Effect of smoking and comorbidities on survival in idiopathic pulmonary fibrosis

Background: Cigarette smoking has been associated with the risk of idiopathic pulmonary fibrosis (IPF). Certain comorbidities have been associated with reduced survival although some studies have indicated that current smokers have a longer survival than ex-smokers. Comorbidities in relation to smoking history have not been previously analyzed. Methods: Retrospective data was collected and patients were categorized according to gender and smoking habits. Comorbidities and medications were collected. Predictive values for mortality were identified by COX proportional hazard analyses. Results: We examined 45 non-smokers (53.3% female), 66 ex-smokers (9.1% female) and 17 current smokers (17.6% female) with IPF. Current smokers were younger at baseline (58.1 ± 8.74 years) compared to non-smokers (71.4 ± 8.74, p < 0.001) and ex-smokers (72.5 ±7.95, p <0.001). Median survival of non-smokers and current smokers was longer (55.0 and 52.0 months, respectively) than that of ex-smokers (36.0 months) (p=0.028 and 0.034, respectively). In age and severity adjusted analyses, smoking was not related to survival. Cardiovascular diseases (CVD) (72.7 %) were the most common comorbidities, current smokers had more chronic obstructive pulmonary disease (COPD) and lung cancer compared to ex-smokers (p<0.001). CVD, COPD and use of insulin were related to poorer survival in adjusted analyses. Conclusions: Smoking seems to influence the course of disease in IPF since current smokers developed the disease at a younger age in comparison to non-smokers and ex-smokers. No significant differences in the major comorbidities were detected between IPF patients with different smoking histories. The mechanism through which smoking influences IPF progression requires further investigation.