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The Gut Health/Long COVID Connection

Someone's intestines with COVID in them

COVID-19 has infected millions of people throughout the world. In the process, hundreds of thousands of those infected have died while others were fortunate enough to survive. Yet not all of the COVID-19 survivors have done so well. According to some statistics, roughly 40% of those who survive the infection develop long-COVID symptoms. Such symptoms persist long after the initial infection is over and involve a variety of frustrating complaints. Scientists have been baffled as to why some people struggle with this and why others don’t. But recent research now suggests the problem may lie within the gut microbiome in COVID-19 long-haulers. In fact, more than one study suggests COVID-19 may have a significant effect on gut health.

(Read more about the effects the initial COVID infection has on gut health in this Bold story.)

When it comes to our immune system, several organs house important cells that attack infectious organisms. The spleen, lymph nodes, and thymus are organs many may recognize as being vital to immune system development. But roughly 75% of the body’s immune cells lie within the intestinal system. Given this, it’s not that farfetched to believe changes to the gut microbiome in COVID-19 could cause lasting effects. This notion is actually what led researchers to explore changes in the microbiome among those with long-COVID symptoms. And their work could lead to new considerations in how to manage COVID long-haulers in the future.

“There are suggestions that the innate immune system may be overstimulated from COVID. It’s not clear why, but after SARS-CoV-2 has cleared, the immune system seems to still be active.” – John P. Haran, MD, PhD., UMass Chan Medical School

An Overview of Long-COVID Symptoms

When it comes to COVID-19 infections, the spikey virus is known to impact the respiratory system quite profoundly. The initial strain of the virus tended to involve the lower respiratory tract to a greater degree. This led to more serious illnesses in many who suffered existing conditions affecting the heart and lungs. It also explained why many lost their sense of smell. Subsequent variants appear to be less severe, and the latest Omicron variant more commonly causes upper respiratory complaints. But as far as long-COVID symptoms go, many symptoms have nothing to do with the respiratory system. Instead, they tend to include a wide variety of issues.

Among those called COVID lang-haulers, some of the most common complaints are rather vague. Fatigue and sleepiness are extremely common among these patients. Likewise, many complain of a brain fog, suggesting neurological effects from the virus. Other symptoms common to this group also involve insomnia, headaches, and muscle aches. Previous theories regarding long-COVID symptoms thought the virus may have left behind some permanent damage in these organs. This may indeed be the case still. But what also now appears to be evident is that the virus also affects the gut microbiome in COVID-19 long-haulers. And some believe this may be a common pathway for many if not all of the lasting complaints in these individuals.

“A pro-inflammatory microbiome could lead to prolonged symptoms even after the virus is cleared. It’s also possible that in some individuals, COVID drives a change in the microbiome toward a pro-inflammatory profile, which leads to prolonged symptoms.”- Evan S. Bradley, MD, PhD., at UMass Chan Medical School

Oral Microbiome Research and Long-COVID Symptoms

When considering the gut microbiome in COVID-19, the entire gastrointestinal tract is being considered. This includes the collection of bacteria and organisms that line the upper gastrointestinal tract including the oral cavity. With this in mind, researchers at UMASS Chan Medical School recently studied this portion of the gut microbiome in COVID-19 patients. Over a 9 month period, they evaluated 84 patients with COVID. Of which 27 had long-COVID symptoms. Using genomic sequencing and advanced algorithms, they determined the make-up of each patient’s oral microbiome.

A cartoon intestinal tract talking about germs
Thanks to a couple years of data, we now know that long-COVID symptoms are tied in some regard to gut health.

Notably, the researchers did not explore the gut microbiome in COVID-19 individuals in its entirety. But even within the patients’ oral microbiome, hundreds of bacterial types still existed and required profiling. When they had finished their analysis, they found something quite interesting. Among those with long-COVID symptoms, there were 19 specific bacterial organisms unique to this group. In other words, they were not present in COVID individuals without long-COVID symptoms or in those without COVID infections. The results thus suggested that changes to the oral microbiome could account for long-hauler COVID presentations.

“Altered gut microbiome composition is strongly associated with persistent symptoms in patients with COVID-19 up to 6 months after clearance of SARS-CoV-2 virus.” – Professor Siew C. Ng, Department of Medicine and Therapeutics, The Chinese University of Hong Kong

The Latest Research in the Gut Microbiome in COVID-19

Additional studies have found similar discoveries in relation to the gut microbiome in COVID-19. In another trial, researchers at the Chinese University in Hong Kong followed 106 patients with COVID for 6 months. The collected stool samples and measured aerobic capacity and endurance in these individuals as well as in 68 individuals without COVID. Of those with the infection, 80% developed long-COVID symptoms. And their stool sample profiles were quite different from the others followed.

In those with long-COVID symptoms, marked disruption in their gut microbiome was noted. Specifically, they had a marked increase in what was considered “unfriendly” bacteria with nearly all the “friendly” bacteria lacking. This was in distinct contrast to normal subjects and those without long-COVID symptoms, who showed normal profiles. The researchers also noted that those receiving the coronavirus vaccine had no real protection from long-COVID symptoms. They concluded their results further supported the gut microbiome in COVID-19 as being the source of the problem in long-haulers.

A Window to Future Discoveries

The latest scientific investigations look to be increasingly implicating the gut microbiome as a key target in long-COVID symptoms. If the coronavirus indeed damages the cells of the microbiome, then it’s easy to appreciate how this could cause lasting complaints. Given that our microbiome is important to digestion, metabolism, and immune function, a variety of symptoms could result. Therefore, further studies are needed to clarify these relationships and to explore potential remedies. Ultimately, the answer may involve therapies like probiotics that can restore a healthy microbiome to affected COVID-19 patients. And these same therapies might help address many other unexplained health conditions beyond COVID-19 as well.


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