Title |
Effect of smoking on physical and cognitive capability in later life: a multicohort study using observational and genetic approaches
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Published in |
BMJ Open, December 2015
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DOI | 10.1136/bmjopen-2015-008393 |
Pubmed ID | |
Authors |
Teri-Louise North, Tom M Palmer, Sarah J Lewis, Rachel Cooper, Chris Power, Alison Pattie, John M Starr, Ian J Deary, Richard M Martin, Avan Aihie Sayer, Meena Kumari, Cyrus Cooper, Mika Kivimaki, Diana Kuh, Yoav Ben-Shlomo, Ian N M Day |
Abstract |
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. 9 British cohorts belonging to the HALCyon collaboration. 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. 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. 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. 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. |
X Demographics
Geographical breakdown
Country | Count | As % |
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United Kingdom | 2 | 33% |
United States | 1 | 17% |
Comoros | 1 | 17% |
Unknown | 2 | 33% |
Demographic breakdown
Type | Count | As % |
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Members of the public | 5 | 83% |
Scientists | 1 | 17% |
Mendeley readers
Geographical breakdown
Country | Count | As % |
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Finland | 1 | 1% |
Unknown | 78 | 99% |
Demographic breakdown
Readers by professional status | Count | As % |
---|---|---|
Researcher | 13 | 16% |
Student > Bachelor | 9 | 11% |
Student > Ph. D. Student | 8 | 10% |
Student > Master | 8 | 10% |
Student > Postgraduate | 5 | 6% |
Other | 18 | 23% |
Unknown | 18 | 23% |
Readers by discipline | Count | As % |
---|---|---|
Medicine and Dentistry | 22 | 28% |
Psychology | 9 | 11% |
Nursing and Health Professions | 5 | 6% |
Pharmacology, Toxicology and Pharmaceutical Science | 4 | 5% |
Biochemistry, Genetics and Molecular Biology | 2 | 3% |
Other | 9 | 11% |
Unknown | 28 | 35% |