Girls hit puberty earlier than ever, and doctors aren't sure why
By Liz Szabo, USA TODAY
About 15% of American girls now begin puberty by age 7, according to a study of 1,239 girls published last year in Pediatrics. One in 10 white girls begin developing breasts by that age — twice the rate seen in a 1997 study. Among black girls, such as Laila, 23% hit puberty by age 7.
"Over the last 30 years, we've shortened the childhood of girls by about a year and a half," says Sandra Steingraber, author of a 2007 report on early puberty for the Breast Cancer Fund, an advocacy group. "That's not good."
Girls are being catapulted into adolescence long before their brains are ready for the change — a phenomenon that poses serious risks to their health, says Marcia Herman-Giddens, an adjunct professor at the University of North Carolina-Chapel Hill.
"This is an issue facing the new generation," says Laila's doctor, Pisit "Duke" Pitukcheewanont, a pediatric endocrinologist at Children's Hospital of Los Angeles, who treats girls with early puberty. "Many parents don't know what is going on."
Researchers don't completely understand why the age of puberty is falling, Herman-Giddens says. Most agree that several forces are at work, from obesity to hormone-like environmental chemicals. There's no evidence that boys are maturing any earlier, says Paul Kaplowitz, author of Early Puberty in Girls.
But data clearly show that girls once matured much later, probably because poor diets and infectious diseases left them relatively thin, Steingraber says. Girls' lack of body fat may have sent a message to their bodies that they weren't yet ready to carry a pregnancy, she says.
In the 1840s, for example, girls in Scandinavia didn't begin menstruating until age 16 or 17, says Kaplowitz, a pediatric endocrinologist at Children's National Medical Center in Washington. As nutrition and living conditions improved, the age at first menstruation occurred two to three months earlier each decade. By 1900, American girls were getting their periods at age 14.
Though the age at which girls get their first period has continued to fall slowly since then, the age at which girls begin developing breasts has declined much more dramatically.
Early puberty increases girls' odds of depression, drinking, drug use, eating disorders, behavioral problems and attempted suicide, according to the 2007 report. When these girls grow up, they face a higher risk of breast and uterine cancers, likely because they're exposed to estrogen for a longer period of time.
Early puberty isn't the only way that childhood is changing.
In only a generation, children have become less connected to nature and, in many ways, less free, says pediatrician Chris Feudtner of Children's Hospital of Philadelphia. Today's children rarely, if ever, are permitted to roam wild or play outdoors alone, out of sight of watchful, worried parents. Schools are eliminating recess, even as they install vending machines in school cafeterias.
No one should be surprised, Feudtner says, that this generation of children is heavier, less active and more prone to chronic disease and hormonal changes.
"It's very concerning that girls are continuing to develop earlier and earlier," Herman-Giddens says. "We need to look at our environment and our culture, and what we're doing to our kids."
While much about early puberty remains a mystery, researchers say that suspects include:
•Obesity. The clearest influence on the age of puberty seems to be obesity, Steingraber says. In general, obese girls are much more likely to develop early than thin ones. And the number of heavy girls is growing, with 30% of children overweight or obese, the Centers for Disease Control and Prevention says.
Obesity raises the levels of key hormones, such as insulin, which helps regulate blood sugar, and leptin, a hormone made in fat cells that helps regulate appetite, Steingraber says. While leptin may not trigger puberty by itself, research suggests that puberty can't start without it.
Scientists aren't yet sure whether insulin — or the body's problems processing it — is a factor in early puberty, Steingraber says.
•Prematurity. Rising rates of prematurity — which have increased 18% since 1990 — may contribute to early puberty, as well.
Babies born early or very small for their gestational age tend to experience "catch-up growth" that can lead them to become overweight, Steingraber says. Children who undergo rapid weight gain tend to become less sensitive to the hormone insulin, putting them at greater risk for diabetes, Steingraber says.
•Genetics. Studies consistently show that black girls in the USA go into puberty earlier than whites, suggesting a possible genetic difference. Yet Steingraber notes that, 100 years ago, black girls actually matured later than whites. And she notes that black girls in Africa enter puberty much later than those in the USA, even when their nutrition and family incomes are comparable.
Kaplowitz notes that black girls in the USA tend to have higher levels of insulin and leptin. He notes that researchers are trying to figure out how problems in the body's response to insulin, which are more common among American blacks, might also affect the start of puberty.
•Environmental chemicals. A variety of chemicals — found in everything from pesticides to flame retardants and perfume — can interfere with the hormone system, Herman-Giddens says. For example, chemicals used to soften plastic, called phthalates, can act like hormones. In a small study of 76 girls in Puerto Rico, researchers found that 68% of girls who went through early puberty had been highly exposed to phthalates, compared with only 3% of girls developing normally.
Steingraber is also concerned about an estrogen-like chemical, called BPA, or bisphenol A, that is found in hard plastics, the linings of metal cans and many other consumer products. Although BPA can cause early puberty in animals, its role in humans isn't as clear. But studies by the CDC show that more than 90% of Americans have BPA in their bodies.
The National Institutes of Health is funding research to answer questions about environmental causes of early puberty and hormonal changes, says Frank Biro, director of adolescent medicine at Cincinnati Children's Hospital Medical Center. Biro and colleagues are testing more than 1,200 girls for their exposure to chemicals such as BPA, phthalates, pesticides and chemical flame retardants. The National Children's Study, also funded by the federal government, will study 100,000 children, from before birth through age 21, looking at a variety of environmental exposures.
•Screen time. There's no evidence that watching sexy TV images can trigger puberty, but spending too much time in front of the screen can harm kids in other ways, such as causing them to gain weight, Steingraber says.
Preliminary research also suggests that screen time may hasten puberty by lowering levels of a critical hormone called melatonin, whose production is regulated by the daily cycles of light and dark, and which appears to keep puberty at bay, Steingraber says.
•Family stress. Family relationships also may play a role in the start of puberty. Preliminary research suggests that girls may be more likely to develop early if they experience more family stress, or if they don't live with their biological fathers, says Julianna Deardorff, a clinical psychologist at the University of California-Berkeley's school of public health.
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