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 (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.

Vitamin D as a novel therapy in inflammatory bowel disease: new hope or false dawn?

“…Two separate published analyses, based on data from women who participated in the Nurses' Health studies in the USA, support this association between higher latitude and higher incidence of IBD (25,27) . Khalili et al reported a significant increase in incidence of both CD and UC according to more northerly latitude of residence (25) . The authors further analysed the latitude of residence across a number of time points and found the strongest association at age 30 years.…”

“…The exact cause of IBD remains unknown; however, the disease is thought to result from a complex interaction between immunological, genetic and environmental factors. Vitamin D status is one such postulated environmental risk factor (24)(25)(26) . Epidemiological studies show a geographic variation in the incidence of IBD, with a higher incidence in countries of more northern latitudes, mirroring sunlight patterns and likely to reflect vitamin D levels.…”

“…Epidemiological studies show a geographic variation in the incidence of IBD, with a higher incidence in countries of more northern latitudes, mirroring sunlight patterns and likely to reflect vitamin D levels. Studies in the USA (25,27) and Europe have linked latitude to risk of both CD and UC (28)(29)(30) . Two separate published analyses, based on data from women who participated in the Nurses' Health studies in the USA, support this association between higher latitude and higher incidence of IBD (25,27) .…”

“…Studies in the USA (25,27) and Europe have linked latitude to risk of both CD and UC (28)(29)(30) . Two separate published analyses, based on data from women who participated in the Nurses' Health studies in the USA, support this association between higher latitude and higher incidence of IBD (25,27) . Khalili et al reported a significant increase in incidence of both CD and UC according to more northerly latitude of residence (25) .…”

Editorial: Vitamin D and IBD: Can We Get Over the “Causation” Hump?

“…Epidemiologically, we know that the incidence of IBD is higher in countries in which ultraviolet exposure is lower or which are more distant from the equator-i.e., countries with a high prevalence of vitamin D defi ciency ( 8 ). Studies examining the individual level ultraviolet exposure based on small-area analysis of postal codes or within larger regions in the country have demonstrated a similar gradient in the incidence of IBD that correlates inversely with predicted levels of vitamin D insufficiency ( 9 ). We also know that vitamin D defi ciency is common in those with IBD, perhaps more so than in the general population, and that this is apparent even in newly diagnosed patients ( 10 ), arguing against such defi ciency being solely a consequence of prolonged disease.…”