Marcia Herman-Giddens first became aware that something was changing for young girls in the late 1980s while she was director of the Children Abuse Team at Duke University Medical Center in Durham, North Carolina.
During examinations of girls who had been abused, Dr. Herman-Giddens noticed that many of them had begun developing breasts as early as age 6 or 7, the New York Times reported.
"It didn't seem normal," said Dr. Herman-Giddens, who is now an associate professor at the Jillings School of Global Public Health at the University of North Carolina. She is interested in whether girls with early breast development are more likely to be sexually abused, but can find no data that track the early puberty in girls in the United States. So she decided to collect this data herself.
A decade later, she published a study of more than 17,000 girls who had undergone medical exams in pediatricians' offices across the country. The data revealed that, on average, girls in their mid-90s began developing breasts, usually the first sign of puberty, at about age 10, more than a year earlier than previously recorded. The decline is even more striking in black girls, who began developing breasts at the age of 9.
"The medical community was shocked by the results and many doubted the dramatic new trend," recalls Dr. Herman-Giddens.
However, the study proved to be a turning point in the medical understanding of puberty. Studies conducted in the following decades confirmed in dozens of countries that, since the 1970s, the age of puberty in girls had been declining by about 3 months per decade. A similar pattern, though less extreme, has been observed in boys.
Although it is difficult to disentangle causes and consequences, earlier puberty can have harmful consequences, especially for girls. Girls who go through early puberty are at higher risk for depression, anxiety, substance abuse, and other psychological problems compared to their peers who reach puberty later on. Girls who entered menstruation earlier may also be at higher risk of developing breast or endometrial cancer later in life.
No one knows what risk factor, or rather what combination of factors, is causing the age decline or why there are large differences between races and genders. Obesity seems to play a role, but it cannot fully explain the change. Researchers are also investigating other potential influences, including chemicals found in some plastics, as well as stress. And for reasons that are unclear, doctors around the world report an increase in cases of early puberty during the pandemic.
"We see these noticeable changes in all our children and we don't know how to prevent them, even if we wanted to," said Dr Anders Juul, a paediatric endocrinologist at the University of Copenhagen who has published two recent studies on the phenomenon.
Around the time Dr. Herman-Giddens published her landmark study, Dr. Juul's research group was studying breast development in a group of 1,100 girls in Copenhagen. Unlike the American children, the Danish group matched a pattern that has long been described in medical textbooks: Girls begin developing breasts at an average age of 11.
"I've been interviewed quite often about the American puberty boom, as we used to call it, and my response was to tell them that this phenomenon doesn't happen in Denmark," Dr. Anders said.
"At that time, the earlier onset of puberty in the US was probably related to the rise in childhood obesity, which was not seen in Denmark," the endocrinologist suggested.
Obesity has been associated with earlier menstruation in girls since the 1970s. Numerous studies since then have found that overweight or obese girls tend to start their periods earlier than girls of normal weight. /BGNES
