B-Complex Vitamins (B1, B2, B3/Niacin, B5, B6, B7/Biotin, B9/Folate, B12) for Fatigue
For people who are already getting enough B vitamins, a B-complex supplement has not been shown to relieve fatigue or boost energy. It reliably helps only when there is a documented or marginal deficiency, which should be confirmed by a doctor.
Why this grade7-layer evidence engine
The grade is weak (Tier C) because the evidence splits sharply by who is taking the supplement. Reviews by Tardy 2020 (PMID 31963141) and Kennedy 2016 (PMID 26828517) confirm B vitamins are essential cofactors in energy metabolism, so correcting a deficiency plausibly eases fatigue. But the highest-quality synthesis, Markun 2021 (PMID 33809274; 16 RCTs, n=6,276), found no cognitive or mood benefit in non-deficient people and could not even pool fatigue because just one trial measured it, leaving an evidence gap rather than proof of benefit.
The positive trials in healthy adults are thin and conflicted. Stough 2011 (PMID 21905094, n=60) and Kennedy 2010 (PMID 20454891, n=215) reported modest drops in subjective strain and mental tiredness, but both were industry-funded, measured self-reported feelings vulnerable to placebo effects, and never screened participants' baseline B-vitamin status, so any benefit may reflect an under-nourished subgroup rather than truly replete people.
Regulators and clinics reinforce this caution. EFSA's authorized claim covers only B vitamins' role in 'normal energy-yielding metabolism' at the population level, not a treatment for clinical fatigue. The UK NHS says a normal diet should supply enough, while Mayo Clinic states there is 'no proof' B12 boosts energy, and Harvard Health is blunter still: 'no evidence of benefit if people without a deficiency take extra B vitamins.' High-dose B6 also carries a real nerve-damage risk.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸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 = 0.424
- 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 + 1 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status