Long-term data on the influence of cigarette smoking, especially cessation, on the risk of Crohn's disease and ulcerative colitis are limited.
Dr Leslie Higuchi and colleagues from Massachussetts, USA conducted a prospective study of 229,111 women in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHS II).
Biennially, the team collected updated data on cigarette smoking, other risk factors, and diagnoses of Crohn's disease or ulcerative colitis confirmed by medical record review.
|Increasing pack-years was associated with increasing risk of Crohn's disease|
|American Journal of Gastroenterology|
Over 32 years in NHS and 18 years in NHS II, the team documented 336 incident cases of Crohn's disease, and 400 incident cases of ulcerative colitis.
Compared with never smokers, the team found that the multivariate hazard ratio of Crohn's disease was 1.9 among current smokers and 1.4 among former smokers.
The researchers observed that increasing pack-years was associated with increasing risk of Crohn's disease, whereas smoking cessation was associated with an attenuation of risk.
By contrast, the multivariate hazard ratio of ulcerative colitis was 0.9 among current smokers, and 1.6 among former smokers.
The team noted that the risk of ulcerative colitis was significantly increased within 2–5 years of smoking cessation, and remained persistently elevated over 20 years.
Dr Higuchi's team commented, "Current smoking is associated with an increased risk of Crohn's disease, but not ulcerative colitis."
"By contrast, former smoking is associated with an increased risk of ulcerative colitis, with risk persisting over 2 decades after cessation."