Epidemiology of the IBD

In the United States, it is currently estimated that about 1 –1.3 million people suffer from IBD.1, 2 The cause of IBD is unknown, and until we understand more, prevention or a cure will not be possible.

We do understand that IBD affects some subpopulations more than others.


  • Ulcerative colitis is slightly more common in males, while Crohn’s disease is more frequent in women.


  • IBD occurs more in people of Caucasian and Ashkenazic Jewish origin than in other racial and ethnic subgroups. Previously noted racial and ethnic differences seem to be narrowing though.2 In spite of incomplete data on certain subgroups including racial and ethnic minorities and geographic regions, reported rates remain in similar ranges.

We still do not have a precise understanding of how many people experience Crohn’s disease and ulcerative colitis because we lack standard criteria for diagnosing IBD. Identifying cases of IBD is often inconsistent or the disease may be classified as another condition.


Prevalence (number of existing cases per 100,000 population)
Crohn’s disease Ulcerative colitis
26 to 199 cases per 100,000 persons2 37 to 246 cases per 100,000 persons2
201 per 100,000 adults1 238 per 100,000 adults1


Incidence Rate (number of newly diagnosed cases per 100,000 person-years
Crohn’s disease Ulcerative colitis
3.1 to 14.6 cases per 100,000 person-years2 2.2 to 14.3 cases per 100,000 person-years2



  • Ulcerative colitis is more common among ex-smokers and nonsmokers, while Crohn’s disease is more common among smokers.2
  • IBD is more common in developed countries. There is north- to- south variation and is more common in urban communities compared with rural areas. These observations suggest that urbanization is a potential contributing factor. It is believed that this is the result of “westernization” of lifestyle, such as changes in diet, smoking, differences in exposure to sunlight, pollution, and industrial chemicals.3


  • Three studies outside of the United States have examined the relationship between socioeconomic factors and IBD. One study found both ulcerative colitis and Crohn’s disease are more prevalent in white-collar occupations.4 Another study found Crohn’s disease and ulcerative colitis were less common in groups with higher education and income.5  A third study found a minor association between specific occupations and IBD.6

Other factors

  • Diet, oral contraceptives, perinatal and childhood infections, or atypical mycobacterial infections have been suggested, but not proven, to play a role in developing IBD.7

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1 Kappelman MD, Rifas-Shiman SL, Kleinman K, Ollendorf D, Bousvaros A, Grand RJ, Finkelstein JA. The prevalence and geographic distribution of Crohn’s disease and ulcerative colitis in the United States. Clin Gastroenterol Hepatol. 2007; 5:1424-9.

2 Loftus EV, Jr. Clinical epidemiology of inflammatory bowel disease: Incidence, prevalence, and environmental influences. Gastroenterology. 2004; 126:1504-17.

3 Hanauer S. Inflammatory Bowel Disease: epidemiology, pathogenesis and therapeutic opportunitiesExternal. Inflamm Bowel Dis 2006;12:S3-9 (Suppl 1).

4 Sonnenberg A. Disability from inflammatory bowel disease among employees in West Germany.External Gut. 1989;30(3):367–70.

5 Bernstein CN, Kraut A, Blanchard JF, Rawsthorne P, Yu N, Walld R. The relationship between inflammatory bowel disease and socioeconomic variables.External
Am J Gastroenterol 2001;96(7):2117–25.

6 Li X, Sundquist J, Sundquist K. Educational level and occupation as risk factors for inflammatory bowel diseases: a nationwide study based on hospitalizations in Sweden.External Inflamm Bowel Dis 2009;15(4):608–15.

7 Feldman M, Friedman LS, Brandt LJ, editors. Sleisenger and Fordtran’s Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, and Management 8th edition. Philadelphia, PA: Publisher Saunders an imprint of Elsevier; 2006.