Maddening but true: Experts can't point to a single cause for this challenging condition. Instead, research suggests a perfect storm of factors come together to wreak havoc on your digestive tract. Here’s what we know so far.
If you’ve been diagnosed with Crohn’s disease, you’re probably wondering: How the heck did I get this? It’s the million-dollar question that the latest research and the most knowledgeable Crohn’s disease experts can’t fully answer. Likely, it’s due to a combination of factors including genetics, environmental triggers, and your unique immune system. Discover what science says could be behind your diagnosis, and what you can do to make life with Crohn’s a little easier.
We went to some of the nation’s top Crohn’s experts to bring you the most scientific and up-to-date information possible.
Jami Kinnucan, M.D.Gastroenterologist, IBD Specialist, and Assistant Professor of Medicine
Neilanjan Nandi, M.D.Director of the Inflammatory Bowel Disease Center
Frank I. Scott, M.D.Gastroenterologist, IBD Specialist, and Assistant Professor of Medicine and Gastroenterology
What Is Crohn’s Disease Again?
To recap: Crohn’s disease causes inflammation of the digestive, a.k.a. gastrointestinal (GI), tract. It’s most likely to strike in the small or large intestine and is referred to as an Inflammatory Bowel Disease (IBD) due to the havoc it can wreak. Of the estimated 3.1 million Americans who have received an IBD diagnosis (which also includes ulcerative colitis and the less common indeterminate colitis and microscopic colitis), about 780,000 have Crohn’s disease, according to the Crohn’s & Colitis Foundation. It affects men and women equally, and can occur at any age, although it is most common between the ages of 15 and 30, and again in your 50s and 60s.
Crohn’s is triggered by the immune system’s white blood cells attacking your body’s healthy tissue. That produces inflammation, causing ulceration and tissue swelling that limits the intestine’s ability to process food, absorb nutrition, and eliminate waste. The result: Abdominal pain, diarrhea, and weight loss.
Although the scientific jury is still out, clues to the roots of Crohn’s are starting to add up. Experts point to a likely combination of factors, including changes in the immune system, genetics, environmental triggers, and a possible imbalance in the microbiome, or gut flora, known as dysbiosis. Let’s look at these factors one by one.
An Immune System Response
Chronic inflammation and ulceration are hallmarks of Crohn’s disease, the result of an overly robust immune response to bacteria in the GI tract. Normally, the immune system protects the body—including the intestinal lining—from harmful pathogens such as bacteria and viruses by sending white blood cells to engulf a foreign invader and prevent it from causing harm. These white blood cells learn to develop antibodies, akin to smart torpedoes, that are specific to each type of harmful organism.
But in Crohn’s disease, the white blood cells are drawn to the intestinal lining by other means and attack whether there is a pathogenic invader or not. The ensuing inflammation causes ulceration and tissue swelling that limits the intestine’s ability to process food, absorb nutrition, and eliminate waste. As a result, patients may experience weight loss, frequent diarrhea, and abdominal pain, as well as complications of the disease. This abnormal immune system response is most likely to occur in people who have genes that make them susceptible. Meanwhile, it's environmental factors that frequently trigger the initial immune system response.
The Role of Genetics
To date, researchers have identified over 270 genes that may contribute to the development of Crohn’s, though we don’t yet know their exact role. Many of these genes program and influence the way white blood cells behave.
However, no one single gene, or even group of genes, has been shown to be the sole cause of Crohn’s. And although it’s clear that IBD can run in families, there’s no guarantee you’ll get Crohn’s disease or ulcerative colitis just because someone in your family has it. Check out what the data says:
Studies show that from 5 to 20% of IBD patients have a first-degree relative—a parent, sibling, or child—with it as well.
The genetic risk is higher for Crohn’s disease than ulcerative colitis.
The genetic risk for Crohn’s is significantly higher—36%—in people with parents who have IBD.
While Crohn’s occurs in people of every ethnic background, it is most common among Caucasians and certain groups, including Jews of Eastern European descent.
The number of cases in the African American population has been increasing.
Very early onset Crohn’s disease (occurring in children under the age of 6) may be more genetically influenced than the disease in adults.
Evidence is mounting that where you live, and how you live, can impact the development of Crohn’s disease. We know that the illness is more common in:
developed countries than undeveloped countries
urban cities and towns rather than rural areas
northern rather than southern climates
Some explanations suggest that people living in less developed areas are exposed to more dirt and germs and develop a stronger immune system as a result, but experts are quick to acknowledge that this “hygiene hypothesis” is simplistic at best.
Still, there has been a statistical increase in Crohn’s disease and ulcerative colitis in places where they were once rare, such as Africa and South Asia, that are becoming increasingly modernized. As for geographic regions, experts think the higher rate up north may be related to lower vitamin D exposure in these less-sunny climates.
Environmental factors also include lifestyle choices, such as:
Smoking: Active tobacco smokers are more than twice as likely to develop Crohn’s disease as non-smokers.
Diet: While no single food triggers the development of Crohn’s, certain foods can impact symptoms. Diets high in processed foods and sugar, which have been linked to inflammation and gut bacteria imbalances, may contribute, too.
Antibiotics: Exposure to antibiotics, especially during childhood, may increase your risk, possibly because they change the balance of your microbiome.
Appendectomy: Children who have their appendix removed may be at higher risk for developing Crohn’s later in life.
NSAIDs: Taking nonsteroidal anti-inflammatory drugs, including aspirin, ibuprofen, and naproxen, may increase your odds of developing Crohn’s. NSAIDs may also aggravate flares.
Birth control pills: Some studies have suggested a link between taking the pill and developing Crohn’s disease.
Chemical toxins: While far from proven, clusters of IBD have been anecdotally observed in areas linked to chemical contamination.
Experts think that when a person with a genetic susceptibility to Crohn’s disease encounters an environmental trigger, inflammation is “turned on” in the digestive tract. But unlike a normal immune response—in which the inflammation subsides once the offending invader is vanquished—Crohn’s disease inflammation never “turns off.”
The trillions of microbes—a.k.a. bacteria, viruses, fungi, and protozoa—that exist in your body are known collectively as the microbiome. Not surprisingly, many of these microbes are housed in the gut and digestive tract. A whopping 70 percent of your immune system also lives in the digestive tract. When the balance of all this gut flora gets thrown off, it’s known as dysbiosis, a state that has been linked to intestinal disorders.
Human digestion relies on gut flora to break down and absorb nutrition from food as it passes through your body. In turn, gut bacteria use this nutrition for their own growth and sustenance. If you have Crohn’s though, you likely have less diversity in your gut flora. (The composition of gut flora is also less diverse in people with chronic diseases outside of the intestinal tract, such as Parkinson’s.)
Here’s why that matters: The intestinal membrane is a crossover point where your body's immune system and white blood cells interact with intestinal gut flora. If your gut flora is out of whack, it alters the signals going to your white blood cells. This, in combination with other environmental triggers like tobacco, creates inflammation in your gut that damages the intestinal lining.
Bottom line: Your gut microbiome plays a key role in the onset of Crohn’s disease. You can help improve the balance of microorganisms in your microbiome through diet. Pay attention to prebiotics, typically found in high-fiber foods, which act as food for gut microflora and can encourage a healthy gut balance.
Frequently Asked QuestionsCrohn’s Disease Causes
I have a family history of Crohn’s disease. Can I do anything to keep myself from getting it?
A family history doesn’t mean you will develop Crohn’s—most people don’t. Also, because there is more than one cause of the disease, it’s hard to predict who will get it. You can improve your odds of staying healthy by avoiding potential environmental triggers such as smoking and eating a highly processed diet.
Does Crohn’s disease ever go away?
Crohn’s disease is a chronic condition, meaning you’ll have it for life. That doesn’t mean you will always be suffering, however. Crohn’s has periods of remission—when there is no disease activity and little to no symptoms—and flares, when inflammation and symptoms return. With proper treatment, you can remain in remission for months or even years.
I have a twin. Will he also get Crohn’s?
The odds of that depend on whether you are identical or fraternal twins. When one identical twin develops Crohn’s, there is a one in three chance that the other twin will eventually have it as well. Fraternal twins have about the same risk of other siblings.
Can I do anything to improve my microbiome?
Yes! Eat a healthy and varied diet that focuses on fruits, vegetables, whole grains, fish, and healthy fats, and avoid highly processed, sugar-packed foods. Regular exercise also promotes diversity of your gut flora, as does getting enough sleep.
Gut flora and Parkinson’s: Journal of Neurogastroenterology and Motility. (2019). Parkinson’s Disease: The Emerging Role of Gut Dysbiosis, Antibiotics, Probiotics, and Fecal Microbiota Transplantation. ncbi.nlm.nih.gov/pmc/articles/PMC6657920/