1. Females with the highest levels of urine-phthalate metabolites had later development of both breasts and pubic hair than those with the lowest levels.
2. The dose-response relationship was more apparent in normal-weight compared to over-weight girls.
Evidence Rating Level: 1 (Excellent)
Study Rundown: This study found that higher levels of urinary phthalates—hormonally active, environmental pollutants found in plastics—were associated with later development of both breasts and pubic hair. The relationship was more profound among normal-weight girls compared to over-weight girls. While other cross-sectional studies achieved similar results, this is the first prospective, longitudinal study. The study utilized a multi-ethnic, multi-geographical cohort with an average follow-up time of 7 years. Exposure was ascertained only once (urinary phthalate levels were only collected at study enrollment). Future studies might evaluate phthalate exposure over the lifecourse, ranging from maternal exposure in utero through adrenarche and menarche, to confirm and better characterize the nature of this association and determine vulnerable developmental periods.
Relevant Reading: Plasma phthalate levels in pubertal gynecomastia
In-Depth [prospective cohort]: Researchers enrolled 1239 girls ages 6-8 years from New York City, Cincinnati, and San Francisco, and collected urine levels of phthalate metabolites (high and low molecular weight). Participants were followed for an average 7 years and height, weight and Tanner stages were recorded 1-2 times annually to identify associations between urinary phthalate level at the time of enrollment and age at transition from Tanner stage 1 to 2.
Among normal weight girls, girls in the highest quintile of urinary high molecular weight phthalate concentration were 9.5 months older on average when they developed Tanner Stage 2 hair growth compared to girls in the lowest quintile (HR=0.70, p-trend=0.005). Comparing these same groups, the age at Tanner Stage 1 breast development was also older (HR=0.083, p-trend=0.018). The association was present in girls of all BMIs, but stronger and more linear in those with a normal BMI. There was no significant association between urinary levels of low-molecular weight phthalates and age of breast/pubic hair development in adjusted models.
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