“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,” said researcher Martin Blaser.
Antibiotics affect gut health
The researchers conducted a two-part experiment on mice to determine the long-term risks associated with prescribing antibiotics to young children.
The first trial tested the effects of amoxicillin and azithromycin on five-day-old mice. They were given either one of the antibiotics or just water, and the team studied them until they matured. After being exposed to dust mites, it was clear that the mice that were given antibiotics during their earliest days were more likely to have allergies.
In the second part of the study, the team exposed new adult mice to fecal samples from mice in the first part of the study. While the adult mice had never been exposed to any kind of germs, the samples were full of new bacteria – including antibiotics – that they had never come in contact with.
The researchers tracked the health outcomes of both the adult mice and their offspring. While the adult mice showed no adverse health outcomes after being exposed to the antibiotics, their babies didn’t fare as well. When the first generation of mice had been exposed to antibiotics, their offspring were much more likely to show signs consistent with allergies and asthma.
“This was a carefully controlled experiment,” Blaser said. “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."
The team explained that these findings hold up because human adults that are prescribed antibiotics aren’t likely to develop serious allergies or asthma. For young kids or infants, they believe that antibiotics kill off healthy bacteria in the gut, which ultimately affects their immune systems long-term.
“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,” Blaser said.