Antibiotic use has grown along with obesity. Coincidence?

We’ve all heard that the overuse of antibiotics is making them less effective and fueling the rise of dangerous drug-resistant bacteria. But did you know it may also be fueling the rise of obesity, diabetes, allergies and asthma?

So says Dr. Martin Blaser, microbiologist and infectious disease specialist at New York University Langone Medical Center who studies the myriad bacteria that live on and in our bodies. He explains his theory in a commentary published in Thursday’s edition of the journal Nature.

In recent years, scientists have developed a growing appreciation for the “microbiome,” the collection of mostly useful bacteria that help us digest food, metabolize key nutrients and ward off invading pathogens. Investigators have cataloged thousands of these organisms through the National Institutes of Health’s Human Microbiome Project, begun in 2008.

Blaser is interested in why so many bacteria have colonized the human body for so long – the simple fact that they have strongly suggests that they serve some useful purpose. But these bacteria have come under attack in the last 80 or so years thanks to the development of antibiotics. The drugs certainly deserve some of the credit for extending the U.S. lifespan, Blaser notes – a baby born today can expect to live 78 years, 15 years longer than a baby born in 1940. But in many respects, an antibiotic targets a particular disease the way a nuclear bomb targets a criminal, causing much collateral damage to things you’d rather not destroy.

“Antibiotics kill the bacteria we do want, as well as those we don’t,” Blaser writes. “Sometimes, our friendly flora never fully recover.”

And that can leave us more susceptible to various kinds of diseases, especially considering that the typical American is exposed to 10 to 20 antibiotics during childhood alone. Blaser points out that the rise (let along overuse) of antibiotics coincides with dramatic increases in the prevalence of allergies, asthma, Type 1 diabetes, obesity and inflammatory bowel disease. That isn’t proof that the two are related, but it’s a question worth exploring, he says.

Take the case of Helicobacter pylori. As Blaser explains, this bacterium was “the dominant microbe in the stomachs of almost all people” in the early 1900s. But 100 years later, it is found in less than 6% of American, Swedish and German kids. One likely reason is that a single course of amoxicillin or another antibiotic to treat an ear or respiratory infection can wipe out H. pylori 20% to 50% of the time.

The consequences of this aren’t clear. H. pylori can cause ulcers and stomach cancers, so there’s probably some upside. But its absence could be behind the increase in gastroesophageal reflux, which can cause Barrett’s esophagus and esophageal cancer.

Intriguingly, scientists are also finding that two hormones produced in the stomach – ghrelin and leptin – behave differently when H. pylori isn’t around. Ghrelin is the hormone responsible for telling the brain that you’re hungry and leptin is supposed to send the signal that you’re full.

In Blaser’s own lab, researchers have discovered that children who lack H. pylori are more susceptible to asthma, hay fever and skin allergies. Others have done experiments in mice that suggest it protects against asthma.

And H. pylori is just one bacterium!

With all this in mind, Blaser urges doctors to dial back on using antibiotics in pregnant women and children. Ideally, researchers can develop new antibiotics that can target pathogens with greater precision, leaving more of the microbiome intact. Also needed will be tests that can rapidly identify the specific pathogen responsible for an illness.

There may even be a role for probiotic drugs, to introduce – or reintroduce – useful bacteria that are missing from our bodies, he says.

The essay is behind a paywall, but a link is available here.