People with high vitamin D levels in midlife may have lower levels of tau protein in their brains years later, according to a study published on April 1, 2026. neurology open accessthe official journal of the American Academy of Neurology. Tau is a protein closely related to dementia.
The researchers note that while the study results show a link, they do not prove that vitamin D directly lowers tau levels or reduces the risk of dementia.
“These results suggest that high vitamin D levels in midlife may protect against the development of tau deposits in the brain, and that low vitamin D levels may be a risk factor that can be modified and treated to reduce the risk of dementia,” said study author Martin David Mulligan, MB BCh BAO, University of Galway, Ireland. “Of course, these results need to be further validated in additional studies.”
Long-term study tracks vitamin D and brain biomarkers
The study followed 793 adults with an average age of 39 who did not initially have dementia. Researchers measured each participant’s blood vitamin D levels at the start of the study.
After about 16 years, the participants underwent brain scans to assess their levels of tau and amyloid beta proteins. All of these proteins are considered biomarkers for Alzheimer’s disease. Vitamin D levels above 30 nanograms per milliliter (ng/mL) are classified as high, and levels below that threshold are considered low.
Overall, 34% of participants had low vitamin D levels, and only 5% reported taking vitamin D supplements.
Increased vitamin D is associated with decreased tau protein
Researchers found years later that elevated vitamin D levels were associated with lower levels of tau protein, after accounting for factors such as age, gender, and symptoms of depression.
However, vitamin D levels were not associated with the amount of amyloid beta protein in the brain.
“These results are encouraging because they suggest a link between increased vitamin D levels in early middle age and decreased tau load an average of 16 years later,” Professor Mulligan said. “Midlife is a time when risk factor modification may have a greater impact.”
Study limitations and need for further research
One of the limitations of this study is that vitamin D levels were not tracked over time and were measured only once.
Highlights:
- People who had higher vitamin D levels in midlife had lower levels of tau protein, a key marker associated with Alzheimer’s disease, later in life.
- Although this study shows an association, vitamin D has not been proven to directly reduce the risk of dementia.
- Researchers found no association between vitamin D levels and amyloid beta, another Alzheimer’s disease biomarker.
- Further research is needed to confirm these findings and better understand the role of vitamin D in brain health.
This research was supported by the National Institute of Aging, the National Institute of Neurological Disorders and Stroke, the Irish Research Council and the Irish Health Research Council.
