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Marcia Herman-Giddens first noticed something changing in young girls in the late 1980s, when she was serving as director of the child abuse team at Duke University Medical Center in Durham, NC, for abused girls. During the evaluation, Dr. Herman-Giddens noticed that many of them started developing breasts by the age of 6 or 7.
“It didn’t feel right,” said Dr. Herman-Giddens, now an assistant professor at the University of North Carolina Gillings School of Global Public Health. She wondered whether girls with early breast development were more likely to be sexually abused, but she found no data tracking the onset of puberty in girls in the United States. So he decided to collect it himself.
A decade later, they published a study of more than 17,000 girls who underwent physical examinations at pediatricians’ offices across the country. The data showed that, on average, girls began developing breasts in the mid-1990s—usually the first sign of puberty—at around age 10, a year earlier than previously recorded . The decline was even greater among black girls, who started developing breasts at an average age of 9.
The medical community was shocked by the findings, and many were suspicious of a dramatic new trend recalled by an unknown medical assistant, Dr. Herman-Giddens. “They were blind,” she said.
But the study proved to be a watershed in the medical understanding of puberty. Decades later, studies in dozens of countries have confirmed that the age of puberty in girls has dropped by about three months per decade since the 1970s. A similar pattern, although less extreme, has been observed in boys.
Although it is difficult to separate cause and effect, earlier puberty can have harmful effects, especially for girls. Girls who go through puberty early have a higher risk of depression, anxiety, substance abuse, and other psychological problems than peers who go through puberty later. Girls who get their periods earlier may also have a higher risk of developing breast or uterine cancer in adulthood.
No one knows what the risk factor – or more likely, what combination of factors – is driving the decline in age or why there are sharp race- and gender-based differences. Obesity appears to play a role, but it cannot fully explain the change. Researchers are also investigating other possible effects, including chemicals found in some plastics and stress. And for unclear reasons, doctors around the world have reported an increase in cases of early puberty during the pandemic.
“We are seeing these remarkable changes in all our children, and we don’t know how to stop it if we want to,” said Dr Anders Juul, a pediatric endocrinologist at the University of Copenhagen, who recently published two studies. Huh. fact. “We don’t know why,
obesity
At the time Dr. Hermann-Giddens published her landmark study, Dr. Zuul’s research group examined breast development in a group of 1,100 girls in Copenhagen. Unlike American children, the Danish group matched a longstanding pattern described in medical textbooks: Girls started developing breasts at an average age of 11 years.
Dr. Zuul said, “I was interviewed a lot about the American puberty boom, as we call it.” “And I said, ‘It’s not happening in Denmark.'”
At the time, Dr. Juul suggested that the onset of puberty in the United States was probably linked to an increase in childhood obesity, which was not the case in Denmark.
Since the 1970s, obesity has been linked to earlier periods in girls. Since then several studies have established that girls who are overweight or obese tend to start their periods earlier than girls of average weight.
In a decade-long study of nearly 1,200 girls in Louisiana published in 2003, childhood obesity was linked to an earlier period: each standard deviation above mean childhood weight with twice the chance of having a period before age 12. was connected.
And in 2021, UK researchers found that leptin, a hormone released by fat cells that limits appetite, acts on a part of the brain that also controls sexual development. Mice and those with certain genetic mutations in this region experienced sexual development later.
National Institute of Environmental Health Sciences pediatric endocrinologist Dr. “I don’t think obesity is a major contributor to early puberty these days,” Natalie Shaw said. Studying the effects of obesity on puberty, Dr. Natalie Shaw said.
Still, he said, many girls who develop early are not overweight.
“Obesity can’t explain it all,” Dr. Shaw said. “It just happened too soon.”
chemicals
In the decade following the Hermann-Giddens study, Dr. Zuul began noticing an increase in the number of referrals to early puberty in Copenhagen, mostly girls who were developing breasts by age 7 or 8.
“And then we thought, ‘Is this a real event? Dr. Juul said. Or, they wondered, did the news coverage of Dr. Herman-Giddens’s study cause parents and doctors to become “hysterical”?
In a 2009 study of nearly 1,000 school-age girls in Copenhagen, her team found that the average age of breast development had dropped by a year since their earlier study, to less than 10 years, with most girls being 7 years old. Was 12 years old. , Girls were also getting their periods earlier, at about age 13, which they did about four months earlier than previously reported.
“This is a very remarkable change in a very short time,” said Dr. Zuul.
But, unlike doctors in the United States, they didn’t think obesity was to blame: the body mass index of Danish children in the 2009 group was no different than it was in the 1990s.
Dr. Zuul has become one of the most vocal proponents of an alternative theory: chemical exposure is to blame. She said in her 2009 study that girls with the earliest breast development had the highest urinary levels of phthalates, substances used to make plastics more durable that are found in everything from vinyl flooring to food packaging.
Phthalates belong to a broad class of chemicals called “endocrine disruptors”, which can affect the behavior of hormones and have become ubiquitous in the environment over the past several decades. But the evidence that they are driving puberty earlier is unclear.
In a review article published last month, Dr. Juul and a team of researchers analyzed hundreds of studies looking at endocrine disruptors and their effects on puberty. Study methods varied widely; Some were done in boys, others in girls, and they tested for many different chemicals at different ages of exposure. Finally, the analysis included 23 studies that were sufficient to make comparisons, but it was unable to show a clear association between any individual chemistry and age of puberty.
,The great thing is that there is a lack of publications and data to explore this question,” said Dr., an environmental epidemiologist at the Harvard T.H. Chan School of Public Health and co-author of the analysis. Russ Hauser said.
The paucity of data has led many scientists to doubt the theory, Dr. Hauser, who recently described how endocrine disruptors affect puberty in boys. “We don’t have enough data to make a strong case for a specific class of chemicals.”
stress and lifestyle
Other factors may also be involved in earlier puberty, at least in girls. Childhood sexual abuse has previously been linked to the onset of puberty. However, the reason arrows are difficult to draw. Stress and trauma may induce earlier development, or, as Dr. Herman-Giddens hypothesized decades ago, girls who develop earlier physically may be more vulnerable to abuse.
Girls whose mothers have a history of mood disorders are also more likely to reach puberty early, as are girls who do not live with their biological fathers. Lifestyle factors such as lack of physical activity have also been linked to changes in the timing of puberty.
And during the pandemic, pediatricians around the world noticed that referrals for earlier puberty in girls were increasing. A study published in Italy in February showed that 328 girls were referred to five clinics across the country during a seven-month period in 2020, compared to 140 during the same period in 2019. (No difference was found in boys.) May occur in India, Turkey and the United States.
“I’ve asked my colleagues across the country and many of them are saying, yes, we’re seeing a similar trend., Paul Kaplowitz, professor emeritus of pediatrics at Children’s National Hospital in Washington. It is not clear whether this trend was due to increased stress, a more sedentary lifestyle, or to parents’ early enough quarters with their children to notice changes.
Several factors together are contributing the most. And many of these issues disproportionately affect low-income families, which may partly explain the racial difference in the onset of puberty in the United States, the researchers said.
a new normal?
For decades, medical textbooks have defined the stages of puberty using the so-called Tanner Scale, which was based on close observation of some 700 girls and boys who lived in an orphanage in England between 1949 and 1971.
The scale defines normal puberty as age 8 or older for girls and 9 or older for boys. If puberty begins at an age younger than those cutoffs, doctors must screen the child for a rare hormonal disorder called central precocious puberty, which can induce puberty as early as infancy. Children with this disorder often undergo brain scans and take prescribed puberty-inhibiting drugs to delay sexual development until an appropriate age.
But some experts argue that the alarm’s age limit should be lowered. Otherwise, he said, healthy children may be referred to specialists and undergo unnecessary medical procedures, which can be physically taxing and costly.
“There is a lot of data that age 8 is not the optimal cutoff for distinguishing abnormal from normal,” said Dr. Kaplowitz. In 1999, he argued that the age cutoff for normal puberty should be lowered to 7 years for white girls and 6 years for black girls. “That didn’t end very well,” he recalled.
However, that stance was reinforced by a recent study by Dr. Zuul’s group, which showed that of 205 young children under the age of 8 who had brain scans, only 1.8 percent of girls and 12.5 percent of boys. There were brain abnormalities indicating central precocious puberty.
But lowering the age cutoff remains controversial, with many pediatricians arguing that the risk of a disorder is still large enough to justify additional precautions. Others, such as Dr. Hermann-Giddens, say that the changes are a sign of a legitimate public health problem and should not be accepted in general.
“It may be normal what the data is showing,” said Dr. Hermann-Giddens, “but I don’t think it’s normal, for lack of a better word, that is what nature intended.”
