Scientists are increasingly studying the role of vitamin D in maintaining health, including its potential in preventing serious diseases. In particular, it is known that vitamin D deficiency in older adults is associated with a higher risk of cognitive impairment and dementia. However, it remained unclear whether having normal vitamin D levels in midlife could reduce the likelihood of developing Alzheimer’s disease later in life.
A partial answer comes from a study published in Neurology Open Access. The authors found that adequate vitamin D levels in midlife are associated with lower accumulation of tau protein — a key biomarker of Alzheimer’s — in later years.
Emer McGrath, lead author from the University of Galway (Ireland), highlights the importance of this approach: “Taking vitamin D in midlife may be an important factor for protecting future brain health.” A distinctive feature of the study is that it is among the first to focus on relatively young individuals (average age 39) — a period when risk factors can still be modified.
The research used data from the Framingham Heart Study (USA). Scientists examined a sample of 793 men and women with no signs of dementia. At the start of the study, all participants had their vitamin D levels measured via blood tests. Approximately 16 years later, about 430 of these individuals underwent positron emission tomography (PET) scans of the brain to assess the presence of tau protein and beta‑amyloid deposits — protein accumulations linked to Alzheimer’s disease.
The results showed no correlation with beta‑amyloid, but a clear pattern emerged for tau protein: participants who had higher vitamin D levels at baseline tended to have lower tau buildup years later. The authors describe this finding as the first of its kind.
It is important to note, however, that the study was observational: it shows an association but does not prove a causal relationship. It cannot be stated with certainty that vitamin D directly reduces tau protein formation.
As McGrath notes, further work — particularly clinical trials — is needed to confirm the effect. Previous experiments with vitamin D supplements did not show a significant impact on tau levels, but those studies involved people aged 70 and older who already reported memory problems. Researchers suggest that a preventive effect might be more pronounced in younger individuals — before any pathological changes appear.
According to the authors, taking additional vitamin D (possibly at higher doses and over a longer period) in middle‑aged people with intact cognitive function could influence the course of the disease. However, without formal clinical trials, it is premature to make such recommendations.
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