Supplements
vitamin B12 improves cognition
Leans against Supplements 💰 Industry COI noted🔬 Includes disconfirming
Part of: 🧪 Vitamin B12
RefutedContestedStrong support
consensus score -0.52
🧭 Read this score with how it was built in mindWe re-read the papers behind these claims and corrected how each one is counted
The claim had been encoded as being about fatigue while its studies and its title were about cognition. Re-encoded, the Cochrane review and a second large trial that found no cognitive benefit in people who are not deficient now count against it, as clean negative results should.
📅 Last reviewed: 2026-07-15 ⓘ
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: All trials, pooled (Meta-analysis)
MechanismIn-vitroAnimalObservationalRCTMeta-analysis
How the studies fall
2 support 2 contradict 0 tested null 0 mixed · 4 sources, 4 independent groups
What the evidence shows
In people who are not deficient, B12 supplementation has not been shown to improve cognition. Trials in replete older adults report no benefit on cognitive scores, and the pooled picture leans against an effect. What the evidence does support is correcting a documented deficiency — a different question from topping up someone who already has enough.
The evidence (8)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Kwok T, Wu Y, Lee J, Lee R, Yung CY, Choi G, Lee V, Harrison J, Lam L, Mok V 2020 · Clin Nutr | RCT | tested-null | moderate | DUPLICATE POPULATION: this trial (Kwok 2020, n=279) is pooled as ref 86 ('Cognitive, depression' outcomes) in the Markun 2021 meta-analysis (markun-2021), which already votes on this claim, so its patients would count twice. Own result: RCT, MCI with homocysteine ≥10 μmol/L, methylcobalamin 500 μg + folic acid 400 μg vs placebo for 24 months: 'At month 24, there was no significant group difference in CDR_SOB or any secondary outcomes (mean changes in CDR_SOB 0.36 versus 0.22 in supplement and placebo groups respectively)'; HDRS lower at month 12 (group difference P = 0.01) but not sustained at 24. Combination product (B12 + folate); no fatigue outcome measured - bears on cognition/depression only. [abstract-grade] |
| Miles LM, Allen E, Clarke R, Mills K, Uauy R, Dangour AD 2017 · Eur J Clin Nutr | observational | tested-null | moderate | OFF-SCOPE: secondary effect-modification analysis restricted to the OPEN trial's intervention arm (n=91), with outcomes 'eleven electrophysiological measures of sensory and motor components of peripheral and central nerve function' - nerve conduction, not fatigue (the claim's object) nor cognition or mood. Finding: 'no evidence that baseline (or change from baseline) vitamin B12 status modifies the effect of vitamin B12 supplementation on peripheral or central nerve conduction'. Within-arm regression, so no randomised comparison: observational design on any claim. The OPEN parent trial (Dangour 2015) is itself pooled in Markun 2021 (ref 72). [abstract-grade] |
| Markun S, Gravestock I, Jäger L, Rosemann T, Pichierri G, Burgstaller JM 2021 · Nutrients | meta-analysis | contradicts | moderate | SR/MA of 16 double-blind placebo-controlled RCTs (6276 participants) without overt B12 deficiency or advanced neurological disease ('Means or medians of baseline vitamin B12 serum levels ranged from 186 to 385 pmol/L'). Cognition: 12 studies (4 B12 alone, 8 B complex). Clean null on the claim's object: 'we found no evidence for an effect of B12 alone and B complex supplementation on any subdomain of cognitive function outcomes. Even upon separate analyses of B12 alone or the B complex, there was no evidence of an effect'. Pooled SMDs executive 0.06 (-0.021 to 0.141), memory 0.028 (-0.011 to 0.067), global 0.061 (-0.001 to 0.123), speed -0.081 (-0.175 to 0.013); B12-alone SMDs executive 0.09 (-0.09 to 0.28), memory 0.04 (-0.19 to 0.26), global 0.02 (-0.17 to 0.21), speed -0.10 (-0.23 to 0.04). Point estimates near zero with mixed signs across subdomains in a well-powered pool - a clean null, not an underpowered trend, so contradicts (CONVENTIONS §5). GRADE: cognition subdomains 'rated as moderate quality'; no funnel-plot asymmetry. Fatigue (the claim's former object) was not pooled - one trial only ('Regarding fatigue, the paucity of available high-quality evidence precludes robust conclusions at this time'). |
| Martínez-Noguera FJ, Alcaraz PE, González Blanc FJ, Huyghe TG, Marín-Pagán C 2026 · Preprints.org | RCT | supports | low | Preprint (Preprints.org 2026, not peer reviewed). 'A randomized, triple-blind, placebo-controlled crossover clinical trial was conducted in 18 amateur cyclists'; methylcobalamin 1 mg/day (branded MecobalActive, HTBA) vs placebo for 3 days. Cognitive endpoint is a light-based reaction test: 'Pre-exercise cognitive performance improved, with a shorter total reaction test time (−4.9%, p < 0.001) versus placebo' - a real effect favouring the claim, supports. Baseline B12 status is not reported in the abstract (plasma B12 'increased by 16.8%'), so the 'without documented deficiency' scope is plausible for trained cyclists but cannot-tell from available text. Quality low: n=18, 3-day exposure, single narrow psychomotor endpoint, preprint, commercial product named; funding/COI not seen. [abstract-grade, Europe PMC PPR1160092] |
| 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 2018 · Cochrane Database Syst Rev | meta-analysis | contradicts | moderate | Cochrane SR (28 RCTs, >83,000 participants, all vitamins and minerals, cognitively healthy adults >=40 y). The subset bearing on this claim: 'We included 14 studies with 27,882 participants which compared folic acid, vitamin B12, vitamin B6, or a combination of these to placebo' - B vitamins pooled, no B12-only estimate in the abstract (indirect: combination exposure). Result: B vitamins 'probably has little or no effect on global cognitive function at any time point up to 5 years (SMD values from -0.03 to 0.06) and may also have no effect at 5-10 years (SMD -0.01)'. Point estimates sit on zero - a clean null on a directional claim, so contradicts (CONVENTIONS §5). Certainty 'moderate or low' per the authors. 'The majority of participants were aged over 60 years and had a history of cardio- or cerebrovascular disease'; not selected for B12 deficiency. [abstract-grade] |
| Morais T, Couto G, Rocha R, Santana G 2026 · Arquivos de gastroenterologia | observational | contradicts | moderate | Integrative review of pharmacologic fatigue treatments in IBD (10 studies, n=2,935) found 'Vitamin B12 has not demonstrated efficacy in alleviating fatigue in IBD patients,' while thiamine, vedolizumab, upadacitinib, and modafinil showed so |
| Zhou L, Bai X, Huang J, Tan Y, Yang Q 2023 · Nutr Hosp | RCT | supports | low | Trial in 115 middle-aged/elderly patients with clinically diagnosed cognitive impairment, 'randomly assigned in equal proportions' to B12 (IM 7 days, then oral cobamamide + methylcobalamin; n=58) vs control (n=57; control regimen not stated in abstract), 6 months, MMSE/MoCA. Result on the claim's object points one way only: 'showed significant improvement, especially in attention, calculation (p < 0.01) and visual-constructional ability (p < 0.05), in their neuropsychological function compared to their matched group' - so supports, not mixed (§5: mixed is for findings pointing both ways on the object). The former 'positive only where deficiency present' reading is not in the abstract: participants' B12 status is not reported, so whether they meet the scope 'without documented deficiency' is cannot-tell from available text (indirect: cognitively impaired clinic population, not the general non-deficient population). Quality low: the abstract calls the design 'a prospective case-control study' while also describing random assignment, gives only selected subdomain p-values with no effect sizes or global-score result, and 115 of 307 enrolled were included without stated reason. [abstract-grade] |
| Yepes-Calderón M, Doorenbos CSE, Stegmann ME, Touw DJ, Harmsen HJM, Heiner-Fokkema MR, van Spronsen FJ, Corpeleijn E, Bakker SJL 2026 · Nutrients | observational | contradicts | moderate | Narrative review of B12 supplementation (0.02-1mg/day oral, 1-5mg/week IM, 4wk-7yr) in populations without proven deficiency; biochemical deficiency is uncommon (~2%) in high-income countries. Concludes supplementation 'has not shown consis |
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