by Rebecca Hiscott
Vitamin D deficiency has been linked to a number of neurologic conditions, including vascular dysfunction, ischemic stroke, and brain atrophy, and has also been presumed to increase the risk of cognitive decline. A new study has confirmed that hypothesis, demonstrating a link between vitamin D deficiency and increased risk of dementia in older adults.
“We expected to find an association between low vitamin D levels and the risk of dementia and Alzheimer’s disease, but the results were surprising – we actually found that the association was twice as strong as we anticipated,” study author David J. Llewellyn, PhD, senior research fellow in clinical epidemiology at the University of Exeter Medical School in the United Kingdom, said in a news release.
The study, published in the August 6 online issue of Neurology, followed 1,658 adults over the age of 65 for a mean of 5.6 years. All participants had taken part in the US population-based Cardiovascular Health Study (CHS) between 1992 and 1999, and were free from dementia, cardiovascular disease, and stroke at baseline. The researchers determined serum 25-hydroxyvitamin D (25(OH)D) concentrations by liquid chromatography-tandem mass spectrometry (LC-MS) from blood samples collected in 1992 and 1993.
During follow-up evaluations, participants were assessed by neurologists and psychiatrists for symptoms of dementia and Alzheimer’s disease according to criteria from the National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA). Evaluation methods included annual cognitive assessments, repeat MRI scans, medical records, questionnaires, and proxy interviews. During follow-up, 171 of the 1,658 participants developed dementia, including 102 cases of Alzheimer’s.
The authors found that participants who had low levels of vitamin D at baseline – defined as 25 to 50 nanomoles per liter (nmol/L) – had an increased risk of dementia of about 51 percent, when compared with participants who had sufficient (more than 50 nmol/L) levels of vitamin D at baseline. Those who were severely vitamin D deficient (less than 25 nmol/L) had an increased dementia risk of about 122 percent. The numbers were comparable for risk of developing Alzheimer’s disease.
The results remained the same after the authors controlled for possible mitigating factors such as education status, sex, body mass index, smoking, alcohol consumption, and significant depression symptoms, and after they performed additional adjustments for diabetes, hypertension, ethnicity, income, and occupation.
“Our results establish that low 25(OH)D concentrations are linked to an increased risk of incident all-cause dementia and AD, and they are consistent with studies suggesting a link with cognitive impairment and cognitive decline,” the authors wrote. Furthermore, the results “clarify that the threshold above which older adults are unlikely to benefit from supplementation with regard to dementia risk is likely to lie in the region of 50 nmol/L when 25(OH)D concentrations are measured using LC-MS,” they added.
In recent years, some doctors have advised older patients to consume supplements or foods rich in vitamin D because of its association with lower risks of rheumatoid arthritis, stroke, and diabetes, among other conditions. But Dr. Llewellyn cautioned that clinical trials are still needed to determine whether vitamin D-rich foods can be clinically proven to delay or prevent the onset of Alzheimer’s disease and dementia.
“We need to be cautious at this early stage and our latest results do not demonstrate that low vitamin D levels cause dementia,” he said. “That said, our findings are very encouraging, and even if a small number of people could benefit, this would have enormous public health implications given the devastating and costly nature of dementia.”
To learn more about the link between vitamin D and risk of dementia, browse our archives here: http://bit.ly/vitaminD-dementia.