The relationship between weight change and inflammatory bowel disease. A population-based cohort study, the HUNT study.

Background: The incidence of inflammatory bowel disease (IBD) is increasing. The prevalence of overweight and obesity is increasing in parallel with IBD and could contribute to IBD development. The aim of this study was to assess the relationship between weight change and the risk for IBD.

Methods: Data gathered from 55,896 adult participants in the three first population-based Trøndelag Health Studies (HUNT1-3), Norway, performed in 1984-2008 was used. The exposure was change in body mass index between two HUNT studies. The outcome was a new IBD diagnosis recorded during a ten-year follow-up period after the exposure assessment. The risk of IBD by weight change was assessed by Cox regression analyses reporting hazard ratios (HRs) and 95% confidence intervals (CIs), adjusted for sex, age, and smoking status.

Results: There were 334 new cases of ulcerative colitis (UC) and 54 of Crohn's disease (CD). Weight loss decreased the risk of a new UC diagnosis by 38% (adjusted HR 0.62, 95% CI 0.39-0.97) and seemed to double the risk of getting a new CD diagnosis (adjusted HR 2.01, 95% CI 0.91-4.46). Weight gain was not associated with a new diagnosis of neither UC (adjusted HR 1.00, 95% CI 0.78-1.26) nor CD (adjusted HR 1.08, 95% CI 0.56-2.08).

Conclusion: In this study, weight loss was associated with decreased risk of UC. However, no associations were seen between weight gain and the risk of UC or CD, suggesting that the increasing weight in the general population cannot explain the increasing incidence of IBD.