B-Complex Vitamins (B1, B2, B3/Niacin, B5, B6, B7/Biotin, B9/Folate, B12) for Cognitive Function
Verdict: Counter-Evidence
Across 8 PubMed studies, the evidence for B-Complex Vitamins (B1, B2, B3/Niacin, B5, B6, B7/Biotin, B9/Folate, B12) in Cognitive Function grades Tier D — counter-evidence. High-quality evidence indicates it is not effective (or is harmful) for this use.
D 🔴 D Counter-Evidence Counter-Evidence
Why this grade7-layer evidence engine
⚖️
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditableRaw score 0.24
D
C
B
A
S
← counter-evidence / ineffectiveeffective / strong evidence →
Final grade
D · Counter-Evidence
Confidence
88%
Highly consistent evidence
Evidence level
E1
Cochrane high-quality SR/MA
▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.241
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (2 篇 > 1 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status
PubMed studies (8)L2 · primary research & systematic reviews
Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial (VITACOG, Smith)
Finding: Mean annual brain atrophy 0.76% with active B vitamins vs 1.08% with placebo (p=0.001); in the subgroup with baseline tHcy >13 micromol/L atrophy rate was 53% lower with active treatment (p=0.001).
View on PubMed Cognitive and clinical outcomes of homocysteine-lowering B-vitamin treatment in mild cognitive impairment: a randomized controlled trial (VITACOG, de Jager)
Finding: B vitamins stabilised executive function vs placebo (p=0.015); benefits on global cognition (p<0.001), episodic memory (p=0.001) and semantic memory (p=0.037) were confined to participants with baseline tHcy above the median (>11.3 micromol/L); CDR and IQCODE improved in the upper tHcy quartile (p=0.02 and p=0.01).
View on PubMed Results of 2-year vitamin B treatment on cognitive performance: secondary data from an RCT (B-PROOF, van der Zwaluw)
Finding: Plasma tHcy fell 5.0 vs 1.3 micromol/L (active vs placebo) but cognitive domain scores did not differ over 2 years; a marginal global-cognition signal (MMSE p=0.05) was attributed by the authors to chance.
View on PubMed The effect of vitamin B6 on cognition (Cochrane Review, Malouf & Grimley Evans)
Finding: Despite biochemical improvement in B6 status, neither pooled trial showed any statistically significant benefit of vitamin B6 alone on mood or cognition; no evidence of short-term benefit.
View on PubMed Effects of homocysteine lowering with B vitamins on cognitive aging: meta-analysis of 11 trials with cognitive data on 22,000 individuals (Clarke, B-Vitamin Treatment Trialists' Collaboration)
Finding: B-vitamin allocation lowered tHcy by ~25% but produced no significant effect on any individual cognitive domain, on global cognitive function, or on the rate of cognitive aging; a 25% tHcy reduction equated to only 0.02 years of cognitive aging per year of treatment, effectively excluding clinically meaningful slowing.
View on PubMed Effect of B vitamins and lowering homocysteine on cognitive impairment in patients with previous stroke or transient ischemic attack: prespecified secondary analysis (VITATOPS, Hankey)
Finding: tHcy lowered by B vitamins, but cognitive impairment incidence was identical (5.51% vs 5.47%; RR 1.01, p=0.976); no effect on cognitive decline (p=0.414) or combined outcome (p=0.855). An accompanying meta-analysis of trials enriched for stroke history was likewise null.
View on PubMed Vitamin B - Can it prevent cognitive decline? A systematic review and meta-analysis (Behrens)
Finding: No significant overall effect on cognitive function (SMD 0.02, 95% CI -0.034 to 0.08; Z=0.87, p=0.39); occasional positive secondary outcomes were attributed to methodological heterogeneity.
View on PubMed Efficacy of B Vitamin Supplementation on Global Cognitive Function in Older Adults: A Systematic Review and Meta-analysis
Finding: After excluding outliers and methodologically weak trials, GRADE high-certainty evidence indicates only a very small benefit of B6/B9/B12 supplementation on global cognition; clinically not meaningful and disappears in trim-and-fill sensitivity analyses.
View on PubMed Regulatory & authoritative positionsL4/L5 · FDA / EMA / NIH ODS / Cochrane / Mayo …
L4a US FDA
Supportive
As part of a well-balanced diet, rich in fresh fruits and vegetables, daily intake of at least 400 mcg folic acid, 3 mg vitamin B6 and 5 mcg vitamin B12 may reduce the risk of vascular disease. source↗
L4b EU EFSA
Supportive
a cause and effect relationship has been established between the dietary intake of niacin and contribution to normal energy-yielding metabolism source↗
L4c UK NHS
Cautious
Taking 200mg or more a day of vitamin B6 can lead to a loss of feeling in the arms and legs known as peripheral neuropathy. ... Do not take more than 10mg of vitamin B6 a day in supplements unless advised to by a doctor. source↗
L4d TW TFDA / 衛福部
Supportive
目前公告之保健功效項目為：胃腸功能改善、調節血脂、護肝、骨質保健、免疫調節、輔助調整過敏體質、不易形成體脂肪、調節血糖、輔助調節血壓、抗疲勞、延緩衰老、輔助調節血鐵、牙齒保健、膝關節保健 source↗
L4e WHO
Cautious
Vitamins B and E, PUFA and multi-complex supplementation should not be recommended to reduce the risk of cognitive decline and/or dementia. source↗
L5a NIH Office of Dietary Supplements
Cautious
B vitamins lower blood homocysteine concentrations, but several large clinical trials found that this reduction did not lower the risk of cardiovascular events. source↗
L5b Mayo Clinic
Against
Your diet is the best way to get the nutrients you need for your health source↗
L5c Cleveland Clinic
Against
Researchers have explored the link between cognition and vitamins B6, B9 and B12. But so far, there isn't evidence that B vitamins improve cognition or prevent dementia. source↗
L5d Harvard Health
Cautious
Although the research has shown that vitamin B12 supplementation reduces homocysteine blood levels, this has not translated into reduced rates of cognitive decline. A Cochrane review on folic acid supplements and cognition, with or without vitamin B12, did not find a significant effect of the supplements vs. placebo on cognitive function in healthy elderly people or people with dementia. source↗
L5e Specialty Society (condition-mapped)
Against
Not a single food, beverage, ingredient, vitamin or supplement has been proven to prevent, treat or cure Alzheimer's disease or to benefit cognitive function or brain health. source↗