Cigarette smoking and age at diagnosis of inflammatory bowel disease

The incidence and age of onset of inflammatory bowel disease (IBD) appear to be changing. The aim of this study was to determine whether the prevalence of cigarette smoking differs among patients with Crohn's disease (CD) or ulcerative colitis (UC) at the time of diagnosis compared with the general population and whether smoking history is related to the type and age of IBD onset.

Prevalence rates of smoking at the time of IBD diagnosis were compared between patients with CD and UC from the IBD Center at the University of Pittsburgh Medical Center versus age-, gender-, and time period-adjusted rates in the Pennsylvania general population. Analyses also were stratified by gender and diagnoses before and after 40 years of age, i.e., early and late onset.

There were 263 IBD patients (144 UC patients and 119 CD patients) seen in the IBD center between August 2000 and December 2002. The prevalence of active smoking was significantly higher at diagnosis in CD patients compared with the Pennsylvania general population (33% versus 24%, P = 0.04), particularly in those with CD onset at 40 years of age or later (47% versus 27%, P = 0.005). In contrast, smoking prevalence was significantly lower in UC patients than the general population (9% versus 28%, P < 0.0001), particularly among those with UC onset before the age of 40 years (6% versus 27%, P < 0.0001). Smoking cessation was associated with an approximate, but nonsignificant, 3-fold higher likelihood of late-onset UC compared with CD.

Cigarette smoking is associated with the development of late-onset CD and is protective against developing UC at any age, particularly early onset. Former smoking is associated with a high likelihood of developing late-onset UC, but not CD.