More Evidence: Vitamin D Protects Cognition

Study indicates that low vitamin D levels could double the risk of Alzheimer’s disease in older adults.

Vitamin D’s role in bone health is well known and scientifically established. Now, growing evidence indicates that low serum vitamin D concentrations increase risk for cognitive decline, dementia, and Alzheimer’s disease. New research findings indicate that older adults with low vitamin D levels may be at more than twice the risk of developing Alzheimer's disease compared with older adults who have adequate levels. This study—large, prospective, and population-based—was published online ahead of print in Neurology on August 6, 2014.

The researchers, an international team from the United Kingdom, France, and numerous American universities, identified 1658 elderly ambulatory adults who had no diagnosed dementia, cardiovascular disease, and stroke at baseline. All study subjects had participated in the US population-based Cardiovascular Health Study between 1992 and 1999. Subjects were followed for a mean of 5.6 years.

Among study subjects, 171 participants developed all-cause dementia with 102 of these cases identified as Alzheimer’s disease. Study subjects who were severely or moderately deficient in vitamin D were 1.53 to 2.25 more likely to develop dementia than subjects with normal vitamin D levels. These finding were confirmed using several analytic methods.

Risk of all-cause dementia and Alzheimer’s disease increased remarkably when vitamin D levels fell below 50 nmol/L. This specific finding is novel; previous studies have not been able to pinpoint the vitamin D level at which risk increases.

The authors discuss several hypotheses about vitamin D’s role in dementia, describing this vitamin’s preponderance throughout the brain and its probable role in stimulating macrophages that clear amyloid plaque. This mechanism may contribute to sustaining cognition.

This study and others like it suggest new roles for vitamin D beyond those already established in skeletal conditions. The study provides support for a link between vitamin D and cognitive decline and dementia, but it does not establish cause and effect. Regardless, when clinicians see patients who have low vitamin D levels, they should be concerned and stay vigilant for signs of dementia. Further studies are needed to determine if supplementation can help prevent cognitive decline.