Higher vitamin D levels in middle-aged people linked to lower dementia biomarker

Scientists have found that middle-aged individuals with higher blood levels of vitamin D after many years exhibit lower levels of tau protein in the brain — a biomarker for dementia. However, they specify that this study does not directly prove a lower risk of dementia, but simply shows an association. 

“These results suggest 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,” says study author Martin David Mulligan from the University of Galway in Ireland.

“Of course, these results need to be further tested with additional studies.”

Vitamin D and dementia markers

The study authors highlight that low circulating vitamin D has been associated with an increased risk of cognitive impairment and clinical dementia.

However, they note previous studies evaluating the association between blood vitamin D and dementia and cognitive function typically have measured this association later in life (age range 58–73 years). Currently, there is a lack of studies looking at early midlife specifically.

“To the best of our knowledge, there have been no previous studies evaluating an association between serum vitamin D and neuroimaging markers of preclinical dementia,” the researchers highlight. Their study finds that tau protein often begins to accumulate in the brain decades before clinical symptoms of Alzheimer’s disease appear.

Low circulating vitamin D has historically been associated with an increased risk of cognitive impairment and clinical dementia.The paper published in Neurology Open Access specifically looked at 25-hydroxyvitamin D (calcidiol), which is the major circulating form of vitamin D in the blood, typically synthesized in the liver from sun exposure, food, or supplements.

The study involved 793 participants (53% women), with an average age of 39, who did not have dementia. Researchers measured their vitamin D blood levels once at the start of the trial.

Around 16 years later, participants completed brain scans that measured levels of tau protein. When evaluating these tests, researchers took into account other factors that could affect tau levels, including age, sex, body mass index, smoking status, and symptoms of depression.

Key findings and limitations

High circulating vitamin D levels were defined as greater than 30 ng/mL, and a low level was anything below that number. The study found a total of 34% of participants had low levels of serum vitamin D, and 5% were taking vitamin D supplements.

The authors found that higher serum vitamin D levels were associated with lower levels of tau protein around 16 years later, specifically in the entorhinal cortex and the inferior temporal gyrus — areas of the brain critical for memory and early-stage tau accumulation.

In the case of the amyloid beta protein, another biomarker for Alzheimer’s disease, serum vitamin D levels did not have any influence.

The results remained consistent even after the researchers adjusted for vascular risk factors like hypertension and diabetes. However, one major limitation of the study is that the blood level of vitamin D was measured only once.

“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,” says Mulligan. “Midlife is a time where risk factor modification can have a greater impact.”

Next to brain health, regular vitamin D supplementation has been linked to rebalancing gut immunity, preventing long COVID symptoms, and improving bone and muscle health.