Risk factors are identified characteristics that seem to increase a person’s likelihood of developing a condition. However, having one or more risk factors does not mean guarantee a person will develop the condition. Inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis, is a condition that is caused by a combination of genetic and environmental factors, as well as an imbalance in the immune system.1
Risk factors for Crohn's disease
In Crohn's disease (CD), factors such as age, ethnicity, and smoking seem to affect the course of the disease. These factors are linked to disease severity and symptoms. They influence which parts of the digestive tract are affected.
Table. Top risk factors for Crohn’s disease
|Factors that increase the risk of Crohn’s disease:|
|Age: 15-35 years|
|Location: Northern United States or Europe|
|Smoking status: Current smoker|
Risk factors for ulcerative colitis (UC)
While some of the risk factors are similar across the different types of IBD, there are some differences. People who have a higher risk for ulcerative colitis are those with a family history of the disease. Whites have a higher risk than other ethnicities.2,3
Table. Top risk factors for ulcerative colitis
|Factors that increase the risk of ulcerative colitis:|
|Age: Between 15 and 30 years of age, or older than 60 years|
|Location: Northern United States or Europe|
Gender and Crohn's or UC
Women are slightly more likely than men to develop Crohn’s disease. In large studies, between 54% and 62% of patients with Crohn’s disease are women.4 Interestingly, among children, boys are more likely than girls to have Crohn’s disease. The change from being a predominantly male disease to a predominantly female disease happens between ages 14 and 17, after puberty.5 These facts suggest that hormones play a role in developing Crohn’s disease.
Ulcerative colitis occurs at almost the same rate in men and women, although some studies have shown a slight increase in men.3,6
At what age does Crohn's or UC diagnosis occur?
Between 60% and 65% of cases of inflammatory bowel disease are diagnosed in adults.5Ulcerative colitis is slightly more common than Crohn’s disease.
IBD is typically diagnosed between ages 15 and 35.1 In Crohn's disease, adults usually are affected in the end of the small intestine (ileum) and colon.2 Adults are more likely than children or elderly individuals to have narrowing (strictures) or tunneling (fistulas) at the time they are diagnosed.5 Adults typically have symptoms such as diarrhea, abdominal pain, weight loss, and fever. However, the older you are when you are diagnosed, the fewer symptoms you are likely to have.5
Between 5% and 25% of cases of inflammatory bowel disease are diagnosed during childhood.5 In this age group, Crohn’s disease is more common than ulcerative colitis. In the United States and Europe, the rate of Crohn’s disease diagnosis is 0.25 to 13.3 children per 100,000 person-years. The rate is on the rise.5 Family history is a strong risk factor in children. This fact suggests that genetics play a big role for early onset Crohn’s disease.
The very youngest children (ages 0-6 years) typically are affected in the colon only.5 Older children tend to also be affected in the ileum. Inflammation is more likely to spread or extend into other areas of the digestive tract in children than in adults or elderly patients.
Common symptoms of Crohn’s disease in children are poor growth and weight gain, vomiting, and weakness.5 Children tend to have more complications than adults.
About 10% to 15% of patients with inflammatory bowel disease are diagnosed after age 60 years. Ulcerative colitis is slightly more common than Crohn’s disease in this age group.5
Elderly individuals typically have less severe disease. The colon and anus are often affected. Rectal bleeding is a common symptom in this age group. Complications such as narrowing (strictures) or tunneling (fistulas) are less common. The inflammation does not usually spread to other parts of the digestive tract.
Race and ethnicity factors for Crohn's and UC
Whites are more likely to have inflammatory bowel disease than African Americans, Asians, Hispanics, or American Indians.7 However, African American patients are being diagnosed with increasing frequency, and the rate of diagnosis is approaching that of whites.6 Ashkenazi Jews are at higher than average risk of both Crohn’s disease and ulcerative colitis.2,3,8
Interestingly, race and ethnicity have been linked to differences in what part of the digestive tract is affected by Crohn’s disease.9 There are also racial and ethnic differences in the role of family history, need for surgery, and non-digestive symptoms.
Although ulcerative colitis seems to affect African Americans and whites similarly, Crohn’s disease is less likely to affect the ileum and more likely to affect the upper digestive tract or rectum of African American patients compared with whites.9 African Americans are more likely to have perianal disease and narrowing (strictures). Eye or joint symptoms are more common. They are less likely to have tunneling (fistulas) or to undergo surgery.9
Hispanics have more extensive ulcerative colitis than whites.9 Hispanic patients with Crohn's disease are less likely than whites to be affected in the food pipe (esophagus), stomach, or first part of the small intestine (duodenum).9 They are just ask likely to have tunneling (fistulas) or narrowing (strictures) but less likely to have surgery.9 Skin symptoms of Crohn's disease are more common in Hispanics than whites.
Family history and risk of Crohn's or colitis
Having a family member with inflammatory bowel disease increases a person's risk for developing the condition. Up to 20% of people with ulcerative colitis have a family member with the disease, and about 15% of people with Crohn’s disease have family members with inflammatory bowel disease.8,10 Family history is a stronger risk factor for whites than African Americans or Hispanics. It is also a stronger risk factor for children.
People who smoke have twice the risk of developing Crohn’s disease.6 Smoking increases complications, recurrence after surgery, and flare-ups. Smokers need more surgery and medications than non-smokers.4,6 Inflammation of the ileum is more common in smokers than non-smokers.9
However, smoking seems to decrease the risk of developing ulcerative colitis. Several studies have found that active smokers are less likely to have ulcerative colitis than people who have never smoked, but the exact mechanism of how smoking affects the development of IBD isn't clear.6,11
Genetics plus environmental factors
Researchers think that some people have genes that make them more likely to develop IBD.11,12 These people are considered to be “susceptible” to Crohn’s disease and ulcerative colitis. However, not everyone with these genes develops IBD. Environmental factors may be necessary to trigger an immune overreaction in a susceptible person. Yet environmental factors alone are not enough to cause IBD. Currently, the specific environmental factors that trigger Crohn’s disease and ulcerative colitis are unknown.
Researchers have observed a so-called North-South pattern of Crohn’s disease. Within the United States, Crohn’s disease and ulcerative colitis are more common in the Northeast and Midwest than in the South or West.13 People in North America, northern Europe, and the United Kingdom are diagnosed with Crohn’s disease and ulcerative colitis more frequently than in central Europe, Asia, Africa, and Latin America.6
IBD is also more common in industrialized countries than in developing nations.6 Possible reasons include:
- Greater awareness and diagnosis of the disease
- Infectious causes of diarrhea are less common in industrialized regions
- Factors related to Western lifestyle, including diet
Appendectomy as a risk of Crohn's disease
Having your appendix removed after age 10 increases your risk of Crohn’s disease. In fact, the risk increases 6.7 times in the first year after an appendectomy. However, if you do not develop Crohn’s disease within 4 years of appendix removal, your risk of getting it returns to normal.4
Having an appendectomy seems to reduce the risk of developing ulcerative colitis, especially in children who have the surgery before age 10.11