Summary: New genetic and observational research links low vitamin D levels to smaller brain volumes and a higher risk of dementia and stroke. The study suggests that raising vitamin D to normal levels (around 50 nmol/L) could potentially prevent a meaningful proportion of dementia cases in some populations—up to about 17%.
Source: University of South Australia
Dementia is a leading cause of disability and dependency in older adults worldwide, producing progressive declines in memory, thinking and behavior. New research raises the possibility that correcting severe vitamin D deficiency could reduce the number of people who develop dementia.
A world-first study led by the University of South Australia used genetic methods alongside observational data to investigate the relationship between vitamin D status, brain structure on imaging, and the risk of dementia and stroke.
Key findings include:
- Low vitamin D levels are associated with smaller overall brain volume and reductions in gray and white matter.
- Very low vitamin D concentrations show a stronger association with increased dementia and stroke risk.
- Genetic (Mendelian randomization) analyses support a causal link between severe vitamin D deficiency and dementia, and modelling indicates that raising levels to 50 nmol/L could prevent up to about 17% of dementia cases in some populations.
Dementia is a chronic, progressive syndrome that impairs cognitive function and daily living. In Australia roughly 487,500 people live with dementia, where it ranks as the nation’s second leading cause of death. Globally, more than 55 million people are estimated to be living with dementia, with around 10 million new cases each year.
Funded by the National Health and Medical Research Council, the study analysed data from the UK Biobank to examine how low serum 25-hydroxyvitamin D concentrations relate to neuroimaging measures and incident dementia and stroke. The research combined large-scale observational analyses with nonlinear Mendelian randomization (MR), a genetic approach that helps test whether an observed association is likely to be causal.
Senior investigator and Director of UniSA’s Australian Centre for Precision Health, Professor Elina Hyppönen, emphasises the potential public health importance of the findings.
“Vitamin D acts as a hormone precursor and is increasingly recognised for wide-ranging effects, including on brain health,” Prof Hyppönen says. “Our study is the first to use robust genetic analyses in a large population to assess the effects of very low vitamin D levels on dementia risk. Where deficiency is common, preventing severe deficiency could have meaningful benefits for population brain health.”
The research examined tens of thousands of adults. Observational analyses adjusted for age, sex, ethnicity, season, socioeconomic and lifestyle factors, sun exposure behaviors, and health conditions. Nonlinear MR was applied to test for a causal effect of vitamin D on neuroimaging measures, dementia and stroke.
Observational results showed nonlinear relationships: both very low and very high vitamin D concentrations were linked to differences in total, gray matter, white matter and hippocampal volumes. Lower vitamin D was also associated with greater white matter hyperintensity volume, a marker of small vessel disease. The strongest risks for dementia and stroke were observed in people with 25(OH)D levels below 25 nmol/L, compared to those in the 50–75.9 nmol/L range.
Mendelian randomization analyses supported a threshold effect for dementia risk: participants with genetically predicted 25(OH)D around 25 nmol/L had a substantially higher dementia risk compared with those at 50 nmol/L, consistent with a causal role of severe deficiency in dementia development. MR did not show a causal effect of vitamin D on neuroimaging outcomes or stroke risk in the same analyses. Using potential impact modelling, the authors estimated that raising 25(OH)D to 50 nmol/L could prevent roughly 17% of dementia cases in populations where deficiency is relatively common.
Prof Hyppönen notes the practical implications: “Most people will maintain adequate vitamin D through sun exposure and diet, but some individuals—for example those with limited sun exposure or with dietary restrictions—may require supplementation to reach safe, normal levels. If severe deficiency can be prevented, it could change outcomes for thousands of people.”
About this vitamin D and dementia research news
Author: Annabel Mansfield
Source: University of South Australia
Contact: Annabel Mansfield, University of South Australia
Image: The image is in the public domain
Original Research: Open access. “Vitamin D and brain health: an observational and Mendelian randomization study” by Elina Hyppönen et al., American Journal of Clinical Nutrition.
Abstract
Vitamin D and brain health: an observational and Mendelian randomization study
Background
Higher vitamin D status has been proposed to benefit brain health.
Objectives
To assess associations between serum 25-hydroxyvitamin D [25(OH)D], neuroimaging features, and the risk of dementia and stroke.
Methods
Prospective data from the UK Biobank (participants aged 37–73 at baseline) were used to analyse associations of 25(OH)D with neuroimaging outcomes (N = 33,523) and with incident dementia and stroke (N = 427,690; 3,414 and 5,339 incident cases, respectively). Observational models adjusted for a broad set of demographic, socioeconomic, lifestyle, sun behavior and health-related covariates. Nonlinear Mendelian randomization analyses were applied to test for causal effects on neuroimaging measures (N = 23,901) and on dementia and stroke (N = 294,514; 2,399 and 3,760 cases, respectively).
Results
Associations between 25(OH)D and brain volumes were nonlinear, with lower volumes observed at both low and high concentrations. Lower 25(OH)D was linked to higher white matter hyperintensity volume. Vitamin D deficiency (<25 nmol/L) was associated with increased risks of dementia and stroke versus 50–75.9 nmol/L (adjusted HR for dementia 1.79; for stroke 1.40). Nonlinear MR confirmed a threshold effect on dementia risk—participants at 25 nmol/L had an estimated 54% higher dementia risk compared with those at 50 nmol/L. MR did not find evidence for causal effects on neuroimaging measures or stroke. Potential impact modelling suggested that raising 25(OH)D to 50 nmol/L could prevent approximately 17% of dementia cases in some settings.
Conclusions
Low vitamin D status is associated with altered brain imaging markers and higher risks of dementia and stroke after extensive adjustment. Genetic analyses support a causal role of severe vitamin D deficiency in dementia, highlighting the potential value of preventing deficiency as part of dementia risk reduction strategies.