Gut doi:10.1136/gutjnl-2011-301095
  • Inflammatory bowel disease
  • Original article

Increased risk of inflammatory bowel disease in women with endometriosis: a nationwide Danish cohort study

Press Release
  1. Nete Munk Nielsen
  1. Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark
  1. Correspondence to Dr Tine Jess, Department of Epidemiology Research, Statens Serum Institut, Oresund Boulevard 5, DK-2300 Copenhagen, Denmark; tjs{at}
  1. Contributors TJ and NMN initiated the study. NMN performed the statistical analyses with support from BVP. All authors were involved in the interpretation of results. TJ drafted the manuscript, which was critically revised by all co-authors. All authors accepted the final version of the manuscript.

  • Revised 14 October 2011
  • Accepted 6 November 2011
  • Published Online First 19 December 2011


Background An association between endometriosis and certain autoimmune diseases has been suggested. However, the impact of endometriosis on risk of inflammatory bowel disease (IBD) remains unknown.

Objective To assess the risk of Crohn's disease (CD) and ulcerative colitis (UC) in an unselected nationwide Danish cohort of women with endometriosis.

Design By use of national registers, 37 661 women hospitalised with endometriosis during 1977–2007 were identified. The relative risk of developing IBD after an endometriosis diagnosis was calculated as observed versus expected numbers and presented as standardised incidence ratios (SIRs) with 95% CIs.

Results Women with endometriosis had a increased risk of IBD overall (SIR=1.5; 95% CI 1.4 to 1.7) and of UC (SIR=1.5; 95% CI 1.3 to 1.7) and CD (SIR=1.6; 95% CI 1.3 to 2.0) separately, even 20 years after a diagnosis of endometriosis (UC: SIR=1.5; 95% CI 1.1 to 2.1; CD: SIR=1.8; 95% CI 1.1 to 3.2). Restricting analyses to women with surgically verified endometriosis suggested even stronger associations (UC: SIR=1.8; 95% CI 1.4 to 2.3; CD: SIR=1.7; 95% CI 1.2 to 2.5).

Conclusion The risk of IBD in women with endometriosis was increased even in the long term, hence suggesting a genuine association between the diseases, which may either reflect common immunological features or an impact of endometriosis treatment with oral contraceptives on risk of IBD.


  • Funding TJ was supported by a female research leader grant (No 09-066323) from the Danish Council of Independent Research.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed

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