Researchers from the New York University School of Medicine and the NYU Wagner School of Public Service found that exposure to antibiotics early in life may kill off healthy intestinal bacteria that helps keep us lean.
The study found that on average, children exposed to antibiotics from birth to five months of age weighed more for their height than children who weren't exposed.
Between the ages of 10 to 20 months, this translated into small increases in body mass percentile, based on models that incorporated the potential impacts of diet, physical activity, and parental obesity.
By 38 months of age, exposed children had a 22 per cent greater likelihood of being overweight.
However, the timing of exposure mattered: children exposed from 6 months to 14 months did not have significantly higher body mass than children who did not receive antibiotics in that same time period.
"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," lead researcher, Leonardo Trasande said in a statement.
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The researchers evaluated the use of antibiotics among 11,532 children born in Avon, United Kingdom, during 1991 and 1992.
They analysed health information on these children during three periods: from birth to five months of age; six months to 14 months; and, finally from 15 to 23 months.
They also examined body mass or weight at five different points of time