Exposure to passive smoking and rheumatoid arthritis risk: results from the Swedish EIRA study

INTRODUCTION: Smoking has consistently been associated with increased risk of developing rheumatoid arthritis (RA). The aim of this study was to estimate the influence of passive smoking on the risk of developing anti-cyclic citrullinated peptide antibodies (ACPA)-positive and ACPA-negative RA. METHODS: A population-based case–control study using incident cases of RA was performed in Sweden, and the study population in this report was restricted to include never-smokers (589 cases, 1764 controls). The incidence of RA among never-smokers who had been exposed to passive smoking was compared with that of never-smokers who had never been exposed, by calculating the OR with a 95% CI employing logistic regression. RESULTS: No association was observed between exposure to passive smoking and RA risk (OR 1.0, 95% CI 0.8 to 1.2 for ACPA-positive RA, and OR 0.9, 95% CI 0.7 to 1.2, for ACPA-negative RA). No suggestion of a trend between duration of passive smoking and RA risk was observed. DISCUSSIONS: No association was observed between exposure to passive smoking and RA risk, which may be explained by a threshold below which no association between smoke exposure and RA occurs.