title: Vitamin D, cognition, and dementia: a systematic review and meta-analysis.
abstract: OBJECTIVE
  To examine the association between cognitive function and dementia with vitamin D concentration in adults.
  
  
  METHODS
  Five databases were searched for English-language studies up to August 2010, and included all study designs with a comparative group. Cognitive function or impairment was defined by tests of global or domain-specific cognitive performance and dementia was diagnosed according to recognized criteria. A vitamin D measurement was required. Two authors independently extracted data and assessed study quality using predefined criteria. The Q statistic and I² methods were used to test for heterogeneity. We conducted meta-analyses using random effects models for the weighted mean difference (WMD) and Hedge's g.
  
  
  RESULTS
  Thirty-seven studies were included; 8 contained data allowing mean Mini-Mental State Examination (MMSE) scores to be compared between participants with vitamin D <50 nmol/L to those with values ≥50 nmol/L. There was significant heterogeneity among the studies that compared the WMD for MMSE but an overall positive effect for the higher vitamin D group (1.2, 95% confidence interval [CI] 0.5 to 1.9; I² = 0.65; p = 0.002). The small positive effect persisted despite several sensitivity analyses. Six studies presented data comparing Alzheimer disease (AD) to controls but 2 utilized a method withdrawn from commercial use. For the remaining 4 studies the AD group had a lower vitamin D concentration compared to the control group (WMD = -6.2 nmol/L, 95% CI -10.6 to -1.8) with no heterogeneity (I² < 0.01; p = 0.53).
  
  
  CONCLUSIONS
  These results suggest that lower vitamin D concentrations are associated with poorer cognitive function and a higher risk of AD. Further studies are required to determine the significance and potential public health benefit of this association.
authors.affiliation: Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Canada. balion@hhsc.ca
authors.forename: Cynthia
authors.initials: C
authors.lastname: Balion
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Griffith
authors.forename: Lisa
authors.initials: L
authors.lastname: Strifler
authors.forename: Matthew
authors.initials: M
authors.lastname: Henderson
authors.forename: Christopher
authors.initials: C
authors.lastname: Patterson
authors.forename: George
authors.initials: G
authors.lastname: Heckman
authors.forename: David J
authors.initials: DJ
authors.lastname: Llewellyn
authors.forename: Parminder
authors.initials: P
authors.lastname: Raina
mesh_terms: D003071:Cognition / Q000502:physiology*; D003072:Cognition Disorders / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology*; D003704:Dementia / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000379:methods / Q000639:trends; D014807:Vitamin D / Q000494:pharmacology*
chemical_list: D014807:Vitamin D