Body mass index and the risk for Crohn's disease and ulcerative colitis: data from a European Prospective Cohort Study (The IBD in EPIC Study).

OBJECTIVES: Obesity is associated with a proinflammatory state that may be involved in the etiology of inflammatory bowel disease (IBD), for which there are plausible biological mechanisms. Our aim was to perform the first prospective cohort study investigating if there is an association between obesity and the development of incident IBD. METHODS: A total of 300,724 participants were recruited into the European Prospective Investigation into Cancer and Nutrition study. At recruitment, anthropometric measurements of height and weight plus physical activity and total energy intake from validated questionnaires were recorded. The cohort was monitored identifying participants who developed either Crohn's disease (CD) or ulcerative colitis (UC). Each case was matched with four controls and conditional logistic regression used to calculate odds ratios (ORs) for body mass index (BMI) adjusted for smoking, energy intake, and physical activity. RESULTS: In the cohort, 177 participants developed incident UC and 75 participants developed incident CD. There were no associations with the four higher categories of BMI compared with a normal BMI for UC (Ptrend=0.36) or CD (Ptrend=0.83). The lack of associations was consistent when BMI was analyzed as a continuous or binary variable (BMI 18.5<25.0 vs. ≥25 kg/m(2)). Physical activity and total energy intake, factors that influence BMI, did not show any association with UC (physical activity, Ptrend=0.79; total energy intake, Ptrend=0.18) or CD (physical activity, Ptrend=0.42; total energy, Ptrend=0.11). CONCLUSIONS: Obesity as measured by BMI is not associated with the development of incident UC or CD. Alternative measures of obesity are required to further investigate the role of obesity in the development of incident IBD.