(CN) – Girls exposed to chemicals commonly found in household cosmetic and hygiene products may experience early puberty, according to research published Monday in Human Reproduction.
Previous studies established a link between the chemicals used in personal care products and early puberty in rats. Researchers at the Center for Environmental Research and Children’s Health (CERCH) teamed up with the University of California, Berkeley, School of Public Health to look at the effects on humans.
The study represents one of a handful of studies to look for signs of early puberty in children exposed to phthalates, parabens and phenols, and the first of its kind to consider long-term effects of prenatal exposure.
Funded by the National Institute of Environmental Health Sciences and the U.S. Environmental Protection Agency, researchers asked: Are there links between exposure to phthalates, parabens, and phenols and the start of puberty?
The simple answer is yes, for girls.
"Specifically, we found that mothers who had higher levels of two chemicals in their bodies during pregnancy – diethyl phthalate, which is used in fragrance, and triclosan, which is an antibacterial agent in certain soaps and toothpaste – had daughters who entered puberty earlier,” said Dr. Kim Harley, associate professor in public health at UC Berkeley, who led the study. “We also found that girls with higher levels of parabens in their bodies at the age of nine entered puberty earlier.”
Researchers collected data from pregnant women enrolled in the Center for the Health Assessment of Mothers and Children of Salinas longitudinal cohort study between 1999 and 2000 in California’s Salinas Valley. Researchers followed up with 338 children when they turned 9, including 159 boys and 179 girls.
To measure concentrations of target chemicals, researchers collected urine samples from mothers during pregnancy and again from the children at age 9. Unsurprisingly – given the prevalence of the chemicals in household products – researchers found all of the chemicals they were testing for except one in 90 percent of urine samples.
From age 9 to 13, the children were assessed every 9 months against Tanner staging, a classification system designed to track the development of secondary sex characteristics during puberty.
Early puberty has been observed for several decades, but the cause of it remains poorly understood. The American Psychological Association estimates the start of an average girl's period has shifted from 16 years old in the early 1900s to 13 years old today.
"This is important because we know that the age at which puberty starts in girls has been getting earlier in the last few decades; one hypothesis is that chemicals in the environment might be playing a role, and our findings support this idea,” Harley added.
The phenomenon comes with warnings of increased risks from mental health problems to higher rates of breast and ovarian cancer.
Today, breast development begins in girls around age 9.2, pubic hair sprouts around age 10.2, and menstruation commences around age 11.7. Of the children who participated in this study, researchers found that by age 9, 39 percent of the girls had developed public hair and 20 percent had begun developing breasts.
“For every doubling in the concentrations of an indicator for phthalates called monoethyl phthalate (MEP) in the mothers' urine, the development of pubic hair shifted 1.3 months earlier in girls. For every doubling of triclosan in the mothers' urine, the timing of the girls' first menstrual period shifted earlier by just under a month,” the researchers report. Additionally, “for every doubling in the concentrations of parabens, the timings of breast and pubic hair development and first menstrual period all shifted approximately one month earlier.”
The effect on the puberty clock is largely limited to girls.
“In boys, we observed no associations with prenatal urinary biomarker concentrations and only one association with peripubertal concentrations: earlier genital development with propyl paraben,” the researchers report.
Researchers also cautioned that because the chemicals tested for quickly break down in the body, their measurement may underrepresent actual exposure. Additionally, the high concentration of parabens around puberty might just reflect consumer habits: Children going through puberty early may be using personal hygiene products early as well.
Nevertheless, this research adds to a growing body of work aimed at understanding how endocrine-disrupting chemicals effect puberty.
“We are concerned about evidence that some widely used chemical in the products that we put on our bodies every day may be having an impact on hormonal and reproductive development,” Harley said.
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