Vitamin D deficiency is associated with increased risk of Alzheimer's disease and dementia: evidence from meta-analysis

In recent years, the associations between vitamin D status and Alzheimer's disease (AD) and dementia have gained increasing interests. The present meta-analysis was designed to estimate the association between vitamin D deficiency and risk of developing AD and dementia. A literature search conducted until February 2015 identified 10 study populations, which were included in the meta-analysis. Pooled risk ratios (RRs) and 95% confidence interval (CI) were calculated with a random-effect model using Stata software package. Results of our meta-analysis showed that subjects with deficient vitamin D status (25(OH)D level < 50 nmol/L) were at increased risk of developing AD by 21% compared with those possessing 25(OH)D level > 50 nmol/L. Similar analysis also found a significantly increased dementia risk in vitamin D deficient subjects. There is no evidence for significant heterogeneity among the included studies. Available data indicates that lower vitamin D status may be associated with increased risk of developing AD and dementia. More studies are needed to further confirm the associations and to evaluate the beneficial effects of vitamin D supplementation in preventing AD and dementia.