Skip to content
Deals

Vitamin D and global cognition: grade C

Limited evidence. Direction: No effect.

C Limited

Educational guidance, not medical advice

Why this grade

Rubric condition met: Evidence is mixed: a preregistered meta-analysis of 24 RCTs (mean age 65.21) found a small pooled effect, while large RCTs in older adults were null on their primary outcome; older-only evidence caps at C; N is not available under the rubric because two independent null RCTs are not established, so C with direction none

A preregistered meta-analysis of 24 trials (7,557 participants, mean age 65.21) found a small effect on global cognition (Hedges' g = 0.128) but none on specific domains, with larger effects in vulnerable and vitamin D-deficient groups. Against this, 2,000 IU a day did not change the rate of change in a global composite score over 2 to 3 years in VITAL (prespecified primary outcome), had no effect on MoCA in DO-HEALTH (2,157 adults aged 70 or older; co-funded by DSM Nutritional Products, Roche, NESTEC, Pfizer and Streuli), and a 24-month trial in 620 adults aged 50 or older with mild to moderate deficiency and early cognitive impairment found no benefit on executive function. All large trials enrolled older adults, so the proposal is C with direction none (Limited, mixed). N under G5 was considered and not taken: DO-HEALTH was co-funded by industry, and the VITAL parent trial's study agents were donated by Pharmavite LLC [8], so two independent null RCTs are not established.

How we grade evidence

Studies this grade rests on

EffectMixedNo effectSize shows participants (n)2015202020252030Meta-analysisSystematic reviewRCTChen 2024, 2024: meta-analysis, n = 7,557, result not recordedKang 2021, 2021: RCT, n = 4,218, result not recordedThe Effect of Vitamin 2025, 2025: RCT, n = 2,492, result not recordedBischoff-Ferrari 2020, 2020: RCT, n = 2,157, result not recordedCorbett 2025, 2025: RCT, n = 620, result not recordedSchietzel 2019, 2019: RCT, n = 273, result not recordedImpact of vitamin D 2022, 2022: systematic review, n not recorded, result not recorded
each study this grade rests on, by publication year and design. Solid: effect versus the comparator; half-filled: mixed; hollow: no effect; dashed: result not recorded yet. Larger marks had more participants.
Show the numbers
StudyYearDesignParticipantsResult
Schietzel 20192019RCT273result not recorded
Bischoff-Ferrari 20202020RCT2157result not recorded
Kang 20212021RCT4218result not recorded
Impact of vitamin D 20222022systematic reviewnot recordedresult not recorded
Chen 20242024meta-analysis7557result not recorded
The Effect of Vitamin 20252025RCT2492result not recorded
Corbett 20252025RCT620result not recorded

Impact of vitamin D on cognitive functions in healthy individuals: A systematic review in randomized controlled clinical trials.

da Silva ABJ, Barros WMA, da Silva ML. Impact of vitamin D on cognitive functions in healthy individuals: A systematic review in randomized controlled clinical trials Front Psychol, 2022. PMID 36524160

Result not recorded
Design
Systematic review of RCTs (narrative, no pooled estimate; PROSPERO CRD42021262413)
Population
Healthy non-athlete adults
Funding
not stated in the PubMed or Crossref record; full text not read

The Effect of Vitamin D3 Supplementation on the Incidence of Diagnosed Dementia Among Healthy Older Adults-The Finnish Vitamin D Trial.

Lönnroos E, Ylilauri M, Lamberg-Allardt C. The Effect of Vitamin D3 Supplementation on the Incidence of Diagnosed Dementia Among Healthy Older Adults-The Finnish Vitamin D Trial J Gerontol A Biol Sci Med Sci, 2025. PMID 40243375

Result not recorded
Design
Placebo-controlled RCT with three arms, up to 5 years (Finnish Vitamin D Trial)
Sample
n = 2,492
Population
Generally healthy older adults free of diagnosed dementia (Finland), largely vitamin D-sufficient
Funding
Academy of Finland, University of Eastern Finland, Juho Vainio Foundation and other foundations (Crossref funders)

Impact of Vitamin D Supplementation on Cognition in Adults With Mild to Moderate Vitamin D Deficiency: Outcomes From the VitaMIND Randomized Controlled Trial.

Corbett A, Taylor R, Llewellyn D. Impact of Vitamin D Supplementation on Cognition in Adults With Mild to Moderate Vitamin D Deficiency: Outcomes From the VitaMIND Randomized Controlled Trial J Am Med Dir Assoc, 2025. PMID 40480279

Result not recorded
Design
Two-arm parallel placebo-controlled RCT, 24 months, remote
Sample
n = 620
Population
Adults aged 50+ with mild to moderate vitamin D deficiency and early cognitive impairment (UK)
Funding
National Institute for Health and Care Research, The Jon Moulton Charity Trust, Alzheimer's Research UK (Crossref funders)

Effect of 2000 IU compared with 800 IU vitamin D on cognitive performance among adults age 60 years and older: a randomized controlled trial.

Schietzel S, Fischer K, Brugger P. Effect of 2000 IU compared with 800 IU vitamin D on cognitive performance among adults age 60 years and older: a randomized controlled trial Am J Clin Nutr, 2019. PMID 31152541

Result not recorded
Design
Double-blind RCT, 2 years, 2000 IU vs 800 IU (secondary outcome analysis; no placebo arm)
Sample
n = 273
Population
Community-dwelling adults aged 60+ after knee replacement for osteoarthritis (Switzerland)
Funding
Swiss National Science Foundation, Velux Stiftung, University of Zurich (Crossref funders)

Effect of Vitamin D Supplementation, Omega-3 Fatty Acid Supplementation, or a Strength-Training Exercise Program on Clinical Outcomes in Older Adults: The DO-HEALTH Randomized Clinical Trial.

Bischoff-Ferrari HA, Vellas B, Rizzoli R. Effect of Vitamin D Supplementation, Omega-3 Fatty Acid Supplementation, or a Strength-Training Exercise Program on Clinical Outcomes in Older Adults: The DO-HEALTH Randomized Clinical Trial JAMA, 2020. PMID 33170239

Result not recorded
Design
Double-blind, placebo-controlled 2x2x2 factorial RCT, 3 years
Sample
n = 2,157
Population
Adults aged 70 or older without major health events in the prior 5 years (Europe)
Funding
Seventh Framework Program of the European Commission (grant agreement 278588), University of Zurich, DSM Nutritional Products, Roche, NESTEC, Pfizer and Streuli (full text, PMC7656284, read 2026-11-11); DSM Nutritional Products provided the capsule ingredients; funders had no role in design, analysis or reporting

Effect of vitamin D on cognitive decline: results from two ancillary studies of the VITAL randomized trial.

Kang JH, Vyas CM, Okereke OI. Effect of vitamin D on cognitive decline: results from two ancillary studies of the VITAL randomized trial Sci Rep, 2021. PMID 34853363

Result not recorded
Design
Two ancillary studies of a 2x2 factorial RCT (VITAL), pooled; prespecified primary outcome
Sample
n = 4,218
Population
Community-dwelling adults aged 60+ free of cardiovascular disease and cancer at entry (US)
Funding
US National Institutes of Health grants (PubMed GrantList; full text PMC8636504 acknowledgements); VITAL study agents donated by Pharmavite LLC (stated in the VITAL-DEP full text, S8 c-s8-fund; not stated in S2, whose authors declare no competing interests)

Effects of Vitamin D Supplementation on Cognitive Outcomes: A Systematic Review and Meta-Analysis.

Chen WY, Cheng YC, Chiu CC. Effects of Vitamin D Supplementation on Cognitive Outcomes: A Systematic Review and Meta-Analysis Neuropsychol Rev, 2024. PMID 37418225

Result not recorded
Design
Systematic review and meta-analysis of 24 RCTs (preregistered, PROSPERO CRD42021249908)
Sample
n = 7,557
Population
Adults, mean age 65.21 years, mixed healthy and vulnerable populations
Funding
Ministry of Science and Technology, Taiwan (MOST-110-2314-B-532-007)

Search and history

Search (): vitamin d[ti] AND (cognition[tiab] OR cognitive[tiab]) AND (meta-analysis[pt] OR systematic review[pt]) AND randomized[tiab]

  • Graded C (proposed): Proposed in the monograph draft
  • C to C (approved): Editor sign-off November 13, 2026: grade matches the editor-approved final page