Vitamin B12 for Fatigue
Verdict: Published
Across 6 PubMed studies, the evidence for Vitamin B12 in Fatigue grades Tier C — weak evidence.
C 🟠 C Weak Evidence Published
Why this grade7-layer evidence engine
⚖️
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditableRaw score 0.48
D
C
B
A
S
← counter-evidence / ineffectiveeffective / strong evidence →
Final grade
C · Published
Confidence
86%
Highly consistent evidence
Evidence level
E2
Multiple high-quality MAs (≥2 independent, consistent)
▸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 = 0.477
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高階證據未達主導 (0 positive vs 1 negative)，由 raw_score 決定
- 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 (6)L2 · primary research & systematic reviews
Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression
Finding: Across 16 RCTs (n=6,276) B12 (alone or with folate/B6) showed no significant effect on any cognitive subdomain or on depressive symptoms, and fatigue could not be pooled because only 1 of 16 trials reported it (k=1, no meta-analytic estimate possible).
View on PubMed Surplus vitamin B12 use does not reduce fatigue in patients with Irritable Bowel Syndrome or inflammatory bowel disease: A randomized double-blind placebo-controlled trial
Finding: Oral cyanocobalamin 1000 ug/day for 8 weeks produced a CIS-fatigue change of -8.1 +/- 9.5 versus -8.3 +/- 10.6 for placebo (between-group difference non-significant, 95% CI -11.65 to 6.71); only the motivation subscale favored B12 (-2.2, 95% CI -4.4 to -0.04).
View on PubMed A functional evaluation of anti-fatigue and exercise performance improvement following vitamin B complex supplementation in healthy humans, a randomized double-blind trial
Finding: B-complex increased running time to exhaustion 1.26-fold versus placebo (p<0.05) and significantly lowered blood lactate and ammonia during and after exercise (p<0.05); however participants were healthy and not screened for deficiency, and endpoints are exercise-performance/biochemical surrogates rather than a validated clinical fatigue scale.
View on PubMed Oral vitamin B12 supplementation in pernicious anemia: a prospective cohort study
Finding: Oral cyanocobalamin 1000 ug/day corrected deficiency in 88.5% of patients by 1 month with significant rises in plasma B12 and falls in homocysteine and MMA (all P<0.0001); deficiency-related symptoms including fatigue improved alongside biochemical correction, but there was no placebo arm and fatigue was not separately quantified.
View on PubMed Clinical and Hematological Characteristics of Vitamin B12 Deficiency and Evaluation of the Therapeutic Response to Vitamin B12 Supplementation
Finding: In overtly deficient adults, fatigue was the most common baseline symptom (66.7%); 6 weeks of weekly IM cyanocobalamin 1000 ug reversed macrocytic anemia (Hb 9.7 to 12.6 g/dL; MCV 104.7 to 91.3 fL) and improved fatigue/neurologic symptoms, with Hb correlating with B12 level (r=0.75, p<0.001); single-arm pre/post, no placebo.
View on PubMed A Systematic Review of Symptoms of Pernicious Anemia
Finding: Across 103 documented PA cases, fatigue was the single most common symptom (55%), ahead of loss of limb sensation (32%), weight loss (27%) and sore tongue (23%), confirming fatigue as a core, prevalent manifestation of B12-deficiency states that resolves with repletion.
View on PubMed Regulatory & authoritative positionsL4/L5 · FDA / EMA / NIH ODS / Cochrane / Mayo …
L4a US FDA
Supportive
NUTRIENT SUPPLEMENT source↗
L4b EU EFSA
Supportive
a cause and effect relationship has been established source↗
L4c UK NHS
Supportive
Adults aged 19 to 64 need about 1.5 micrograms a day of vitamin B12. source↗
L4d TW TFDA / 衛福部
Supportive
維生素B12之足夠攝取量(AI)成人為每日2.4微克 source↗
L4e WHO
Supportive
Vitamin B12 or folate supplementation during pregnancy is not recommended as an intervention to improve maternal and infant health outcomes source↗
L5a NIH Office of Dietary Supplements
Supportive
Vitamin B12 supplementation appears to have no beneficial effect on performance in the absence of a nutritional deficit. source↗
L5c Cleveland Clinic
Cautious
Fatigue and weakness are common symptoms of vitamin B12 deficiency source↗