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    Antibiotic Overuse May Be Bad for Body's Good Bacteria

    Some Researchers Believe Changes in Helpful Bacteria May Be Contributing to Obesity, Asthma

    Disappearing Bacteria

    As antibiotic use has increased, studies have shown that the kinds of bacteria that we live with are changing.

    Blaser says he thinks some bacterial species that live in our bodies are going extinct. He points to the example of H. pylori, the bacterium best known for causing ulcers.

    One hundred years ago, H. pylori was the main microbe that people carried in their stomachs.

    Today, studies show that less than 6% of children born in the U.S., Sweden, and Germany carry that organism. That shows that the species is disappearing from its human hosts.

    The health consequences of that aren't clear. Neither is the reason for the disappearance.

    Blaser's point is that if one species of gut bacteria is disappearing, others are, too.

    “We know there are impacts” from antibiotic use, “impacts we don’t even have the tools yet to study,” says Lita Proctor, PhD, who coordinates the Human Microbiome Project at the National Institutes of Health.

    Links to Chronic Disease

    Blaser says it’s clear those impacts go far beyond infections.

    Farmers, for example, discovered decades ago that animals fed small amounts of antibiotics, below the doses used to treat infections, gain more weight.

    “That works so well that it accounts for more than half of antibiotic use in the United States,” Blaser says. “Since it works in chicken, turkeys, cows, and sheep, I presumed it would work in mice, and it does.”

    Antibiotics, he thinks, may also be contributing to obesity in humans, though Blaser says no one yet understands how.

    Beyond obesity, he says studies have shown that a child’s risk for inflammatory bowel disease increases with the number of courses of antibiotics taken.

    He also says antibiotics may be a factor behind the unexplained rises in allergies, asthma, and type 1 diabetes in children.

    But his commentary in Nature does not prove that. Blaser's paper is his opinion, not a new study.

    Other research, directed by the Human Microbiome Project, which aims to catalogue and understand the microorganisms that live in the body, has suggested that a bacterial environment that’s out of balance in the stomach and esophagus may contribute to cancer.

    An out-of-balance bacterial environment in the digestive system may lead to inflammation, and inflammation may cause changes in cells that lead to cancer, Proctor says.

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