Maintaining healthy vitamin D levels during middle age may help protect the brain from changes linked to Alzheimer's disease later in life, according to a study published in Neurology Open Access. The findings suggest that vitamin D status in early adulthood could influence long-term brain health, although the study does not prove a cause-and-effect relationship.
Researchers from the University of Galway analyzed data from 793 participants in the US-based Framingham Heart Study, none of whom had dementia at the beginning of the research. The participants were about 39 years old when their blood vitamin D levels were measured.
Around 16 years later, approximately 430 participants underwent positron emission tomography (PET) brain scans to assess the accumulation of tau and amyloid beta proteins, two key biomarkers associated with Alzheimer's disease.
The researchers found that participants with higher vitamin D levels in midlife had lower levels of tau protein deposits in the brain during later-life scans. However, no significant association was observed between vitamin D levels and amyloid beta accumulation.
Tau proteins are known to form harmful tangles inside brain cells and are strongly linked to the progression of Alzheimer's disease. Lower tau accumulation may therefore indicate a reduced risk of future neurodegeneration.
Because the study was observational, the researchers emphasized that the findings show only an association and cannot confirm that vitamin D directly prevents Alzheimer's-related brain changes.
The team noted that previous studies mainly examined adults aged 70 years and older, whereas this research focused on younger, cognitively healthy adults, offering a greater opportunity to study preventive factors before disease develops.
The researchers believe future clinical trials are needed to determine whether long-term vitamin D supplementation during midlife can reduce tau accumulation or help prevent dementia. They suggest that earlier intervention may provide a better opportunity for protecting long-term brain health.
REFERENCE: Martin David Mulligan, Qiong Yang, et al.; Association of Circulating Vitamin D in Midlife With Increased Tau-PET Burden in Dementia-Free Adults; Neurology Open Access; 2026; https://doi.org/10.1212/WN9.0000000000000057
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