Vitamin D levels in Alzheimer's and Parkinson's diseases: A meta-analysis

Objective: Recent accumulating evidence shows that vitamin D deficiency is prevalent in individuals with AD and PD. The purpose of the present study is to perform a meta-analysis on the 25-hydroxyvitamin D (25(OH)D) status in this population of patients. Methods: We searched all articles in English published up to March 2012 concerning the 25(OH)D level in AD and PD patients. For AD, six studies covering 319 patients and 573 controls were included in the meta-analysis. For PD, five studies discussing 434 patients and 3451 controls were included. Results: It was found that AD patients had lower levels of 25(OH)D than healthy controls (summary standardized mean difference [SMD], -1.39; 95% confidence interval [CI], -2.79 to 0.01). Similar results were found for PD patients versus healthy controls (summary SMD, -1.33; 95% CI, -2.44 to -0.21). Conclusion: The results indicate that despite the similar mean age between patients and healthy controls in each identified study, both AD and PD patients have lower levels of 25(OH)D than controls. (c) 2013 Elsevier Inc. All rights reserved.