Age at onset is associated with the seasonal pattern of onset and exacerbation in inflammatory bowel disease

Environmental factors are suggested to affect the pathogenesis of several diseases, including inflammatory bowel disease (IBD). The seasonality of disease onset and exacerbation in IBD, however, are not well established. We herein aimed to clarify the disease seasonality and to investigate the underlying characteristics in IBD patients exhibiting seasonality of the disease course. This was a multicenter observational study comprising 20 institutions (Osaka Gut Forum) in Japan. Data were collected from November 2013 to August 2014 using survey forms for physicians and questionnaires for patients. Multivariate analysis was performed to clarify the independent factors affecting disease seasonality. A total of 1055 patients, including 298 patients with Crohn's disease (CD) and 757 patients with ulcerative colitis (UC), were enrolled. The proportion of CD patients with disease onset in the summer was significantly larger than that in the other seasons, while UC patients exhibited no seasonality of disease onset. More than half of the IBD patients (51.1%) experienced seasonal exacerbation of IBD, and winter was the most common season for disease exacerbation in both CD and UC patients. Seasonality of disease onset and exacerbation was observed in young-onset patients (<= 40 years old), but not in elderly-onset patients. Age at onset was independently associated with the seasonality of both disease onset and exacerbation. Seasonality of disease onset and exacerbation was observed especially in young-onset IBD patients. Underlying pathophysiologic triggers for disease initiation and exacerbation may be influenced by age at disease onset.