Objective: The ages of patients with Crohn's disease and ulcerative colitis are characterized by a bimodal distribution. This study used separate hospital statistics from England and Scotland to follow the changes in the age distribution of inflammatory bowel disease. The objective of the analysis was to check whether the time trends of hospitalization would show different patterns among different age groups.

Methods: Hospital statistics from England (1989-2006) and Scotland (1981-2007) were obtained through special requests to the national statistical offices. Hospitalizations (with Crohn's disease or ulcerative colitis listed as primary or primary plus secondary discharge diagnosis) were expressed as age-specific and sex-specific rates per 10 000 living population. The separate age-specific rates of Crohn's disease and ulcerative colitis of consecutive 6-year or 7-year time intervals were plotted against their respective age group.

Results: The hospital data reveal a bimodal age distribution, with a more prominent first peak occurring in younger patients with Crohn's disease and a more prominent second peak occurring in older patients with ulcerative colitis. During the past two decades, the hospitalization rates for both diseases increased in all age groups. However, the increase was relatively more pronounced in the elderly, especially with ulcerative colitis. The age-shift towards older patients was also more evident for Crohn's disease or ulcerative colitis listed as secondary than primary discharge diagnosis.

Conclusions: The age-related shift in the occurrence of inflammatory bowel disease could reflect the impact of a birth-cohort pattern that underlies the long-term time trends of ulcerative colitis and Crohn's disease.