Pulmonary dysfunction, smoking, socioeconomic status and the risk of developing rheumatoid arthritis.

OBJECTIVES: Environmental risk factors are of potential interest for both prevention and treatment of RA. The purpose of this study was to examine the effect of pulmonary function, smoking and socio-economic status on the future risk of RA.
METHODS: Between 1974 and 1992, 22 444 men and 10 902 women were included in the Malmö Preventive Medicine Program (MPMP). Pulmonary function was assessed by a standard screening spirometry. Chronic obstructive pulmonary disease (COPD) and restrictive pulmonary dysfunction were defined based on pulmonary function tests. Individuals who developed RA were identified by linking the MPMP database to national and local RA registers. The patients were classified according to the 1987 ACR criteria for RA. Four matched controls for every case were selected.
RESULTS: We identified 290 cases of incident RA (151 men/139 women; mean age at diagnosis 60 years). The median time from inclusion to diagnosis was 12 years. Forced vital capacity and forced expiratory volume within 1 s values were similar in cases and controls, overall and also in separate analysis of those screened ≤8 years before diagnosis. There was no association between COPD or restrictive pulmonary dysfunction and subsequent development of RA. Current smoking was a strong predictor for RA [odds ratio (OR) 1.79; 95% CI 1.32, 2.42]. Blue-collar workers had an increased risk of RA (OR 1.54; 95% CI 1.12, 2.10), independent of smoking.
CONCLUSION: Pulmonary dysfunction did not predict RA, but smoking and low socio-economic status were independent risk factors for RA. Other effects of smoking may be important for RA susceptibility.