Inflamed airways are hypothesized to contribute to rheumatoid arthritis (RA) pathogenesis due to RA-related autoantibody production, and smoking is the strongest environmental RA risk factor. However, the role of chronic airway diseases in RA development is unclear. We undertook this study to investigate whether asthma and chronic obstructive pulmonary disease (COPD) were each associated with RA.
We performed a prospective cohort study of 205,153 women in the Nurses' Health Study (NHS, 1988-2014) and NHSII (1991-2015). Exposures were self-reported physician-diagnosed asthma or COPD confirmed by validated supplemental questionnaires. The primary outcome was incident RA confirmed by medical record review by 2 rheumatologists. Covariates (including smoking pack-years/status) were assessed via biennial questionnaires. Multivariable hazard ratios (HRs) and 95% confidence intervals (CIs) for RA were estimated using Cox regression.
We identified 15,148 women with confirmed asthma, 3,573 women with confirmed COPD, and 1,060 incident RA cases during 4,384,471 person-years (median 24.0 years/participant) of follow-up in the NHS and NHSII. Asthma was associated with increased RA risk (HR 1.53 [95% CI 1.24-1.88]) compared to no asthma/COPD after adjustment for covariates, including smoking pack-years/status. Asthma remained associated with increased RA risk when analyzing only never-smokers (HR 1.53 [95% CI 1.14-2.05]). COPD was also associated with increased RA risk (HR 1.89 [95% CI 1.31-2.75]). The association of COPD with RA was most pronounced in the subgroup of ever-smokers age >55 years (HR 2.20 [95% CI 1.38-3.51]).
Asthma and COPD were each associated with increased risk of incident RA, independent of smoking status/intensity and other potential confounders. These results provide support for the hypothesis that chronic airway inflammation may be crucial in RA pathogenesis.