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Effect of smoking on physical and cognitive capability in later life: a multicohort study using observational and genetic approaches

North, TL; Palmer, TM; Lewis, SJ; Cooper, R; Power, C; Pattie, A; Starr, JM; ... Day, IN; + view all (2015) Effect of smoking on physical and cognitive capability in later life: a multicohort study using observational and genetic approaches. BMJ Open , 5 (12) , Article e008393. 10.1136/bmjopen-2015-008393. Green open access

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Abstract

OBJECTIVES: The observed associations between smoking and functional measures at older ages are vulnerable to bias and confounding. Mendelian randomisation (MR) uses genotype as an instrumental variable to estimate unconfounded causal associations. We conducted a meta-analysis of the observational associations and implemented an MR approach using the smoking-related single nucleotide polymorphism rs16969968 to explore their causal nature. SETTING: 9 British cohorts belonging to the HALCyon collaboration. PARTICIPANTS: Individual participant data on N=26,692 individuals of European ancestry (N from earliest phase analysed per study) of mean ages 50-79 years were available for inclusion in observational meta-analyses of the primary outcomes. PRIMARY OUTCOMES: Physical capability, cognitive capability and cognitive decline. The smoking exposures were cigarettes per day, current versus ex-smoker, current versus never smoker and ever versus never smoker. RESULTS: In observational analyses current and ever smoking were generally associated with poorer physical and cognitive capability. For example, current smokers had a general fluid cognition score which was 0.17 z-score units (95% CI -0.221 to -0.124) lower than ex-smokers in cross-sectional analyses. Current smokers had a walk speed which was 0.25 z-score units lower than never smokers (95% CI -0.338 to -0.170). An MR instrumental variable approach for current versus ex-smoker and number of cigarettes smoked per day produced CIs which neither confirmed nor refuted the observational estimates. The number of genetic associations stratified by smoking status were consistent with type I error. CONCLUSIONS: Our observational analysis supports the hypothesis that smoking is detrimental to physical and cognitive capability. Further studies are needed for a suitably powered MR approach.

Type: Article
Title: Effect of smoking on physical and cognitive capability in later life: a multicohort study using observational and genetic approaches
Location: England
Open access status: An open access version is available from UCL Discovery
DOI: 10.1136/bmjopen-2015-008393
Publisher version: http://dx.doi.org/10.1136/bmjopen-2015-008393
Additional information: This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/
Keywords: EPIDEMIOLOGY, GENETICS, GERIATRIC MEDICINE
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > Institute of Cardiovascular Science
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > Institute of Epidemiology and Health
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > Institute of Epidemiology and Health > Epidemiology and Public Health
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health > ICH Pop, Policy and Practice Prog
URI: http://discovery.ucl.ac.uk/id/eprint/1478084
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