Today rates of allergies, autoimmune and other inflammatory diseases are rising dramatically across the globe. We are also beginning to understand that many mental health problems, including depression and anxiety disorders, as well as unexplained health concerns that evade modern medicine are associated with unruly inflammation. Some have speculated that being too clean is fuelling this inflammatory health fire. But how clean is too clean? According to the “hygiene hypothesis,” first formulated in 1989 by an epidemiologist called Dr Strachan, the driver of escalating rates of non-infectious diseases due to our obsession with eliminating germs. This, he suggests, has led to a lower incidence of infections and microbial exposure during childhood, which has a negative impact on the proper development of our immune system leaving it prone to react inappropriately.
Although the hygiene hypothesis has been around for a while, receiving considerable attention in the media, it is a bit of a misleading misnomer. If the problem is that we are too clean, then, hypothetically, the issue can be easily resolved. We just need to get dirty and lower our hygiene standards, right? Wrong. Getting dirty doesn’t help our immune system and good hygiene does more good than harm by helping to ward off countless infectious illnesses. Scientists propose it’s now time to abandon this idea of being too clean – what we really have is a biodiversity issue. Our clean, indoor-centred lives, with diets low in fibre and routines high in stress deplete us of our ‘old friends’ – the bugs that we have evolved with, that live on us and in us, forming our microbiome.
The “old friends” theory (often called the biodiversity hypothesis) developed by University College London microbiologist Graham Rook in the early 2000s is broader than the hygiene hypothesis. We know quite conclusively that a rich and diverse microbiome is essential for proper immune development and regulation. Biodiversity starts at birth beginning with an initial ‘vertical inheritance’ of bugs from your mother. Type of birth, breastfeeding and your childhood home environment all play a major role in seeding our microbial diversity, however these are things we can’t really change. Antibiotics also have a hugely depleting influence that is often temporary but can leave a lingering effect.
It is unlikely we are going to go back to pre-industrialised hunter-gatherer lifestyle, but can we reclaim what is missing and cultivate a healthy crop of microbes? There are a few things within our control. Most of our immune system in our gut, making it the prime site to cultivate a diverse microbiome. We might all exposed to similar bacteria in our day-to-day environment but the primary driver of gut microbial diversity is our diet. Dietary fibre is the critical ingredient in supporting our microbiome. The gut bugs eat what we eat and love to break down those resistant starches in plant based foods to produce our own personalised pharmacy of health inducing nutrients. These bugs also train our immune system to respond to infection, or not respond to benign challenges such as potential allergens and our own tissues.
There are some products that might, in theory, support a more hunter-gatherer-like bacterial flora, by exposing us to the kind of bacteria we don’t encounter anymore, but they haven’t been tested in clinical trials. Probiotics, generally formulations of bacteria such as bifidobacteria and lactobacilli, also found in many fermented foods such as Natto, Kimchi, kombucha, sauerkraut and yoghurt, are safe to use in support of gut biodiversity. It’s probably impossible to replicate the complex ecosystem in our gut through taking a pill alone but we do know that maintaining correct levels of vitamin A and vitamin D are also important to maintaining immune regulation.
Diversity doesn’t only refer to what we put into our bodies but also refers to living in a world of relatively limited exposure to diverse environments. Getting contact with the soil and outdoor environments exposes us to soil microbes that, unlike probiotics, don’t take up permanent residence in our gut. As we spend more time in indoor environments, with clean and controlled surfaces, we get less contact with a very wide variety of environmental microbes. These environmental bugs are more like transient hitchhikers, having a positive impact on the resident bugs in our body before moving on through. What we are now learning is that exposure to these diverse environmental microbes can shape not only our microbiome and therefore immune system, affecting a child’s likelihood of developing autoimmune conditions like eczema and asthma, but also the hormone and nervous system impacting mental and physical health.
It’s quite reasonable to worry about germs and dirt since good hygiene helps ward off countless infections and illnesses. In fact, improved sanitation therefore reducing the burden of infectious disease globally is probably the biggest factor improving overall human health and wellbeing. Although they have their caveats, both “old friends” and the “hygiene hypothesis,” are contingent on microbial biodiversity in every corner of our lives. Rather than nursing a preoccupation with the art of disinfection, put down the hand sanitiser and do the basics of good hygiene, then get out and explore the diverse microbial ecosystem around us.