Are antibiotics making children fat?

It seems yet another reason exists not to overprescribe antibiotics, particularly in infancy. They increase body mass into childhood.

New research finds that babies exposed to antibiotics during the first 6 months have consistent increases in body mass from 10 to 38 months, corresponding to about a 90-g increase in weight in a 38-month-old child. These children are 22% more likely to be overweight for height than children not exposed to antibiotics during the same time period.

Exposure between 6 and 14 months showed no association with body mass but exposure between 15 and 23 months was again consistently associated with increased body mass index (BMI) Z-score at 7 years. Nonantibiotic medications had no effect.

Researchers looked at more than 11,500 children born weighing at least 2,500 g in the Avon Longitudinal Study of Parents and Children, a population-based study of children born in the United Kingdom during 1991 and1992.

They found that almost one-third of the children were exposed to antibiotics in the first 6 months. By 2 years, only one-quarter of the children remained completely unexposed.

Intravenous antibiotics are often used to treat neonatal sepsis, and the findings suggest that this route of administration might contribute differently from the oral route to changes in gut flora that promote weight gain.

The investigators realize that the association between exposure to antibiotics and weight gain is potentially confounded by a myriad of social, behavioral, and biologic factors. They also concede that depending on parental recall of exposures and timing introduces potential imprecision. Exposure timing matters, they say, and although the effects on individuals are modest, the effects on the population could be substantial.

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