Scientists from the University of South Australia have found a direct link between low vitamin D levels and an increased risk of dementia.
Vitamin D is essential for many aspects of health.
It helps the body absorb calcium, which is vital for strong bones, and works with calcium to prevent osteoporosis—a condition that weakens bones and increases fracture risk.
Beyond bone health, vitamin D supports muscle function, nerve signaling between the brain and body, and immune system activity. Higher vitamin D levels have also been suggested to support healthy brain function.
Only a few foods naturally contain vitamin D, and fortified foods provide most of the vitamin D in typical diets, especially in countries like the United States.
Dementia is a condition marked by severe decline in cognitive abilities, including thinking, memory, and reasoning, to the extent that daily activities become difficult. Many people with dementia also experience changes in emotional control and personality.
Stroke—also called cerebrovascular accident or transient ischemic attack—occurs when blood flow to the brain is interrupted, cutting off oxygen and nutrients. Without these, brain cells begin to die within minutes. Sudden bleeding in the brain can also cause stroke.
In this study, researchers examined the relationship between vitamin D levels and the risks of dementia and stroke. They analyzed data from adults aged 37–73, linking vitamin D levels with brain imaging findings as well as future diagnoses of dementia and stroke.
The team found that vitamin D deficiency was strongly associated with abnormal brain imaging results. More importantly, low vitamin D levels were linked to a higher risk of dementia, especially among individuals with 25-hydroxyvitamin D [25(OH)D] levels below 25 nmol/L.
People with vitamin D levels of 25 nmol/L had a 54% higher risk of dementia compared with those whose levels were 50 nmol/L. Further analysis suggested that raising vitamin D levels to 50 nmol/L could potentially prevent up to 17% of dementia cases.
However, the researchers did not find evidence that vitamin D levels were associated with stroke risk.
Based on these findings, the team concluded that vitamin D deficiency has a causal relationship with dementia risk but not with stroke. The results highlight the importance of maintaining adequate vitamin D levels for long-term brain health.
The study was conducted by Professor Elina Hyppönen and colleagues and published in The American Journal of Clinical Nutrition.
