Supplements
vitamin B12 decreases fatigue
Part of: 🧪 Vitamin B12
📅 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: Human trials (RCT / n-of-1)
How the studies fall
What the evidence shows
Vitamin B12 supplementation improves fatigue / cognition / mood (object generalized; "fatigue" node as anchor) — in people who are NOT deficient.
The evidence (8)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Kwok T, et al. 2020 · Clin Nutr | RCT | tested-null | moderate | B-vitamins lowered homocysteine but gave no significant cognitive benefit overall. |
| Miles LM, Allen E, Clarke R, Mills K, Uauy R, Dangour AD 2017 · Eur J Clin Nutr | RCT | tested-null | moderate | Secondary analysis of the OPEN randomised trial: B12 supplementation did not improve neurologic function in older people with MARGINAL (non-deficient) B12 status; neither baseline B12 status nor 12-month change altered effectiveness. Reinforces that any benefit requires genuine deficiency rather than low-normal status. |
| Markun S, et al. 2021 · Nutrients | meta-analysis | tested-null | low | No effect of B12 (±folate) on any cognitive subdomain, depression, or fatigue in people WITHOUT deficiency/neuro disease. |
| Martínez-Noguera FJ et al 2026 · Preprints.org | RCT | supports | low | Randomized triple-blind placebo-controlled crossover trial, n=18 amateur cyclists (not selected for B12 deficiency), 3-day methylcobalamin 1mg/day. Pre-exercise cognitive reaction-test time improved -4.9% vs placebo (p<0.001); plasma B12 ro |
| Rutjes AW, Denton DA, Di Nisio M, et al. 2018 · Cochrane Database Syst Rev | meta-analysis | tested-null | high | Cochrane SR, 28 trials / >83,000 participants: 'We did not find evidence that any vitamin or mineral supplementation strategy for cognitively healthy adults in mid or late life has a meaningful effect on cognitive decline or dementia.' Authors note the evidence does not permit definitive conclusions - most trials were not designed for cognitive outcomes and used brief measures. |
| Morais T et al 2026 · study_type: observational | 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 Y, et al. 2023 · Nutr Hosp | RCT | mixed | moderate | B12 improved attention/calculation & visual-construction at 6 mo IN cognitive-impairment context (positive only where impairment/deficiency present). |
| Yepes-Calderón M et al 2026 · study_type: observational | 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 |
Disagree, or know a study we missed?
We grade by evidence, not opinions. The way to weigh in is to point us to a study we haven't cited (check the evidence table above first), or to flag a problem with one we have. Every submission is reviewed; if it holds up, the grade updates and shows in Science Changes Its Mind.
Opens a short form. You'll sign in with Google so submissions are tied to a real account — we don't display your identity, and we only accept a link we can verify (PubMed, DOI, ClinicalTrials.gov).
Educational only, not medical advice. Grades and scores reflect published evidence weighted by study design and quality; see the methodology.