On New Year’s Eve, while the world was preparing to celebrate the arrival of 2020, local health authorities in Wuhan reported cases of pneumonia with an unknown etiology. The rest of the story is now familiar, with nearly 35 million cases and more than 1 million deaths to date over the course of the Covid19 pandemic, caused by the novel coronavirus SARS-CoV-2. Recently, some scientists have begun to claim there might be a supporting actor, so far underestimated, in this horror story, namely the gut microbiota.

One of the researchers behind this claim is Francisco Guarner. He is the principal researcher within the Physiology and Pathophysiology of the Digestive Tract group at Vall d’Hebron Hospital (Barcelona), as well as a member of ESNM’s board of directors on “Gut Microbiota and Health”. In an article in the Spanish newspaper La Vanguardia, Doctor Guarner argued that it might be feasible to consider that a healthy gut microbiota might protect against COVID-19.

Let’s break this down.  Pandemic statistics highlight that the elderly over 65 are, together with people suffering from obesity, diabetes, cancer or cardiovascular and lung disease, the most at-risk group of contracting COVID-19 and developing severe symptoms. Most of the people who have passed away of or have been severely affected by the infection have similar underlying medical conditions. They suffer from high blood pressure, are diabetic and/or obese.

Because the changes in gut microbiota composition observed in these metabolic diseases are the same as those related to aging – what is the gut microbiota’s role in this relationship? As explained in previous articles, the gut’s community of microorganisms is not quite stable and evolves through our lifespan. Microbial colonisation starts from birth; adult like maturity is reached around the first three years of life and a decrease in diversity occurs while aging. This reduction is further exacerbated among people living in nursing homes.

Notably, and according to a report by the International Long Term Care Policy Network, although numbers differ between countries, residing in a nursing home during the lockdown increased the probability of mortality due to COVID-19, compared to the elderly residing at home.

As Guarner points out in the article, in most cases infection from the coronavirus can be asymptomatic and mild. “Death occurs when the immune system overreacts” and “excess deaths in nursing homes could be linked to an inappropriate inflammatory response to the coronavirus infection.”

Gut microbiota plays a key role in training the immune system in early life and also guarantees its good functioning later on. One natural process linked to aging is the inability to generate immune responses that are adapted to pathogens, along with excess cytokine-mediated inflammation. According to a study published in 2012, Guarner mentions chronic activation of cytokines—which is very common in aging—is also linked to the loss of gut microbiota diversity, thus leading to a vicious circle of associated factors.

“This situation of permanent inflammation—called inflammaging—is significantly more frequent in the elderly living in nursing homes for the long term than for those living  at home close to relatives,” he states in the article. Guarner also adds “that loss of gut microbiota diversity could be due to the frequent use of antibiotics in nursing homes” and could also be linked to  an unbalanced diet.

Some bacterial species are beneficial as they have anti-inflammatory properties or promote low inflammation. Similarly, they also play different roles in training and regulating the immune system, which means they may have the potential to prevent or alleviate the immune alterations that lead to severe cases of COVID-19.

As such, scientists have started working on elucidating the gut microbiota’s possible role in either protecting against or on the contrary increasing the risk of contracting Covid19 and developing severe symptoms. According to Guarner, one of the hypotheses is that gut microbiota profiling could help identify individuals who are aging with more health complications (i.e. with greater levels of inflammation) and intervene in terms of diet or with medical treatment to re-establish a suitable gut microbiota composition. He goes on to conclude that: “These measures might protect the most at risk groups against the severe symptoms linked to COVID-19 infection and reduce mortality among the elderly living in nursing homes.”