The functioning of the human body can be compared to a chemical factory, where many individual chemical processes are integrated into a single unit with a common purpose – to keep us alive.
Just like any factory, the body needs raw materials to fuel these chemical production processes. The body’s supply chain has two main points of entry, the nose, and the mouth. When we breathe in, oxygen-containing air reaches the lungs, where life-giving oxygen is absorbed into the blood stream, which then carries oxygen to the rest of the body. Oxygen is crucial for nearly all bodily functions.
The mouth is the entry point for food and fluids, which becomes the fuel for the chemical processes of digestion in the 8-meter long gastro intestinal tract (known as the gut) that breaks food and liquids down into nutrients, which get absorbed into the blood stream and carried to every cell in the body.
The oxygen and nutrients in the blood stream are vital for life, as it fuels the magnitude of chemical processes that take place in all the physiological systems in the body, such as the endocrine system, the nervous system, the cardiovascular system, the muscle-skeletal system, the pulmonary (respiratory) system, the renal system, as well as in complex chemical processes taking place in every single cell in the body, and there are an estimated 30 trillion of them!
The two main points of entry are anatomically distinct from each other. Not so, says the scientists. The lungs are affected by gut health, and vice versa. Unhealthy conditions (called dysbiosis) in one affects the other through a direct link called the gut-lung axis. Although the primary direction of cross-talk occurs from the gut to the lung, there is evidence of communication in the other direction, as chronic lung disorders such as asthma and cystic fibrosis is suspected to cause dysbiosis in components of the gut, such as irritable bowel syndrome. Dysbiosis and inflammatory conditions in the gut have been linked to a higher prevalence of pulmonary diseases. Scientists are only starting to uncover the mechanisms through which gut health and lung health impact each other.
How does the gut-lung axis work?
(Our body’s network of lymph vessels and lymph nodes form part of the immune system. It collects fluid, waste material, and things like viruses and bacteria that are in the body tissues, outside the bloodstream. Lymph vessels are similar in nature to the veins that collect and carry blood through the body. Instead of carrying blood, these vessels carry clear watery fluid called lymph, which flows out from capillary walls to bathe the body’s tissue cells, and are filtered through the lymph nodes. Lymph fluid also contains white blood cells, which help fight infections. Some lymph nodes are seated deep inside the body, such as between the lungs or around the bowel, to filter fluid in those areas. The lymph fluid slowly flows in from all around the body, making its way back to the thoracic duct, near the point where the blood enters the heart, from where the filtered fluid, salts, and proteins are released into the bloodstream.)
Apart from the mesenteric lymphatic system, the primary role in the gut-lung axis is played by the gut and lung microbiota – the trillions of microorganisms such as bacteria, viruses, and fungi that function in a symbiotic/commensal relationship in a specific area in their host.
The chemical processes in various parts of the body, such as the skin, the lung, the mouth and nose, and the gut are aided by colonies of microorganisms. In a healthy environment with beneficial bacteria, they not only help to break down the raw materials into fuel, but also keep an eye out for harmful substances, such as viruses, amongst the raw material. In fact, these bacteria play an important role as they form part of the body’s immune surveillance system.
Not much is known about the lung microbiota, but the gut microbiota has been well studied and the composition of a well-balanced gut microbiota is known to have a major influence on the effectiveness of lung immunity.
The gut bacteria assist the body to digest certain foods that the stomach and small intestines are unable to digest and is key to proper digestive functioning. The beneficial bacteria also are vital for maintaining the integrity of the gut epithelial barrier, and for maintaining intestinal immune homeostasis, thus combatting aggressions from other microorganisms, such as harmful bacteria and viruses.
Gut-lung axis and dysbiosis in COVID-19
The advent of COVID-19 (named by the World Health Organisation after the Corona Virus Disease 2019, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-Cov-2), the seventh coronavirus species known to cause human disease) and the way it manifests in the human body, has highlighted the possibility that the gut-lung axis may play a role in the way this disease affects patients. Although COVID-19’s main point of entry is the respiratory channel and it mainly causes lung infection, there have also been gastrointestinal symptoms and traces of the virus in the stool of infected people.
The main symptoms of COVID-19 are fever, cough, and acute respiratory distress syndrome. A significant number of patients also manifest with gastrointestinal symptoms, such as diarrhea, nausea, vomiting, loss of appetite and abdominal pain.
Gut microbiota (micro meaning too small to be seen by the human eye) has a major effect on general health, while also interacting with the regulation of the immune system and its inflammatory response.
Dysbiosis in the gut microbiota results in permeability of the lining of the gut, leaving the way open for invading organisms and harmful substances to enter the blood stream. Scientists believe that disruption of the effectiveness of the gut barrier integrity (permeability) may lead to translocation of viruses such as COVID-19. After initially infecting the lungs, COVID-19 is suspected to migrate through damage in the lung tissue (bronchial-associated lymphoid tissue) to the intestine via the lymph circulation system and the blood stream. It is doubtful that oral transmission of COVID-19 would reach the large intestine, due to harsh biological barriers such as acid in the stomach and bile salts in the small intestine.
Significance of the gut-lung axis for the COVID-19 pandemic.
Scientists studying COVID-19 speculate that COVID-19 can possibly be managed by targeting the gut-lung microbiota axis. Diversity of the gut microbiota and the presence of beneficial microorganisms in the gut may play an important role in the course of this disease, as an imbalance of gut microbiota (dysbiosis) can possibly influence the clinical manifestation in COVID-19. The use of probiotics, prebiotics, and a healthy balanced diet in aid of a balanced gut microbiota may contribute to reduced inflammation and strengthening the response of the immune system in reaction to COVID-19 infection.
Improving the gut microbiota may help to maintain an optimal immune system and help to prevent the excessive inflammatory reactions associated with COVID-19.
Ways to improve the gut microbiota:
- Probiotics – Taking daily supplements of a good quality probiotic, preferably of human origin.
- Prebiotics are non-digestible types of dietary fiber (from high-fiber foods) that feed the friendly bacteria in the gut, leading to a healthier digestive system.
- A healthy balanced diet is characterized by the high consumption of vegetables, fruit, wholegrains, plant oils such as extra virgin olive oil, and oily fish, while avoiding sugar, saturated fat, processed foods, red meats and sugar-containing beverages, along with ample physical exercise.
For more information see the Health Insight blogs:
Probiotic strains from human origin
The Mediterranean Diet.
How to boost your immune system against the Coronavirus.
Gut bacteria
Use food to reduce inflammation.
Sources:
Gut-lung axis and dysbiosis in COVID-19. Published 21 June 2020. Turkish Journal of Biology. Pub Med Central (PMC). National Center for Biotechnology Information. US National Library for Medicine. National Institutes of Health. (www.ncbi.nlm.nih.gov/pmc)
Gut microbiota and COVID-10 – possible link and implications. Published 13 May 2020. Pub Med Central (PMC). National Center for Biotechnology Information. US National Library for Medicine. National Institutes of Health. (www.ncbi.nlm.nih.gov/pmc)
Intestinal flora as a potential strategy to fight SARS-Cov-2 infection. Published 9 June 2020. Frontiers in Microbiology. (www.frontiersin.org)
The gut-lung axis in health and respiratory disease. Published 19 February 2020. Frontiers in Cellular and Infection Microbiology. (www.frontiresin.org)
Targeting the gut-lung microbiota axis by means of a high-fiber diet and probiotics may have anti-inflammatory effects om COVID-19 infection. Published 29 June 2020. Therapeutic Advances in Respiratory Disease (Journal). Sage Journals. (www.journals.sagepub.com)
Microbes, metabolites, and the gut-lung axis. Published 11 April 2019. Mucosal immunology, Nature. (www.nature.com)
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