Several studies discussed the relations between asthma and rheumatoid arthritis (RA) but the results were controversial. These studies were either questionnaire based or with small study populations. We aimed to examine the risk of asthma among RA patients in a nationwide population.
We conducted a cohort study using data from the National Health Insurance system of Taiwan. The RA cohort included 27 602 patients who were newly diagnosed and recruited between 1998 and 2008. Each patient was randomly frequency-matched with three people without RA on age group, sex and the year of index date from the general population. The occurrence of asthma was followed up until the end of 2010. The relative risks of asthma were estimated using Cox proportional hazard models after adjusting for age and comorbidities.
The overall incidence rate of asthma was 2.07-fold greater in the RA cohort than in the non-RA cohort (4.56 vs. 2.22 per 1000 person-years, 95% CI = 1.99-2.15). Stratified analyses by gender, age group and comorbidity revealed that the risk of asthma associated with RA was higher in females (adjusted hazard ratio (HR) = 2.18, 95% CI = 1.97-2.41), individuals younger than 40 years old (adjusted HR = 3.26, 95% CI = 2.09-5.11) and without comorbidity (adjusted HR = 2.17, 95% CI = 1.97-2.39).
Patients with RA had a significantly higher risk of developing asthma than healthy people in all sex and age subgroups. Stratified analyses indicated that there was a higher risk in women with RA than in men with RA when compared to their counterpart. Similarly, the HR of asthma associated with RA was higher in younger subjects, although the incidence rate increased with age.