Seasonal variation in flares of inflammatory bowel disease

Previous research has yielded conflicting data as to whether the natural history of inflammatory bowel disease follows a seasonal pattern. The purpose of this study was to determine whether relapse of inflammatory bowel disease follows a seasonal pattern either across a cohort of patients or within individual patients.

We used 1988 to 1997 data from the General Practice Research Database to conduct a retrospective cohort study of 1587 patients with Crohn's disease (mean age at start of follow-up, 41 +/- 17 years) and 2773 patients with ulcerative colitis (mean age at start of follow-up, 48 +/- 16 years). Flares of disease were identified by receipt of a new prescription for either corticosteroids or 5-ASA medications following an interval of at least 4 months without prescriptions for either class of medication. Logistic regression was used to adjust the association of season of the year and flare of disease for potential confounding variables.

There was no association between season of the year and flare of Crohn's disease (P = 0.66). Season of the year was only weakly associated with flares of ulcerative colitis (P = 0.02). Compared with winter, spring had very slightly higher rates of flares (OR = 1.13, 95% CI: 1.05-1.23). We did not observe seasonal patterns within individual patients experiencing multiple flares (P > 0.05 for Crohn's disease and ulcerative colitis).

Although we observed a slight increase in exacerbations of ulcerative colitis in the spring, in general, these data do not support an association between season of the year and flares.