Study Suggests Early Antibiotics Could Affect Adult Health and Behavior

When you were just learning to walk, you probably bonked your head on the edge of the coffee table or something. Maybe you got stitches and the doctor gave you an antibiotic for it. It wouldn't be unusual — oral antibiotics are the drugs most frequently dispensed to children around the world. But amid growing concern in the medical community about just how good antibiotics are for our short- and long-term health, a question has emerged: Could that round of early childhood antibiotics affect your health and behavior as an adult? And if so, is there anything that can be done about it?

Past research has shown that large doses of broad-spectrum antibiotics can affect behavior in adult animals, but until now, no one has looked at what impacts a narrow-spectrum antibiotic like penicillin can have on how we act. According to a new study published in Nature Communications and funded by United States Office of Naval Research, those rounds of low-dose penicillin you took as a baby — or even the one your mother took late in her pregnancy — could have had long-lasting effects on your brain, your gut bacteria and even your behavior. However, taking a specific probiotic alongside the antibiotic seemed to curtail some of these effects. At least that's what these researchers from McMaster University found in the mice that were the subjects for this study.

The research team treated pregnant mice with the equivalent of a pediatric dose of penicillin within a week before giving birth, and their pups continued receiving the dose until they weaned. The antibiotic-treated mice experienced long-lasting effects in their gut bacteria, as well as changes to their frontal cortex, exhibiting less anxiety and increased aggression. However, the groups of mice that were given supplements of the probiotic (Lactobacillus rhamnosus) experienced fewer of these detrimental side effects.

"There are almost no babies in North America that haven't received a course of antibiotics in their first year of life," says senior author Dr. Bienenstock, director of the Brain-Body Institute at St. Joseph's Healthcare Hamilton at McMaster University, in a press release. "Antibiotics aren't only prescribed, but they're also found in meat and dairy products. If mothers are passing along the effects of these drugs to their as-yet unborn children or children after birth, this raises further questions about the long-term effects of our society's consumption of antibiotics."

Consider that 70 percent of North American children receive at least two rounds of antibiotics before their second birthday, and this is something scientists see as worth investigating. But it's also worth noting that mice are not people, and though mice and rats have roughly the same number of genes as we do, rodents struck out on a different evolutionary path from our human ancestors tens of millions of years ago. Many drugs successfully tested on mice do not end up working on human subjects, though many do, so more research is needed before we start refusing our children antibiotics when they're necessary. Consider it a course of study in progress.

A 2014 study found that giving penicillin to mice in late pregnancy and early life made them more vulnerable to obesity later in life.

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