Omega-3 / Fish Oil for Cognitive Function
Omega-3 (fish oil) has only weak, inconsistent evidence for cognitive function: a few higher-dose meta-analyses hint at benefit in people without dementia, but the largest rigorous trial found no effect, and no major health authority endorses fish oil supplements for brain health or dementia prevention.
Why this grade7-layer evidence engine
This earns a weak (Tier C) grade because the evidence is genuinely split. The largest, highest-quality study—the double-blind VITAL trial of 4,218 older adults (PMID 35415212)—found no cognitive benefit from 1 g/day of marine omega-3 over 2–3 years. An Alzheimer's-specific meta-analysis (Spandidos br.2025.1940) likewise found no significant effect on ADAS-Cog scores (mean difference 1.37, P=0.05).
The positive signals are real but limited. A 2024 dose-response meta-analysis in people without dementia (PMID 38468309) saw a trend-level benefit for executive function at >500 mg/day, largest in those with adequate baseline DHA/EPA, and a 2025 dose-response meta-analysis (PMID 40836005) reported large gains (SMD ~0.87–1.08 per 2000 mg/day). However, these were heterogeneous and likely inflated by small positive studies. A 2023 review (PMID 36637075) captured the split: 7 of 15 trials showed benefit, 8 did not, with DHA helping mild cognitive impairment but not Alzheimer's.
Authorities reinforce caution. The FDA, EFSA and NHS endorse omega-3 only for cardiac function and general fish intake, not cognition; EFSA's DHA "normal brain function" claim is a maintenance nutrient claim, not a treatment for cognitive decline. Harvard Health states fish oil supplements "haven't shown the same effect" as eating fish, while the Alzheimer's Association, Mayo Clinic and Cleveland Clinic call the cognitive evidence insufficient and still under research.
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 = 0.433
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高階證據未達主導 (1 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