Background: Early onset of puberty could have significant impacts on childhood health, but the extent to which it was affected by phthalate esters (PAEs) and sex hormone disruption was not understood. The aim of this study is to investigate the associations between exposure to PAEs and sex hormone disruption and early onset of puberty in children.

Methods: A longitudinal cohort study was conducted in China from May 2017 to Oct 2020, involving 740 children during consecutive visits. The onset of puberty was evaluated using Tanner definition, and early puberty was defined as an onset age less than the first 25%, with cut-offs of 10.33 and 8.97 years for boys and girls, respectively. Serum testosterone (TT), estradiol (E2) and urinary PAE metabolites were measured during three visits. Generalized linear models were used to explore the associations between PAE and sex hormones with the age of puberty onset, while log-binomial regressions were applied to assess the associations of persistent exposure to PAEs and sex hormones with early pubertal onset.

Results: Approximately 86.0% of boys and 90.2% of girls completed puberty onset from pre-puberty, and more than 95% of participants had PAE concentrations higher than the limit of detection. Boys showed higher exposure to PAE pollutants and higher TT levels. Persistent exposure to PAEs was positively associated with early pubertal onset in girls (ARR=1.97, 95%CI=1.12, 3.46). Moreover, persistent exposure to PAEs and E2 had synergistic associations with early pubertal onset in both boys (ARR=4.77, 95%CI=1.06, 21.54) and girls (ARR=7.07, 95%CI=1.51, 33.10). However, PAEs and TT had antagonistic associations only in boys (ARR=0.44, 95%CI=0.07, 2.58).

Conclusion: Long-term exposure to PAEs might increase the risk of early pubertal onset, and it appears to work in synergy with E2, while in antagonism with TT in boys’ early pubertal onset. Reducing PAEs exposure might promote pubertal health.