Neurology September 25, 2012 vol. 79 no. 13 1397-1405
Cynthia Balion, PhD, balion at hhsc.ca ,Lauren E. Griffith, PhD, Lisa Strifler, BSc, Matthew Henderson, PhD, Christopher Patterson, MD, George Heckman, MD, David J. Llewellyn, PhD and Parminder Raina, PhD
From the Departments of Pathology and Molecular Medicine (C.B., M.H.), Clinical Epidemiology and Biostatistics (L.E.G., L.S., P.R.), and Medicine (C.P.), and R. Samuel McLaughlin Center on Gerontological Research and Education (P.R.), McMaster University, Hamilton; Department of Health Studies and Gerontology (G.H.), University of Waterloo, Schlegel-UW Research Institute for Aging, Kitchener, Canada; and Peninsula College of Medicine and Dentistry (D.J.L.), University of Exeter, Devon, UK.
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Six studies presented data comparing Alzheimer disease (AD) to controls but 2 utilized a method withdrawn from commercial use.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).
Conclusion: 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.
Study funding: Ontario Research Coalition of Research Institutes/Centres on Health & Aging, Ontario Ministry of Long-Term Care. Parminder Raina holds a Canada Research Chair in GeroScience and Raymond and Margaret Labarge Chair in Research and Knowledge Application for Optimal Aging.
Supplemental data at www.neurology.org
Received August 11, 2011, Accepted May 1, 2012, Copyright © 2012 by AAN Enterprises, Inc.
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