People with higher levels of vitamin D in midlife may have lower levels of tau protein in the brain years later, according to a study published April 1, 2026, in Neurology Open Access, an official journal of the American Academy of Neurology. Tau is a protein closely linked to dementia.
The researchers note that the findings show a relationship, not proof that vitamin D directly reduces tau levels or lowers the risk of dementia.
“These results suggests that higher vitamin D levels in midlife may offer protection against developing these tau deposits in the brain and that low vitamin D levels could potentially be a risk factor that could be modified and treated to reduce the risk of dementia,” said study author Martin David Mulligan, MB BCh BAO, of the University of Galway in Ireland. “Of course, these results need to be further tested with additional studies.”
Long-Term Study Tracks Vitamin D and Brain Biomarkers
The study followed 793 adults who were an average of 39 years old and free of dementia at the beginning. Researchers measured each participant’s blood vitamin D level at the start of the study.
About 16 years later, participants underwent brain scans to evaluate levels of tau and amyloid beta proteins, both of which are considered biomarkers of Alzheimer’s disease. A vitamin D level above 30 nanograms per milliliter (ng/mL) was classified as high, while levels below that threshold were considered low.
Overall, 34% of participants had low vitamin D levels, and only 5% reported taking vitamin D supplements.
Higher Vitamin D Linked to Lower Tau Protein
After accounting for factors such as age, sex and symptoms of depression, the researchers found that higher vitamin D levels were associated with lower levels of tau protein years later.
However, vitamin D levels were not linked to the amount of amyloid beta protein in the brain.
“These results are promising, as they suggest an association between higher Vitamin D levels in early middle-age and lower tau burden on average 16 years later,” Mulligan said. “Mid-life is a time where risk factor modification can have a greater impact.”
Study Limitations and Need for Further Research
One limitation of the study is that vitamin D levels were measured only once rather than tracked over time.
Highlights:
People with higher vitamin D levels in midlife had lower levels of tau protein later on, a key marker linked to Alzheimer’s disease The study shows a link, but it does not prove that vitamin D directly reduces dementia risk Researchers found no connection between vitamin D levels and amyloid beta, another Alzheimer’s biomarker Further research is needed to confirm these findings and better understand the role of vitamin D in brain health
The study was supported by the National Institute on Aging, National Institute of Neurological Disorders and Stroke, Irish Research Council and Health Research Board of Ireland.