COVID-19 and Gut Health

Did you know that keeping your gut in a healthy state is one of the best things you can do to protect yourself against viruses, including COVID-19? It is estimated that 70 - 80% of the immune is located within the gut, so it makes sense to do what we can to keep it healthy. A recent paper published in The British Journal of Nutrition (October 2020), highlights the links between the gut microbiome and COVID-19 infection, and nutritional strategies that may exert not only a preventative or prophylactic effect, but as a useful intervention for those suffering with the infection. The following diagram shows the possible prebiotic and probiotic mechanisms in the epithelial cells of the gut, in the fight against COVID-19. This shows how increasing these positive microorganisms can have a detrimental effect on potentially pathogenic microorganisms, by competitive exclusion, and by increasing the production of short-chain fatty acids (SCFAs). Both increased SCFAs and Bifidobacterium are associated with improved tight intestinal junctions, as shown in the image. This can lead to an overall healthier gut barrier function. The gut barrier is the interface between our external environment and our inner environment, therefore it's crucial that we keep it in a healthy state. The gut lining is the immune system's 'first line of defense', protecting us from potentially pathogenic bacteria and viruses.

Previous studies have shown prebiotics and probiotics to be supportive in reducing the symptoms of respiratory tract infections, and may also be a useful additional tool for supporting the immune system. Prebiotic galacto-oligosaccharides (GOS) enhances the production of beneficial microbes, including Bifidobacterium, having an anti-inflammatory effect in the gut epithelium, and therefore a healthier gut ecosystem.

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Immune System Support Some of the best ways of supporting our immunity lies in our diet and lifestyle choices.

  • Eating a wide and varied Mediterranean-type diet that includes extra virgin olive oil, good quality protein, oily fish, and a wide variety of vegetables, fruit, whole grains, nuts, seeds, and legumes is shown to be the most effective at nourishing the gut bacteria.

  • Include fermented foods and drinks such as yoghurt, miso, kimchi, sauerkraut, kefir and kombucha.

  • Spending time in natural environments such as parks, gardens, countryside and seaside exposes us to different microbes that are beneficial to our health.

  • Getting vitamin D from the sun.

  • Regular exercising.

However, sometimes we might need some additional support in the form of supplements. BANT, the British Association for Nutrition and Lifestyle Medicine, recommends ‘extraordinary measures’ of Vitamin C and Vitamin D supplementation for all adults as part of a wider prevention strategy for COVID-19. In light of the increasing numbers of COVID-19 infections, BANT recommends all adults supplement 1000mg of Vitamin C and a minimum of 600-800 IU/d vitamin D3 daily, increasing to a higher therapeutic dose of 5000 IU/d should symptoms develop (1). "An adequate intake of Vitamins C and D is vital for immune resilience. Food sources of both are imperative for maintenance but unlikely to provide adequate quantities in case of infection. Supplementation of both nutrients at the given levels is safe, effective, and an inexpensive way to encourage individuals to take preventative measures to support their immune system. Vitamin D insufficiency is especially common in northern hemisphere countries where limited exposure to sunlight reduces our ability to naturally synthesise it through skin. For this reason, Public Health England recommend 10 micrograms of Vitamin D daily throughout the winter months. Vitamin D is a potent immune modifying micronutrient and deficiency has been shown to correspond to a greater risk of respiratory tract infections, and acute respiratory distress in SARS-CoV-2 infections (1). A recent large meta-analysis (looking at 10,933 people in 25 trials), showed that vitamin D supplementation reduced the risk of cold and flu patients developing acute respiratory infections (ARIs) from 60% to 32% (2). Similarly, hospital data on early intervention with Vitamin D supplementation in SARS-CoV-2 infections reduced severity of the infection and lowered ICU admissions (3). The most abundant food sources of Vitamin D are oily fish, mushrooms and egg yolks. Three foods which are often absent in the nation’s regular dietary intake, and which alone cannot provide adequate levels, reinforcing the possible need for supplementation. In some individuals, testing and supplementation via their general practitioner may be best advised. Evidence on Vitamin C is equally compelling. A potent antioxidant, Vitamin C plays an immuno-protective role to protect against oxidative damage to the cells, helping moderate inflammatory cytokines and reduce both the severity and longevity of infection (4). Whilst Vitamin C is readily available in foods such as citrus fruits and leafy greens, low storage capacity means a regular intake of it is necessary for adequate plasma levels. BANT urges the government to make clear recommendations as part of a wider prevention strategy for COVID-19 to empower individuals to make informed decisions about their food choices and need for additional supplementation."

References (1) Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths, 2020, (2) Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis, 2019, (3) Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study, 2020,

(4) Vitamin C and Immune Function, 2017,

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