Conflicting data have been reported about the seasonal variation in flare-up of inflammatory bowel disease (IBD). The aim of this study was to assess the occurrence of seasonal variations in flare-up of IBD in the Korean population.

Patients with IBD, who underwent more than 1 year of follow-up and showed more than 1 episode of flare-up, were included. Flares of disease were refined as follows; receipt of a new prescription and increasing dose of corticosteroids, 5-ASA or immunosuppressant; hospitalized or operated due to development and worsening of symptoms; elevation of inflammatory marker due to worsening of Crohn's Disease Activity Index (CDAI) or Mayo score. In addition, for patients with more than two episodes of flare-up, they were investigated in a monthly and seasonal pattern.

Of 573 patients with IBD, 46 patients with Crohn's disease and 61 patients with ulcerative colitis were enrolled. There was no association between month of the year and flare of Crohn's disease ( P =0.06) or ulcerative colitis ( P =0.58). Further, no association between season of the year and flare of Crohn's disease ( P =0.06) or ulcerative colitis ( P =0.68). However, in Crohn's disease who experience 2 or more flare-ups, symptoms occurred more frequently during winter, especially December ( P =0.029).

In the Korean population, there was no association of seasonal and monthly variation in flares of Crohn's disease and ulcerative colitis. However, in Crohn's disease, individuals with 2 flar-up or more, symptoms occurred more frequently during December.