Geographical variation and incidence of inflammatory bowel disease among US women

Abstract

Objective Geographical variation in the incidence of Crohn's disease (CD) and ulcerative colitis (UC) according to the latitude of residence has been reported in Europe. However, there are no comparable data in the USA. The incidence of CD and UC in relation to latitude was assessed in a geographically diverse population of women enrolled in two large prospective studies in the USA. Design A prospective study was undertaken of women enrolled in the Nurses' Health Study I (NHS) in 1976 and in the NHS II in 1989. Information on state of residence at the time of birth, at age 15 years and age 30 years was collected in 1992 in NHS I and in 1993 in NHS II. Reported diagnoses of incident CD or UC to the end of 2003 were confirmed by medical record review. Cox proportional hazards models were used to calculate HRs and 95% CIs for risk of CD and UC. Results In both cohorts, among 175 912 women reporting their residence in 1992, 257 cases of CD and 313 cases of UC were documented over 3 428 376 person-years of follow-up. The incidence of CD and UC increased significantly with increasing latitude (p_trendinteraction=0.26 for CD and 0.99 for UC). Conclusion In a population of US women, increasing latitude of residence was associated with a higher incidence of CD and UC.