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Inflammatory Bowel Disease: Overview and Risk Factors

The most prevalent chronic inflammatory disorders of the digestive tract are ulcerative colitis and Crohn's disease, referred to collectively as inflammatory bowel disease (IBD). Approximately 1 million Americans have some form of IBD. Although the disorders share some clinical and pathologic features, each is a distinct condition. Crohn's disease can affect any part of the gastrointestinal tract from the mouth to the anus, often invading the deep layers of affected tissues, whereas ulcerative colitis affects the mucosa of the colon and rectum.

Causes of IBD have not been fully established, but the disorder is believed to be caused by abnormal immune system activation, which results in chronic inflammation and ulceration. Individuals with ulcerative colitis or pan-colitis have a higher risk of colon cancer, chronic active hepatitis, cirrhosis, arthritis, and nutritional deficiencies.

Risk Factors

Genetics. Nod2 gene mutations are present in 30% of patients with Crohn's disease.

Environment. IBD is more common in developed countries, urban areas, colder climates, and among people of high socioeconomic status. Incidence also increases in populations that migrate from low-risk to high-risk areas.

Age. Onset usually occurs in people between the ages of 15 and 35.

Race. Whites have the highest risk. Also, Ashkenazi Jews have up to an 8-fold greater risk of developing IBD, compared with the general population. Caucasians and African Americans are more likely to have IBD than Hispanics and Asian Americans. Recently, however, Crohn's disease has become as frequent in Japan as in the United States, likely due to westernized lifestyle, including diet, increasing urbanization, and industrialization.

Family history. People with an affected relative have a 10-fold greater risk of having IBD. If the relative is first-degree, the risk is 20 to 35 times greater.

NSAIDs. Use of nonsteroidal anti-inflammatory drugs may trigger or cause relapse of IBD. Large intestinal ulcers, bleeding, strictures, and perforation are occasionally due to NSAIDs.1

Additional possible risk factors that require further study include the following:

Smoking. Studies on smoking and IBD risk, including maternal smoking during pregnancy and risk to the child for future IBD, show conflicting results.

Lack of breast-feeding. Some evidence suggests that breast-feeding may reduce risk, but more studies are needed to assess this possibility. See Nutritional Considerations for more information.

Inflammatory Bowel Disease: Diagnosis >>