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Gut Health, Your Immune System, and COVID-19 (Coronavirus)

Updated: Jun 1, 2020

Is your gut health linked to your immune system? YES.

Recent research suggests that COVID-19 may be related to the gut microbiome. This is because one of the entry points of the virus is ACE2, a receptor found in the lungs and the small intestines. ACE2 is important in controlling intestinal inflammation and its disruption may lead to diarrhea. And, we're seeing about 10% of COVID cases presenting with diarrhea. Mutations of ACE2 may result in decreased production of antimicrobial peptides that help to fight infections, and possibly a disrupted gut ecology.

In early February, Guidance from China’s National Health Commission (Version 5) recommend that in the treatment of severe patients with COVID-19 infection, probiotics can be used to maintain the balance of intestinal microecology and prevent secondary bacterial infection

How does the gut-lung cross talk even happen? One study has shown that it is through IFN receptor expression that is driven by the gut microbiome. Increased IFNAR1 levels promote a lung environment resistant to early influenza virus replication.

Let’s dive into the microbiome and gut health to see if we can find some novel ways to support your immune system by optimizing your gut.

The human intestine harbors a whole microbial ecosystem containing over 100 trillion microorganisms that collectively have a total genome (the microbiome) consisting of 100-fold more genes than the human genome. We have known for a long time that microbes have the ability to influence our health beyond the location they reside. So gut microbes affect a whole host of mechanisms outside of the gut- ranging from the heart, kidneys, liver and the rest of the body. And, what’s more, 70% of your immune system is located around the gut. You have tissue known as the GALT, gut-associated lymphoid tissue. This lymphatic tissue is there to protect us from the outside environment.

So, what the heck does this GALT do? It is pivotal in your body's defense, and it relies on plasma cells, which are antibody producing B-cells. These plasma cells produce antibodies to foreign pathogens so that our body can recognize them if they are exposed to them again. Basically if we are exposed to a virus our body takes a picture of it and produces an antibody against it so that if we come across it again we already have antibodies to it and we can defend ourselves much faster than the original exposure. Your GALT has more plasma cells than the number of plasma cells in your spleen, lymph nodes and bone marrow combined. You see, your gut is actualLy a barrier. Your gastrointestinal tract is in fact the outside of your body. This is why protecting our gut mucosa is important for protecting us from pathogens like viruses and bacteria.

Our gut has several ways at protecting us from invading pathogens. SIgA is one of these defense mechanisms. SIgA is an immunoglobulin produced in the GALT and excreted into the intestines. SIgA has also been shown to prevent viral infections by blocking virus adhesion to epithelial cells. We know that a lot of things affect the production of this immunoprotective compound. Elevated cortisol levels over a prolonged period of time reduce our bodies’ production of sIgA, making us more susceptible to infections and damage of the intestinal lining. This also means that things that help keep cortisol in check likely benefit our immune system, possibly by ensuring adequate sIgA production. Mindfulness meditation has been found to regulate cortisol levels in as little 5 days of practice - just 5 days and a shift in stress hormone production was seen. Vitamin A is involved in the production of sIgA. It is the retinoic acid version of vitamin A that increases the production of this compound though, not the beta carotene version found in orange foods like sweet potatoes. Foods that are high in retinoic acid are beef liver, cod liver oil, sweet potato and eggs. Colostrum, an immunoglobulin secreted in the early stages of breast-feeding has been shown to stimulate sIgA levels. Germ-free mice also have lower amounts of sIgA, so we know that the composition of the microbiome affects its production.

Speaking of the gut microbiome this is another big player in how our gut health affects our immune system. One way we study our microbiome is by looking at these GERM free mice. The research shows that mice lacking a microbiome have underdeveloped spleens and lymph nodes, which is where a large percentage of our immune system resides; fewer peyer patches; decreased plasma cells; decreased IGA and IGG; and abnormal cytokine production.

So, what does this mean? This means that our gut microbiome is essential in immunity and preventing infections and supporting our immune system. The effects of our gut microbiome are not just due to our microbes though. They are likely due in large part to the post-biotics that they produce. Your microbiome codes for about 2-20 million genes (100-1,000 fold more than the human genome). These genes code for proteins, and some of these proteins interact with our human cells to produce beneficial effects. Examples of post-biotics are things called SCFA. And, some of these SCFA help to activate and support the immune system so our body can recognize pathogens and respond to them to protect our body.

Now, I like to make everything actionable since it doesn't do much good if it isn’t actionable. There have been some probiotics studied for their ability to support the immune system. To my knowledge none have been studied for COVID-19 because all of this is still so new. Two meta-analyses published by the York Health Economics Consortium (YHEC) and Cochrane reported the efficacy of probiotics in reducing incidence and duration of respiratory tract infections (RTIs). Bifidobacterium lactis HN019 has been shown to increase NK cells and CD4 t cells, which are involved in viral infections. Lactobacillus rhamnosus HN001 supplementation for 3 weeks increased NK cells activity by 147% in one study. These above two strains can be found in UltraFlora® Acute Care.

I am launching my Gut Health course soon so if you have not already done so, make sure to sign up now for free. We will do a deep dive for 10 days on how the gut works and how to support it from an evidence-based perspective.

Is gut support or probiotics the solution to COVID-19? NO. However, it is a piece of the prevention puzzle. And, after we have moved past this acute issue, there will still be things that threaten our immune system and our health so I can not stress the importance of prevention now more than ever.

The other clear piece about COVID-19 is that flattening the curve is essential and with this comes physical isolation or quarantine. Let’s be clear that this is physical isolation though and not social isolation. Social isolation has been found to weaken the immune system on its own. Make sure to reach out to those that are home alone during this time. Let’s use technology to our benefit and facetime, call, or video chat with loved ones. We need to come together as a nation, not let physical distance create social isolation.

Please reach out to me with any questions.

In health,

Dr. Mary

This has been a transcript of an embedded video by Dr. Mary and the modrn med team.


  1. Winkler, P., et al. "Effect of a dietary supplement containing probiotic bacteria plus vitamins and minerals on common cold infections and cellular immune parameters." International Journal of Clinical Pharmacology & Therapeutics 43.7 (2005).

  2. Bradley, Konrad C., et al. "Microbiota-Driven Tonic Interferon Signals in Lung Stromal Cells Protect from Influenza Virus Infection." Cell reports 28.1 (2019): 245-256.


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