Changes in prevalence and incidence of inflammatory bowel disease over 30 years: a population-based cohort study, the HUNT study.

Background: The prevalence of inflammatory bowel disease (IBD) is rising, while the incidence varies between countries.

Objective: To determine changes in prevalence and incidence of IBD in a Norwegian general population.

Design: This study was based on the Trøndelag Health Study (HUNT), a series of population-based health surveys in Nord-Trøndelag County, Norway, conducted since the 1980s. All adult residents aged 20 years and above were invited. The total number of unique participants in HUNT is 123,000. Those diagnosed with IBD were identified and verified by linkage to hospital records. Annual age-standardized prevalence and incidence rates were calculated from 1990 to 2022.

Results: The prevalence of IBD was 0.22% in 1990, increasing to 1.6% in 2022. An increase in ulcerative colitis (UC) accounted for the largest rise, from 0.16% to 1.12%. The prevalence of Crohn's disease (CD) rose from 0.06% to 0.27%. IBD unclassified (IBDU) was rarely diagnosed in the early years of the study but accounted for 0.19% in 2022. The incidence of IBD showed an average annual increase of 0.72% in the observation period. This was mainly due to an increase in UC in women, while the incidence was relatively stable in men. The incidence of IBD was highest, but stable, for those under 30 years, while the incidence rose in the older age groups, mostly in those above 70 years.

Conclusion: In this Norwegian adult population, the prevalence of IBD has been high and rising over the last 30 years. It is the highest prevalence of IBD reported in Europe.