Vitamin D levels in midlife tied to lower dementia risk marker

Having higher levels of vitamin D in the blood in middle age is associated with lower levels of tau protein in the brain, which is a sign of dementia, years later, according to a study published April 1, 2026, in Neurology^® Open Access, an official journal of the American Academy of Neurology. The study does not prove that vitamin D levels lower the level of tau and the risk of dementia; it only shows an association.

"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 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."

The study involved 793 people with an average age of 39 who did not have dementia. All of the participants had the level of vitamin D in their blood measured at the start of the study. They had brain scans an average of 16 years later that measured levels of tau and amyloid beta proteins in the brain, which are both biomarkers for Alzheimer's disease. A high level of vitamin D was defined as greater than 30 nanograms per milliliter (ng/mL) and a low level was less than that number.

A total of 34% of participants had low levels of vitamin D and 5% were taking vitamin D supplements.

The researchers took into account other factors that could affect tau levels, such as age, sex and symptoms of depression.

Higher vitamin D levels were associated with lower levels of the Alzheimer's biomarker tau protein years later.

There was no relationship between vitamin D levels and the amount of amyloid beta protein in the brain.

"These results are promising, as they suggest an association between higher Vitamin D levels in early middle-age and lower tau burden on average 16 years later," Mulligan said. "Mid-life is a time where risk factor modification can have a greater impact."

A limitation of the study is that the blood level of vitamin D was measured only once.

The study was supported by the National Institute on Aging, National Institute of Neurological Disorders and Stroke, Irish Research Council and Health Research Board of Ireland.