Parkinson's Disease Among Immigrant Groups and Swedish-Born Individuals: A Cohort Study of All Adults 50 Years of Age and Older in Sweden

Background: There is a lack of studies of Parkinson's disease (PD) in immigrants. Objective: To study the association between country of birth and incident PD in immigrants in Sweden versus Swedish-born individuals. Methods: Study population included all adults aged 50 years and older in Sweden (n = 2775736). PD was defined as having at least one registered diagnosis of PD in the National Patient Register. The incidence of PD in different first-generation immigrant groups versus Swedish-born individuals was assessed by Cox regression, expressed as hazard ratios (HRs) and 95% confidence intervals (CI). The models were stratified by sex and adjusted for age, geographical residence in Sweden, educational level, marital status, neighbourhood socioeconomic status and co-morbidity. Results: Totally 35833 individuals had an incident diagnosis of PD (20401 men and 15432 women). Incidence rates per 100,000 person-years were for all Swedish-born 95.9 and for all foreign-born 60.1; for all men 112.3 and for all women 73.4, with a male to female ratio of 1.53, with the highest incidence rates for the group 80-84 years of age. After adjusting for potential confounders, the overall relative risk of PD was lower in immigrant men (HR 0.78; 95% CI 0.74-0.82) and women (HR 0.92; 95% CI 0.87-0.98). Among immigrant subgroups, a higher risk of PD was found among women from Finland (HR 1.13; 95% CI 1.05-1.23). Conclusion: In general, the risk of PD was lower in first-generation immigrant men and women compared to Swedish-born. The only group with a higher risk of PD was women from Finland.