Breastfeeding in first 4 to 6 months of life linked to lower central precocious puberty risk

Breastfeeding during the first 4 to 6 months of life was associated with a lower central precocious puberty (CPP) risk in boys and girls, according to a nationwide, retrospective cohort study published in JAMA Network Open.¹

Pubertal age onset has declined over recent decades, having decreased by by a mean of nearly 3 months per decade from 1977 to 2013.² Accompanying the decline has been a rising incidence of CPP globally, which is associated with an increased risk of adult health issues, such as cardiovascular disease, diabetes, and cancer.¹

“Human milk is the first source of nutrition that newborns receive immediately after birth and usually serves as the sole source of nutrition during the first 4 to 6 months of life before complementary foods are introduced,” wrote the study authors. The World Health Organization recommends breastfeeding exclusivity for the first 6 months of life and continued feeding with complementary foods for up to 2 years of age.

Prepubertal obesity, the authors wrote, is thought to affect pubertal development differently among boys and girls, with multiple studies having already investigated these associations based on sex. However, mechanisms underlying the differences in adiposity-related pubertal development remain unclear.

“This study investigated the association between primary feeding type during the first 4 to 6 months of life and the risk of CPP in South Korea. Additionally, we explored whether being overweight or obese during the prepubertal period mediates this association,” wrote the authors.

The main outcome of the study was the incidence of CPP. The association between feeding practices and incidence of CPP was assessed using a multivariable Cox proportional hazards model to estimate adjusted hazard ratios (AHRs) and 95% CIs.

Of the 322,731 children included in the retrospective study (58.1% female), 46% were exclusively breastfed and 34.9% were formula-fed, with 19.1% mixed-fed. Compared to exclusively breastfed children, those who were formula-fed had a great risk of CPP in boys (adjusted hazard ratio [AHR], 1.16; 95% CI, 1.10-1.21 [P < .001]) and girls (AHR, 1.60; 95% CI, 1.24-2.06 [P < .001]). Mixed-fed had the next highest risk, with AHR in boys of 1.14 (95% CI, 1.07-1.20) and 1.45 in girls (95% CI, 1.07-1.97 [P < .001]).

Kaplan-Meier survival curves demonstrated significant differences in the cumulative incidence of CPP by primary feeding type among both sexes. The lowest risk observed was among children who were exclusively breastfed (log-rank P < .001). Additionally, low birth weight was significantly associated with increased CPP risk in boys and girls (AHR, 1.99; 95% CI, 1.21-3.26; [P = .007]; AHR, 1.17; 95% CI, 1.05-1.30; [P = .003]). Prepubertal overweight or obesity partially mediated the association between primary feeding type and CPP in both boys and girls.

This study had several limitations, the authors noted, including the lack of maternal age at menarche data and the inclusion of only children treated with GnRH agonists under the insurance reimbursement system, which may have led to potential overdiagnosis of CPP, though diagnostic criteria helped mitigate this concern. The study also could not examine dose-dependent effects of breastfeeding duration, distinguish between bottle-fed and directly breastfed infants, or fully account for temporal variability in overweight or obesity since it was modeled as a fixed covariate. Finally, the observational design prevents causal inference due to the possibility of unmeasured or residual confounding.

While concluding that exclusive breastfeeding in early infancy was linked to a lower CPP risk in boys and girls, “further longitudinal prospective studies are needed to evaluate the association of breastfeeding with pubertal timing and progression,” stated the study authors.

References:

1. Choe Y, Ryu S, Choi J, et al. Breastfeeding, Prepubertal Adiposity, and Development of Precocious Puberty. JAMA Netw Open. 2025;8(8):e2527455. doi:10.1001/jamanetworkopen.2025.27455
2. Eckert-Lind C, Busch AS, Petersen JH, et al. Worldwide secular trends in age at pubertal onset assessed by breast development among girls: a systematic review and meta-analysis. JAMA Pediatr. 2020;174(4):e195881. doi:10.1001/jamapediatrics.2019.5881