Could This Be Behind the Early Puberty Trend in Girls?

George W. Citroner


January 28, 2019

The 'Early Puberty' Trend

During the past couple of decades, the age of puberty onset in US girls has been declining.[1] Although environmental causes have been suspected, the reasons for earlier puberty have been somewhat of a mystery.

It is a concern because early puberty can come with significant health risks.[2] Molly Regelmann, MD, a pediatric endocrinologist at Children's Hospital at Montefiore, Bronx, New York, said "Early menarche, the first menstrual period, is associated with higher rates of obesity, cardiovascular disease, polycystic ovarian syndrome, and certain cancers, such as breast cancer, later in life." Regelmann, who was not associated with this study, added "The normal range for the start of puberty in girls is between 8 and 13 years."

Kim Harley, PhD, from the University of California, Berkeley, said, "The onset of puberty has been getting younger for girls over the last 15 to 20 years, and we're concerned." She continued, "Obesity has something to do with it. We're in the middle of a childhood obesity epidemic, and we know that overweight girls enter puberty at earlier ages."[3]

Other research suggests high levels of psychosocial stress might influence the onset of puberty.[4,5]

However, Harley said that exposure to certain endocrine-disrupting chemicals in our environment may be a significant factor. Her research at the University of California has shown that the daughters of mothers with high levels of diethyl phthalate, triclosan, phenols, and parabens in their bodies during pregnancy entered puberty earlier than their peers.[6] These chemicals are commonly found in a broad range of cosmetics, toothpaste, soaps, and other personal care products.

Harley explained, "Chemicals in household products and in the environment seem to mimic estrogen and other hormones,[7] and we wanted to find out if these hormone-disrupting chemicals were also contributing to this shift in earlier puberty we've observed."

Endocrine-Disrupting Chemical Exposure in Pregnancy

Harley's study looked at 179 girls and 159 boys in California who were born to mothers who were pregnant between 1999 and 2000. It is the first study to look at how prenatal exposure to endocrine-disrupting chemicals may influence age at puberty.

Harley said, "Other studies have looked at the chemicals in these personal care products. A few studies have looked at childhood exposure to these chemicals and whether that was associated with earlier puberty."

Many commonly used perfumes, deodorants, shampoos, cosmetics, and other scented products contain phthalates. Parabens may be added to these products as a preservative, and toothpaste, soap, lipstick, and skin lotions often contain phenols.

"In our study, we looked at the prenatal period. We were looking at exposure in the womb, and that's important because we know that hormone-disrupting chemicals have these windows of susceptibility, and the prenatal period is a particular window of susceptibility," explained Harley.

The study participants were mothers and children who were enrolled in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS),[8] a longitudinal birth cohort that examined the effects of in utero and early-life environmental exposures on children's health and development.

Mothers were interviewed twice during pregnancy (at an average of 14.0 and 26.9 weeks), and again when their children were 9 years old. Pubertal assessments of the children were conducted every 9 months between ages 9 and 13 years, and included clinical Tanner staging. The investigators measured the levels of various chemicals in urine samples of mothers during pregnancy, and in the children at age 9 years.

The study population was predominantly Latino, and 73% of the mothers had lived in the United States fewer than 11 years at the time of their pregnancies. By 9 years of age, 55% of the children were overweight or obese, and 69% were living below the federal poverty threshold.

Differential Effects on Puberty

Associations between higher prenatal chemical exposure and early onset of puberty were seen in girls. High prenatal monoethyl phthalate concentrations were associated with earlier development of pubic hair, whereas high levels of prenatal triclosan, propyl paraben, and 2,4-dichlorophenol were linked to earlier onset of menarche in the children. Methyl paraben and 2,5-dichlorophenol in urine were associated with earlier breast and pubic hair development. The daughters of women with the highest levels of these substances in their urine started their periods an average of 4 months earlier. However, there was no evidence that boys were similarly affected by prenatal chemical exposure.

Timothy N. Hickman, MD, a board-certified reproductive endocrinologist at Houston Methodist Hospital in Texas, who was not associated with the study, said "There is biologic plausibility that [prenatal] exposure to exogenous estrogen and other toxins in the environment is affecting sexual development in girls."

The endocrine-disrupting chemicals detected in this study have estrogenic activity, which is known to affect sexual development.[9] "We can show a link that makes sense. We already have evidence from laboratory research that these chemicals mimic estrogen. We have evidence from animal studies[10] that they may significantly impact reproductive development and timing of puberty," Harley said.

Harley also acknowledged that "this is an observational study; it's epidemiologic, so we can't prove causality. This is the first study of its kind, and more research will be needed."

A growing number of studies, however, suggest that the cause for concern is not misplaced. Regelmann confirms that population and cohort studies, as well as case reports, "make a strong case for the association of endocrine-disrupting chemicals and early onset of puberty."[11,12,13]

Minimizing Exposure

The levels of chemicals found in the bodies of women and children in this study are not unusual. In the United States, well over 90% of women have been shown to have detectable concentrations of phthalate, phenol, and parabens metabolites in their urine.[14,15,16]

Regelmann offered suggestions for reducing exposure to endocrine-disrupting chemicals during pregnancy. "Wash fruits and vegetables to remove potential chemicals used in farming practices, and try to limit the use of plastics and synthetic materials for food preparation and storage."

She also recommends "limiting exposures to tea tree oil and lavender, because there are reports of exposure being associated with early breast development."[17]

Harley advised, "If someone is concerned, they can easily find personal care products that don't contain phthalates or parabens. They can just go to the natural or 'green' section of the store and find products that specifically say 'no parabens, no phthalates.' If people change the products that they're using, they can rapidly reduce the levels of these chemicals in their bodies."


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