Higher midlife vitamin D levels linked to lower Alzheimer's markers

Higher blood concentrations of vitamin D in midlife are associated with lower levels of tau protein in the brain - one of the hallmarks of Alzheimer's disease - years later. This is shown by a new study published on April 1, 2026, in "Neurology Open Access", a publication of the American Academy of Neurology. The discovery adds to the growing body of data suggesting that maintaining sufficient vitamin D may play a protective role against dementia.

New data from a 16-year follow-up

The study, led by Martin David Mulligan of the University of Galway, Ireland, included 793 people with an average age of 39, who did not have dementia at the beginning. At the start of the study, the participants' blood vitamin D levels were measured, and about 16 years later, they underwent a brain scan to assess tau and beta-amyloid accumulation.

The scientists found that higher vitamin D levels were associated with less tau protein deposits, but found no association with the amount of beta-amyloid. Low vitamin D, defined as below 30 nanograms per milliliter, was reported in 34% of the participants. According to Mulligan, the results suggest that vitamin D deficiency may be a factor that can potentially be influenced.

"These results show that a higher vitamin D level in midlife may provide protection against the formation of tau deposits in the brain and that low vitamin D could potentially be a modifiable risk factor that can be corrected and treated to reduce the risk of dementia," he said. At the same time, he warns that the study shows an association, but does not prove a causal link.

A step on previous key studies

The new work builds on a landmark study from 2014, published in "Neurology", which first quantified the link between vitamin D deficiency and dementia. In it, a team led by David Llewellyn of the Exeter Medical School followed 1,658 people over the age of 65 for an average of six years and found that in participants with moderate deficiency, the risk of dementia of any type was increased by 53%, while in severe deficiency the risk increased by 125%.

The risk increases sharply when vitamin D levels fall below 50 nanomoles per liter. A separate study from 2023, involving over 12,000 participants, shows that taking vitamin D as a supplement is associated with a 40% lower number of new dementia diagnoses within ten years. Together with the new data on tau protein, this forms a more complete picture of the potential role of vitamin D in brain health.

Why more evidence is needed before supplements are recommended

Despite consistent results from observational studies, scientists remain cautious and do not recommend vitamin D specifically for the prevention of dementia. Randomized controlled trials to date have yielded more mixed results. For example, a 2025 study showed that five years of vitamin D3 intake did not reduce the incidence of dementia in a population where most participants had sufficient baseline vitamin D levels.

Researchers emphasize that additional clinical trials are needed, focusing on groups with a clear vitamin D deficiency, to assess whether correcting low levels can actually slow or prevent cognitive decline. Until then, experts recommend that vitamin D be used primarily according to current guidelines - for maintaining bone health and general deficiency - and not as a standalone strategy to protect against Alzheimer's disease.