• Inflammatory bowel disease;
  • Crohn's disease;
  • Ulcerative colitis;
  • Smoking;
  • Epidemiology;
  • Therapy


Smoking is associated with Crohn's disease and nonsmoking with ulcerative colitis. The aim of this study was to compare the clinical features at diagnosis and during the first year of follow-up in smokers and nonsmokers with inflammatory bowel disease (IBD). In 19 centers across Europe, a prospective study was performed of 457 newly diagnosed patients with Crohn's disease and 930 with ulcerative colitis. The characteristics of the disease were recorded by the treating physician by using a standard protocol at the time of diagnosis. Treatment characteristics were assessed after 1 year of followup. Weight loss occurred significantly more often in smoking patients with Crohn's disease, as well as in smokers with ulcerative colitis (p < 0.02), and diarrhea was more frequent in smoking patients with Crohn's disease compared with non-smoking individuals (p < 0.01). Patients with Crohn's disease who smoke were less likely to have colonic involvement (p < 0.01) and were more often prescribed immunosuppressive medication (p < 0.02). The study suggests that (a) smoking protects the colon from inflammation and (b) is associated with more active disease in Crohn's disease. The association between weight loss and smoking in both diseases is probably due to a general effect of smoking. The reported relation between smoking and the course of Crohn's disease is a strong argument for encouraging patients to give up smoking.