Antibiotics are life-saving medicine, but their overuse has been linked to a number of health concerns, not least of which include antibiotic-resistant superbugs that kill thousands of people each year.
Now, new research adds to growing evidence that over-exposure to antibiotics contributes to another problem: weight gain.
In the largest study on the subject to date, researchers from Johns Hopkins Bloomberg School of Public Health found that children who take antibiotics regularly throughout their childhood gain weight significantly faster than those who do not. The findings were published in the International Journal of Obesity.
For the study, Dr. Brian Schwartz, a professor in the Department of Environmental Health Sciences at the Bloomberg School, and his team analyzed the health records of more than 160,000 children between the ages of 3 and 18 from 2001 to 2012. They collected data on height and weight to determine body mass index (BMI), as well as antibiotic use in the previous year and any earlier years for which health records were available.
The results showed that at age 15, children who had received antibiotics seven or more times during childhood weighed about three pounds more than those who had never taken the drugs. Approximately 21 percent of the study participants -- about 30,0000 kids -- had taken antibiotics seven or more times during childhood.
Additionally, Schwartz said the findings most likely underestimate weight gain resulting from exposure to antibiotics, as the researchers did not have health records for participants throughout their entire childhood and because the effect of certain antibiotic types was even stronger than the overall average.
"Our models suggest that the effect likely continues into adulthood and the BMI trajectories of children who did and did not receive antibiotics are increasingly diverging at older ages," Schwartz told CBS News. "Although we did not observe children past 18 years, I would bet that this kind of pattern would continue."
Scientists have long known that antibiotics promote weight gain in animals, which is why they are given to livestock in animal feed at modern industrialized farms.
But growing evidence shows that in humans, antibiotics could lead to weight gain because of the effect they have on the microbiota or microbiome -- microorganisms that inhabit the body. Antibiotics work by killing off harmful bacteria but the medicine can also deplete "good" bacteria that are vital to health. Research shows repeated antibiotics use can forever alter the microbiome, which can change the way it breaks down food in the digestive tract, increasing the calories absorbed and leading to weight gain.
Of course, the findings don't suggest that children should never take antibiotics, but Schwarz said physicians need to be diligent in prescribing the drugs only when needed.
For parents, he gives the following advice: "Bottom line: If your doctor tells you that you or your child does not need antibiotics, don't ask for them, don't take them, don't try to find another doctor who will provide them. Eat healthy and your gut microbiota will be very good to you. Don't change your gut microbiota unnecessarily by taking antibiotics if you don't need them."