[The role of smoking as a risk factor in inflammatory bowel diseases: single center study in Korea]

Cigarette smoking is the most significant environmental factor identified in inflammatory bowel disease (IBD). Smoking has a beneficial effect on ulcerative colitis (UC) patients. In contrast, Crohn's disease (CD) is associated with smoking, and a detrimental effect of smoking on the course of CD has been demonstrated. The aim of this study was to explore the prevalence in smoking in CD and UC at the time of diagnosis compared with the general population in a single center study.

Prevalence of smoking at the time of IBD diagnosis were compared between CD and UC patients in Kyung-Hee Medical Center with healthy general population at age-, gender-, and time period-adjusted rates. We investigated the smoking status of IBD patients at the time of diagnosis by telephone interview. There were 178 IBD patients (98 UC patients and 80 CD patients) between January 1995 and December 2004.

The male to female ratio in CD and UC were 2:1 and 1:1.4, respectively. The onset of age was 28.2 years and 38.8 years, respectively. The prevalence of smoking was significantly lower in CD and UC patients than in the general population (CD; odds ratio 0.21, 95% confidence interval 0.12-0.41, p<0.001, UC; odds ratio 0.06, 95% confidence interval 0.03-0.14, p<0.001). After statistical adjustment for gender and age at the diagnosis of IBD, the odds ratio of a current smoker diagnosed as UC was 73% lower than that of CD (adjusted odds ratio 0.27, 95% confidence interval 0.12-0.59, p<0.001). In contrast, being a former smoker showed a risk of approximate 1.27-fold higher likelihood of having UC diagnosis (adjusted odds ratio 1.27, confidence interval 0.41-3.95, p=0.68).

Cigarette smoking is protective against developing UC at any age, but is not associated with the development of CD in Korean population. Former smoking is not the high risk factor in developing UC.