Background/Purpose: Smoking has consistently been associated with increased risk of developing rheumatoid arthritis (RA). We investigated the influence of passive smoking on the risk of developing 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). Cases and controls answered an extensive questionnaire. 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% confidence interval (CI) employing logistic regression.

Results: No association was observed between exposure to passive smoking and risk of ACPA positive or ACPA negative RA, regardless if the exposure took place within 10 years prior to index, or earlier in life.

Compared with those who had never been exposed to passive smoking, the OR was 1.0 (95% CI 0.7-1.2) for ACPA positive RA, and 0.9 (95% CI 0.7-1.2) for ACPA negative RA among those ever exposed to passive smoking. There were no significant age or gender related differences.

There was no suggestion of a trend between duration of passive smoking and RA risk. Long term exposure to passive smoking for 20 years or longer was not significantly associated with increased disease susceptibility (table 1).

Conclusion: No association was observed between exposure to passive smoking and risk of ACPA positive or ACPA negative RA among never smokers. Our finding may be explained by a threshold below which no association between smoke exposure and RA occurs.