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The Epidemiology of IBD

About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD
While inflammatory bowel disease (IBD) is a perplexing group of diseases that tends to be difficult to diagnose and treat, researchers have collected a significant amount of information concerning the genetics, distribution, and contributing environmental factors for IBD. Overall, IBD is a disease of white persons living in developed countries and tends to be diagnosed most commonly in adolescents and young adults.
While Crohn’s disease (CD) and ulcerative colitis (UC) do appear to run in families, the connection is not always direct (such as from parent to child). The risk of inheriting IBD is generally low, except in cases where both parents have a form of IBD.
At what age is IBD most common?:

IBD is often considered a disease of adolescents and young adults because it is most commonly first diagnosed in people between the ages of 15 and 25 years (at least one source indicates peak incidence to be between 15 to 35 years[1]). Of the estimated 1.4 million people in the United States who have IBD, 10% are children. At about age 50 there is another increase in the diagnosis of IBD.[1]

Is IBD more common in one gender?:

IBD appears to affect both genders equally.

In what geographic areas is IBD more prevalent?:

IBD is more common in:

  • Developed countries
  • Urban areas
  • Northern climates
UC is most common in the United States and in northern European countries and least common in Japan and South Africa.
How many people have IBD?:

It is widely estimated that between 1 and 1.4 million people in the United States have IBD. (Some experts indicate that this number may be an overestimate.) In Europe, the number of people with IBD is estimated to be 2.2 million.[2]

In the United States, the prevalence of IBD is:

  • UC: 100 to 200 people per 100,000 people
  • CD: 30 to 100 people per 1000,000 people

Does ethnicity affect the risk of developing IBD?:
  • Ashkenazi Jews are more likely to develop IBD.
  • IBD is more common in white people, but the incidence in African Americans is increasing.
What environmental factors affect the risk of developing IBD?:

Two factors, appendectomy and a history of cigarette smoking, have been shown to have an affect on the development of IBD. The results of 13 studies conducted between 1987 and 1999 suggest that removal of the appendix could lessen the risk of developing UC by up to 69 percent.

Former smokers are at the highest risk for developing UC, while current smokers have the least risk. This tendency indicates that smoking cigarettes helps prevent the onset of UC. Smoking cigarettes actually has an inverse effect on CD; people who smoke, or who have smoked in the past, have a higher risk of developing CD than non-smokers.
What is the risk of inheriting IBD?:
  • There seems to be a stronger risk of inheriting CD than UC, especially in families of Jewish descent.
  • Children who have one parent with CD have a 7 to 9% lifetime risk of developing the condition and a 10% risk of developing some form of IBD.[3]
  • Children of two parents who have IBD have a 35% risk of developing some form of IBD.
  • Approximately 20% of people with IBD have a family member with IBD.
  • The risk of IBD for persons who have a family member who has IBD is 10 times higher than for persons in the general population.
  • The risk of IBD for persons who have a sibling with IBD is 30 times higher than for persons in the general population.

Other factors, such as diet, use of oral contraceptives, and infections are being studied, but their role is still unclear.[2]

References:
1. The Crohn’s and Colitis Foundation of America. Available at: http://www.ccfa.org/about/press/epidemiologyfacts. Last accessed January 6, 2005.
2. Loftus EV Jr. Clinical epidemiology of inflammatory bowel disease: Incidence, prevalence, and environmental influences. Gastroenterology. 2004 May;126(6):1504-17.
3. Peeters M, Nevens H, Baert F, et al. Familial aggregation in Crohn's disease: Increased age, adjusted risk and concordance in clinical characteristics. Gastroenterology. 1996;111:597-603.

Updated: October 19, 2006
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