Vitamin D for Cognitive Function
For healthy or even mildly deficient older adults, taking vitamin D does not appear to prevent dementia or improve cognition; the large, recent trials came up empty. Low vitamin D is linked to higher dementia risk in observational data, but that link does not mean a supplement fixes it.
Why this grade7-layer evidence engine
The grade is held to Weak (C) mainly because the strongest evidence is negative. Two large 2025 randomized trials, the Finnish FIND trial (PMID 40243375, n=2,492 over ~5 years; HR 0.72-0.77, not significant) and the UK VitaMIND trial (PMID 40480279, n=620 over 24 months), found that vitamin D3 did not lower dementia incidence or improve cognition versus placebo. Notably, VitaMIND saw no benefit even in adults with mild-to-moderate deficiency, undercutting the popular 'it only helps if you're low' assumption.
The case for any link rests on observational meta-analyses: Zhang 2024 (PMID 38461506) tied vitamin D deficiency to ~1.42x higher dementia and ~1.57x Alzheimer's risk, and a 2025 dose-response pooling (PMC12457182) reported ~1.49x risk in the lowest versus highest group. These show correlation, not cause; reverse causality (early dementia reducing sun exposure and diet) is the consensus explanation. One older single-center AD trial (PMID 31296588, n=210) showed cognitive gains but has not been replicated.
Clinical and regulatory bodies echo this caution rather than endorsement. Mayo Clinic ('more study is needed'), Cleveland Clinic ('no evidence that they boost memory, cognition'), Harvard Health ('do not prove that taking extra vitamin D can prevent dementia'), and neurology groups all decline to recommend it for the brain, even while FDA, EFSA, and NHS back vitamin D as a basic nutrient. A contested Taiwan signal of possible harm from chronic high-dose use (PMID 35822270) was formally rebutted and is not treated as definitive. Bottom line: correct a real deficiency for other health reasons, but do not take vitamin D to protect memory.
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 = 0.448
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 無高階證據可裁決
- 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