Risk of developing Parkinson's disease among patients with asthma: a nationwide longitudinal study

Background: A cross-sectional retrospective study suggested a link between allergic diseases and Parkinson's disease. However, the temporal association between asthma and Parkinson's disease remains unknown. Methods: From the Taiwan National Health Insurance Research Database, 10 455 patients who were diagnosed with asthma between 1998 and 2008 and aged >= 45 years and 41 820 age- and sex-matched controls were selected for our study and observed until the end of 2011. Those who developed Parkinson's disease during the follow-up period were identified. We also examined the asthma severity, as indicated by the frequency of admission (times per year) for asthma exacerbation, and the risk of subsequent Parkinson's disease. Results: Patients with asthma had an increased risk of developing Parkinson's disease (hazard ratio [HR]: 3.10, 95% confidence interval [CI]: 2.20-4.36) after we adjusted for demographic data, health system use, medical comorbidities, and medication use. Sensitivity tests yielded consistent findings after we excluded observations on the first year (HR: 2.90, 95% CI: 2.04-4.13) and first 3 years (HR: 2.46, 95% CI: 1.64-3.69). Patients with asthma who had more frequent admissions (times per year) during the follow-up period exhibited a greater risk of subsequent Parkinson's disease (>2: HR: 16.42, 95% CI: 5.88-45.91; 1-2: 12.69, 95% CI: 5.03-31.71; 0-1: HR: 2.92, 95% CI: 1.91-4.49). Conclusion: Patients with asthma had an elevated risk of developing Parkinson's disease later in life, and we observed a dose-dependent relationship between greater asthma severity and a higher risk of subsequent Parkinson's disease.