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Smoking Is Associated with an Increased Risk of Dementia: A Meta-Analysis of Prospective Cohort Studies with Investigation of Potential Effect Modifiers

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  • Guochao Zhong
  • Yi Wang
  • Yong Zhang
  • Jeff Jianfei Guo
  • Yong Zhao

Abstract

Background: Previous studies showed inconsistent results on the association of smoking with all-cause dementia and vascular dementia (VaD), and are limited by inclusion of a small number of studies and unexplained heterogeneity. Our review aimed to assess the risk of all-cause dementia, Alzheimer’s disease (AD) and VaD associated with smoking, and to identify potential effect modifiers. Methods and Findings: The PubMed, Embase, Cochrane Library and Psychinfo databases were searched to identify studies that provided risk estimates on smoking and incidence of dementia. A random-effects model was used to yield pooled results. Thirty-seven studies were included. Compared with never smokers, current smokers showed an increased risk of all-cause dementia (risk ratio (RR) 1.30, 95% confidence interval (CI) 1.18–1.45), AD (RR 1.40, 95% CI 1.13–1.73) and VaD (RR 1.38, 95% CI 1.15–1.66). For all-cause dementia, the risk increased by 34% for every 20 cigarettes per day (RR 1.34, 95% CI 1.25–1.43). Former smokers did not show an increased risk of all-cause dementia (RR 1.01, 95% CI 0.96–1.06), AD (RR 1.04, 95% CI 0.96–1.13) and VaD (RR 0.97, 95% CI 0.83–1.13). Subgroup analyses indicated that (1) the significantly increased risk of AD from current smoking was seen only in apolipoprotein E ε4 noncarriers; (2) current smokers aged 65 to 75 years at baseline showed increased risk of all-cause dementia and AD compared to those aged over 75 or under 65 years; and (3) sex, race, study location and diagnostic criteria difference in risk of dementia was not found. Conclusions: Smokers show an increased risk of dementia, and smoking cessation decreases the risk to that of never smokers. The increased risk of AD from smoking is more pronounced in apolipoprotein E ε4 noncarriers. Survival bias and competing risk reduce the risk of dementia from smoking at extreme age.

Suggested Citation

  • Guochao Zhong & Yi Wang & Yong Zhang & Jeff Jianfei Guo & Yong Zhao, 2015. "Smoking Is Associated with an Increased Risk of Dementia: A Meta-Analysis of Prospective Cohort Studies with Investigation of Potential Effect Modifiers," PLOS ONE, Public Library of Science, vol. 10(3), pages 1-23, March.
  • Handle: RePEc:plo:pone00:0118333
    DOI: 10.1371/journal.pone.0118333
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    1. Giorgia Adani & Tommaso Filippini & Caterina Garuti & Marcella Malavolti & Giulia Vinceti & Giovanna Zamboni & Manuela Tondelli & Chiara Galli & Manuela Costa & Marco Vinceti & Annalisa Chiari, 2020. "Environmental Risk Factors for Early-Onset Alzheimer’s Dementia and Frontotemporal Dementia: A Case-Control Study in Northern Italy," IJERPH, MDPI, vol. 17(21), pages 1-18, October.
    2. Pei-Hsuan Weng & Jen-Hau Chen & Jeng-Min Chiou & Yu-Kang Tu & Ta-Fu Chen & Ming-Jang Chiu & Sung-Chun Tang & Shin-Joe Yeh & Yen-Ching Chen, 2018. "The effect of lifestyle on late-life cognitive change under different socioeconomic status," PLOS ONE, Public Library of Science, vol. 13(6), pages 1-15, June.
    3. Chengbo Li & Chun Long & Mei Zhang & Luyu Zhang & Mengyao Liu & Meiqi Song & Yunfei Cheng & Gong Chen, 2022. "The Influence of Alcohol Consumption on Tobacco Use among Urban Older Adults: Evidence from Western China in 2017," Sustainability, MDPI, vol. 14(13), pages 1-14, June.

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