How to maintain a healthy biome in a COVID-19 world

This year, we have all grappled with the now essential measures of reducing the risk of being infected with the SARS-CoV-2 coronavirus that causes COVID-19, including wearing masks, staying at home, washing and sanitising our hands and disinfecting the surfaces we touch.

The importance of these distancing and sanitising practices cannot be underestimated in reducing viral transmission. Beyond airborne transmission, there is evidence that SARS-CoV-2 can survive on human skin for up to 9 hours, and remain viable for up to 28 days on surfaces such as glass and stainless steel.

Questions remain as to how infectious these surfaces remain over time. Nevertheless, sanitising techniques have been shown to be incredibly effective in risk reduction for respiratory illnesses, like COVID-19.

Our bodies are home to a spectrum of bacterial, fungal, and viral communities, collectively termed the ‘human microbiota’.

Although some microorganisms are linked to disease pathways, most have coevolved with us to be mutually beneficial. Indeed, we provide our resident bacteria with nutrient-rich environments, and in turn they are critical to our digestion and may benefit us with things like reduced systemic inflammation, enhanced immunity and better perceived quality of life.

While we are just beginning to understand the complex mechanisms underlying the ‘good bugs’ that live with us, there is strong evidence for vast differences between the microbiomes of generally healthy people.

What we do know is that microbial diversity is generally correlated with better health outcomes.

We also know that compositional shifts (‘dysbiosis’) in our microbiomes are often linked to changes in disease state. For example, the skin and gut microbiome exhibit distinct composition and diversity patterns in disease states ranging from diabetes and gastrointestinal disorders, to autism and psoriasis.

So what do lockdown measures have to do with our microbiomes?

Our microbiomes are shaped by a combination of biological factors like age and genetics, as well as environmental and lifestyle factors. This includes contact with surfaces, animals and people, as well as inhalation, and importantly, what we eat and drink.

Reduced gut microbial diversity

Evidence suggests that gut and skin microbial communities can be transferred between people and environments. This is particularly critical in the postnatal period.

That we are all spent less time outdoors may therefore reduce our link to the wider diversity of microorganisms associated with nature – including soil and water. In addition, having decreased exposure of UVB light from the sun, which leads to lower vitamin D levels, is also linked to reduced microbial diversity in the gut.

It is clear that unhealthy eating and reduced exercise has gone up since the pandemic started, particularly affecting at-risk populations, like those with obesity. Increased and prolonged consumption of ultra-processed foods has been associated with reductions in bacterial diversity and gut dysbiosis, which can upregulate inflammatory responses in the brain.

Furthermore, in a time where poor mental health has increased in the general population, this may be causing perturbations in the gut microbiome which has been linked to our mood. In fact, there seem to be distinct intestinal changes in individuals with chronic depression, as reflected by reductions in beneficial bacterial strains.

Skin changes

Although the exact composition varies by location, the microbiome that resides on the top layer of our skin (the stratum corneum) tends to be relatively stable overtime.

However, excessive intervention by alcohol-based sanitising, and hand washing with soap or chemical applications, can change this equilibrium, depending on the frequency and type of product applied. For example, while frequent hand washing may not necessarily affect bacterial diversity per se, it can lead to a shift in community composition and/or proliferation of microbes due to impairments in the skin’s biological habitat (such as its acidic pH and moisture levels), or physical barrier.

This may reduce the beneficial strains that protect our skin barrier and allow invaders to colonise, predisposing the skin to infection and inflammation.

The good news is there are many actions that we can take to support the microbes within and around us.

If you have a green thumb, or a fluffy, tail-wagging friend, they offer your bugs the same joy as they do to you at home. Both plants and pets can make positive contributions to microbial diversity, even in built environments.

Beyond their effects on the biodiversity of the skin-gut microbiome, the benefits of pets and greenery also extend to potentially buffering against heightened stress responses.

Where local restrictions allow, heading outdoors for hikes and walks can boost your microbial exposure. Even if just in the local neighbourhood, green, vegetated areas are homes to an assemblage of microbes. Staying physically active in general may help to positively augment the intestinal microbiota and promote an anti-inflammatory state.

Another way of supporting a thriving intestinal community is through having a whole-foods based diet, such as the Mediterranean diet.

The emphasis on minimally-processed plant foods is associated with beneficial gut microbiota shifts, particularly the increase of short-chain fatty acids. These anti-inflammatory metabolites are positively associated with host health, like improving insulin sensitivity. Importantly, these beneficial dietary effects may even be protective against poor mental health. Finally, while excessive sanitisation practices may be unavoidable at this time, the good news is that in the absence of impaired skin, the hand microbiome is relatively resilient to short-term changes brought about by both alcohol rubs and soap washes.

It is therefore important to maintain our skin’s physical health (like ensuring it is hydrated) so that it supports a healthy microbiome overtime.

Finally, given that the gut and skin microbiomes are linked, keeping our gut microbes healthy will have far-reaching effects on other body sites, like our skin.

As we continue to face unpredictable social, health, and economic challenges around the globe, it may seem as though microbes are the common enemy right now. However, we are only starting to uncover the vast potential of the microbial life - within and around us - in supporting our physical and mental health.

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