Background

The relationship between antibiotic use in early childhood and children’s body weight is still unclear, despite results from several observational studies. In a large, diverse national cohort in the PCORnet research network, we explored the associations of antibiotic use before 2 years of age with BMI-z and weight class between 4 and 6 years (“age 5”).

Methods

From electronic health records in 37 health systems, we captured data on children who had at least one same-day height and weight measure at each of three ages: 1) less than 12 months, 2) 12 to 30 months, and 3) 4 to 6 years. For the exposure, we examined both any vs. no antibiotics before age 2 years as well as the number of antibiotic courses (0, 1, 2, 3, 4+). The outcomes were age- and sex-specific BMI-z and the prevalence of overweight or obesity (BMI ≥85th %tile) at age 5. We used mixed linear and logistic regression models to estimate associations, corrected for clustering by health system and adjusted for sex, race/ethnicity, corticosteroid use, asthma diagnosis, and the number of infections diagnosed before age 2.

Results

Among the 356,294 children included in the analysis, 52% were male; 52% were white, 27% were Black, and 18% were Hispanic. 58% of children received an antibiotic prescription before age 2; at age 5, 28% had overweight or obesity, and mean (SD) BMI-z was 0.40 (1.19). In fully adjusted models, we estimated a 0.05 unit higher mean BMI-z associated with obtaining any (v. no) antibiotic courses before age 2 (95% CI 0.04, 0.06) and higher odds of overweight or obesity at age 5 (OR 1.04; 95% CI 1.03, 1.06). We also estimated a 0.09 unit higher mean BMI-z associated with receiving 4+ (v. no) antibiotic courses before age 2 (95% CI 0.07, 0.10) and higher odds of overweight or obesity (OR 1.09; 95% CI 1.07, 1.12).

Conclusions

Antibiotic use before age 2 years was associated with higher BMI-z and odds of overweight or obesity at age 5; however, the strength of these associations may not be clinically significant.