Early Antibiotic Use Linked to Overweight and Obesity in Dutch Twins

Early-life exposure to antibiotics has been proposed as a driver of childhood weight gain, potentially through alterations in the gut microbiota that influence metabolic pathways. With obesity now recognized as a persistent public health challenge—starting early and often continuing into adulthood—researchers are keen to clarify whether early antibiotic courses raise later risk of overweight or obesity.

To probe this question, investigators used data from the Netherlands Twin Register and applied a co-twin control design. This approach examines pairs of twins who differ in outcomes, helping to account for confounding linked to shared genetics and shared early-life environment. The retrospective cohort comprised 34,142 twins aged 4.5–15.4 years, enabling robust statistical comparisons with both dichotomous and continuous measures of body mass.

Antibiotic exposure was defined as any use before age 2, reported for 24.6% of children. Over the same developmental window, 1.06% of participants met criteria for obesity and 9.23% met criteria for overweight/obesity, based on sex- and age-specific BMI cutoffs drawn from the International Obesity Task Force and the World Health Organization.

The analyses incorporated covariate adjustment for sex, delivery mode, gestational age, birthweight, breastfeeding, maternal BMI, and parental education, aiming to reduce residual confounding. Outcomes were assessed both as binary endpoints—obesity and overweight/obesity—and as BMI Z-scores, which standardize BMI relative to age and sex.

After adjustment, early-life antibiotic use showed no meaningful association with obesity risk (odds ratio [OR] 0.82, 95% CI 0.60–1.14). Likewise, there was no association with overweight/obesity (OR 1.00, 95% CI 0.90–1.12). These null findings were reinforced by matched co-twin analyses, which similarly found no evidence that twins exposed to antibiotics early were more likely to develop higher weight categories later.

Importantly, BMI Z-scores also did not differ according to antibiotic exposure, suggesting that any potential microbiota-mediated metabolic effects—if present—were not detectable at the level of population BMI trajectories in this twin-based framework.

Overall, the study concludes that early-life antibiotic use is not linked to an increased risk of overweight or obesity during childhood, challenging a widely discussed mechanistic hypothesis about antibiotics and long-term weight regulation. As antibiotic prescribing continues to evolve, the findings highlight the value of genetically informed designs in disentangling correlation from causation.

These results provide timely evidence for clinicians and public health stakeholders evaluating how early medical exposures may shape later health outcomes.