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What Causes Inflammatory Bowel Disease?

The Cause Of IBD Has Been Linked To Genetics And Environment


Updated June 04, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

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Question: What Causes Inflammatory Bowel Disease?

Answer: Scientists are not certain what causes inflammatory bowel disease (IBD), which consists of ulcerative colitis and Crohn's disease. It's considered an "idiopathic" disease, or a disease with an unknown cause. However, there are several theories about the origins of IBD, as well as the conditions that may contribute to its development.

Genetics and IBD

With the discovery of certain genes that may cause IBD, it has become apparent that there is a hereditary component to IBD. First-degree relatives of people who have IBD are significantly more likely to also have the disease. However, the majority of people who have IBD have no family history. So while IBD clearly does run in families, it is not the only factor to be taken into consideration when looking at the possible causes of IBD.

IBD's Inflammatory Response

IBD is an autoimmune disease, a disease that is triggered by the immune system. Seasonal flare-ups -- during the spring or autumn -- sometimes occur in people with IBD. One theory is that this is an IgE-mediated allergic response.

The allergic response sets off a chain of events resulting in an excess of eosinophils (cells that try to fight the allergic response) in the body. These eosinophils release four toxic compounds, three of which are found in statistically significant amounts in the stool of IBD patients. This leads some researchers to conclude that an allergic response may have a role in the development of IBD.

An emerging area of research is the role that cytokines play in the development of IBD. Cells called T helper cells are a type of white blood cell that are responsible for removing foreign bodies or unhealthy bacteria from the body. In people who have ulcerative colitis or Crohn's disease, there is an imbalance of T cells that may promote inflammation in the intestine.

Environmental Factors in IBD

There are some clear trends in the epidemiology of IBD that may point to one or more environmental causes. IBD tends to occur most often in developed countries and amongst those with higher socioeconomic status. IBD also tends to occur more often in the urban areas of developed countries. These factors have led researchers to think that there may be some connection between IBD and the lifestyles or environment of people living in developed countries, although no one knows yet what this could be.

One suggested theory is that industrialized nations are "too clean", and because children and adolescents are exposed to fewer bacteria, their immune systems may be inadequate, which leads to autoimmune disease.


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Crohn's and Colitis Foundation of America. "About the Epidemiology of IBD." CCFA.org 2009. 27 Aug 2012.

National Institute of Diabetes and Digestive and Kidney Diseases. "Ulcerative Colitis." National Institutes of Health Feb 2006. 3 Mar 2010.

Peterson CG, Sangfelt P, Wagner M, Hansson T, Lettesjö H, Carlson M. "Fecal levels of leukocyte markers reflect disease activity in patients with ulcerative colitis." Scand J Clin Lab Invest 2007; 67:810-820. 3 Mar 2010.

Saitoh O, Kojima K, Sugi K, Matsuse R, et al. "Fecal eosinophil granule-derived proteins reflect disease activity in inflammatory bowel disease." Am J Gastroenterol 1999 Dec; 94:3513-3520. 3 Mar 2010.

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