The changes in prevalence and risk of irritable bowel syndrome over time in a population-based cohort, the HUNT study, Norway

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-Trondelag county, Norway, over 20 years of age was invited to participate in the Trondelag 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.