Background/Purpose: Smoking is one of the most established risk factors for rheumatoid arthritis (RA). The aim of this study was to estimate how age at smoking debut, smoking cessation, duration, intensity, and cumulative dose of smoking influence the risk of developing ACPA positive and ACPA negative RA.
Methods: The present report is based on a Swedish population-based, case-control study with incident cases of RA (3655 cases, 5883 matched controls). Using logistic regression models, subjects with different smoking habits were compared regarding risk of developing the two subsets of RA, by calculating odds ratios (OR) with 95% confidence intervals (CI).
Results: Smoking increased the risk of developing both ACPA positive (OR 1.9, 95% CI 1.7-2.1) and ACPA negative RA (OR 1.3, 95% CI 1.2-1.5). For both subsets of RA, a cumulative dose of smoking less than five pack years was not significantly associated with increased disease risk. A dose-response association was observed between cumulative dose of smoking (exceeding five pack years) and risk of developing both ACPA positive and ACPA negative RA (p values for trend <0.0001) (table 1). Duration of smoking had a higher influence on the association between smoking and RA than did intensity of smoking (table 2). Among both subsets of RA, the detrimental effect of smoking decreased after smoking cessation. Twenty years after smoking cessation, there was no longer an association between smoking and risk of ACPA negative RA, whereas the association between smoking and ACPA positive RA risk persisted and was dependent on the cumulative dose of smoking (table 3).
Conclusion: Smoking increases the risk of both subsets of RA with a more pronounced influence on the risk of ACPA positive RA. Preventive measures in order to reduce smoking are essential and may result in a decline in RA incidence.