Who Has a Greater Risk of Developing IBD?

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 affects people of all genetic backgrounds, but it seems to have a higher prevalence in western and developing countries. It also tends to be diagnosed most commonly in adolescents and young adults.

While Crohn's disease and ulcerative colitis do appear to run in families, the connection is not always direct (such as from parent to child). The risk of inheriting is a complex process with many factors, influenced by both one's genetic predisposition and environment.

Age IBD Is 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). Of the estimated 1.6 million people in the United States who have IBD, 10% are children.

After about age 50 there is another increase in the diagnosis of IBD. This is often referred to as a "bimodal peak"—that is, incidence spikes at younger ages and also older ages.

More Common in Men Or Women?

IBD appears to affect both men and women in equal amounts.

Geographic Areas IBD Is More Prevalent

IBD is more common in:

• Developed countries
• Urban areas
• Northern climates

Ulcerative colitis is most common in the United States and in northern European countries and least common in Japan and South Africa. Some theories as to why IBD prevalence is higher in western, developed countries is because there is a higher use of antibiotics, and possibly the effect of western diets on the microbiome.

How Many People Have IBD?

It is widely estimated that approximately 1.6 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.

In the United States, the prevalence of IBD is:

• Ulcerative colitis: 100 to 200 people per 100,000 people
• Crohn's disease: 30 to 100 people per 1000,000 people

Ethnicities at a Higher Risk 

• Ashkenazi Jews are more likely to develop IBD.
• IBD is most common in Caucasians and African Americans, and least common in people of Hispanic and Asian descent.

Who Is The Risk of Inheriting IBD?

• There seems to be a stronger risk of inheriting Crohn's disease than ulcerative colitis, especially in families of Jewish descent.
• Children who have one parent with Crohn's disease have a 7 to 9% lifetime risk of developing the condition and a 10% risk of developing some form of IBD.
• 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.