Meta-Analysis of Memory and Executive Dysfunctions in Relation to Vitamin D

Background: Hypovitaminosis D is associated with global cognitive impairment in adults. It remains unclear which domain-specific cognitive functions are affected with hypovitaminosis D. Objective: To systematically review and quantitatively synthesize the association of serum 25-hydroxyvitamin D (25OHD) concentrations with episodic memory and executive functions in adults. Methods: A Medline and PsycINFO (R) libraries search was conducted on May 2012, with no limit of date, using the Medical Subject Headings (MeSH) terms Vitamin D OR Hydroxycholecalciferols combined with the MeSH terms Memory OR Memory Disorders OR Executive Function OR Attention OR Cognition OR Cognition disorders OR Dementia OR Alzheimer disease OR Neuropsychological Tests. Fixed-effects meta-analysis was performed from 12 eligible studies using an inverse-variance method. Results: Of the 285 selected studies, 14 observational studies (including 3 prospective cohort studies) and 3 interventional studies met the selection criteria. All were of good quality. The number of participants ranged from 44-5,692 community-dwellers (0-100% women). In the pooled analysis, although episodic memory disorders showed only modest association with lower 25OHD concentrations (summary effect size of the difference (ES) =-0.09 [95% CI:-0.16;-0.03]), associations of greater magnitude were found with executive dysfunctions (processing speed: mean difference of Trail Making Test (TMT)-A score = 4.0 [95% CI: 1.20;6.83]; mental shifting: mean difference of TMT-B score = 12.47 [95% CI: 6.78; 18.16]; information updating tests: ES =-0.31 [95% CI:-0.5;-0.09]). The pooled risk of incident decline of TMT-B score was OR = 1.25 [95% CI: 1.05; 1.48] in case of initial lower 25OHD concentrations. Vitamin D repletion resulted in improved executive functions (ES =-0.50 [95% CI:-0.69;-0.32] for before-and-after comparison), but exhibited no difference with control groups (ES = 0.14 [95% CI:-0.04; 0.32] for between-group comparison after intervention). Conclusion: Lower serum 25OHD concentrations predict executive dysfunctions, especially on mental shifting, information updating and processing speed. The association with episodic memory remains uncertain.