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What Causes Ulcerative Colitis?

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Story at-a-glance

  • The exact cause behind this condition is still unknown, but researchers believe that it’s triggered by an overreaction of the immune system
  • Smoking is a widely studied environmental factor linked to ulcerative colitis. The risk of developing this condition is higher in nonsmokers and ex-smokers
  • According to the Crohn’s and Colitis Foundation of America, around 5% to 20% of patients with this disease have a first-degree relative who suffers from a form of IBD as well

Ulcerative colitis was first identified by two English physicians in 1875, although there were already reports of a disease with the same symptoms as ulcerative colitis years before.1 The exact causes behind this condition are still unknown even though it’s been more than a century since it was distinguished from the other gastrointestinal problems.

What is known, though, is that ulcerative colitis is the most common type of inflammatory bowel disease, with six to 15 new cases diagnosed each year for every 100,000 persons. This adds up to about 907,000 people currently living with ulcerative colitis in the U.S.2 The prevalence of this condition gave researchers ample epidemiologic data to observe it, and numerous studies show that ulcerative colitis affects certain subpopulations more than others.3

Ulcerative Colitis Is Linked to an Overactive Immune Response

Ulcerative colitis is characterized by an inflammation of the colon and rectum. Researchers believe that this condition is triggered by an overreaction of the immune system.

It’s important to note that inflammation is the immune system’s way of eliminating foreign invaders, such as bacteria and viruses, and reducing their harmful effects on the body. It causes redness, swelling and pain, which eventually go away once the harmful foreign invaders are destroyed.

In people with ulcerative colitis, the immune system mistakes the food and bacteria inside the large intestine for harmful foreign substances. As a result, it produces cytokines (which are chemical messengers that trigger inflammation) and targets the lining of the large intestine. This abnormal immune response causes the colon and rectum to become raw and inflamed chronically, which may lead to serious complications over time.4

Environmental Factors Are One of the Possible Triggers

Ulcerative colitis is not just caused by an overreaction of the immune system alone. In fact, studies suggest that environmental factors may also trigger (if not directly cause) this disease.

Smoking is a widely studied environmental factor linked to ulcerative colitis. The risk of developing this condition is higher in nonsmokers and ex-smokers. On the other hand, smokers with ulcerative colitis experience lower rates of relapse and reduced need for colectomy. While the mechanism by which smoking influences inflammatory bowel diseases (IBD) is still unclear, researchers have been able to confirm that this environmental factor has an inverse association with ulcerative colitis.5

Appendectomy is another strong environmental risk factor that may influence the occurrence of ulcerative colitis, and studies suggest that it also has an inverse association with this disease. This means that people who underwent appendectomy have a lower risk of developing ulcerative colitis.6

The other environmental risk factors that were explored include oral contraceptives, diet, breastfeeding and nonsteroidal anti-inflammatory drugs (NSAIDs). However, it’s still unclear whether these factors have any influence on the occurrence of ulcerative colitis.7,8

Genetics May Play a Role in the Development of IBD

Scientific evidences confirm that heredity is one of the possible causes of ulcerative colitis. According to the Crohn’s and Colitis Foundation of America, around 5% to 20% of patients with this disease have a first-degree relative who suffers from a form of IBD as well. The risk of developing ulcerative colitis also becomes higher when both parents have an IBD.

It’s important to note that genetics does not guarantee the occurrence of ulcerative colitis — it simply increases a person’s susceptibility to this disease. Researchers suggest that environmental factors and immune response must also come into play for a person to develop this condition.9


Ulcerative Colitis: Introduction

What Is Ulcerative Colitis?

Ulcerative Colitis Symptoms

Ulcerative Colitis Causes

Types of Ulcerative Colitis

Ulcerative Colitis Treatment

Ulcerative Colitis Prevention

Ulcerative Colitis Diet

Ulcerative Colitis FAQ

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Types of Ulcerative Colitis

Sources and References

  • 1, 9 Crohn's & Colitis Foundation of America, The Facts About Inflammatory Bowel Diseases
  • 2
  • 3, 5 Centers for Disease Control and Prevention, Epidemiology of the IBD
  • 4 Crohn's & Colitis, Ulcerative Colitis Causes
  • 6, 8 Gastro-Hep Communications, Inc., Environmental Risk Factors for Inflammatory Bowel Disease, 2010 May; 6(5): 339–346
  • 7 Current Gastroenterology Reports, Environmental Triggers for Inflammatory Bowel Disease, 2013 Jan; 15(1): 302
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