Abstract Background Smoking is the best-known environmental risk factor for poor outcome of Crohn’s disease (CD). Since smoking cessation improves the prognosis of CD, patients are encouraged to quit smoking. This study aimed to assess the smoking behaviour among CD patients and explore changes after diagnosis of CD. Methods This is a retrospective single tertiary center cohort study of 1267 patients with CD with a median follow-up of 16.8 years (IQR - 18.3) whose characteristics are recorded via a validated data software (IBDIS, Inflammatory Bowel Disease Information System). Smoking behaviour was categorized into never smokers, current smokers, and ex-smokers (those who quit smoking at any point). The primary objective was smoking cessation during follow-up. The probability of smoking was calculated for those CD patients who smoked at the time of diagnosis of CD by means of Kaplan-Meier estimates. Statistical analyses were conducted using R software, employing log-rank tests for estimating differences with a significance level of alpha = 0.05. Results In total 1,128 CD patients with a complete data set were analysed (Table 1). 161 (14.2%) patients started and stopped smoking prior to diagnosis of CD. At the time of diagnosis, 541 patients (47.9%) were smokers, and 239 (44.2%) of them quit smoking during follow up. The median time from CD diagnosis to cessation for the 239 patients who were smokers at the time of diagnosis and subsequently quit was 8.6 years (IQR - 10.6 years). 80 patients (7%) started smoking after diagnosis, with 50 of these patients quitting thereafter. The probability of smoking in those CD patients who smoked at the time of diagnosis decreased over time to 0.96 (95% CI 0.95-0.98) at 1yr, 0.85 (95% CI 0.83-0.89) at 5 yrs, 0.71 (95% CI 0.67-0.76) at 10 yrs, and 0.52 (95% CI 0.47-0.57) at 20 yrs after diagnosis for the entire cohort with no significant difference between genders (p=0.76) (Figure 1a). Patients who were diagnosed 2010 and later (n=182) were more likely to stop smoking than patients diagnosed before 2010 (n=359) (p<0.001) (Figure 1b). However, the probability to smoke 10 years after the diagnosis was still high in both groups (0.62 (95% CI 0.52-0.74) and 0.75 (95% CI 0.71-0.79), respectively). Conclusion A substantial proportion of CD patients smoked at the time of diagnosis. 20 years after diagnosis around half of the patients still continued to smoke. Improved smoking cessation programs are needed to reduce the impact of smoking on the course of the disease.
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