Do we need to rethink our relationship with bacteria?

Is our need for clean making our children – and us – sick?

In our increasingly sanitary world, we wipe away thousands of bacteria and viruses – some harmful, some completely harmless. Although we are killing those bugs that could make us sick, we’re also killing those responsible for keeping us healthy, increasing our susceptibility to allergic diseases and asthma by supressing the natural development of our immune system.

In 1989, epidemiologist David P Strachan first used the term ‘hygiene hypothesis’. He analysed data from 17,414 British children and concluded that those with more siblings were less likely to have allergies like eczema and hay fever because they had been exposed to more microbially rich world via their siblings – and other similar studies from around the world have shown comparable results.

Our immune system needs exposure to bacteria – early childhood encounters teach our body what is harmful and what isn’t, and primes the immune response we’ll have for the rest of our lives. Without this exposure, the immune system becomes oversensitive and overreacts to non-threats like pollen. Without a healthy immune system we also become susceptible to excessive inflammation causing autoimmune diseases and many papers published over the years have linked over-cleanliness with inflammation which causes cancers.

And when harmful bacteria do make us sick, we take course after course of antibiotics – allowing the bacteria to become resistant to the antibiotic’s effects. And with fewer new antibiotics making it to the market, we’re running out of effective treatments for resistant bacteria.

The Government has recently published a five-year strategy aimed at protecting the few antibiotics that remain effective against resistant bacteria. Under the strategy, they aim to educate healthcare professionals so that they have a good understanding of antibiotic resistance and best practice for their use, and identify new funding to tackle and resolve the problem of resistance. The strategy also aims to educate the general public about antibiotic resistance not only in medical use, but how their widespread use in homes and industrial settings contributes to the problem.

“We welcome the publication of the strategy,” said Dr Nicholas Brown, President of The British Society for Antimicrobial Chemistry. “It provides a much needed framework through which government can take responsibility for, and initiate steps to protect, the few antibiotics we have that remain effective against resistant bacteria, and through which encouragement of appropriate use of antibiotics across all sectors can be affected.”

But it’s not just antibiotic resistance our unhealthy hygiene habit plays a role in. Dr Molly Fox has uncovered a positive relationship between a nations’ wealth and hygiene, and the Alzheimer’s burden on the population.

Fox used age-standardised data – a single summary rate that reflects to incidence of Alzheimer’s expected if the compared populations were of identical age – to show that high-income, highly industrialised countries with large urban areas and better hygiene exhibit much higher rates of Alzheimer’s.

“The ‘hygiene hypothesis’, which suggests a relationship between cleaner environments and a higher risk of certain allergies and autoimmune diseases is well established. We believe we can now add Alzheimer’s to this list of diseases,” said Fox. “There are important implications for forecasting future global disease burden, especially in developing countries as they increase in sanitation.”

The study states that since increasing global urbanisation at the turn of the 19^th Century, wealthier nations have had very little exposure to microbes due to diminishing contact with animals, faeces and soil. The introduction of antibiotics, sanitation, clean drinking water and paved roads have led to lower rates of exposure to these microorganisms omnipresent for the majority of human history.

This lack of contact can lead to insufficient development of white blood cells, particularly T-cells, a deficiency of which has links to inflammation commonly found in the brains of Alzheimer’s patients. Although the hygiene hypothesis is typically related to childhood, researchers believe that regulatory T-cell numbers peak at various points in a person’s life, so exposure to microorganisms across a lifetime might be related to Alzheimer’s risk.

This just illustrates that our very being is interlinked with exposure to outside forces in ways that we could never have imagined. Who would have through that our exposure to microbes throughout our life would be so interwoven with a neurological disease like Alzheimer’s?