Antibiotic use before age 2 linked to higher childhood BMI

Antibiotic use before age 2 linked to higher childhood BMI | Image Credit: © greenapple78 - stock.adobe.com.

Children who are exposed to antibiotics during their first 2 years of life may be at greater risk of becoming overweight or obese later in childhood, according to a new study presented at the 2025 Pediatric Academic Societies (PAS) Meeting in Honolulu, Hawaii.^1,2

The research, led by investigators from the University of Oulu in Finland, examined whether the timing of antibiotic exposure—from before pregnancy to early childhood—affected weight outcomes in children. The study analyzed data from 33,095 vaginally born children using national health registers, medical records, and electronic growth charts.

Early life antibiotic use tied to higher BMI and obesity risk

The study found that antibiotic use within the first 24 months of life was associated with higher body mass index-for-age z-scores (zBMI) at 2 years old. Specifically, children who received antibiotics in this time frame had a mean zBMI increase of 0.067 (95% confidence interval: 0.041 to 0.094) compared to unexposed children. In long-term follow-up through age 12, these children had a 20% increased risk of developing obesity (adjusted hazard ratio [HR] 1.20; 95% CI, 1.10 to 1.31).

Additionally, early antibiotic exposure was linked to a 9% increased risk of becoming overweight by age 12. These findings remained consistent after adjusting for several covariates.

“Antibiotic exposure in the first 2 years of life has a stronger association with childhood weight gain than exposure during pregnancy stages or other early ages,” said Sofia Ainonen, MD, PhD, a medical doctor at the University of Oulu and the study’s presenting author.

No impact found from exposure before or during pregnancy

The researchers also explored whether exposure to antibiotics before pregnancy, during pregnancy, or in the perinatal period had any association with overweight or obesity in children. According to the findings, no such associations were observed.

Among the study population, 39% of mothers had used antibiotics 1 year before pregnancy, 27% during pregnancy, and 21% of children were exposed in the perinatal period. These exposures, however, did not show a statistically significant connection to increased BMI or weight-related outcomes later in childhood.

Antibiotic prescribing in young children remains widespread

The majority of children in the study—68%—were prescribed antibiotics in their first 2 years of life, underscoring how common early exposure is. While antibiotics are often necessary for treating bacterial infections, researchers highlighted that they are frequently prescribed for conditions like upper respiratory tract infections, where the benefits may be limited.

“Providers need to be cautious about prescribing antibiotics for young toddlers, especially unnecessary antibiotics for upper respiratory tract infections,” Ainonen said.

Implications for clinical practice and research

The findings contribute to a growing body of evidence suggesting that the early postnatal period may be a sensitive window during which antibiotic exposure could influence long-term health outcomes, including body weight. The authors emphasized that future studies seeking to understand the mechanisms behind early antibiotic use and obesity should focus specifically on exposure within the first 2 years of life.

Childhood obesity continues to pose a global health challenge. In 2022, over 159 million school-aged children worldwide were diagnosed with obesity. This study highlights the importance of antibiotic stewardship in early childhood as a potential avenue for reducing the risk of long-term health consequences, including obesity.

References:

1. Ainonen S. Timing of Early Antibiotic Exposure and the Risk of Being overweight and Obesity in Children. Abstract. Presented at: 2025 Pediatric Academic Societies Annual Meeting. Honolulu, Hawaii.

2. Pediatric Academic Societies. Study: Antibiotic exposure before age two linked to childhood obesity. Pediatric Academic Societies. Press release. April 25, 2025. Accessed April 25, 2025.