Smoking and Crohn's disease.

In a case-control study 82 patients with Crohn's disease and matched controls drawn from general practice lists were questioned about their smoking habits. Patients with Crohn's disease were significantly more likely to be smokers than the controls, and the association was stronger for smoking habit before the onset of the disease than for current smoking habit, the relative risks for smokers compared with non-smokers being 4.8 and 3.5 respectively. Taken in conjunction with earlier data showing an association between non-smoking and ulcerative colitis, these results suggest that smoking habit may be an important determinant of the type of inflammatory bowel disease that develops in predisposed subjects.