Environmental, Nutritional, and Socioeconomic Determinants of IBD Incidence: A Global Ecological Study

The wide variation in inflammatory bowel disease [IBD] incidence across countries entails an opportunity to recognise global disease determinants and hypothesise preventive policies.

We fitted multivariable models to identify putative environmental, nutritional, and socioeconomic determinants associated with the incidence of IBD (i.e. ulcerative colitis [UC] and Crohn's disease [CD]). We used the latest available country-specific incidence rates, and aggregate data for 20 determinants, from over 50 countries accounting for more than half of the global population. We presented the associations with exponentiated beta coefficients (exp[β]) indicating the relative increase of disease incidence per unit increase in the predictor variables.

Country-specific incidence estimates demonstrate wide variability across the world, with a median of 4.8 new UC cases (interquartile range [IQR] 2.4-9.3), and 3.5 new CD cases [IQR 0.8-5.7] per 100 000 population per year. Latitude (exp[β] 1.05, 95% confidence interval [CI] 1.04‒1.06, per degree increase), prevalence of obesity [1.05, 1.02‒1.07, per 1% increase], and of tobacco smoking [0.97, 0.95‒0.99, per 1% increase] explained 71.5% of UC incidence variation across countries in the adjusted analysis. The model for CD included latitude [1.04, 1.02‒1.06], expenditure for health (1.03, 1.01‒1.05, per 100 purchasing power parity [PPP]/year per capita increase), and physical inactivity prevalence [1.03, 1.00‒1.06, per 1% increase], explaining 58.3% of incidence variation across countries. Besides expenditure for health, these associations were consistent in low/middle- and high-income countries.

Our analysis highlights factors able to explain a substantial portion of incidence variation across countries. Further high-quality research is warranted to develop global strategies for IBD prevention.