Second peak in the distribution of age at onset of ulcerative colitis in relation to smoking cessation

Background and Aim: The prevalence of ulcerative colitis (UC) is increasing steadily in Japan. In Western countries, a bimodal distribution, with UC onset peaks in youth and middle age, is observed, and smoking cessation is reported as a risk factor for UC. However, there are few reports on a bimodal distribution of onset age among Japanese patients. Therefore, the distribution of onset age and factors related to late onset (i.e. onset at 50 years old or later) were investigated in UC patients in Japan. Methods: A questionnaire survey of UC patients was conducted to investigate the distribution of the age of onset and factors that may be related to UC onset in a Japanese university hospital. Results: Among 465 UC patients, 343 patients responded. In the distribution of onset age, a large peak was seen in patients aged 10-20s, and small peaks were seen at age 40-44 years and then in 50-60s. In addition, the onset age was older in the UC patients diagnosed in 2001 or later than in those diagnosed in 2000 or earlier. Late onset was more common among the UC patients diagnosed in 2001 or later (vs 2000 or earlier: interaction odds ratio = 4.98, 95% CI: 2.21-11.25, P < 0.01) and among former smokers (vs never-smokers:interaction odds ratio = 2.93, 95% CI: 1.40-6.14, P < 0.01) on multivariate analysis. Conclusions: Similar to UC patients in Western countries, a bimodal distribution of onset age was also observed in Japanese UC patients, and smoking cessation may partly contribute to the increase in late-onset UC patients in recent years in Japan.