Background/Purpose

Smoking is a known risk factor for rheumatoid arthritis (RA) and there is evidence suggesting that many patients with RA continue to smoke. The proportion of patients with RA who smoke is therefore higher than the general population. Smoking is associated with several serious adverse events and so is likely to reduce life expectancy. The aim of this study was to examine the influence of smoking status on all-cause mortality in patients with RA.

Methods

Incident cases of RA were identified from a large UK primary care database using a validated algorithm. Patients were followed from their first code for RA until death, leaving their general practice or the last data collection date within the study window of March 1991 to January 2014. Read codes, codes for smoking cessation therapy and additional clinical information were used to define smoking status at baseline and as a time- varying exposure during follow-up. Smoking status was classified as non-, current or former. Date of death was available in the database. The Cox regression model was used to compare mortality rates between smoking categories, adjusting for gender and diagnosis date (pre/post January 2000). Age, cardiovascular disease (CVD), diabetes, depression, use of immunosuppressive DMARDs, any code for painkillers in the past 6 months and any code for respiratory infections, oral steroids, cardiovascular medication and antidepressants in the past year were included in the model as time-varying covariates. As the effect of smoking status was not constant over time, the interaction between smoking status and year of follow-up was also included in the model.

Results

13154 adult RA patients were identified, of whom 12431 (94.5%) had a baseline smoking status recorded and were included in the analysis. 68.9% were female and the median age was 60.8 years (IQR 50.2, 71.0). At baseline, all covariates differed significantly between the smoking categories. Former smokers had the highest prevalence of CVD, diabetes, and respiratory infection whilst current smokers had the highest prevalence of depression. The total follow-up time was 75467 person-years and there were 1719 deaths, giving a crude mortality rate of 22.8 per 1000 person years. The crude mortality rate for smoking status at baseline was 19.8, 25.6 and 24.8 per 1000 person years for non-, current and former smokers respectively. In the adjusted models, using time-varying smoking status, the risk of mortality for current smokers was nearly 80% greater than that of non-smokers (hazard ratio 1.79 (95% CI 1.46, 2.20) (Table).

Conclusion

Current smoking significantly increases the risk of death at any time after RA diagnosis compared to both non- and former smokers. Adjusted risk of death is similar for former smokers and non-smokers. Stopping smoking prior to the development of associated comorbidities may therefore help to reduce the risk of smoking-related mortality.