The vast majority of people who develop long COVID experience neurological issues, like brain fog and chronic fatigue, but growing evidence shows the condition involves many different body systems, like the heart, lungs, kidneys — and even the gut.
A recent study found that people who had COVID have a 36% higher chance of developing long-term gastrointestinal problems, including disorders like gastroesophageal reflux disorder (GERD) and irritable bowel syndrome (IBS), along with more benign symptoms like constipation and diarrhea.
According to doctors who work in long COVID clinics, there isn’t a clear rhyme or reason as to who’ll encounter digestive issues after COVID. Some people were hospitalized with COVID, some weren’t. Some had preexisting gut disorders that flared up after COVID, others were perfectly healthy until they got sick. As scientists learn more about post-COVID conditions, it’s become increasingly clear that, despite being overlooked, gastrointestinal disease is a not-so-rare facet of long COVID.
“GI symptoms are common, but because of the intensity and prevalence of all the other symptoms, which are so much more debilitating, the GI symptoms are not commonly sought after or treated — but they are still pretty common,” Dr. Surendra Barshikar, the director of UT Southwestern Medical Center’s long COVID clinic, told HuffPost.
The most common GI symptoms associated with long COVID
Other studies that have looked at the most common GI complaints in long COVID patients have found constipation, abdominal pain and diarrhea to be the biggest issues. Heartburn, nausea, vomiting and loss of appetite are also top the list.
Dr. Andrew Schamess, an internal medicine physician and clinical co-leader of The Ohio State University Wexner Medical Center’s Post-COVID Recovery Program, says that while gut issues aren’t nearly as common as brain fog or shortness of breath, he sees a good amount of people with diarrhea and irritable-bowel type symptoms come into the long COVID clinic he works at.
“Some people had some mild IBS beforehand, but now it’s a lot worse. Some people had no GI problems and now they’re having diarrhea, sometimes alternating with constipation, or sometimes more toward constipation,” he said.
Most people who develop long-term gastrointestinal problems weren’t hospitalized with COVID, Barshikar said. Their infections were mild, and it wasn’t until after they recovered from COVID that their gut health became an issue. “It doesn’t matter how severe your initial COVID was, you may still have GI symptoms,” Barshikar said.
According to the first study, the overall risk of developing GI issues after COVID is relatively small, but when you account for the fact that COVID’s burden is so ginormous, the number of long COVID patients dealing with gut issues becomes pretty hefty. Barshikar estimates that 25 to 30% of patients in his long COVID clinic have some type of GI symptom alongside their primary symptoms, like fatigue or shortness of breath, and approximately 5 to 10% are mainly there to get help for their GI issues.
Why long COVID may cause gut problems
There are multiple theories as to why some people develop gut problems after COVID. The most convincing one, according to Barshikar, is that there’s ongoing inflammation in the intestines.
We know, for example, that SARS-CoV-2 infects our cells by way of ACE-2 receptors. These receptors are best known for lining the respiratory tract (hence the breathing issues caused by COVID), but they’re scattered across the GI tract, too.
“Even in acute disease the virus does bind with ACE-2 receptors in the GI tract and cause acute inflammation,” Barshikar said. It takes time for inflammation to clear up, which may be why some people report digestive symptoms for months after COVID.
Some scientists believe that the virus lingers in the GI tract and continues to activate immune and inflammatory responses. Studies have found that the ongoing presence of SARS-CoV-2 in the GI tract is correlated with ongoing gastrointestinal symptoms. “The gut is one place where scientists really have found evidence that that’s a harbor for COVID,” Schamess said.
Another theory is that COVID disrupts the gut microbiome. One report found that long COVID patients have higher levels of pathogenic bacteria and lower levels of anti-inflammatory microbiota in their microbiome that may contribute to more intestinal inflammation. We depend on a balanced microbiome for many physiological functions, including dietary digestion and immune function. If the gut microbiome gets altered, it’s reasonable to expect some level of gut dysfunction, Schamess said.
Lastly, COVID may ignite an autoimmune response. Evidence shows that people who had COVID face a much higher risk of developing an autoimmune disease like rheumatoid arthritis, ankylosing spondylitis, lupus along with IBS and celiac disease compared to people who were never infected. And though researchers are still working to understand how COVID may trigger autoimmune diseases, they have found higher levels of autoantibodies, or antibodies that go after a person’s own tissues, in many people with long COVID.
At his long COVID clinic, Barshikar regularly sees people who suddenly have new food intolerances after COVID. When they eliminate certain foods, like gluten or carbohydrates, from their diet, their GI symptoms improve. “That makes me believe there’s some form of autoimmune mechanisms behind this as well,” he said.
Our understanding of long COVID — what causes, treats and prevents it — is all in flux. One thing we do know is that the brain and gut are intimately connected, and if one thing goes awry in the body, there’s a good chance there will be a cascade of negative health effects.
Automatic nervous system dysfunction is a major theme in long COVID patients, Schamess said, and while this often manifests as a rapid heart rate or dizziness, it can also impair gut function. To Schamess, the prevalence of post-COVID GI symptoms “is just another way that the automatic nervous system is misbehaving.”