Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers.
<h4>Background</h4>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 dem...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Public Library of Science (PLoS)
2015-01-01
|
| Series: | PLoS ONE |
| Online Access: | https://doi.org/10.1371/journal.pone.0118333 |
| _version_ | 1819176028553084928 |
|---|---|
| author | Guochao Zhong Yi Wang Yong Zhang Jeff Jianfei Guo Yong Zhao |
| author_facet | Guochao Zhong Yi Wang Yong Zhang Jeff Jianfei Guo Yong Zhao |
| author_sort | Guochao Zhong |
| collection | DOAJ |
| description | <h4>Background</h4>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.<h4>Methods and findings</h4>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.<h4>Conclusions</h4>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. |
| first_indexed | 2024-12-22T21:04:15Z |
| format | Article |
| id | doaj.art-9b9069a731b64e7fa2115eba1682754c |
| institution | Directory Open Access Journal |
| issn | 1932-6203 |
| language | English |
| last_indexed | 2024-12-22T21:04:15Z |
| publishDate | 2015-01-01 |
| publisher | Public Library of Science (PLoS) |
| record_format | Article |
| series | PLoS ONE |
| spelling | doaj.art-9b9069a731b64e7fa2115eba1682754c2022-12-21T18:12:43ZengPublic Library of Science (PLoS)PLoS ONE1932-62032015-01-01103e011833310.1371/journal.pone.0118333Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers.Guochao ZhongYi WangYong ZhangJeff Jianfei GuoYong Zhao<h4>Background</h4>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.<h4>Methods and findings</h4>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.<h4>Conclusions</h4>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.https://doi.org/10.1371/journal.pone.0118333 |
| spellingShingle | Guochao Zhong Yi Wang Yong Zhang Jeff Jianfei Guo Yong Zhao Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers. PLoS ONE |
| title | Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers. |
| title_full | Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers. |
| title_fullStr | Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers. |
| title_full_unstemmed | Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers. |
| title_short | Smoking is associated with an increased risk of dementia: a meta-analysis of prospective cohort studies with investigation of potential effect modifiers. |
| title_sort | smoking is associated with an increased risk of dementia a meta analysis of prospective cohort studies with investigation of potential effect modifiers |
| url | https://doi.org/10.1371/journal.pone.0118333 |
| work_keys_str_mv | AT guochaozhong smokingisassociatedwithanincreasedriskofdementiaametaanalysisofprospectivecohortstudieswithinvestigationofpotentialeffectmodifiers AT yiwang smokingisassociatedwithanincreasedriskofdementiaametaanalysisofprospectivecohortstudieswithinvestigationofpotentialeffectmodifiers AT yongzhang smokingisassociatedwithanincreasedriskofdementiaametaanalysisofprospectivecohortstudieswithinvestigationofpotentialeffectmodifiers AT jeffjianfeiguo smokingisassociatedwithanincreasedriskofdementiaametaanalysisofprospectivecohortstudieswithinvestigationofpotentialeffectmodifiers AT yongzhao smokingisassociatedwithanincreasedriskofdementiaametaanalysisofprospectivecohortstudieswithinvestigationofpotentialeffectmodifiers |