Background: Obesity is associated with intestinal-specific inflammation. Nonetheless, a specific role of obesity in the etiology of inflammatory bowel disease is unclear.
Methods: We conducted a prospective cohort study of U.S. women enrolled in 1989 in the Nurses' Health Study II. At baseline, we collected information on height, weight, waist and hip circumference, weight at age 18, and body shape at age 20. We used Cox proportional hazard models to calculate hazard ratios and 95% confidence intervals (CIs).
Results: Among 111,498 women (median age, 35 yr), we documented 153 cases of Crohn's disease (CD) and 229 cases of ulcerative colitis (UC) more than 18 years of follow-up, encompassing 2,028,769 person-years. Compared with women with normal BMI, the multivariate-adjusted hazard ratios of CD were 2.33 (95% CI, 1.15-4.69) for obese women at age 18 and 1.58 (95% CI, 1.01-2.47) for obese women at baseline. Increasing weight gain between age 18 and baseline was associated with increased risk of CD (Ptrend = 0.04). Adolescent body habitus was also associated with risk of CD with a multivariate-adjusted hazard ratio of CD of 1.63 (95% CI, 1.07-2.50) for women with overweight/obese body shape compared with women with a thin/slender body shape. We did not observe a significant association between any of these anthropometric measures and risk of UC.
Conclusions: In a large prospective cohort of U.S. women, measures of adiposity were associated with an increased risk of CD but not UC. Additional studies are needed to elucidate the biological mechanisms by which excess adiposity may increase the risk of CD.