Declining trends in the incidence of Parkinson's disease: A cohort study in Germany

BackgroundEpidemiologic evidence from different countries shows both increasing and decreasing incidence rates of Parkinson's disease over time without clear trends.ObjectiveWe aimed to investigate age-specific incidence rates of Parkinson's disease and possible explanations for the observed trends in Germany over a 10-year period.MethodsTwo different random samples of subjects aged ≥50 years included in 2004-2009 and 2014-2019, each consisting of 250,000 individuals, were drawn from Germany's largest health care insurance company followed up for new Parkinson's disease cases. We compared the age-specific incidence rates of Parkinson's disease for both cohorts and performed Cox regression models to calculate the hazard ratios (HR) of PD in the second period compared with the first period, adjusted for age, sex, and risk factors for Parkinson's disease.ResultsFor most age groups in men and in women, we found lower age-specific Parkinson's disease incidence rates in the second period. Cox regression analysis showed an overall 18% risk reduction in Parkinson's disease incidence (HR = 0.82, 95% confidence interval [0.76-0.89]). Mean age at diagnosis increased in men (+1.9 years) and women (+0.8 years). After adjustment for risk factors, the HR was 0.78 [0.72-0.85]. Sensitivity analysis considering the competing event of death showed an HR of 0.79 [0.73-0.86]), demonstrating the independence of time trends from changes in death rates.ConclusionsOur data show that the risk of Parkinson's disease has decreased over time and that this decrease is independent of factors such as changes in death rates, age structure, sex, and specific risk factors.