Respiratory diseases linked to RA risk among nonsmokers

Patients with respiratory diseases risk developing seropositive or seronegative rheumatoid arthritis (RA), although this association is limited only to nonsmokers, a study has found.

Researchers used data from the Epidemiological Investigation of Rheumatoid Arthritis study and identified 1,631 incident RA patients (median age at enrolment, 57 years; 71 percent female) and 3,283 matched controls.

In the RA group, 1,088 of 1,573 patients (69 percent) were positive for anticitrullinated peptide antibody (ACPA) while 1,059 of 1,615 (66 percent) were positive for rheumatoid factor (RF). As expected, smoking was strongly associated with RA risk, especially ACPA-positive RA.

In multivariable logistic regression models, respiratory disease diagnoses were associated with an increased risk of RA. Specifically, acute upper respiratory disease conferred a 20-percent risk increase (adjusted odds ratio [aOR], 1.2, 95 percent confidence interval [CI], 0.8–1.7), chronic upper diseases a 40-percent increase (aOR, 1.4, 95 percent CI, 1.1–1.9), acute lower diseases a 140-percent increase (aOR, 2.4, 95 percent CI, 1.5–3.6), and chronic lower diseases a 60-percent increase (aOR, 1.6, 95 percent CI 1.2–2.3).

The associations were independent of RF or ACPA status, although somewhat stronger for RA patients positive vs negative for ACPA/RF. Furthermore, the risk increase associated with any respiratory disease and RA was more pronounced for nonsmokers (aOR, 2.1, 95 percent CI, 1.5–2.9) than smokers (aOR, 1.2, 95 percent CI, 0.9–1.5).

The findings raise the hypothesis that smoking and airway disease are associated with RA development through partly different mechanisms, which suggest that taking precautions to prevent respiratory diseases may be just as important as smoking cessation in individuals at risk of RA, according to the researchers. They pointed out that stratifying by smoking status may reveal additional risk factors and pathogenic mechanisms underlying RA, which would otherwise be masked.