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What is ulcerative colitis?

Ulcerative colitis (UC), like Crohn’s disease (CD), is a subcategory of inflammatory bowel disease (IBD) characterized by inflammation in the gut that may be related to a dysregulated immune response to microbes.1

Inflammation in ulcerative colitis is generally restricted to the innermost lining, or mucosa, of the colon and rectum. This inflammation occurs in an uninterrupted way throughout the affected area, with no segments of normal tissue.2 The main symptoms of UC are bloody diarrhea, abdominal pain, and fatigue, all of which can significantly reduce daily functioning and quality of life.

According to the Center for Disease Control and Prevention (CDC), three million American adults reported a diagnosis of IBD in 2015.3 UC prevalence rates are highest in Europe (505 per 100,000), Canada (248 per 100,000), and the USA (214 per 100,000).4 Ulcerative colitis often first appears in early adulthood, although recent data shows a moderate increase in first onset in late life. In general, UC is a chronic condition. When untreated, relapses are common.5.

In the gastrointestinal tract, mucosa refers to the innermost layer, directly surrounding the open space within the tube.

What are the common symptoms?

The main symptoms of UC are:

  • Abdominal pain
  • Bloody stool
  • Diarrhea
  • Fatigue
  • Fever
  • Reduced appetite
  • Weight loss

UC patients may have periods of active illness (known as “flares”) followed by periods of remission in which the symptoms decrease or even disappear. Moderate symptoms of the disease include progressive loose stools, abdominal pain, and diarrhea. More severe stages can result in reduced appetite, fatigue, weight loss, and anemia due to nutrient deficiency.2,6

 What are the causes?

There is no single clear cause of UC, but it may be related to an abnormal immune response in susceptible individuals.7 Recent studies have found that the inner mucosal layer in the colon separates bacteria from epithelial cells, and that defects in the genes related to preservation of this mucus layer may allow bacteria to reach the epithelium, activating the immune system and causing colonic inflammation.5,8

As mentioned, genetics also play a role in the development of UC; between 8–14% of patients have a family history of the disease, and first-degree relatives have four times the risk of developing it. Several environmental causes are also thought to encourage development of UC. One is a lack of exposure to infectious microorganisms during childhood (potentially due to increased sanitation in industrialised countries) which can trigger an inappropriate immune response. Another is a “western style” diet, which includes high quantities of sugar, fat, and processed foods. Smoking is one of the strongest risk factors. Consumption of non-steroidal anti-inflammatory drugs (NSAIDs) may also increase the permeability of the mucosal colon lining and contribute to colonic bleeding.4,9

How does this topic relate to my microbiome?

Patients with UC have an altered colonic microbiome compared with healthy individuals. Decreased diversity in these individuals gut microbiota can affect the balance between beneficial vs. pathogenic bacteria. This can alter the ability of the microbiome to adapt and resist infections, environmental changes, and natural disturbances.10 In addition, there is evidence that pathogenic bacteria may play a key role in UC. Potential pathogens associated with UC include Escherichia coli, Clostridium difficile, and Shigella.2

Which diseases/topics are related to ulcerative colitis?

Ulcerative Colitis is a systemic illness that has been associated with multiple extraintestinal complications. These include11,12:

  • Anxiety
  • Arthritis
  • Depression
  • Osteoporosis
  • Primary sclerosing cholangitis
  • Renal stones
  • Skin disorders
  • Venous and arterial thromboembolism
  • Vitamin B12 deficiency

Primary sclerosing cholangitis is a chronic liver disease defined by a progressive obstruction of the normal flow of bile. It is associated with inflammation and fibrosis of the biliary ducts.13

How can I take action?

If you are experiencing changes in your bowel habits or if you have symptoms of ulcerative colitis, it’s important to consult your doctor. Your doctor can then conduct tests to check for UC. UC diagnosis is based on medical history, physical examinations, and imaging examinations. Tests and procedures can be ordered, including:

  • Blood or stool tests
  • Endoscopy or colonoscopy
  • Imaging procedures

Once diagnosed, the activity, severity, and extent of UC should be evaluated to adequately manage progression, intervention, and remission. Treatment may include medications, changes in lifestyle, probiotics, intervention treatments, and pain management.14,15,16


1. Manichanh, C., Borruel, N., Casellas, F., & Guarner, F. (2012). The gut microbiota in IBD. Nature Reviews Gastroenterology & Hepatology, 9(10), 599–608.

2. Head, K. a, & Jurenka, J. S. (2003). Inflammatory bowel disease Part 1: ulcerative colitis–pathophysiology and conventional and alternative treatment options. Alternative Medicine Review : A Journal of Clinical Therapeutic, 8(3), 247–283.

3. Dahlhamer, J. M., Zammitti, E. P., Ward, B. W., Wheaton, A. G., & Croft, J. B. (2016). Prevalence of Inflammatory Bowel Disease Among Adults Aged ≥18 Years — United States, 2015. Morbidity and Mortality Weekly Report, 65(42), 1166–1169.

4. Ungaro, R., Mehandru, S., Allen, P. B., Peyrin-Biroulet, L., & Colombel, J. F. (2017). Ulcerative colitis. The Lancet, 389(10080), 1756–1770.

5. Ford, A. C., Moayyedi, P., & Hanauer, S. B. (2013). Ulcerative colitis. British Medical Journal, 346, f432–f432.

6. Silverberg, M. S., Satsangi, J., Ahmad, T., Arnott, I. D., Bernstein, C. N., Brant, S. R., Warren, B. F. (2005). Toward an Integrated Clinical, Molecular and Serological Classification of Inflammatory Bowel Disease: Report of a Working Party of the 2005 Montreal World Congress of Gastroenterology. Canadian Journal of Gastroenterology, 19(suppl a), 5A–36A.

7. Moayyedi, P., et al. (2015). Fecal Microbiota Transplantation Induces Remission in Patients With Active Ulcerative Colitis in a Randomized Controlled Trial. Gastroenterology, 149(1), 102–109.

8. Johansson, M. E. V, et al. (2014). Bacteria penetrate the normally impenetrable inner colon mucus layer in both murine colitis models and patients with ulcerative colitis. Gut, 63(2), 281–291.

9. Molodecky, N. A., & Kaplan, G. G. (2010). Environmental risk factors for inflammatory bowel disease. Gastroenterology & Hepatology, 6(5), 339–346.

10. Shi, Y., Dong, Y., Huang, W., Zhu, D., Mao, H., & Su, P. (2016). Fecal Microbiota Transplantation for Ulcerative Colitis: A Systematic Review and Meta-Analysis. PLOS ONE, 11(6), e0157259.

11. López-San Román, A., & Muñoz, F. (2011). Comorbidity in inflammatory bowel disease. World Journal of Gastroenterology, 17(22), 2723–2733.

12. Navaneethan, U. (2014). Hepatobiliary manifestations of ulcerative colitis: an example of gut-liver crosstalk. Gastroenterology Report, 2(3), 193–200.

13. Hirschfield, G. M., Karlsen, T. H., Lindor, K. D., & Adams, D. H. (2013). Primary sclerosing cholangitis. The Lancet, 382(9904), 1587–1599.

14. Matsuoka, K., Kobayashi, T., Ueno, F., Matsui, T., Hirai, F., Inoue, N., … Shimosegawa, T. (2018). Evidence-based clinical practice guidelines for inflammatory bowel disease. Journal of Gastroenterology, 53(3), 305–353.

15. Carter, M. J. (2004). Guidelines for the management of inflammatory bowel disease in adults. Gut, 53(suppl_5), v1–v16.

16. Crohn’s & Colitis Foundation. Diagnosing and Managing IBD. (2011).