Vitamin D & Alzheimer’s Risk: Does it Offer Protection?

Higher levels of vitamin D in middle age are associated with lower levels of the tau protein in the brain years later, a potential sign of dementia, according to a study published April 1, 2026, in Neurology® Open Access. However, the study does not prove that vitamin D *causes* lower tau levels or reduces dementia risk; it only demonstrates an association.

Researchers found the association while studying 793 individuals with an average age of 39 who did not have dementia at the study’s outset. Participants had their vitamin D levels measured at the beginning of the study and underwent brain scans an average of 16 years later to assess levels of tau and amyloid beta proteins – both biomarkers for Alzheimer’s disease.

Vitamin D and Tau Protein

The study defined high vitamin D levels as greater than 30 nanograms per milliliter (ng/mL), and low levels as less than that. Approximately 34% of participants had low vitamin D levels, and 5% were taking vitamin D supplements.

“These results suggest 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.

No Link to Amyloid Beta

Importantly, the study found no relationship between vitamin D levels and levels of amyloid beta, another biomarker associated with Alzheimer’s disease. This suggests that vitamin D’s potential protective effect, if any, may be specific to the development of tau tangles.

Existing Research on Vitamin D and Dementia

The potential link between vitamin D and dementia has been a subject of ongoing research. A meta-analysis published in 2014, as reported by the National Center for Biotechnology Information (NCBI), aimed to evaluate the association between vitamin D levels and dementia risk.

According to the NCBI, vitamin D deficiency has also been linked to vascular dysfunction and an increased risk of ischemic stroke, as well as brain atrophy. However, researchers have also noted the possibility of reverse causation – meaning that early, undiagnosed dementia could potentially *lead* to lower vitamin D levels, rather than the other way around.

A recent study, as reported by Verywell Health, suggests that vitamin D supplements may reduce the risk of dementia by 40%. This study was published in the journal Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring.

Another study, highlighted by the American Academy of Neurology (AAN), found an association between vitamin D levels and levels of Alzheimer’s biomarkers, but cautioned that it does not prove cause and effect. The AAN emphasized that the results need to be confirmed with further research.

Implications and Future Research

While the current study doesn’t establish a causal link, it adds to the growing body of evidence suggesting a potential role for vitamin D in brain health. The findings highlight the importance of maintaining adequate vitamin D levels, particularly during midlife, as a potentially modifiable risk factor for dementia.

Further research is needed to determine whether vitamin D supplementation can effectively prevent or delay the onset of dementia, and to identify the optimal levels of vitamin D for brain health. Researchers also need to investigate the mechanisms by which vitamin D might influence tau protein levels and protect against neurodegeneration.