Infants who were given multiple courses of broad-spectrum antibiotics had a 20% increased risk of becoming obese toddlers, according to new research presented last week in a poster at Obesity Week 2013: The American Society for Metabolic and Bariatric Surgery and the Obesity Society Joint Annual Scientific Meeting.

Many infants receive antibiotics, and while "in the whole universe of a child's life, this is probably not the key factor contributing to obesity…it is a modifiable risk factor," lead author Charles Bailey, MD, from Children's Hospital of Philadelphia, Pennsylvania, told Medscape Medical News.

In this study, narrow-spectrum antibiotics consisted of penicillin and amoxicillin and broad-spectrum antibiotics included all other types.

Clinicians should be aware that "one of the side effects of [prescribing a] broad-spectrum antibiotic is not just an upset stomach…not just a little bit of diarrhea that will go away in a week, but…an increased risk of being obese 3 years later," Dr. Bailey noted.

If an infant truly requires and is prescribed a broad-spectrum antibiotic, the pediatrician should more closely monitor the child's weight at subsequent visits, he suggested.

Gut Biome Changes and Obesity

Multiple genetic, environmental, and developmental factors may contribute to early childhood obesity, Dr. Bailey explained. One research area of increasing interest is how antibiotics can alter the gut microbiome — the colony of bacteria living there — and contribute to weight gain. This has been shown in animal studies, but evidence for a link between antibiotic use and obesity in children is limited, he noted.

In one recent study, Leonardo Trasande, MD, from the New York University School of Medicine, and colleagues examined data from the Avon Longitudinal Study of Parents and Children on more than 11,000 babies born in the United Kingdom in 1991–1992. They reported that infants who had received antibiotics in the first 6 months of life had a greater risk of being obese when they were about 1 to 3 years old.

However, that study did not reflect current antibiotic prescribing habits or distinguish between classes of antibiotics.

Dr. Bailey and colleagues retrieved data for 65,400 children who were seen in about 30 pediatric practices affiliated with Children's Hospital of Philadelphia from 2004 to 2013.

They looked at the children's exposure to medications from birth until age 2 years — specifically, the number of 6-month intervals in which the children had been prescribed a medication. They then determined whether the children were overweight or obese at ages 2 to 4 years, based on body mass index (BMI).

The sample included about an equal number of boys and girls; 51% were white, 33% were black, and 16% were of other ethnic origins.

The pediatric practices were a mixture of urban (34%) and suburban (66%). Most visits were covered by commercial or private insurance (58%), and the rest were mostly covered by Medicaid or other public insurance (41%).

By the time they were 2 years old, about half of the children had visited a pediatrician 11 to 19 times, but about a quarter of them had been seen by a pediatrician 20 or more times. At this age, about 3 out of 4 children had been prescribed antibiotics, while about 1 in 4 had received steroids or antireflux medications.

Clinicians Can Shift Away From Broad-Spectrum Antibiotic Use

The children who had been prescribed steroids or antibiotics as infants had a significantly increased risk of being overweight or obese as toddlers, but this was not true for antireflux medications.

Being male or Hispanic, having a diagnosis of asthma, seeing a pediatrician in an urban practice, frequently using antibiotics or steroids, or being seen in certain pediatric practices were all associated with having an increased risk of being overweight or obese at age 2 to 4 years.

The children who used steroids frequently tended to have asthma, which is itself related to risk for obesity, said Dr. Bailey.

"For antibiotics, the story [was] a little bit more complicated," he continued. "We didn't see a connection between risks of obesity and the kinds of antibiotics — penicillin and amoxicillin — that most clinical guidelines recommend that you prescribe for common things [such as] strep throat, ear infections, sinusitis, and pneumonia."

But repeated use of a broad-spectrum antibiotic as an infant drove up the risk for childhood obesity, with the risk increasing as the number of exposures went from 1 to 2 to 3.

To lower the likelihood of potential childhood obesity, "it's much harder to change an urban environment, it's impossible to change the genome that you get at birth, but…broad-spectrum antibiotics, that's something that [clinicians] can more easily shift away from," Dr. Bailey summarized.

The study was supported by a grant from the Healthy Weight Program at  Children's Hospital of Philadelphia.

Obesity 2013: The Obesity Society Annual Scientific Meeting. Poster T330, presented November 14, 2013.

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