Association of Repeated Antibiotic Exposure Up to Age 4 Years With Body Mass at Age 4.5 Years

Importance Antibiotic exposures in early life may affect weight by altering gut microbiota, potentially increasing the likelihood of childhood obesity. Objective To examine whether repeated antibiotic exposure by age 48 months is associated with higher body mass index (BMI) at age 54 months. Design, Setting, and Participants This research was undertaken within a prospective cohort study in New Zealand (Growing Up in New Zealand) that recruited 6853 children antenatally during 2009 to 2010. At the 54-month follow-up, 5734 of 6156 children (93%) had their weight and height measured. Community pharmacy antibiotic dispensing data were obtained from the New Zealand Pharmaceutical Collection database for children whose parents consented to external data linkage. The analytic sample comprised singletons with 54-month weight and height measurements, community antibiotic dispensing and birth weight data, gestational age greater than 27 weeks, and no congenital anomalies. Data analysis took place from 2017 to 2018. Exposures Antibiotic exposure (yes or no), the number of dispensings, age at first exposure, and timing (age) of exposures between birth and age 48 months. Main Outcomes and Measures World Health Organization BMI-for-age z scores; and International Obesity Task Force overweight and obesity cutoff points that pass through adult BMI values of 25 and 30. Results Of the 5128 singletons (2622 [51%] male; mean [SD] birth weight of 3527 [542] g), 4886 (95%) had an antibiotic prescription by age 48 months and 437 (9%) had obesity at age 54 months. Adjusted mean (SE) BMI-for-age z scores increased significantly with the number of antibiotic dispensings for 4 to 6, 7 to 9, and more than 9 dispensings (unexposed, 0.87 [0.09]; 1-3 exposures, 0.92 [0.06] [P = .57]; 4-6 exposures, 1.06 [0.06] [P = .02]; 7-9 exposures, 1.06 [0.06] [P = .02]; >9 exposures, 1.08 [0.05] [P = .01]). Additionally, receiving more than 9 dispensings was associated with greater likelihood of obesity compared with no exposure (adjusted odds ratio, 2.41; 95% CI, 1.07-5.41). Children whose exposure began in the first year of life had a higher adjusted mean (SD) BMI-for-age z score than those not exposed (1.06 [0.05] vs 0.89 [0.09]; P = .03), whereas those whose exposure commenced after the first year of life did not (1.02 [0.06] vs 0.89 [0.09]; P = .10). Conclusions and Relevance In this study, repeated antibiotic exposure in early childhood was associated with higher mean BMI-for-age z score and an increased likelihood of obesity. Future research could examine whether interventions such as antibiotic stewardship programs, which are designed to reduce overprescribing of antibiotics, also reduce early childhood obesity. Question Is repeated antibiotic exposure by age 48 months associated with higher body mass index (BMI) and the likelihood of overweight or obesity at age 54 months? Findings In this cohort study that included 5128 children, those repeatedly exposed to antibiotics had significantly higher BMI than those not exposed. As the number of antibiotic exposures increased, the adjusted mean BMI-for-age z scores and likelihood of obesity increased significantly. Meaning As repeated antibiotic exposure is a potentially modifiable risk factor for childhood obesity, interventions designed to reduce overprescribing of antibiotics in primary care could examine whether reducing overprescribing decreases the prevalence of childhood obesity. This cohort study examines the association between repeated antibiotic exposure by age 48 months and body mass index at 54 months.