Babies who are prescribed antibiotics before they're 2 years old may be more likely to become obese children, new research suggests.
Acid reflux medications may also up the risk, though that connection was not as strong.
The findings come from the tracking of infant medication histories and childhood obesity incidence among hundreds of thousands of children up until age 8. All had received care through the U.S. military health care system.
As to why a link was seen, investigators theorized it could have to do with the impact such medications have on the delicate microbial environment (microbiome) found in a growing child's gut.
"We did not evaluate the microbiome status of these children," stressed study author Dr. Cade Nylund, a lieutenant colonel with Medical Corps of the U.S. Air Force. "And this was an observational study, so we can only demonstrate the findings of an association, not a specific cause.
"So we presume this has to do with changes in a child's microbiome brought on by these medications," he added. "But it could also just be the result of having an infection. Or having a fever, maybe with or without taking antibiotics. Or it might have something to do with the psychosocial dynamics of a family. We don't yet know."
As to what parents should make of these findings, Nylund said the most important thing is to ensure that children take the medications they need, but not when it isn't warranted.
For example, Nylund noted that acid reflux medications -- such as histamine blockers and proton pump inhibitors -- "are often prescribed in infants when they're not indicated. Acid reflux is normal in infants, and not really a good reason to put them on reflux meds. And most infants grow out of the problem by 12 months."
On the other hand, Nylund acknowledged that "antibiotics play a big role in treating infections, and they always will.
"And I would certainly hate for a parent to not treat a child with antibiotics for an infection out of a concern for obesity," he added.
In the study, published Nov. 1 in the journal Gut, researchers followed roughly 333,000 children born between 2006 and 2013.
More than 241,000 had been prescribed antibiotics before the age of 2. Nearly 40,000 had been prescribed histamine blockers, while more than 11,000 had been prescribed proton pump inhibitors. Almost 6,000 kids had been prescribed all three drugs.
Based on an average of four pediatrician visits after age 2 and up until age 8, investigators determined that nearly 47,000 children (14 percent) became obese. Of these, about 9,600 had never been prescribed an antibiotic or acid reflux medication while an infant; the rest had.
After stacking medication histories up against obesity incidence, the research team concluded that infants prescribed antibiotics faced a 26 percent greater risk for childhood obesity by the age of 3. That risk rose the longer an infant had taken antibiotics, and among infants who had taken medications in multiple antibiotic classes.
Acid reflux medications also appeared to raise childhood obesity risk, though the connection was characterized as "weak."
Dr. Ruchi Gupta, a senior scientist in child health research at Northwestern University's Feinberg School of Medicine in Chicago, said the findings are interesting because they raise "questions about factors such as antibiotics and medications that alter gut microbiome and can potentially influence other health conditions." She was not involved with the study.
But Gupta cautioned that for now the findings should only be viewed as an "important association." More research will be needed "to truly understand cause and effect, as it is a complex condition influenced by many environmental, behavioral and genetic factors," she said.