Ulcerative Colitis Causes and Risk Factors, Explained

If you find yourself shaking your fists at the sky, demanding to know the truth behind the causes of ulcerative colitis (UC), you’ve probably had your fair share of less-than-pleasant bathroom time.

Ulcerative colitis is a type of inflammatory bowel disease (IBD), and it’s more common than you might think. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) estimates that between 600,000 and 900,000 people in the United States live with this chronic condition, but it’s likely even more than that.

When you have ulcerative colitis, an abnormal immune response leads to an increase in inflammation in the colon, causing ulcers to appear on its inner lining. This ultimately leads to symptoms like bloody diarrhea, abdominal cramping, and the urge to go (like now).

The good news is, with treatment, people diagnosed with ulcerative colitis often have periods of remission, where symptoms go away for a while. Remission can last for weeks or even for several years. If and when ulcerative colitis symptoms return, it’s called an ulcerative colitis flare-up or relapse.

To understand the possible ulcerative colitis causes, it’s important to first understand a little bit about the structure of your colon, which is your large bowel or large intestine.

Mucus coats the colon’s walls to not only serve as a lubricant for stool moving through your bowels but to also help keep germs and harmful substances away from the cell layer that lines the colon. The scientific name for this layer of cells is the epithelium. The epithelium itself is an important barrier to potentially harmful substances and is fortified by tight connections between each cell. Located below the epithelium is an area called the lamina propria, which is made up of connective tissue and is home to several types of immune cells, according to a 2016 study published in the journal Inflammatory Bowel Diseases.¹

In ulcerative colitis, the barriers provided by mucus and the epithelium are dysfunctional. This means that the epithelial cells and nearby immune cells are increasingly exposed to bacteria and potentially other substances, like yeast, that are found in the colon.

Because the immune response is abnormal, this can have several damaging effects in the colon and throughout the body, such as an expanded presence of immune cells that attack the lining of the colon, increased inflammation, and further disruption of the colon’s lining, Nicole Fay, Ph.D., an immunotherapeutics researcher and a director of pharmacology at Nutcracker Therapeutics, tells SELF.

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The one thing experts know for sure about the inherent cause of ulcerative colitis is that “the immune system is in overdrive,” Ariela Holmer, M.D., a gastroenterologist at the Inflammatory Bowel Disease Center of NYU Langone Health, tells SELF.

Doctors and researchers aren’t exactly sure what sets off the immune system to begin with. However, it’s generally accepted that ulcerative colitis is caused by a very complex interaction of several factors. “Evidence has been found for genetic causes, environmental factors, and gut microbiome as drivers to our body’s own immune damage,” Dr. Fay says. Here’s a bit more about each one:

Your colon is full of bacteria. These help you digest food and are also important for overall gut health. Normally, your immune system ignores or tolerates these microbes because a majority of them are beneficial to the body.

Your microbiome, which is the makeup of microbes in your gut, is altered in ulcerative colitis. A 2020 systematic review published in the journal Frontiers in Medicine analyzed the microbiomes of five groups of people with IBD. Researchers were able to detect significant differences in the microbiomes between people with IBD and people without IBD. Additionally, they were also able to find differences in the microbiomes of people with different types of IBD, such as ulcerative colitis and Crohn’s disease.²

It’s currently unknown if changes in the microbiome are a direct cause or a consequence of inflammation in ulcerative colitis. For example, increases in some types of bacteria may ratchet up inflammation in the colon, contributing to ulcerative colitis symptoms. Alternatively, a dysfunctional immune system may no longer tolerate some types of beneficial gut bacteria and attack them instead, depleting their numbers. Environmental factors like diet or digestive infections can alter the microbiome, too, according to a 2021 study published in the journal Frontiers of Cellular and Infection Microbiology.³ Regardless of how it happens, shifts in the makeup of the microbiome can negatively impact the gut and immune function.

The incidence of IBD, including ulcerative colitis, has been increasing around the world. A study published in Lancet Gastroenterology and Hepatology looked into the prevalence of IBD worldwide, finding that it increased from 79.5 per 100,000 people in 1990 to 84.3 per 100,000 people in 2017. Because of this, it’s believed that environmental factors may also play a role in promoting the development of ulcerative colitis.⁴

IBD is more common in industrialized countries. Some examples include the United States, Canada, and western and northern Europe. One idea of why this has happened is called the “hygiene hypothesis.” Simply put, people in these countries are typically exposed to fewer microbes due to living in extremely clean homes, particularly early in life. This may lead to alterations in gut bacteria, raising the risk of IBD in some people.

What other types of environmental factors are important? A big one that has been explored is a “Western-style diet,” which is defined as being high in processed carbohydrates and animal proteins or fats, while being lower in dietary fiber and fresh fruits and vegetables. A systematic review and meta-analysis published in the Journal of Digestive Diseases looked at nine studies, which included 1,491 people with IBD and 53,089 people without IBD. The researchers found that consuming a Western-style diet prior to IBD diagnosis was associated with an increased risk of developing IBD, including ulcerative colitis. The researchers theorize that diet may contribute to the development of IBD by affecting helpful gut bacteria.⁵ However, more research is necessary to understand the true impact of diet on ulcerative colitis risk.

Another environmental factor that may contribute to ulcerative colitis symptoms is a history of prior digestive infections, such as the “stomach flu.” A systematic review in the journal Alimentary Pharmacology and Therapeutics included 63 studies and investigated the role of digestive infections in new IBD diagnoses. Researchers found that infections with salmonella bacteria, campylobacter bacteria, C. difficile bacteria, and norovirus were consistently associated with a higher risk of IBD.⁶

The researchers hypothesize that these infections may potentially raise IBD risk in a variety of ways, such as affecting the balance of the microbiome, altering the immune response in the gut, or directly damaging the lining of the colon. However, they also note that additional research is needed to determine exactly how these infections may contribute to IBD risk.

Genetics can play a role in causing ulcerative colitis. Because of this, if you have a close family member with ulcerative colitis or Crohn’s disease, you’re more likely to develop a form of IBD as well. “Up to 20% of diagnosed patients have a first-degree relative with UC,” Dr. Holmer says. (First-degree relatives include parents, siblings, and children.)

According to a review article published in the journal Lancet, over 200 genetic risk locations (areas on chromosomes) for IBD have been identified. Interestingly, many of these locations contribute to both ulcerative colitis and Crohn’s disease. This suggests similarities in the inflammatory processes between these two conditions.⁷

Another review article, published in Mayo Clinic Proceedings, points out that some of the genetic locations associated with IBD are involved in epithelium function and regulation of the immune system, both of which are important in the ulcerative colitis disease process. However, the exact role that many of these genetic locations play in IBD risk isn’t fully understood.⁸

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Before we dive in, it’s important to know that having ulcerative colitis risk factors doesn’t mean that you’ll definitely develop the condition in the future. It simply means you’re at elevated risk compared to others without risk factors. According to the Mayo Clinic, here are two more to keep in mind beyond your gut health, environment, and genetics:

Age is another potential risk factor. While you can develop ulcerative colitis at any age, it most often shows up in younger individuals, although researchers are still trying to figure out why. According to the NIDDK, people between the ages of 15 and 30 are most likely to develop UC.

The condition may also affect children differently. “Children diagnosed with ulcerative colitis generally experience more of an aggressive disease course than adults,” Dr. Holmer says. She notes that, in children, the entire colon is often involved at the time of an ulcerative colitis diagnosis. This is in contrast to adults, in which ulcerative colitis is often limited to the rectum or the left side of the colon at diagnosis.

Ulcerative colitis also occurs more commonly in Ashkenazi Jewish people. This group of people has a high prevalence of founder mutations, which are genetic changes that are seen frequently within a community that shares a common ancestry and has been or currently is geographically or culturally isolated.

Founder mutations can increase the risk of various health conditions. In addition to ulcerative colitis, some examples of other health conditions that occur more commonly in the Ashkenazi Jewish population include Tay-Sachs disease, Gaucher disease, and cystic fibrosis.

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In Crohn’s disease, areas of your digestive tract become irritated and inflamed. This can lead to symptoms like cramping, diarrhea, and unintentional weight loss, which heavily overlap with those of ulcerative colitis. While ulcerative colitis only affects your colon, Crohn’s disease can impact any part of your digestive tract. The most commonly affected areas are the last part of your small intestine, called the ileum, and the first part of your colon.

Much like ulcerative colitis, the exact causes of Crohn’s disease remain unclear. Similar factors are believed to play a role, including a dysfunctional immune response and genetics.

According to the NIDDK, the risk factors for Crohn’s disease include family history, smoking cigarettes, and being between the ages of 20 and 29. It’s also possible that eating a high-fat diet or using medications like NSAIDs, antibiotics, or birth control pills may also slightly increase the risk of Crohn’s disease.

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No, ulcerative colitis is not contagious. That means that it cannot be passed from one individual to another and does not make the list of potential ulcerative colitis causes.

However, it’s worth pointing out that there are some types of colitis that are contagious. Bacteria such as E. coli, salmonella, and campylobacter can all cause infectious colitis, which differs from ulcerative colitis because the symptoms go away once the infection is treated. Some viruses can lead to infectious colitis as well, including norovirus and rotavirus.

Infectious colitis can spread via the fecal-oral route. This means you can become sick by touching something that’s been contaminated with fecal particles from someone who is sick and then touching your mouth. You can also get sick by consuming contaminated food or water.⁹

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It’s currently unclear if there are ways to prevent ulcerative colitis. It’s possible that adjusting your diet may have some benefits when it comes to managing symptoms, though.

“Maintaining a diet low in processed food and saturated fats, and high in fruits, vegetables, and omega-3 fatty acids has overall health benefits in many chronic illnesses, including IBD,” Dr. Holmer says. She also mentions that questions about diet are by far the most commonly asked by people with IBD, but the consensus surrounding the link between the two is still unclear. Ultimately, Dr. Holmer hopes future research can help to clarify the effect of diet on ulcerative colitis and Crohn’s disease.

When it comes to finding an ulcerative colitis cure, the hunt is still on. The good news is that if you are diagnosed with ulcerative colitis, there are a variety of ulcerative colitis treatments that can greatly reduce your symptoms, and possibly even put them into remission. These include medications to reduce inflammation in the colon, and surgery if you aren’t responding well to medications.

Researchers are also currently working hard to develop newer treatments for ulcerative colitis (and inflammatory bowel disease, in general) and Dr. Fay is optimistic about what’s on the horizon—she stresses that “great progress is being made.”

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Sources:

1. Inflammatory Bowel Diseases, An Overview of the Innate and Adaptive Immune System In Inflammatory Bowel Disease.
2. Frontiers in Medicine, Gut Microbiota and Metabolic Specificity in Ulcerative Colitis and Crohn’s Disease
3. Frontiers in Cellular and Infection Microbiology, Viral Infections, the Microbiome, and Probiotics
4. Lancet Gastroenterology and Hepatology, The Global, Regional, and National Burden of Inflammatory Bowel Disease in 195 Countries and Territories
5. Journal of Digestive Diseases, Systematic Review and Meta-Analysis: Association of a Pre-Illness Western Dietary Pattern With the Risk of Developing Inflammatory Bowel Disease.
6. Alimentary Pharmacology and Therapeutics, Systematic Review: Gastrointestinal Infection and Incident Inflammatory Bowel Disease.
7. Lancet, Ulcerative Colitis.
8. Mayo Clinic Proceedings, Mechanisms of Disease: Inflammatory Bowel Diseases
9. StatPearls, Infectious Colitis

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• 9 People Describe How They Were Diagnosed With Ulcerative Colitis
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• Everything You Need to Know About Ulcerative Proctitis