Is our antimicrobial obsession making us sick?
Killing bugs has become a modern-day pastime. Just scan the products on offer at your local supermarket. There's anti-bacterial this and antiseptic that. Antibacterial soap, often with triclosan added for its supposed antifungal and antiviral properties, is a popular choice on the personal hygiene aisle even though the U.S. Food and Drug Administration states on its website that "the agency does not have evidence that triclosan in antibacterial soaps and body washes provides any benefit over washing with regular soap and water.” (See more here.) And these days it seems that everywhere you turn there's a handy little dispenser of hand sanitizer, some with triclosan and others alcohol-based.
If you are up on your reading, however, you are no doubt aware of a growing body of data (see here, here and here) that suggest that this all-out war on germs may be counterproductive, may in fact be making us sick. Instead of making your home as antiseptic as possible, you may be a lot better off rolling around in the dirt with all those little bugs or doing it by proxy by cohabiting with a dog or other low-to-the-ground, dirt-loving creature.
Why, you may ask, would it be good to get down and dirty with the bugs? How, you may ask, can killing germs make us sick? A nice summary of the evidence in support of a microbially friendlier lifestyle appeared recently as a perspective piece in the Proceedings of the National Academy of Sciences by Graham Rook of the University College London. He argues that our immune system requires "microbial input from the environment," and to get that input, he advises finding green spaces.
We All Know Green Spaces Are Good for Us
The idea that green spaces are good for us is certainly not news. Most everyone knows that hanging out in a park or hiking in the woods feels good, so it's got to be good for you, right? Well, yes, there are data to back that up. Previous studies (see here, here and here) have documented a host of what might be termed psychological benefits. The data suggest, Rook writes, that living close to nature
“reduces overall mortality, cardiovascular disease, and depressive symptoms and increases subjective feelings of well-being. … Looking at green spaces or walking in parkland or forests cause rapid … changes that can be demonstrated not only by psychological testing but also by mobile electroencephalograms and by measurements of cerebral blood flow, various cardiac parameters, blood pressure, and salivary cortisol."
But the author sounds two cautionary notes with regard to the significance of these data.
- These studies lack suitable scientific controls. As Rook writes, "Would any suitably relaxing environment -- a quiet comfortable café, or a cinema showing a feel-good film in the urban environment -- have the same psychological effects.” Maybe.
- And there's the question of long-term benefits. There is no evidence that "the measurable rapid short-term ... changes that follow exposure to natural environments (whether specific for such environments or not)," Rook writes, "translate into long-term health benefits."
So does that mean that Rook rejects the notion that green spaces provide health benefits? Hardly.
The Real Benefits of Green Spaces Come From the Bugs
While most folks think that hanging out in nature is beneficial because it soothes and calms, Rook argues that much more substantial benefits come from the exposure to microbes that green spaces afford. While some microbes are without doubt harmful and disease-causing, the vast majority are not and in fact many are beneficial. And it's exposure to these bugs that make green spaces so essential in Rook’s view.
Immunological Benefits
We are witnessing an alarming growth in autoimmune diseases ranging from chronic inflammation to asthma to potentially life-threatening conditions such as lupus. In each case, Rook writes, the "cause is at least partly a failure of immunoregulation, so that the immune system is attacking inappropriate targets, such as self, harmless airborne antigens (allergens) and gut contents." He goes on to point out that more and more studies (see here, here and here) are showing that exposure to bugs, especially at an early age, is essential for training and calibrating our immune system, teaching it, in a sense, what are the things it should attack and what it shouldn't. And without appropriate calibration, the immune system can mistake the good guys for the bad guys.
By raising babies in urban environments devoid of bug-rich green spaces, we may very likely be depriving them of exposure to the diversity of bugs needed to form a healthy immune system and thereby setting them up for a life of chronic pain and illness. (Along similar lines, it’s been argued that C-section births lead to a deficit in good microbes in babies.) Rook refers to the bugs needed to train our immune system as our "Old Friends" defined as "organisms ... from mankind's evolutionary past that needed to be tolerated and therefore evolved roles in driving immunoregulatory mechanisms."
Microbiota Effect
The other benefit of exposure to bugs arises from the fact that a good part of each and every one of us is actually a huge microbial community. As we grokked about last year, we humans share our bodies, mostly in harmony, with trillions of microbes -- on our skin, in our guts, and just about every place in between. These bugs, especially those in our gut, carry out critical functions like digesting food, fending off infections, helping to build the heart and other organs and possibly influencing our diet and behavior. A number of recent studies suggest that our microbiome may play a critical role in promoting or preventing obesity. (See also here.)
Here again living in an environment devoid of green spaces without exposure to a suitable diversity of microbes may deprive ourselves of bugs that play essential roles for our own health.
Ecosystem Services
There are any number of reasons to preserve the natural environment. For some people, the intrinsic value of a green space is self-evident -- meadows, forests, mountains, et cetera should be protected regardless of their value to people. Many others don't share those sentiments and feel that human needs must come first. They want more objective, economic metrics to justify preservation. To address that need, scientists have developed the concept of ecosystem services -- the valuation of services such as clean water, clean air, pollution abatement that natural ecosystems provide. (See also here.) In many cases the value of such ecosystem services far outweighs the economic value of exploiting the ecosystem and therefore justifies its preservation.
Rook argues that the microbes one finds in green spaces are "a major component of the beneficial effect of green space, and a neglected ecosystem service that is essential for our well-being." When tallying up the value of a green space, we should add in the value it provides in support of our physical health. Is that valuable? You tell me.
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