Giving children antibiotics may increase their chances of developing a deadly condition in later life, experts have said. New research has shown that early exposure to antibiotics can kill healthy gut bacteria which could lead to asthma in adulthood.

Millions of parents may have to think twice about giving their young children antibiotics. Scientists from Rutgers University have found that exposure to antibiotics early in life can kill healthy bacteria in the digestive tract, potentially leading to persistent, long-term allergies and asthma problems.

Study authors say this is the strongest collective evidence to date suggesting a causal link between antibiotic exposure in early childhood and the development of asthma and allergies later in life.

“The practical implication is simple: Avoid antibiotic use in young children whenever you can because it may elevate the risk of significant, long-term problems with allergy and/or asthma,” says senior study author Martin Blaser, director of the Centre for Advanced Biotechnology and Medicine at Rutgers, in a university release.

In collaboration with researchers from New York University and the University of Zurich, study authors noted that antibiotics are “among the most used medications in children, affect gut microbiome communities and metabolic functions. These changes in microbiota structure can impact host immunity.”

Common antibiotic for kids triggers allergies
During the study’s first portion, the team gave five-day-old mice water, along with either azithromycin or amoxicillin. Once the rodents matured, researchers exposed them to a common allergen created via household dust mites. Mice given either of the antibiotics (but especially azithromycin) displayed higher levels of “immune responses” (allergies).

Next, the second and third parts of the experiment tested study authors’ hypothesis that exposure to antibiotics early in life specifically brings about allergies and asthma by killing certain healthy gut bacteria. When alive, those bacteria support the proper development of the immune system.

Initially, lead study author Timothy Borbet transferred bacteria-rich faecal samples from the first set of mice to a second set of adult mice with no exposure to any bacteria or germs. Some received given samples from mice exposed to azithromycin or amoxicillin as infants, while others received normal samples from mice that had just been drinking water.

The rodents given antibiotic-altered samples were no more likely than other mice to develop immune responses to household dust mites. This result mirrors how people taking antibiotics during adulthood are no more likely to develop asthma or allergies than others. In other words, only antibiotic exposure as a child appears to produce this detrimental effect.

Parents can pass this problem to their children
Things changed, however, for the next generation. The offspring of mice exposed to antibiotic-altered samples reacted more to dust mites than others whose parents received samples unaltered by antibiotics. This finding, again, mirrors how mice given antibiotics as babies tended to react more to the allergen than those that received water.

“This was a carefully controlled experiment,” Blaser explains. “The only variable in the first part was antibiotic exposure. The only variable in the second two parts was whether the mixture of gut bacteria had been affected by antibiotics. Everything else about the mice was identical.”

“These experiments provide strong evidence that antibiotics cause unwanted immune responses to develop via their effect on gut bacteria, but only if gut bacteria are altered in early childhood,” he concludes.

The study is published in the journal Mucosal Immunology.

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