Rheumatoid arthritis (RA) is postulated to originate at mucosal surfaces, particularly the airway mucosa. To investigate this hypothesis, we determined the association between RA and asthma, passive smoke exposure, and age at start of smoking.
For this case-control study, we identified 1,023 cases of RA (175 incident) within a single-center biobank population, using a rules-based algorithm that combined self-report with 2 diagnostic codes. Exposures were self-reported on biobank questionnaires. Logistic regression models were used to calculate the association of exposures with RA, adjusting for potential confounders. Odds ratios (ORs) with 95% confidence intervals (95% CIs) were calculated.
After adjustment for allergies, urban environment, and passive smoke exposure, asthma was found to be associated with RA in the full cohort (OR 1.28 [95% CI 1.04-1.58; P = 0.02]) but not the incident RA cohort (OR 1.17 [95% CI 0.66-2.06; P = 0.60]). History of allergic disease was associated with RA in both the full cohort (OR 1.30 [95% CI 1.12-1.51; P < 0.001]) and the incident RA cohort (OR 1.61 [95% CI 1.11-2.33; P = 0.01]), especially food allergy, which was significantly associated with RA in the full cohort (OR 1.38 [95% CI 1.08-1.75; P = 0.01]) and showed a trend toward significance in the incident RA cohort (OR 1.83 [95% CI 0.97-3.45; P = 0.06]). Passive smoke exposure at home or work was not associated with RA. Finally, age at start of smoking was not associated with increased odds of developing RA in either the full cohort (OR 1.03 [95% CI 1.00-1.06; P = 0.03]) or the incident RA cohort (OR 1.00 [95% CI 0.92-1.08; P = 0.98]).
Asthma and allergies may be associated with increased risk of RA. Passive smoke exposure and early age at start of smoking do not appear to influence risk of RA.