Quick Facts

• Vitamin D deficiency raises dementia risk by 19-25% across all types, according to UK Biobank study of 269,229 people
• Regular vitamin D supplementation cuts Alzheimer’s disease risk by 17% and vascular dementia by 14%
• Over half of study participants had vitamin D deficiency or insufficiency despite availability of supplements

A massive UK study tracking 269,229 adults for 14 years found vitamin D deficiency significantly increases dementia risk. The research, published in The American Journal of Clinical Nutrition, represents one of the largest investigations into vitamin D’s role in brain health.

Participants with vitamin D deficiency – blood levels below 30 nmol/L – faced a 19% to 25% higher risk of developing dementia compared to those with adequate levels. Those with vitamin D insufficiency (30-50 nmol/L) showed a 10% to 15% increased risk.

The study revealed stark vitamin D status among participants aged 55 to 69. Researchers found 18.3% had vitamin D deficiency and 34% had insufficiency. Only 5% reported regular vitamin D use and 19.8% took multivitamins.

Regular vitamin D supplementation showed protective effects. Users had a 17% lower risk of Alzheimer’s disease and 14% lower risk of vascular dementia compared to non-users.

Professor Zahinoor Ismail from the University of Calgary and University of Exeter explained the timing factor. “We found evidence to suggest that earlier supplementation might be particularly beneficial, before the onset of cognitive decline,” Ismail said.

A separate 2025 meta-analysis of 22 studies involving 53,122 participants reinforced these findings. People in the lowest vitamin D category had a 49% higher dementia risk than those in the highest category. Each 10 nmol/L increase in vitamin D linked to a 1.2% lower dementia risk.

Dr. William Grant, a vitamin D expert, emphasized optimal blood levels. “All the evidence shows that you need a blood level of vitamin D above 75 nmol/L to be healthy, and the same is proving true for the brain,” Grant said.

The mechanism involves brain protection. Vitamin D may reduce dementia risk by clearing amyloid that accumulates in the brain and reducing inflammation.

However, recent clinical trials show mixed results. The Finnish Vitamin D Trial found five-year supplementation did not affect dementia incidence in 2,492 participants who were largely vitamin D sufficient. The VitaMIND trial also showed no cognitive improvements in older adults with mild to moderate deficiency.

Dr. David Llewellyn cautioned about drawing definitive conclusions. “We need to be cautious at this early stage and our latest results do not demonstrate that low vitamin D levels cause dementia,” Llewellyn said.

The global dementia burden makes these findings significant. Dementia cases are projected to reach 78 million by 2030 and 139 million by 2050, with annual costs reaching $2 trillion by 2030.

Researchers emphasize that vitamin D supplementation is safe, inexpensive, and easy to implement at population levels. Well-designed randomized controlled trials are needed to confirm optimal vitamin D thresholds for cognitive protection.

Read more: This Vitamin Majorly Reduces Dementia Risk (Per Research On 69,643 People)