Cigarette Smoking and the Risk of IBD in Women
Cigarette Smoking and the Risk of IBD in Women
Objectives: Long-term data on the influence of cigarette smoking, especially cessation, on the risk of Crohn's disease (CD) and ulcerative colitis (UC) are limited.
Methods: We conducted a prospective study of 229,111 women in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHS II). Biennially, we collected updated data on cigarette smoking, other risk factors, and diagnoses of CD or UC confirmed by medical record review.
Results: Over 32 years in NHS and 18 years in NHS II, we documented 336 incident cases of CD and 400 incident cases of UC. Compared with never smokers, the multivariate hazard ratio (HR) of CD was 1.90 (95% confidence interval (CI), 1.42–2.53) among current smokers and 1.35 (95% CI, 1.05–1.73) among former smokers. Increasing pack-years was associated with increasing risk of CD (Ptrend< 0.0001), whereas smoking cessation was associated with an attenuation of risk. By contrast, the multivariate HR of UC was 0.86 (95% CI, 0.61–1.20) among current smokers and 1.56 (95% CI, 1.26–1.93) among former smokers. The risk of UC was significantly increased within 2–5 years of smoking cessation (HR, 3.06; 95% CI, 2.00–4.67) and remained persistently elevated over 20 years.
Conclusions: Current smoking is associated with an increased risk of CD, but not UC. By contrast, former smoking is associated with an increased risk of UC, with risk persisting over two decades after cessation.
The etiologies of Crohn's disease (CD) and ulcerative colitis (UC), the two main forms of inflammatory bowel disease (IBD), remain unknown, but are thought to be multifactorial, with both genetic and environmental influences. Multiple studies have reported significant associations between cigarette smoking and the risk of IBD, although the effect of smoking appears to differ between CD and UC. In previous analyses, current smoking has been associated with a higher risk of CD but a lower risk of UC. Moreover, smoking cessation may increase UC risk. Nonetheless, the majority of previous studies that assessed the relationship between smoking and IBD were retrospective, case–control studies limited by recall and selection biases. The few prospective cohort studies that have examined smoking included only a small number of cases and did not collect updated smoking status exposure data over long-term follow-up.
We therefore performed a post-hoc analysis of smoking information, obtained before diagnosis, on the risk of IBD among 229,111 women enrolled in two large ongoing, prospective cohort studies. Over 32 years of follow-up, we documented 736 incident cases of CD and UC. Moreover, in both cohorts, smoking data was updated biennially, thereby minimizing misclassification of smoking exposure and allowing a detailed assessment of the influence of smoking cessation on the risk of incident CD and UC.
Abstract and Introduction
Abstract
Objectives: Long-term data on the influence of cigarette smoking, especially cessation, on the risk of Crohn's disease (CD) and ulcerative colitis (UC) are limited.
Methods: We conducted a prospective study of 229,111 women in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHS II). Biennially, we collected updated data on cigarette smoking, other risk factors, and diagnoses of CD or UC confirmed by medical record review.
Results: Over 32 years in NHS and 18 years in NHS II, we documented 336 incident cases of CD and 400 incident cases of UC. Compared with never smokers, the multivariate hazard ratio (HR) of CD was 1.90 (95% confidence interval (CI), 1.42–2.53) among current smokers and 1.35 (95% CI, 1.05–1.73) among former smokers. Increasing pack-years was associated with increasing risk of CD (Ptrend< 0.0001), whereas smoking cessation was associated with an attenuation of risk. By contrast, the multivariate HR of UC was 0.86 (95% CI, 0.61–1.20) among current smokers and 1.56 (95% CI, 1.26–1.93) among former smokers. The risk of UC was significantly increased within 2–5 years of smoking cessation (HR, 3.06; 95% CI, 2.00–4.67) and remained persistently elevated over 20 years.
Conclusions: Current smoking is associated with an increased risk of CD, but not UC. By contrast, former smoking is associated with an increased risk of UC, with risk persisting over two decades after cessation.
Introduction
The etiologies of Crohn's disease (CD) and ulcerative colitis (UC), the two main forms of inflammatory bowel disease (IBD), remain unknown, but are thought to be multifactorial, with both genetic and environmental influences. Multiple studies have reported significant associations between cigarette smoking and the risk of IBD, although the effect of smoking appears to differ between CD and UC. In previous analyses, current smoking has been associated with a higher risk of CD but a lower risk of UC. Moreover, smoking cessation may increase UC risk. Nonetheless, the majority of previous studies that assessed the relationship between smoking and IBD were retrospective, case–control studies limited by recall and selection biases. The few prospective cohort studies that have examined smoking included only a small number of cases and did not collect updated smoking status exposure data over long-term follow-up.
We therefore performed a post-hoc analysis of smoking information, obtained before diagnosis, on the risk of IBD among 229,111 women enrolled in two large ongoing, prospective cohort studies. Over 32 years of follow-up, we documented 736 incident cases of CD and UC. Moreover, in both cohorts, smoking data was updated biennially, thereby minimizing misclassification of smoking exposure and allowing a detailed assessment of the influence of smoking cessation on the risk of incident CD and UC.