OBJECTIVE: To study the changes in prevalence of irritable bowel syndrome (IBS), the distribution between the sexes and age groups, and risk factors for the disease and its subtypes. MATERIAL AND METHODS: Every inhabitant of Nord-Trøndelag county, Norway, over 20 years of age was invited to participate in the Trøndelag Health Study (HUNT). In HUNT3 (2006-2008) and HUNT4 (2017-2019), IBS was assessed by a questionnaire. The standardized prevalence was calculated, and risk factors were assessed by multivariable logistic regression, reporting odds ratios (OR) and 95% confidence intervals (CI). RESULTS: In HUNT3 and HUNT4, 41,198 and 42,669 individuals were included, respectively. The prevalence of IBS was 7.5% in HUNT3 and 9.5% in HUNT4. Both surveys showed higher prevalence among women and among young adults. In HUNT4, the most prevalent subtype was mixed IBS (46.1%). Women had increased risk of IBS compared to men (OR 1.82, 95% CI 1.69-1.96). Age ≥40 years decreased the risk of IBS compared to age <40 years (OR 0.82, 95% CI 0.75-0.90). Being unmarried increased the risk for IBS compared to being married (OR 1.21, 95% CI 1.11-1.32). Both previous (OR 1.28, 95% CI 1.20-1.38) and current (OR 1.35, 95% CI 1.20-1.51) smokers had increased risk of IBS compared to never smokers. CONCLUSIONS: IBS is a prevalent disease, and the prevalence has increased between 2006-2008 and 2017-2019. Risk of IBS was increased among women, young adults, smokers and unmarried participants.
