A new study found that middle-aged individuals with higher vitamin D levels had a reduced accumulation of tau, a brain protein associated with an increased risk of dementia. Alzheimer’s disease, the primary cause of dementia, has tau protein as a biomarker. Vitamin D levels were associated with the development of tau but not with amyloid beta, another key biomarker of the condition. More research is needed before doctors may recommend regular vitamin D tests or supplementation for the prevention of dementia.
Alzheimer’s disease continues to challenge scientists and clinicians worldwide, with its complex biology and lack of definitive prevention strategies. Among the many factors under investigation, vitamin D, a nutrient long recognized for its role in bone health, has emerged as a surprising candidate in brain health research.
A recent study adds to this growing interest, suggesting that higher vitamin D levels in middle age may be linked to reduced accumulation of tau, a protein closely associated with an increased dementia risk.
While the findings do not yet translate into clear clinical recommendations, they offer an intriguing glimpse into how a simple, widely accessible nutrient might influence the processes underlying Alzheimer’s disease and open new directions for future research.
Neurology Open Access, an official journal of the American Academy of Neurology, published this research [1].
What is Vitamin D?
Vitamin D is a fat-soluble nutrient that functions more like a hormone than a typical vitamin, playing a crucial role in maintaining overall health.
It is best known for regulating calcium and phosphorus levels in the body, which are essential for building and maintaining strong bones. However, its influence extends far beyond skeletal health. It can also help to reduce inflammation, boost the immune system, and regulate glucose levels [2].
The body produces vitamin D naturally when the skin gets exposed to sunlight, specifically ultraviolet B (UVB) rays. It can also be obtained in smaller amounts through certain foods, including fatty fish, egg yolks, and fortified products or dietary supplements. The body converts vitamin D into its active form, which helps regulate a wide range of biological processes.
The Role of Vitamin D in the Brain.
In recent years, researchers have become increasingly interested in the role of vitamin D in the brain.
Research indicates that vitamin D plays a role in immune regulation and helps to modulate inflammatory responses, including those within the central nervous system [3]. It has also been shown to influence brain immune cells, such as microglia, and reduce neuroinflammation, a key factor in many neurodegenerative diseases [4].
Additionally, experimental studies indicate that vitamin D may help protect neurons by limiting inflammatory damage and supporting cellular signaling pathways in the brain [5].
These functions have led scientists to explore whether adequate vitamin D levels might influence the development of neurodegenerative conditions, including Alzheimer’s disease. Research on vitamin D highlights its potential significance for long-term brain health.
The Recent Research: What did the Researchers Measure?
The researchers examined 793 individuals without dementia for the study. At the beginning of the study, the average age of the participants was 39.
Researchers used blood tests to determine the participants’ vitamin D levels at the start of the study.
The research team categorized high vitamin D levels as more than 30 nanograms per milliliter (ng/mL). They classified a vitamin D level as low if it was below this threshold.
At this point, 5% of the individuals were taking a vitamin D supplement, and approximately 34% of them had low vitamin D levels.
After an average of 16 years, they performed brain scans to determine the levels of tau and amyloid beta proteins present in the participants’ brains. The accumulation of these two proteins in the brain is linked to the development of Alzheimer’s disease, the most prevalent form of dementia.
The researchers adjusted for factors that could influence tau levels, such as age, gender, and depression, and found that higher vitamin D levels were associated with lower tau protein levels. However, they found no correlation between vitamin D and amyloid-beta levels.
According to study author Martin David Mulligan, MB BCh BAO, of the University of Galway in Ireland, tau accumulation in some parts of the brain may happen before amyloid buildup. The study’s participants were relatively young when blood samples were collected; thus, a relationship between vitamin D and tau, rather than amyloid protein, may be more likely to be discovered in a younger population [6].
According to Mulligan, these findings are promising since they indicate a link between higher vitamin D levels in early middle age and a lower tau burden 16 years later. Midlife is a period when making changes to risk factors can have a greater impact [7].
What are the Limitations of the Study?
This study has several limitations. A major limitation is that the researchers only had one vitamin D evaluation at the start of the study. The participants’ vitamin D levels may have changed dramatically in the years before the brain scans.
The researchers assessed vitamin D levels at a specific time, making it impossible to predict how changes in vitamin D levels over time would influence future dementia risk.
Additionally, the researchers’ method of measuring vitamin D levels was somewhat limited, categorizing a participant’s levels as either high or low, with no intermediate levels.
Labeling values exceeding 30 ng/mL as high implied that someone with a level of 30 ng/mL would be classified as low. According to experts, values of 20 ng/mL and above are sufficient for general health [2].
The researchers selected a cutoff value above 20 ng/mL because it had been previously utilized in studies involving older individuals. On the other hand, very few individuals in the study’s sample had levels below 20 ng/mL.
Another limitation is that the participants were primarily white, suggesting that the findings may not be relevant to individuals from other races or ethnic groups.
Further Research is Required
Despite the limitations, senior study author Emer McGrath, MB, PhD, an associate professor of medicine at the University of Galway and a consultant neurologist at Galway University Hospital in Ireland, said that the study added to the evidence that vitamin D levels may be one potential risk factor for dementia that people can control.
According to McGrath, their findings suggest that low vitamin D levels during midlife may be a modifiable factor in reducing the risk of dementia later in life. However, the findings do not prove that vitamin D deficiency causes dementia. More research is needed before routine vitamin D tests may be recommended in the community.
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References
- Mulligan, M.D., Scott, M.R., Yang, Q., Wang, R., Ghosh, S., Johnson, K.A., Beiser, A.S., Seshadri, S. and McGrath, E.R., 2026. Association of Circulating Vitamin D in Midlife With Increased Tau-PET Burden in Dementia-Free Adults. Neurology open access, 2(2), p.e000057.
- Vitamin D. National Institute of Health Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/. Updated: 27th June, 2025. Accessed: 11th May, 2026.
- Briones, T.L. and Darwish, H., 2012. Vitamin D mitigates age-related cognitive decline through the modulation of pro-inflammatory state and decrease in amyloid burden. Journal of neuroinflammation, 9(1), p.244.
- Lee, P.W., Selhorst, A., Lampe, S.G., Liu, Y., Yang, Y. and Lovett-Racke, A.E., 2020. Neuron-specific vitamin D signaling attenuates microglia activation and CNS autoimmunity. Frontiers in neurology, 11, p.19.
- Huang, Y.N., Ho, Y.J., Lai, C.C., Chiu, C.T. and Wang, J.Y., 2015. 1, 25-Dihydroxyvitamin D3 attenuates endotoxin-induced production of inflammatory mediators by inhibiting MAPK activation in primary cortical neuron-glia cultures. Journal of neuroinflammation, 12(1), p.147.
- McIntosh, J. Is Vitamin D associated with lower levels of Alzheimer’s biomarkers? Medical News Today. https://www.medicalnewstoday.com/articles/is-vitamin-d-associated-with-lower-levels-of-alzheimers-biomarkers. Published Online: 7th April, 2026. Accessed: 12th May, 2026.
- American Academy of Neurology (AAN), Is Vitamin D Associated with Lower Levels of Alzheimer’s Biomarkers? News Wise. https://www.newswise.com/articles/is-vitamin-d-associated-with-lower-levels-of-alzheimer-s-biomarkers/. Published Online: 1st April, 2026. Accessed: 12th May, 2026.
- Rapaport, L. Study Links Higher Vitamin D Levels to Lower Dementia Risk. Everyday Health. https://www.everydayhealth.com/neurological-disorders/study-links-higher-vitamin-d-levels-to-lower-dementia-risk/. Published Online: 1st April, 2026. Accessed: 12th May, 2026.
- Nield, D. Common Vitamin May Reduce Buildup of Alzheimer’s Proteins, Study Finds. Science Alert. https://www.sciencealert.com/common-vitamin-may-reduce-buildup-of-alzheimers-proteins-study-finds. Published Online: 10th April, 2026. Accessed: 12th May, 2026.
