New York University researchers using the Avon Longitudinal Study of Parents and Children with data on more than 11,000 children have purportedly found a consistent association between antibiotic exposure in the first six months of life with “elevations in body mass index with overweight and obesity from ages 10 to 38 months.” L. Trasande, et al., “Infant antibiotic exposures and early-life body mass,” International Journal of Obesity, August 21, 2012 (online).  

The researchers suggest that the administration of antibiotics during early life, “a critical period for gut colonization,” may disrupt “ancient patterns of intestinal colonization.” U.S. farmers since the late 1940s have apparently given low-dose antibiotics to domesticated mammalian and avian species to hasten weight gain with the understanding that “alterations in the microbiota change ‘feed efficiency.’” Thus, the researchers explored the possibility of similar effects in human children. According to lead researcher Leonardo Trasande, “Microbes in our intestines may play critical roles in how we absorb calories, and exposure to antibiotics, especially in early life, may kill off healthy bacteria that influence how we absorb nutrients into our bodies, and would otherwise keep us lean.” Confounders accounted for included parental body mass index (BMI), smoking, breastfeeding, timing of food introduction, and lifestyle variables, among others. The study was limited to the use of two medications: antipyretics and eye ointment.  

While exposures during the birth-6 month window were consistently associated with elevations in body mass, exposure during the 6-14 month window was not, and “[t]he pattern of association for exposure 15-23 months was less clear.” Those in this exposure window “were significantly associated only with elevated standardized BMI score at 7 years, but not with consistently elevated scores in the interim.” The study found that “[a]t 38 months, children who had been exposed to antibiotics during [the] earliest period had significantly higher standardized BMI scores, and were 22% more likely to be overweight than children who had not been exposed.”

While the researchers conclude that the study “reinforces concerns that earlylife antibiotic exposure may cause increases in body mass later in life,” they note that important limitations are presented by “multiple social, behavioral and biological factors” as well as parental recall regarding antibiotic usage. They call for additional research “to disaggregate the effect of early exposures to antibiotics from those occurring in the prenatal and perinatal periods, and to quantify the life-course implications for body mass and cardiovascular risks, at the population level.” See, August 2012.