"The evidence on endocrine-disrupting chemicals or compounds that mimic hormones like estrogen is less clear... More studies are needed on this, as well as on exposure to antibiotics through the food supply, which has also been raised as a potential factor."
For More Children, Puberty Signs Start at 8
by Sumathi Reddy, The Wall Street Journal, 20 June 2016
Photo: The age onset of puberty appears to be moving earlier and earlier and often begins in the elementary school ages now. WSJ’s Sumathi Reddy joins Lunch Break with Tanya Rivero to discuss the health implications for children going through puberty at an early age. Photo: Getty
When Frank Biro walks into a class of second- or third-graders these days, there are almost always a couple of girls who look different than the rest.
“There will be quite a few girls that look like they’re going into early puberty,” says Dr. Biro, a professor of pediatrics at Cincinnati Children’s Hospital Medical Center who gives talks about puberty at schools occasionally.
Dr. Biro researches a phenomenon that has increasingly captured the attention of researchers: Puberty appears to be starting earlier in healthy girls, and possibly even boys. At Kaiser Permanente in Northern California, clinicians begin assessing girls for changes related to puberty at age 6.
“In general, we think that 7 is now probably a normal age to have some signs of puberty,” saysLouise Greenspan, a pediatric endocrinologist at Kaiser Permanente who also researches puberty. “So the cutoff for precocious puberty is a gray zone now.”
Precocious puberty is a medical term for puberty that begins in girls under 8 and boys under 9, sometimes from an underlying condition, such as a brain tumor. Often the cause remains unknown. Treatment is often used to halt or slow it down.
The health consequences of earlier onset of puberty are myriad. A study published in the journal Pediatrics in May found that girls who started puberty earlier had a higher risk of depression in early adolescence.
“We know that the early-maturing girls are at an increased risk of some of these risk-taking behaviors: alcohol use, smoking, drug use and earlier engagement in sexual behaviors,” Dr. Biro says. “We also know some of the longer-term consequences. As adults they’re at higher risk for having obesity, Type 2 diabetes and breast cancer.”
Experts speculate this change is due to a longer lifetime exposure to estrogen.
Studies indicate that puberty in girls is starting on average a year earlier. A 2013 study published in Pediatrics following a group of more than 1,200 girls in the U.S. over 12 years found that the start of breast development—considered the first sign of puberty—wastaking place around age 9. African-American girls were showing signs earlier, with more than half having started breast development by age 8. The study recruited 6- to 8-year-old girls at three sites.
“I don’t know if girls can go through puberty any earlier,” says Dr. Biro, who is first author on the study, which also included researchers from Mount Sinai School of Medicine in New York City and Kaiser Permanente, including Dr. Greenspan. “We may be approaching a biological minimum.”
The process of puberty takes about four years for girls. While the average age for the onset of the menstrual cycle, called menarche, dropped precipitously in the early 20th century, it’s remained about the same in recent decades, at about 12 to 12.5, Dr. Biro says.
The data in boys is more disputed, though a 2012 study in Pediatrics evaluating data from 4,131 boys found that the mean ages of the onset of puberty was six months to two years earlier than mean ages found in past studies.
Experts say a lot of the earlier onset of puberty in girls can be explained by increasing childhood obesity rates. Body fat releases the hormone estrogen, which is released from the ovaries during puberty, causing the start of breast development.
“A larger BMI [body-mass index] is probably the single biggest reason,” Dr. Biro says. “Some of the larger BMI may be precipitated by exposure to endocrine-disrupting chemicals that are associated with greater BMI.”
Such chemicals include phthalates, often used in the production of plastics, and phenols, used in many sanitizers and sunscreen. How much such chemical exposures affect the timing of puberty is still being researched.
Researchers are also starting to look at prenatal factors.
In a study published earlier this month in the American Journal of Epidemiology, researchers at Kaiser Permanente found that mothers who were overweight before pregnancy and developed gestational diabetes when pregnant had daughters who started puberty earlier, independent of the girls’ own weight. The study has been tracking more than 400 girls since 2005.
The study looked at breast development and early pubic hair development. It only found an association with pubic hair likely, because it’s connected to metabolic dysregulation, says Ai Kubo, lead author of the study and a scientist at Kaiser Permanente’s Department of Research. Pubic hair is associated with the androgen hormone, which is influenced by insulin and glucose, she says.
“My hypothesis was, if a girl is exposed in utero to her mom’s hyperglycemia, they would have a similar metabolic disorder, manifesting as early appearance of pubic hair,” she says.
The study found that if mothers were overweight before pregnancy and developed gestational diabetes, their daughters developed pubic hair on average about one year earlier—at age 10 rather than 11—than girls born to mothers of normal weight who didn’t develop gestational diabetes. The study controlled for factors such as race and girls’ BMI.
Dr. Greenspan, a co-author of the American Journal of Epidemiology study, says other studies have found that toxic stress likely plays a role in girls’ starting puberty earlier.
“Girls who grow up in families with a lot of strife or violence in their neighborhood are more likely to develop earlier,” she says. Girls who grew up without a biological father are twice as likely to get their period before age 12, her research has found.
The evidence on endocrine-disrupting chemicals or compounds that mimic hormones like estrogen is less clear, Dr. Greenspan says. More studies are needed on this, as well as on exposure to antibiotics through the food supply, which has also been raised as a potential factor.
The idea that puberty is starting earlier isn't universally accepted.
“There is no evidence that puberty is occurring earlier,” says Clifford Bloch, a pediatric endocrinologist in Denver. “We have a very large pediatric endocrine practice, and I have not seen an increase in referrals for early puberty, and my colleagues haven’t either.”
He says studies that have shown earlier signs of pubic hair or breast development don’t necessarily translate into earlier puberty. “We’ll see some girls referred for breast development, and it’s transient, it goes away,” he says. “Or they may have a little breast development, but it never progresses and they don’t have any other signs of puberty.”
The cause of precocious puberty is often undetermined for the majority of cases in girls. In some cases, frequent exposure to an essential oil will cause breast development, because essential oils are derived from plants, which use estrogen as part of their metabolism, Dr. Bloch says.
Dr. Bloch was senior author of a 2007 New England Journal of Medicine study that found that boys who used a combination of lavender and tea tree oil in hair and other products started to develop breasts. Once such essential oils stop being used, the changes are usually reversible, he says.
Dr. Biro of Cincinnati Children’s Hospital says the best advice for parents worried about early puberty is to make sure your children are eating healthy and are active to prevent becoming overweight. Look for personal care products without phthalates or parabens, he says. Don’t microwave plastic, because it may leach out phthalates.
Insecticides and pesticides may also have endocrine-disrupting chemicals. While it’s hard to completely avoid them, buying organic fruits and vegetables may help, Dr. Biro says.
Eating a diet very high in fiber has also proven to delay puberty by up to five months, according to a study published in 2013 in the journal Nutritional Research.
Write to Sumathi Reddy at firstname.lastname@example.org