Smoking Cessation, Weight Change, and Risk of Parkinson's Disease: Analysis of National Cohort Data

Background and Purpose To determine whether the postcessation weight gain modifies the protective effect of smoking on the development of Parkinson's disease (PD). Methods This nationwide cohort study included 3,908,687 Korean males aged >= 40 years who underwent at least 2 health checkups biennially between 2009 and 2015. They were grouped into current smokers; quitters with body mass index (BMI) increase, maintenance, and decrease; and never smokers. The occurrence of incident PD was tracked, and Cox proportional-hazard models were used to adjust for potential confounding factors. We also analyzed the impact of weight change regardless of smoking status in the study population. Results There were 6,871 incident PD cases observed during the 13,059,208 person-years of follow-up. The overall risk of PD was significantly lower in quitters than in never smokers [hazard ratio (HR)=0.78, 95% confidence interval (CI)=0.70-0.86]. The risk of PD was still lower in quitters with BMI increase (HR=0.80, 95% CI=0.65-0.98) and in those with BMI maintenance (HR=0.77, 95% CI=0.68-0.87). This tendency was also observed in quitters with BMI decrease (HR=0.76, 95% CI=0.55-1.06), although it was not as robust as in the other two groups. With respect to weight change alone, BMI increase (HR=1.10, 95% CI=1.02-1.18) but not BMI decrease (HR=1.06, 95% CI=0.98-1.14) significantly increased the PD risk compared to BMI maintenance. Conclusions Postcessation weight gain in males did not offset the protective impact of smoking on PD development, although overall weight gain predicted an increased risk of PD.