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Meta-Analysis
. 2017 Jan 9;12(1):e0169650.
doi: 10.1371/journal.pone.0169650. eCollection 2017.

Head Injury as a Risk Factor for Dementia and Alzheimer's Disease: A Systematic Review and Meta-Analysis of 32 Observational Studies

Yanjun Li  1 , Yongming Li  1 , Xiaotao Li  2 , Shuang Zhang  1 , Jincheng Zhao  1 , Xiaofeng Zhu  3 , Guozhong Tian  1
Affiliations
Meta-Analysis

Head Injury as a Risk Factor for Dementia and Alzheimer's Disease: A Systematic Review and Meta-Analysis of 32 Observational Studies

Yanjun Li et al. PLoS One. .

Abstract

Background: Head injury is reported to be associated with increased risks of dementia and Alzheimer's disease (AD) in many but not all the epidemiological studies. We conducted a systematic review and meta-analysis to estimate the relative effect of head injury on dementia and AD risks.

Methods: Relevant cohort and case-control studies published between Jan 1, 1990, and Mar 31, 2015 were searched in PubMed, Web of Science, Scopus, and ScienceDirect. We used the random-effect model in this meta-analysis to take into account heterogeneity among studies.

Results: Data from 32 studies, representing 2,013,197 individuals, 13,866 dementia events and 8,166 AD events, were included in the analysis. Overall, the pooled relative risk (RR) estimates showed that head injury significantly increased the risks of any dementia (RR = 1.63, 95% CI 1.34-1.99) and AD (RR = 1.51, 95% CI 1.26-1.80), with no evidence of publication bias. However, when considering the status of unconsciousness, head injury with loss of consciousness did not show significant association with dementia (RR = 0.92, 95% CI 0.67-1.27) and AD (RR = 1.49, 95% CI 0.91-2.43). Additionally, this positive association did not reach statistical significance in female participants.

Conclusions: The findings from this meta-analysis indicate that head injury is associated with increased risks of dementia and AD.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Flowchart for the selection of eligible studies.
Fig 2
Fig 2. Pooled relative risk for any dementia, comparing individuals with head injury to those without head injury.
Box sizes are in proportion to study weights. TBI = traumatic brain injury.
Fig 3
Fig 3. Pooled relative risk for Alzheimer’s disease, comparing individuals with head injury to those without head injury.
Box sizes are in proportion to study weights. TBI = traumatic brain injury.
Fig 4
Fig 4. Sensitivity analyses for estimated risks of any dementia (A) and Alzheimer’s disease (B).
TBI = traumatic brain injury. NINCDS-ADRDA = National Institute of Neurological and Communicative Diseases and Stroke-Alzheimer Disease and Related Disorders Association. DSM = Diagnostic and Statistical Manual of Mental Disorders.
Fig 5
Fig 5. Funnel plot to explore publication bias in the estimates of any dementia (A) and Alzheimer’s disease (B).
The vertical line is at the mean effect size.
See this image and copyright information in PMC

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