July 25, 2012
1 min read

Smoking associated with Crohn's disease, previous smoking with ulcerative colitis

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People who smoke may be at an increased risk for developing Crohn’s disease, while former smokers may be at increased risk for ulcerative colitis, according to study results.

In a prospective study, researchers collected data on Crohn’s disease (CD) and ulcerative colitis (UC) diagnoses, as well as cigarette smoking and other risk factors, from 229,111 women across Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHS II).

CD was documented in 336 patients, and UC was diagnosed in 400 participants from 1976-2008 in NHS and from 1989-2007 in NHS II. Through multivariate analysis, current smokers (HR=1.90; 95% CI, 1.42-2.53) and previous smokers (HR=1.35; 95% CI, 1.05-1.73) were more likely to be diagnosed with CD than nonsmokers. Investigators also found an association between increased CD risk and increased pack-years of smoking (P<.0001 for trend) that remained in effect when limited to current (P<.0001) or previous smokers (P=.0002). An association also existed between smoking cessation and a reduction in risk for CD during 20 years of follow-up (P=.03).

Multivariate analysis indicated an adjusted HR of 0.86 (95% CI, 0.61-1.20) for UC among current smokers and of 1.56 (95% CI, 1.26-1.93) among previous smokers compared with nonsmokers. Among former smokers, UC risk increased significantly between 2 and 5 years after quitting (adjusted HR=3.06; 95% CI, 2.00-4.67) and remained elevated across the subsequent 20 years (HR=1.64; 95% CI, 1.02-2.64). An increased number of pack-years also increased risk for UC among previous smokers (P<.0001), but not among current smokers.

“To our knowledge, [this] represents the largest cohort study with prospectively collected and updated smoking information, examining the associations between smoking and IBD,” the researchers wrote. “Further studies may clarify the mechanisms by which smoking and smoking cessation influence the risk of IBD.”

Disclosure: See the study for a full list of relevant disclosures.