Effects of smoking on the presentation and clinical course of inflammatory bowel disease

Objective: To evaluate the influence of regular smoking on the presentation and clinical course of inflammatory bowel disease. Methods: We performed a case-control study interviewing 160 inflammatory bowel disease patients (63 with Crohn's disease (CD) and 97 with ulcerative colitis (UC)) and 740 first-degree relatives as controls. The risk of developing the disease relative to a smoking habit was calculated as the odds ratio. Furthermore, to evaluate the influence of smoking on the subsequent course of inflammatory bowel disease, we performed a multivariate analysis that included pertinent variables such as the need for surgery, number of hospitalizations and relapses. Results: The pattern of smoking in UC patients was different from that in CD patients. In UC there was a significant predominance of non-smokers and ex-smokers (P = 0.02), whereas smoking habits in CD were not different from those in controls. Giving up smoking was a risk factor to develop UC (odds ratio: 3.2, P=0.02). In UC, non-smokers and specially ex-smokers need surgery more frequently than smokers (P <0.01). Otherwise the relapse/year index was not influenced by smoking. In CD there was a non-significant association between smoking habits and the various clinical parameters analysed. UC patients who begin smoking after diagnosis of the disease present a significant reduction in the number of recurrences. Conclusion: Smoking habit significantly affects the presentation and clinical course of UC, whereas in CD, a smoking habit does not have any apparent influence on the disease.