Is This Microbe Helping You or Hurting You?

Doctors have long been prescribing antibiotics to anyone with gastric discomfort, including ulcers. The goal was to eliminate the bad guy—the H. pylori bacteria. But over time, scientists have discovered that the bad guy actually is a good guy as well. On the one hand, H. pylori increases your risk for ulcers and then later for stomach cancer, but on the other hand, it is good for the esophagus, protecting you against GERD and its consequences, including a different cancer, and it may even protect against asthma and weight gain.

We talked with renowned scientist Martin J. Blaser, MD, who has studied H. pylori for nearly 30 years and is the author of the recent book Missing Microbes. Here he explains what this means for you…


Antibiotics are effective at killing bacteria and stopping infections. But they’re not very discriminating. Each dose kills many different organisms, including ones that you may need to stay healthy.

In 2010, health-care practitioners in the US prescribed 258 million courses of antibiotics—about 833 prescriptions for every 1,000 people. The average child in the US receives about 17 courses of antibiotics before he/she is 20 years old.

Do we need all of these drugs? Absolutely not. In Sweden, where doctors are slower to write prescriptions, antibiotic use is only about 47% of US levels. Swedish children, in the first three years of life, are receiving less than one-and-a-half courses of antibiotics versus about four in US children—and the death rate in Swedish children is lower than in US children.

In the US, doctors routinely prescribe antibiotics for infections that usually are caused by viruses (which aren’t affected by the drugs) or for conditions that usually get better with no treatment.

Result: Many people no longer have the bacteria that they may need to stay healthy. Examples…


In the 1980s, researchers discovered that most ulcers were caused by H. pylori, a common stomach organism. Doctors can test for it using a blood test or a stool test. Now ulcers are routinely cured with antibiotics that kill the bacterium.

The catch: The same microbe that causes ulcers is simultaneously protective. Researchers speculate that diminished populations of H. pylori—caused by improved sanitation as well as antibiotics—could explain why heartburn, known as gastroesophageal reflux disease (GERD), now affects about 18.6 million people in the US.

What’s the connection? In the past, most people lived with H. pylori all their lives. It gradually damaged stomach cells and reduced acid levels. Less acid meant that GERD was less common, and less severe, than it is today.

This paradox is one of nature’s trade-offs. People who take antibiotics to eliminate H. pylori won’t have ulcers, but they’re twice as likely to develop GERD. They also have an increased risk for Barrett’s esophagus, tissue damage that can lead to esophageal cancer.

You should take antibiotics if you’ve been diagnosed with an ulcer. But the majority of patients with ulcerlike symptoms don’t actually have ulcers. They’re far more likely to have non-ulcer dyspepsia, a condition that isn’t helped by antibiotics.


There’s some evidence that the nation’s obesity epidemic is caused in part by antibiotics. In laboratory studies, mice given antibiotics have increases in body fat even when their diets stay the same. Livestock producers routinely give antibiotics to uninfected animals not to ward off illness but because it increases their body weight.

The same bacterium that causes ulcers (and protects against GERD) also appears to regulate the activity of two stomach hormones—ghrelin, a hormone that triggers appetite when your stomach is empty, and leptin, a hormone that signals the brain when it’s time to stop eating.

Children who get the typical courses of antibiotics may grow up without any H. pylori in their stomachs. This could increase their appetites by causing ghrelin levels to remain steady even after they’ve already eaten.

Antibiotics are just one factor that could affect bacteria and, in turn, contribute to obesity. Another is the increasing use of Cesarean-section childbirths. When researchers reviewed data from 15 separate studies with more than 38,000 participants, they found that babies delivered by Cesarean section—who aren’t exposed to the same bacteria as those delivered vaginally—are 26% more likely to be overweight as adults.


Many patients with GERD also develop wheezing, constricted airways and other asthmalike symptoms. Once again, a missing bacterium might be to blame. In one study, researchers collected blood samples from more than 500 people. They found that those who tested positive for H. pylori were 30% less likely to have asthma than those who didn’t have H. pylori.

It is possible that stomach inflammation triggered by some strains of H. pylori triggers the activity of immune cells that help prevent asthma and allergies. Also, it is possible that the higher acid levels (discussed above) in those without H. pylori could lead to asthma symptoms.


Antibiotics can be lifesaving drugs. I don’t advise people to never take them. But doctors need to prescribe antibiotics more judiciously. Important…

Don’t insist on antibiotics just because you (or your child) has an ear, sinus or upper-respiratory infection. The vast majority of these infections are caused by viruses. Even when bacteria are to blame, the infections usually clear up on their own. Ask your doctor if he/she is sure that an infection needs to be treated.

Ask for a narrow-spectrum drug. Doctors often prescribe high-powered, broad-spectrum antibiotics (such as the Z-Pak) because they knock out many common infections. But the broad-spectrum drugs also kill more innocent organisms.

When possible, it’s better to take a narrow-spectrum antibiotic (such as penicillin) that’s less likely to kill beneficial organisms. It’s not a perfect solution, because all antibiotics kill multiple strains of bacteria. But “targeted” drugs may be somewhat less likely to cause long-term problems than broad-spectrum antibiotics.

On the horizon: In 1998, I predicted in the British Medical Journal that we would one day be giving H. pylori back to our children. Since then, the support for this idea has only grown deeper, but we are not there yet.