No association was observed between exposure to passive smoking and rheumatoid arthritis (RA) risk, which may be explained by a threshold below which no association between smoke exposure and RA occurs, according to a recent study. 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. A population-based, case-control study using incident cases of RA was performed, and the population was restricted to include never-smokers (589 cases, 1,764 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 odds ratio (OR) with a 95% CI employing logistic regression. Researchers found:

• 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.