There are lots of theories about why food allergies, asthma, celiac disease and intestinal disorders like Crohn's disease have been on the rise. Dr. Martin Blaser speculates that it may be connected to the overuse of antibiotics, which has resulted in killing off strains of bacteria that typically live in the gut.
Blaser is an expert on the human microbiome, which is the collection of bacteria, viruses, fungi and other microbes that live in and on the body. In fact, up to 90 percent of all the cells in the human body aren't human at all — they're micro-organisms.
Blaser is the director of NYU's Human Microbiome Program and a former chairman of medicine there. His new book is called Missing Microbes: How the Overuse of Antibiotics Is Fueling Our Modern Plagues.
He tells Fresh Air's Terry Gross that with the overuse of antibiotics, as well as some other now-common practices like cesarean sections, we've entered a danger zone — a no man's land between the world of our ancient microbiome and an uncharted modern world.
Interview Highlights
On why he thinks the number of diseases has risen
Since World War II, we've seen big rises in a number of diseases: asthma, allergies, food allergies, wheat allergy, juvenile diabetes, obesity. ... These are all diseases that have gone up dramatically in the last 50 or 70 years. One of the questions is: Why are they going up? Are they going up for 10 different reasons, or perhaps there is one reason that is fueling all of them.
My theory is that the one reason is the changing microbiome; that we evolved a certain stable situation with our microbiome and with the modern advances of modern life, including modern medical practices, we have been disrupting the microbiome. And there's evidence for that, especially early in life, and it's changing how our children develop.
On the potential link between antibiotics and obesity
We have experiments in mice where, since we're very interested in obesity, if we put mice on a high-fat diet, they gain weight; they get fat. If we put them on antibiotics early in life, they also get fat. If we put [them] on both together, they get very fat. ... It's clear that the effects of the antibiotics potentiate the effects of the high-fat diet. We're not letting [the] high-fat diet off the hook, we're saying that there's another factor there. ...
There's a choreography; there's a normal developmental cycle of the microbiome from birth over the first few years of life, especially the first three years, [that] appear[s] to be the most important. And that's how nature has, how we have, evolved together so that we can maximize health and create a new generation, which is nature's great purpose. And because of modern practices, we have disrupted that. And then the question is: Does that have consequence[s]? Our studies in mice show that it does have consequences. We've done epidemiologic studies in people that show that some of these modern practices are increasing the risk of obesity as well.
On how the birth process informs a baby's microbiome
As far as we know, when the baby is inside the womb it is apparently sterile. ... The big moment of truth is when the membranes rupture, the water breaks, and the baby starts coming out. And that's where they first get exposed to the bacteria of the world, and the first bacteria they're exposed to is their mother's bacteria in the birth canal. So as labor proceeds, the babies are in contact with the microbes lining their mother's vagina and, as they're going out, they're covered by these bacteria. They swallow the bacteria; it's on their skin. ...
That's their initial exposure to the world of bacteria. That's how mammals have been doing it for the last 150 million years, whether they're dolphins or elephants or humans. ... And we know a little about what those bacteria are. The most common bacteria are lactobacillus and there's evidence that over the course of pregnancy the microbiome in the vagina changes, just as many other parts of the body are changing. The microbiome is changing in its composition in terms of maximizing lactobacilli, and these are bacteria that eat lactose, which is the main component of milk. So the baby's mouth is filled with lactobacilli. The first thing that happens is they go up against their mom's breast and they inoculate the nipple with lactobacilli and now milk and lactobacilli go into the new baby and that's the foundation for their microbiome and that's how they start their life. ...
You could project that if they didn't acquire these organisms or they didn't acquire them normally or at the normal time, then the foundations might be a little shaky.
On a study comparing the microbiomes of babies born via C-section and those born vaginally
Shortly after birth, they compared the microbiomes in the babies that came out. The babies that were born vaginally, their microbiome, not surprisingly, looked like the mom's vagina everywhere in the body — in their GI tract, on their skin, in their mouth. But the babies born by C-section, their microbiome looked like skin and it didn't even necessarily look like the mom's skin, maybe it was somebody else in the operating room. So it's clear that the microbiome is different immediately depending on the kind of birth.
There have been more and more epidemiologic studies asking the question, really for the first time: Are there long-term health consequences of being born by C-section?
On how the microbiome can determine a person's immunity and allergies
I'm concerned that the microbiome is part of our whole developmental process and if we disrupt it early, there are potentially consequences. ...
What I can tell you is that our immune system is quite complex. There are many kinds of immune cells. There are cells that strongly recognize foreign substances, there are ones that try to damp [the immune system] and down-regulate it. There's what we call innate immunity, which is the immunity we're all born with, and then there's adaptive immunity — the immunity that develops when we experience different kinds of exposures. So it's very complex.
It's developing early in life. That's what sets, in essence, [the] immunological tone that will determine how allergic a person is, or how stoical a person is in an immunologic sense.
On probiotics
There are many different probiotics. If you go to the grocery store, the health food store, the drugstore, there are shelves and shelves full of probiotics [with] different names, different compositions. I think I can say three things: The first is that they're almost completely unregulated; second is that they seem to be generally safe; and third is that they're mostly untested. ...
Right now, it's the Wild West. I'm actually a big believer in probiotics; I think that's going to be part of the future of medicine, that we're going to understand the science of the microbiome well enough so that we can look at a sample from a child and say this child is lacking such-and-such an organism and now we're going to take it off the shelf and we're going to give it back to that child. ... Just as today the kids are lining up for the vaccines, in the future, maybe the kids are going to be drinking certain organisms so that we can replace the ones that they've lost.
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