Study Links Midlife Vitamin D to Lower Tau in Alzheimer's

Because blood vitamin D levels can be measured in midlife and linked to later brain imaging, researchers have explored their relationship over time, and a new study shows that higher midlife vitamin D levels are associated with lower tau accumulation years later. However, the findings are associative and do not establish that vitamin D reduces tau levels or lowers the risk of dementia.

The American Academy of Neurology (AAN) detailed a study published April 1, 2026, in Neurology Open Access, its official journal. The research examined whether blood vitamin D levels measured in early middle age are associated with later brain levels of tau and amyloid beta detected by brain scans. Investigators emphasized that the analysis shows association and does not establish cause and effect.

The study included 793 participants with an average age of 39 years who did not have dementia at baseline. All participants had blood vitamin D measured at study start and underwent brain scans an average of 16 years later to quantify tau and amyloid beta. A high vitamin D level was defined as greater than 30 ng/mL; low levels were below this threshold. Overall, 34% of participants had low vitamin D, and 5% reported taking vitamin D supplements. The analysis accounted for potential confounders including age, sex, and symptoms of depression.

Higher vitamin D levels were associated with lower levels of tau protein years later, while no relationship was observed between vitamin D and amyloid beta. The authors noted a key limitation: vitamin D was measured only once. The results require confirmation in additional studies. 

“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 Martin David Mulligan, MB BCh BAO, study author, University of Galway. “Of course, these results need to be further tested with additional studies.”