Treating infants with antibiotics could increase their chances of being overweight as older children, according to a new US study.
Researchers from the New York University School of Medicine studied more than 11,000 children and found those exposed to antibiotics in the first six months of their life were 22 percent more likely to have a higher body mass index (BMI) when they were aged 10 to 38 months than infants who weren't exposed.
"We typically consider obesity an epidemic grounded in unhealthy diet and exercise, yet increasingly studies suggest it's more complicated," researcher Dr Leonardo Trasande said in a media release.
"Microbes in our intestines may play critical roles in how we absorb calories, and exposure to antibiotics, especially early in life, may kill off healthy bacteria that influence how we absorb nutrients into our bodies, and would otherwise keep us lean."
Timing of the exposure appears to be important — the researchers found babies on antibiotics between six months and 14 months showed no difference in BMI to babies who hadn't been on antibiotics.
Dr Trasande, whose study was published in the International Journal of Obesity, conceded more research needs to be done.
"For many years now, farmers have known that antibiotics are great at producing heavier cows for market," said Dr. Blustein.
"While we need more research to confirm our findings, this carefully conducted study suggests that antibiotics influence weight gain in humans, and especially children too."
For some time, scientists have been concerned about the overuse of antibiotics in infants and children. They worry that antibiotics impact the microbiome –– the trillions of microbial cells that inhabit our bodies –– which can have an effect on obesity, bowel disease and other conditions.
But Professor Leonard Storlien, from the Boden Institute of Obesity, Nutrition, Exercise & Eating Disorders, told ninemsn the health benefits of antibiotics outweigh any possible negatives.
"Antibiotic use is absolutely critical in a number of babies in the first few months of life," he said.
Professor Storlien said gut microbiota develops in the first six months of our lives and the challenge is to find a way to prevent negative effects on the gut microbiota from antibiotics.
"We may find antibiotic use in the first six months is detrimental to the gut and the gut microbiota, but it is absolutely critical for health in the face of things like sepsis and other very serious diseases," he said.
"What we need now to work out is how to restore the gut microbiota to its healthiest form quickly after an antibiotic treatment."
This is the first study to analyse the link between antibiotics and body mass in infancy.
The researchers analysed the children in three periods — between birth and five months; between six and 14 months; and between 15 and 23 months.
They measured the children's body mass index at six weeks, 10 months, 20 months, 38 months and seven years old and were careful to take diet, physical activity and parental obesity into account.
It appeared antibiotics only had a significant effect on BMI in those infants given antibiotics in their first five months.
The study did show that children who took antibiotics between 15 and 23 months had a higher BMI for their age and gender by the time they were seven, however the researchers said it wasn't enough to classify them as overweight or obese.