Risk Factors

Genetic factors play a role in who develops ulcerative colitis; indeed, the most firmly established risk factor is a family history of it. Approximately 10 percent of patients with ulcerative colitis have a first-degree relative with the illness. Jewish heritage greatly increases the risk of UC, but rates among Jews vary from country to country. The prevalence of UC is higher among Jews born in Europe or the United States than for those born in Asia or Africa, suggesting that environmental factors also play a role.

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In epidemiological studies of twins, identical twins share a stronger risk of UC than do fraternal twins. However, there is not a perfect concordance of the disease among identical twins, providing further evidence that factors other than genetics, such as environment, also play a role. It's likely that a group of genes working together, and influenced by environmental factors, lead to ulcerative colitis, although these genes have not been identified.

Among the possible environmental factors, no specific foods have been identified as a cause of ulcerative colitis. However, many people with UC are intolerant of cows' milk and find that dairy products may aggravate symptoms.

Cigarette smoking actually reduces the risk, though what component of tobacco has a beneficial effect on the colon lining is not clear. Smokers have only about 40 percent of the risk of developing ulcerative colitis of nonsmokers. Among one group of 30 intermittent smokers with UC, resuming smoking a pack of cigarettes per day over a six-week period led to an improvement in symptoms in 50 percent of these patients. Stopping smoking seems to increase the risk of developing UC. Former smokers are about 1.7 times more likely to develop the disease than are those who have never smoked. Some researchers have theorized that nicotine could be the element in tobacco that reduces the risk of UC. Controlled trials of a nicotine patch as therapy for UC suggest nicotine may play a role in preventing the disease. On the other hand, a high proportion of nonsmokers experienced unacceptable side effects from nicotine patches. A trial of nicotine gum among patients with UC was unsuccessful.