Background: Obesity is associated with a proinflammatory state.
Aim: To determine whether obesity at diagnosis is a risk factor for Crohn's disease vs. ulcerative colitis and also vs. community controls and whether there is a U-shaped relationship between body mass index at diagnosis and risk of Crohn's disease versus ulcerative colitis.
Methods: A total of 524 consecutive inflammatory bowel disease patients attending gastroenterology clinics were administered a questionnaire inquiring about weight at diagnosis and height as well as other risk factors for inflammatory bowel disease. An opportunistic control group of 480 community controls aged 50-70 were randomly selected from the registers of four local general practices as part of another study.
Results: Obesity at diagnosis was more common in subjects with Crohn's disease versus ulcerative colitis odds ratio 2.02 (1.18-3.43) p = 0.0096 and also Crohn's disease versus community controls in the 50-70 year age group (odds ratio 3.22 (1.59-6.52) p = 0.001). There was evidence of a 'dose response' with increasing degrees of obesity associated with increased risk. Low BMI at diagnosis was also associated with risk of Crohn's disease versus ulcerative colitis. A U-shaped relationship between BMI and risk of Crohn's was supported by the strong inverse association of BMI at diagnosis (p = 0.0001) and positive association of BMI at diagnosis squared (p = 0.0002) when they were fitted together into the model.
Conclusions: Obesity may play a role in the pathogenesis of Crohn's disease and it may be that obesity-related enteropathy is a distinct entity or a sub-type of Crohn's disease.