The study, which analyzed over 10,000 children and was published in the International Journal of Obesity, found that kids who weighed more for their height were those who were exposed to antibiotics from birth to 5 months of age.
The ages of 10 to 20 months consisted of small increases in body mass percentile, based on models that incorporated the possible effects of physical activity, parental obesity, and diet. Exposed infants had a 22% greater chance of being overweight by 30 months of age.
Babies that were exposed from 6 months to 14 months did not have a body mass that was significantly higher than those who did not use antibiotics in that same time period, meaning that the timing of exposure was important.
The research does not prove that young infants are going to become overweight if they receive antibiotics in early life, but it does show that there is a correlation, explained the NYU School of Medicine researchers. In order to further explore this correlation and find a direct causal link, further research needs to be conducted.
Leonardo Trasande, MD, MPP, lead author and associate professor of pediatrics and environmental medicine, said:
"We typically consider obesity an epidemic grounded in unhealthy diet and exercise, yet increasingly studies suggest it's more complicated. 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."
Scientists have become increasingly concerned about the overuse of antibiotics, particularly in young kids. Preliminary research on the microbiome (the trillions of microbial cells inhabiting our bodies and outnumber our own cells 10 to 1) implicate asthma, obesity, inflammatory bowel disease, and other conditions with changes in the microbiome. Although there has been little research in the field, no one has yet seen evidence that altering the composition of bacteria in the body can cause disease.
Previous research had discovered a link between obesity at the age of 7 and using antibiotics in early infancy, but had not identified any potential effects of antibiotic use later in infancy on body weight in childhood. This current study is the first to analyze the association between antibiotic use and body mass starting in infancy.
The team examined 11,532 children receiving antibiotics from Avon, United Kingdom, during 1991 and 1992. These children are part of the Avon Longitudinal Study of Parents and Children (ALSPAC), a long-term study that provides detailed information on these children's health and development.
The infants were analyzed during 3 different time periods (birth to 5 months; 6 to 14 months; 15 to 23 months). Body mass or weight was also observed at 5 different times (6 weeks, 10 months, 20 months, 38 months, and 7 years of age).
Only children exposed to antibiotics from birth to 5 months of age appeared to be affected by antibiotic use, showing that it has an impact on very young infants. Even though infants who received antibiotics at 15 to 23 months had slightly greater body mass indices (BMI) for their age and gender by age 7, there was no significant increase in their being overweight or obese.
Jan Blustein, MD, PhD, professor of population health and medicine and leading author with Trasande, concluded:
"For many years now, farmers have known that antibiotics are great at producing heavier cows for market. 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."