The influence of adiposity status and the trajectories of obesity indicators on earlier puberty onset in girls: a longitudinal cohort study in Shanghai, China

A global trend toward earlier onset of puberty in girls has been reported, with increasing prevalence observed in countries such as Denmark, South Korea, and China. Early puberty is associated with a range of adverse physical and psychological outcomes. Obesity is a key modifiable factor potentially contributing to early pubertal development; however, most existing evidence is based on cross-sectional studies. In China, longitudinal studies using objective measurements are scarce, particularly those examining the impact of obesity status across multiple time points. This study aimed to investigate the associations between prepubertal obesity, trajectories of obesity indicators, and early pubertal development in girls using data from a school-based cohort in Shanghai. A total of 1, 030 first-grade girls in Pudong, Shanghai were enrolled in 2020 and followed annually to assess body mass index (BMI), waist circumference (WC), breast, and pubic hair development. Group-based trajectory modeling identified distinct body mass index and waist circumference trajectories before puberty, and log-binomial regression was used to evaluate their associations with early puberty. Girls who were overweight or obese before puberty had a higher risk of early pubic hair development compared to non-overweight peers, while only obesity was associated with earlier breast development. Prepubertal abdominal obesity was also linked to increased risks of early breast and pubic hair development. BMI and WC trajectories were categorized into gradual, persistent, and rapid increase groups. Compared to the gradual group, girls with persistent and rapid increases in BMI (RR: 2.28, 995%CI: 1.40–3.72; RR: 3.34, 95%CI: 1.79–6.23) and WC (RR: 2.43, 95%CI: 1.52–3.89; RR: 2.68, 95%CI: 1.22–5.88) had significantly higher risks of early pubic hair development; persistent BMI (RR: 1.70, 95%CI: 1.25–2.29) and WC (RR: 1.81, 95%CI: 1.34–2.44) increases were also associated with earlier breast development, while rapid BMI/WC increases did not accelerate breast development compared to gradual trajectories. Sustained gains in BMI or WC, rather than single-point obesity, substantially heighten the risk of earlier pubertal onset in girls, underscoring the value of longitudinal weight monitoring for early intervention.