Fifteen to 20 percent of people with ulcerative colitis or Crohn's have a parent, sibling, or child who also has the disease. Because IBD occurs more often among people living in cities and industrial nations, it's possible that environmental factors, including a diet high in fat or refined foods, may play a role. Risk Factors Crohn's disease and ulcerative colitis can strike at any age, but you're most likely to develop IBD when you're young. Thirty percent of people with the disease are ages 10 through 19, and most are between the ages of 15 and 35. The average age at diagnosis is 27.
Whites have the highest risk for the disease.
But it can strike any race or ethnic group. If you're Jewish and of European descent, you're five times more likely to have IBD than other whites. You're also at higher risk if you have a close relative, such as a parent, sibling or child, with the disease. If both your parents have IBD, you have a 50 percent chance of developing the disease. If you live in an urban area, or in an industrialized country, you're more likely to develop either Crohn's disease or ulcerative colitis.