Abstract
ObjectiveTo investigate the causal relevance of current tobacco smoking for the risk of Parkinson disease (PD).MethodsWe compared the risks of death from PD with smoking habits in 30,000 male doctors in the British Doctors cohort study in 1951 and in survivors who had been resurveyed periodically for 5 decades. Cause-specific mortality was monitored for 65 years and included 283 deaths from PD. The relative risks (RRs) of PD (and 95% confidence intervals [CIs]) were estimated using Cox models for smoking habits (smoking status, amount smoked, and years since quitting) at baseline or updated habits at resurvey.ResultsThe prevalence of current smoking declined progressively during follow-up from 67% to 8% between 1951 and 1998. The crude rates of PD death were lower in current smokers than in never smokers at baseline (30 vs 46/100,000 persons-years). After adjustment for age at risk, current smokers at baseline had a 30% lower risk of PD (RR 0.71; 95% CI 0.60–0.84), and continuing smokers classified using updated smoking habits at resurvey had a 40% lower risk (RR 0.60; 95% CI 0.46–0.77) of PD compared with never smokers. The risks of PD were inversely associated with the amount of tobacco smoked. The protective effect of current smoking vs never smoking for PD was attenuated by increasing duration since quitting smoking.ConclusionsIn contrast to previous suggestions, the present report demonstrates a causally protective effect of current smoking on the risk of PD, which may provide insights into the etiology of PD.
Highlights
The crude rates of Parkinson disease (PD) death were lower in current smokers than in never smokers at baseline (30 vs 46/100,000 persons-years)
After adjustment for age at risk, current smokers at baseline had a 30% lower risk of PD (RR 0.71; 95% CI 0.60–0.84), and continuing smokers classified using updated smoking habits at resurvey had a 40% lower risk (RR 0.60; 95% CI 0.46–0.77) of PD compared with never smokers
The risks of almost all noncommunicable diseases were found to be higher in current smokers than in nonsmokers,[4,5,6] except for Parkinson disease (PD), which is reported to be inversely associated with smoking.[11,12]
Summary
We compared the risks of death from PD with smoking habits in 30,000 male doctors in the British Doctors cohort study in 1951 and in survivors who had been resurveyed periodically for 5 decades. The relative risks (RRs) of PD (and 95% confidence intervals [CIs]) were estimated using Cox models for smoking habits (smoking status, amount smoked, and years since quitting) at baseline or updated habits at resurvey. A Cox proportional hazards model assessed the effect of smoking habits at baseline in 1951 (hereafter, the “baseline model”). A Cox proportional hazards model assessed the effect of smoking habits updated periodically after each resurvey questionnaire (hereafter, the “updated model”). Updates in smoking habits took effect in the model only 10 years after they were reported to ensure that changes in habits were not caused by underlying disease. RRs were adjusted for age at risk (i.e., current age during follow-up) rather than age at baseline to account for the e2134 Neurology | Volume 94, Number 20 | May 19, 2020
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