associations between Diet and Cognitive Function in Stroke Survivors: A Systematic Review and Meta-analysisAmanat S, et al. · Advances in nutrition (Bethesda, Md.) · 2025PMID 40355028 ↗06A Systematic Review of Symptoms of Pernicious AnemiaSeage CH, et al. · Food and nutrition bulletin · 2024PMID 38987871 ↗

Search PubMed ↗Find clinical trials ↗

What trials found, in numbers

Summaries of published trial results for this compound, grouped by condition. Numbers are reported exactly as the researchers published them — we never calculate or convert.

How to read this table

Benefit: What the trial saw happen: whether the measured outcome moved in the helpful direction in that one study (the tag on each row: “Benefit seen”, “No clear benefit” or “Unclear”). It is a study result — not advice, and not a promise it will work for you.
Evidence: How strong the research behind that result is. A meta-analysis pools many studies (strongest); a systematic review collates them; an RCT tests against a control (placebo); observational studies only watch — they can suggest, not prove.
Effect size: How large the measured change was, exactly as the researchers published it. “No number reported” means the abstract gave no effect size — we never invent one.

In short: benefit is what was observed; evidence is how much you should trust the observation. A “Benefit seen” tag on a weak study counts for far less than the same tag on a meta-analysis.

Cognitive Function (3 outcomes)

Outcome measured	What trials found	Effect size	People studied	Duration	Type of evidence	Study
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	no number reported	—	—	Meta-analysis · 2003	PMID 12918012
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	no number reported	115	six months	RCT · 2023	PMID 37334792

Outcomes & conditions

Why people look into Vitamin B12 — and what they report

Associated conditions and community-reported outcomes, wrapped together on one page. Aggregates appear only once enough reports arrive.

Outcomes & conditions →

Important: This page reflects observational, aggregate-only community reporting and independent published research. It is not medical advice, and it does not claim any compound treats, cures, or is effective for any condition. Always consult a qualified healthcare professional before starting, stopping, or changing any supplement or treatment.

Availability

Where to get Vitamin B12 (UK)

How this compound is sold in the UK, and where our readers typically find it.

Retailer search links — we may earn commission on purchases at no cost to you. Commission never affects our evidence ratings.

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