Vitamin D supplement use was associated with accelerated decline in global cognitive function and executive function over 6 years among older US adults, with the effect confined to those with normal baseline serum 25(OH)D levels.
Key Findings
Results
Vitamin D supplement users experienced accelerated decline in global cognitive function compared to non-users over 6 years of follow-up.
Difference in the rate of change: -0.052 points/year (95% CI -0.092 to -0.013, p=0.010)
Analysis used linear mixed model adjusted for multiple covariates
Follow-up spanned HRS waves 12–15 (6 years)
Total sample: 5065 participants, of whom 2004 (39.6%) were vitamin D supplement users
Results
Vitamin D supplement users experienced accelerated decline in executive function scores compared to non-users.
Difference in the rate of change: -0.021 points/year (95% CI -0.037 to -0.005, p=0.010)
This finding was observed alongside the global cognitive function decline
Results were estimated by linear mixed model adjusted for multiple covariates
Results
The accelerated cognitive decline associated with vitamin D supplementation was only observed among users with normal baseline serum 25(OH)D levels, not among those with insufficient or deficient levels.
Accelerated cognitive decline was statistically significant in users with normal baseline serum 25(OH)D (p=0.004)
No statistically significant association was found in users with insufficient/deficient baseline serum 25(OH)D levels (p=0.826)
This finding emerged from sensitivity analyses stratified by baseline vitamin D status
Methods
The study population was drawn from the Health and Retirement Study (HRS) wave 12 and was predominantly female and White.
Total of 5065 participants included with complete data on dietary supplement use and cognitive assessment
Mean age: 67.5 ± 10.2 years
61.6% female, 76.6% White ethnicity
2004 participants (39.6%) were vitamin D supplement users
Conclusions
The authors concluded that their findings do not support vitamin D supplementation as a means of preventing or slowing cognitive decline in older people with adequate vitamin D status.
The authors recommend that healthcare providers encourage adequate vitamin D intake from dietary sources and moderate sun exposure rather than supplements
Caution was advised when recommending vitamin D supplements to older adults without a clear indication
The paper characterizes existing real-world evidence on vitamin D supplementation and cognitive outcomes as 'scant and controversial'
Hua R, Lam C, Mok V, Cheung Y. (2026). Association between vitamin D supplement use and cognitive functioning: a longitudinal cohort study.. BMJ open. https://doi.org/10.1136/bmjopen-2025-106050