LAUSR

Cigarette smoking is a well-established environmental risk factor for rheumatoid arthritis (RA),1–3 particularly anticitrullinated protein antibody (ACPA)-positive RA.2 We previously observed an association between silica exposure and increased risk of seropositive RA.4 5 While the additive interaction between silica exposure and smoking has been demonstrated,5 considerably less is known regarding the dose of smoking required to elicit this effect. In this study, we extend our previous findings on smoking and silica exposure by investigating the additive interaction between silica exposure and dose of smoking as well as between silica exposure and duration of smoking cessation, with regard to the risk of developing ACPA-positive RA. Our study is based on the Swedish Epidemiological Investigation of Rheumatoid Arthritis project,3 an ongoing population-based study comprising incident cases (American College of Rheumatology 1987 or 20106 7 criteria) and controls aged ≥18 years living in Sweden between 1996 and 2014. Information …