Antibiotics may promote weight gain among children through direct effects on growth and metabolic consequences associated with alternations of the microbiome. In a recent study in the National Patient-Centered Clinical Research Network (PCORnet), we found that antibiotic use <24 months was associated with slightly higher, but clinically insignificant, BMI-z and overweight/obesity prevalence at 5 years. The objective of this study was to examine these associations with 10-year outcomes.


We used electronic medical record data from 2009-2016 from 10 healthcare institutions in PCORnet. We included 56,727 children with same-day height and weight measures at 0-<12m, 12-<30m, and 108-<132m (“10y”). Using multivariable mixed models, we examined associations of any antibiotics <24m with BMI-z and overweight/obesity at 10y, stratified by complex chronic condition status.


52% of the children were male, 49% were white, and 57% received at least one antibiotic prescription <24m. At 10y, mean (SD) BMI-z was 0.54 (1.14), and 36% had overweight or obesity. Among children without a complex chronic condition, obtaining any (v. no) antibiotics <24m was associated with a slightly higher, but clinically insignificant, BMI-z (β 0.04; 95% CI 0.02, 0.06) and odds of overweight/obesity (OR 1.03; 95% CI 0.99, 1.07). For 4+ (v. no) antibiotic courses, the estimates were 0.07 higher BMI-z (95% CI 0.04, 0.11) and OR of 1.09 (95% CI 1.02, 1.16) for obesity/overweight. Results were similar for children with a complex chronic condition.


In this large national study, antibiotic use <24 months was associated with slightly higher body weight at 10 years, with evidence for a dose response. Although these small associations may have population level impacts on obesity, the individual-level clinical significance is negligible. In addition, such small associations could be explained by unmeasured confounding.