This Green Life
A monthly journal of sorts by Sheryl Eisenberg

AUGUST 2012: Nine out of ten cells in the human body belong to microbes. Don't let it bug you. We couldn't live without them.

The Ecosystem Within
A new light on sickness and health

When Walt Whitman wrote, "I am large, I contain multitudes," little did he know the truth behind the metaphor.

Recent science reveals that a hundred trillion microorganisms live in the human body, outnumbering our own cells ten to one. It could legitimately be said that we are more them than us—or that the very idea of our being discrete organisms is fundamentally wrong.

Whichever way you frame it, one thing is indisputable: our bodies are their home.

Scientists working on the federally funded Human Microbiome Project are now in the process of cataloging our tenants, known collectively as our microbiome. More than 10,000 species have been identified so far.

Our microbial residents aren't all moochers. Many provide vital services that we can't perform for ourselves. They produce enzymes needed for digestion, anti-inflammatory agents used by our immune system and moisturizer that helps to keep our skin supple and crack-free so pathogenic microbes don't get in.

Speaking of pathogens—research shows that they can be present in the body without acting up. The dread E. coli, which can be a killer, has been found living peaceably in healthy guts with no apparent damage done.

The new findings are upending some of our most basic ideas about sickness and health, leading some scientists to ask whether the exclusive focus on good and bad microbes is a case of missing the forest for the trees. That's why the Human Microbiome Project is not just cataloging the individual species but attempting to understand how the whole system works.

One interesting discovery is that the microbes within us live in "communities" at specific body sites, with populations varying by location. For instance, the distribution of species under the arm differs from the distribution on the foot (which accounts for the different smells in those places when we get hot and sweaty). And the populations in our gut are a different kettle of fish altogether.

Think of the many body sites as the microbes' habitats—their ponds and fields—and of the populations and habitats together as "ecosystems." I am not being figurative. This is the language scientists use.

An important finding is that microbiomes are not generic. Yours is different from mine.

The difference is due to nurture, not nature. Our microbiomes were first seeded at birth, before which we were largely sterile. You picked up your mother's species as you made your way through her birth canal, and I picked up mine. If you happened to be born by Caesarian section, you were colonized (another scientific term) by species on the skin where you exited.

Once out in the world, you and I accumulated more microorganisms from the things we ate and came in physical contact with. At some point our microbiomes must have matured and stabilized because research on adult microbiomes suggests they are relatively stable over time. They are also unique— enough perhaps to serve as fingerprints in a crime investigation.

That said, microbiomes can and do change.

Let's say you take antibiotics to get rid of an infection. Today's antibiotics cast a wide net, just as broad spectrum pesticides do, so the drug will not only kill the pathogens causing the infection but innocent bystanders, too. While the original microbiome, or something like it, will eventually reconstitute itself in healthy people, new pathogens may gain a foothold in those with compromised immunological systems.

This happened to my 89-year-old mother-in-law last year. After taking a strong course of antibiotics for pneumonia, she ended up with a debilitating C. difficile infection of the intestines, which was finally eliminated only to make a comeback a couple of months later, as it so often does. This is a common problem for older people in hospitals and other facilities.

The food you eat can also affect your microbiome, as a number of research projects show, including a recent study of the elderly which found a correlation among diet, gut microbiota and health.

What about eating conventionally raised animals that have been pumped up with a steady diet of antibiotics? Research shows that even a low, short-term dose of antibiotics increases antibiotic-resistant bacteria in the animals, including bacteria resistant to antibiotics not even administered, which can be passed onto you through the meat. Whether or not this causes any long-term change to your microbiome, it could result in a disease that is hard to beat.

Your physical environment may also shape your microbiome. An intriguing study conducted in Finland finds an association between a person's microflora and exposure to nature. Essentially, people who live in closer contact with natural features have more diverse microbiotic communities, which researchers consider a good thing for health.

So, what's the takeaway?
  1. Don't take or request prescriptions for antibiotics for conditions they cannot cure, such as viral diseases, or "just to be on the safe side." Unnecessary antibiotic use leads to antibiotic-resistant "super bugs."
  2. Avoid antimicrobial soaps, sponges and other household products. Not only can that create antibiotic-resistance, the specific agents used in cleansers and other such items are endocrine disruptors that can cause other health problems.
  3. Wash your hands vigorously for 20 to 30 seconds with warm water and regular (not antimicrobial) soap to get rid of unwanted germs.
  4. If you eat meat and animal products, buy organic. The regulations for organic food prohibit all use of antibiotics.
  5. Spend a little time every day—or as often as possible—in or close to nature.
—Sheryl Eisenberg

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Play video
THE HUMAN MICROBIOME PROJECT seeks to answer a simple question: what are the bacteria that live in our bodies and how do they contribute to sickness and health? Watch the video to learn more about the project and how new technologies are making it possible.

ONE WAY TO THINK ABOUT YOUR MICROBIOME: It lends you use of the microbes' DNA, in effect extending your gene pool exponentially.


National Institutes of Health
Human Microbiome Project Defines Normal Bacterial Makeup of the Body

The New York Times
In Good Health? Thank Your 100 Trillion Bacteria

Tending the Body's Microbial Garden

The Economist
The Human Microbiome: Me, Myself, Us

Saving Antibiotics

Lack of Nature Increasing Allergies

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Sheryl Eisenberg is a writer, web developer and long-time advisor to NRDC. With her firm, Mixit Productions (, she brought NRDC online in 1996, designed NRDC's first websites, and continues to develop special web features for NRDC. She created and, for several years, wrote the Union of Concerned Scientists' green living column, Greentips, and has designed and contributed content to many nonprofit sites. Sheryl makes her home in Tribeca (NYC), where—along with her children, Sophie and Gabe, and husband, Peter—she tries to put her environmental principles into practice. No fooling.
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