According to the study, which surveyed health records of more than 64,000 children, antibiotic use before the age of 2 is associated with increased obesity risk before age 5. Those children who were given four or more courses of common antibiotics before age 2 were at particularly high risk of developing childhood obesity. Strikingly, 69 percent of children studied had been given antibiotics in their first two years of life.
“Our hope is that we can find out what the risk factors are in early childhood and do a better job not just at preventing this, but of identifying the kids . . . who then can change their path by changing their lifestyle and changing the healthcare they get,” study author Charles Bailey of the Children’s Hospital of Philadelphia told Time.
Broad-spectrum antibiotics, which kill a range of different bacteria, appeared to drive this association; narrow-spectrum antibiotics did not show a significant link with childhood obesity. “[I]f we use broad-spectrum antibiotics a lot of the time, are we creating unintended effects down the road that we didn’t appreciate when we were sitting in the office?” Bailey told Time.
One possible mechanism that would link antibiotic use and obesity are the drugs’ effects on the body’s commensal microorganisms, which have been linked to metabolic changes. “It’s coming in every direction. We’re really assaulting our microbiome,” Martin Blaser, director of the Human Microbiome Program at New York University and author of Missing Microbes: How the Overuse of Antibiotics is Fueling Our Modern Plagues, told USA Today. “Right now, everyone is giving antibiotics, thinking they are ‘free,’” he adds. “Once there is evidence that they have costs, the calculation begins to change.”
Clarification (October 2, 2014): The subhead for this story has been updated to clarify that this is an observational study, and antibiotic use was simply correlated with increased risk of obesity. The Scientist regrets the confusion.