Map of life expectancy at birth from Global Education Project.

Thursday, March 24, 2005

The World Within

No, I'm not talking about anything mystical. Assuming you are an adult of approximately normal size, almost three pounds of your body weight consists of the microorganisms that inhabit your body. That's less than 2% by weight, but it's more than 10 times as many microbial cells (mostly bacteria) than we have human cells. And by the way, I'm assuming you are free of any infectious disease. These organisms aren't making us sick, they just live inside us. And as a matter of fact, many of them are keeping us alive.

We aren't just organisms, we're ecosystems. Our microbial inhabitants are busy competing, cooperating, eating each other, recycling each other's waste, and of course eating us, feeding us, and modifying our insides physically and chemically, for better or for worse. I'm inspired to note this now by a review of "Microbial Inhabitants and Humans: Their Ecology and Role in Health and Disease," by Michael Wilson, in the new JAMA. The reviewer, Dr. David Haburchak, writes that "After reading this book, I have haunting thoughts of burned-over forests inside patients to whom I have administered broad-spectrum antibiotics."

Indeed, your host took antibiotics for an ear infection a couple of years back and ended up with an extremely unpleasant candidiasis infection of the throat -- commonly called thrush -- because the antibiotics wiped out the symbiotic ecosystem that normally keeps me safe and allowed the malevolent fungus to move in.

There are a bewildering variety of complex ecological regimes on our skin, in our eyes, sinuses, mouths, throats, stomachs, intestines, bloodstreams, urinary tracts -- including the notorious helicobacter pylori that cause stomach ulcers in some people, but protect us from gastroesophogeal reflux and from esophogeal and stomach cancer. One more thing to think about the next time your doctor gives you a prescription for antibiotics.

1 comment:

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