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 (ptrend<0.01), with residence at age 30 years more strongly associated with risk. Compared with women residing in northern latitudes at age 30, the multivariate-adjusted HR for women residing in southern latitudes was 0.48 (95% CI 0.30 to 0.77) for CD and 0.62 (95% CI 0.42 to 0.90) for UC. The effect of latitude of residence on risk of CD and UC did not vary according to smoking history (pinteraction=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.
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- Inflammatory bowel disease
- Crohn's disease
- ulcerative colitis
- nurses' health study
- crohn's colitis
- cancer epidemiology
- health service research
- gastrointestinal haemorrhage
- IBD clinical
- cancer prevention
- non-steroidal anti-inflammatory drugs
Funding Funded by National Institute of Health R01 CA137178, P01 CA55075, P01 CA87969, DK043351, and the Broad Medical Research Program of The Broad Foundation. ATC is a Damon Runyon Cancer Research Foundation Clinical Investigator. HK is supported by a career development award from the IBD Working Group and the Crohn's and Colitis Foundation of America. ANA is supported by a career development award from the American Gastroenterological Association.
Competing interests ATC has previously served as a consultant for Bayer Healthcare and Millennium Pharmaceuticals.
Patient consent This study is based on two large ongoing prospective studies of NHS and NHS II. These participants gave consent to be part of these studies in 1976 and 1989, respectively.
Ethics approval Ethics approval was obtained from the Institutional Review Board at the Brigham and Women's Hospital.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Requests for access to data, statistical code, questionnaires and technical processes may be made by contacting the corresponding author at .
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