Children treated with antibiotics through their childhood years gain weight at a significantly faster rate than children not given such drugs, a new study has found.
The findings suggest childhood antibiotic use can have an ongoing effect on body weight that continues well into adulthood.
In a study looking at more than 160,000 children in Pennsylvania, the researchers discovered that healthy children age 15 who had been treated with antibiotics seven or more times during childhood weighed, on average, 3 pounds more than their contemporaries who had taken no antibiotics.
There is a growing body of evidence linking antibiotic use with weight, and not just in humans; farmers have turned to giving doses of antibiotics in animal feed to promote growth in livestock.
In humans, the problems can begin early, researchers say, but are not limited to childhood.
"Antibiotics at any age contribute to weight gain," explains study lead author Brian S. Schwartz at the Johns Hopkins Bloomberg School of Public Health.
In children, the researchers suggest, antibiotics may be killing off some kinds of bacteria in the gut while leaving others that break down food differently.
That may result in permanent alterations of the microbiome, the populations of organisms that live in the human digestive system, the researchers say in the study appearing in the International Journal of Obesity.
The change may result in an increase in the amount of calories in the nutrients absorbed, they say.
In most cases, children treated with an antibiotic will gain a small amount of weight but lose it over the course of a year. However, with repeated treatments the weight gain can become cumulative and progressive, the researchers point out.
"This would suggest that this effect is not going to stop at age 18 [and] what's happening is permanent," says Schwartz.
There is also evidence that the effects of antibiotics can begin even before birth; latest study in Denmark on thousands of schoolchildren showed that a mother's use of antibiotics while pregnant can result in an increased risk of a child eventually becoming overweight or obese.
The researchers emphasize there are times when antibiotic use is appropriate, such as in the case of some bacterial illnesses that can be serious or even fatal if not treated.
However, Schwartz notes, there is concern that parent are demanding antibiotics for conditions that don't warrant their use, such as simple ear infections, or for viruses that antibiotics aren't really effective against.
"We've got to totally dissuade parents from advocating for antibiotics," he says. "As parents we want to feel like we're doing something active for our kids, but I think we're doing our kids damage.
"If your doctor says you don't need them, don't take them."
