The average age of the onset of puberty has been dropping in the last century—with some girls starting to develop breasts as early as age six or seven. These shifts in the reproductive development timeline could have serious consequences for the physical and psychological health of the female population, experts say.
In a meta-analysis involving 30 studies, researchers found that the average age of the onset of puberty in girls throughout the world has dropped by three months per decade from 1977 to 2013—which adds up to more than a year earlier. The initial sign of puberty in girls is the development of breast tissue, with the onset of menstruation (a.k.a., menarche) coming later.
Now a new study in the May 2024 issue of JAMA Network Open suggests the timeline for both physiological markers seems to be getting younger. This study found that among 71,341 females born in the U.S. between 1950 and 2005, girls have been getting their first periods at a younger age and it’s taking longer for them to become regular. During the 55-year span covered in the study, the number of people experiencing early menarche (defined as younger than age 11) nearly doubled to 16 percent.
“It’s well documented, and it’s a worldwide phenomenon,” says Lisa Swartz Topor, an associate professor of pediatrics at The Warren Alpert Medical School of Brown University and Hasbro Children’s Hospital in Providence, Rhode Island. As for why it’s happening, at this point, “there are more questions than there are answers,” Topor says. “This is a confluence of a lot of different things—the overarching theme is changes to our world in the last two centuries.”
At any age, the onset of puberty is triggered by the hypothalamus in the brain, which secretes gonadotropin-releasing hormone (GnRH). GnRH—which has been called “the key regulator of the reproductive axis”—in turn stimulates the pituitary gland to secrete luteinizing hormone and follicle-stimulating hormone, which get puberty started. In girls, these two hormones signal the ovaries to start releasing estrogen and progesterone, which leads to breast development, the development of pubic hair, the onset of menstruation, and body shape changes.
Besides the potential long-term health repercussions, with early puberty, “your child might start to look or act like a teenager before you expected,” says Natasha Chaku, a psychologist and an assistant professor in the department of psychological and brain sciences at Indiana University in Bloomington. As a result, “parents may need to have conversations about how their bodies are going to change earlier than they expect.”
What’s responsible for the early timetable
It’s a multifactorial issue, according to experts. For one thing, childhood obesity rates have been rising since the 1970s and some studies have linked obesity to early puberty (a.k.a., precocious puberty) in girls.
This is partly because body fat is no longer viewed as an inert tissue; rather, it’s now known to act as an endocrine organ, secreting various hormones that can have head-to-toe effects throughout the body.
In particular, “obesity can be associated with the release of different hormones—including insulin, insulin-like growth factor 1, and leptin—into the bloodstream,” says Aviva Sopher, an associate professor of pediatrics at the Columbia University Irving Medical Center in New York. These hormones can affect appetite and satiety and the accumulation of body fat, among other bodily functions, and they can impact the hypothalamic-pituitary-gonadal axis and thus the timing of puberty.
In addition, girls with obesity have been found to have higher concentrations of estradiol (a form of estrogen)—which may contribute to early breast development and early puberty—than girls with a normal weight.
The quality of kids’ diets also may play a role, especially if they’re low in fruits and vegetables, high in animal protein and highly processed foods, “which are associated with higher levels of sex steroids like estrogen,” notes Frank Biro, a professor of pediatrics at Cincinnati Children’s Hospital Medical Center. In fact, when researchers in China compared three different diets—a traditional, an unhealthy, and a high protein one—they found that consuming a diet heavy in snacks, desserts, fried foods, and soft drinks (the “unhealthy diet”) was associated with precocious puberty in girls.
In addition, stress, including early life adversity tied to socioeconomic hardship or some form of abuse, may be a contributing factor. A study in a 2023 issue of the journal Psychoneuroendocrinology linked high stress levels in early childhood with a higher risk of precocious puberty in girls.
“The timing of puberty is stress-sensitive,” says Jane Mendle, a clinical psychologist specializing in mental health during the transition from childhood to adolescence and an associate professor of psychology at Cornell University. “Kids with prepubertal histories of stress and adversity are more likely to go through puberty early.” One hypothesis is that this is because the stress response is also governed by the hypothalamic-pituitary-adrenal (HPA) axis, which influences the onset of puberty.
Some research has even suggested that stressors during the COVID-19 pandemic—including increased screen time, social isolation, physical inactivity, less access to healthy food, and other factors—may be associated with a recent increase in precocious puberty in girls in New York City.
These factors are associated with overproduction of sex hormones such as estrogens and testosterone, rather than direct effects on the brain.
Endocrine disrupting chemicals
Meanwhile, a growing body of research suggests that endocrine disrupting chemicals, such as phthalates, bisphenols, and others, that are found in everyday items may be contributing to these changes.
“A lot of endocrine disrupting chemicals that are ubiquitous in our environment have similar actions to estrogens,” Sopher says. As a result, high exposure to these chemicals can essentially hijack the body’s hormonal environment in ways that alter reproductive development.
For example, a study in a 2023 issue of BMC Medicine found that precocious puberty in girls may be driven partly by exposure to perfluorinated compounds, which are present in numerous everyday products, including stain repellents, paints, waxes, polishes, electronics, food packaging, and more.
A study in a 2023 issue of Environmental Health Perspectives concluded that girls with higher residential exposure to particulate matter in air pollution—while they’re in the womb and throughout childhood—tend to get their periods earlier than those with low exposure.
It’s likely that a combination of these factors is leading to early puberty in some girls, Biro says.
The potential fallout
These reproductive development changes can have physical and emotional repercussions down the road. In the short term, “girls who go through puberty earlier grow faster and stop earlier,” says Biro. This can lead to a shorter ultimate height than they might have had if puberty occurred at the usual time.
In the long run, early puberty is associated with a higher risk of developing breast cancer, as well as a higher risk of obesity during adulthood, notes Biro. It’s also associated with an increased risk of developing high blood pressure, type 2 diabetes, metabolic syndrome, cholesterol abnormalities, and cardiovascular disease, experts say.
“If you start puberty early, your brain and body are exposed to sex hormones that are higher than they are for other girls your age,” says Chaku. “Other kids have to catch up to you.” Besides causing these girls to feel out of sync with their peers, experiencing early puberty can lead to a greater risk of certain mental-health challenges.
“With early puberty, psychologically it tends to be a more difficult transition,” says Mendle. “Kids who mature early miss the chance to develop all the social and emotional resources that help them with the transition.”
Research has found that girls who undergo precocious puberty have high levels of depression, stress and anxiety, poorer body image, and more challenges with emotional regulation.
“They may have changes in stress reactivity, reacting to stress in more pronounced ways,” says Chaku. “Puberty sensitizes the parts of the brain that are invoked by social experiences. Some of these effects dissipate but depression may persist.”
“Puberty is about much more than just the biological piece,” says Mendle. “There are interpersonal and social transitions that are happening because they look older. The rest of the world starts to treat them differently and they may experience difficulties in friendships.”
Indeed, girls who experience early puberty are more likely to be bullied by their peers, and they may get sexual attention before they’re emotionally ready to handle it.
“People think they’re older than they are because of how they look,” Biro says. “They may be 12, look 15, but feel and act like a 12-year-old.”
This change in appearance can lead adults, including teachers and parents, to expect these girls to act older than they are. If they start to hang out with an older peer group, girls who go through early puberty may engage in risky behaviors such as drinking alcohol or having sex, Mendle adds.
Managing the changes
A girl who is suspected of maturing too young should be seen by a health-care provider, Biro says. In most instances, her development will simply be monitored and she’ll be counseled about physical and emotional changes to expect.
“If it’s very early or quickly progressing, girls should be evaluated to make sure it’s just a timing issue and not a pathological cause such as a tumor in the brain,” Topor says. In these instances, the abnormality in the brain can cause puberty to begin at an early age. “We can hit the pause button with medications if it’s occurring very early,” Topor adds.
In such cases, doctors may want to intervene by giving the girl a medication—such as a gonadotropin releasing hormone (GnRH) agonist (like Lupron, an injection, or Supprelin, a surgical implant)—to slow down early puberty in order to prevent some of the detrimental effects such as compromised height. Research has shown that these drugs can increase final height (at age 18) in girls who experience early puberty.
Regardless of when puberty starts, it’s important for parents to normalize the experience as best they can. Remind a child of their age and how to take care of themselves—even if their body looks like it’s 12 or 13 but they’re eight, they need to treat their body as an-eight-year-old body in terms of their diet and sleep habits, Topor says.
“Treating your child as the age they are, even if their body looks older, is really important,” Topor says. This can help girls develop a sense of comfort with their own bodies, protect their self-esteem, and take proper care of themselves, physically and emotionally.
“A lot of aspects of the transition feel very powerless,” says Mendle. “It’s something that happens regardless of whether kids are ready for it.”
That’s one reason why what parents say and do can make a difference, for better or worse.
“There are a lot of aspects of puberty, especially menstruation, that we’re socialized to think of as embarrassing,” Mendle says. “The less stigma we attach to the transition, the better.”
To that end, she adds, it helps if parents can be open to talking about puberty and share their own experiences with it.
“If girls can take away lessons and gain some form of insight from the experience,” Mendle adds, “they do better”—and can establish a sense of “continuity between their past, present, and future selves.”
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