We are vastly, ridiculously, hopelessly, humblingly outnumbered: For every one human cell, there are an estimated ten single-cell microbes in us or on us, at least 100 trillion in all, nestled in our guts and in our urogenital tracts, lying on our skin and happily ensconced in our mouths and noses—entire civilizations of fungi, protozoa, and (mostly) bacteria that eat, breathe, evolve, reproduce, and die.
Before you reach in horror for the hand sanitizer or industrial-strength mouthwash, keep this in mind: A profusion of research in just the past five years is showing that our microbial hitchhikers, collectively called the human microbiota (and so small that they account for only 1 or 2 percent of our body weight), play a key role in maintaining our health. And we disrupt them at our peril.
“It’s not possible to understand human health and disease without exploring the massive community of microorganisms we carry around with us,” says George Weinstock, a professor at Washington University in St. Louis. Knowing which microbes live in healthy people “allows us to better investigate what goes awry in diseases that are thought to have a microbial link, like Crohn’s and obesity.”
The microbes in our body—especially some of the 10,000 or so species of bacteria—have indeed been implicated in disorders as diverse as obesity and Crohn’s and also in asthma, heart disease, sinusitis, and possibly even mood disorders. These bacteria may influence how big or small our appetite is and what foods we crave. They synthesize vitamins and affect how quickly we metabolize drugs such as acetaminophen (Tylenol). Given this robust job description, it’s hardly surprising that scientists are discovering that, when perturbed, the microbiota can tip us into poor health or outright illness.
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