Puberty starts earlier than before, no one knows why

Marcia Herman-Giddens first realized something was changing among young girls in the late 1980s when she led the child abuse team at the University Medical Center. Duke University in Durham, North Carolina. When assessing abused girls, Ms.^me Herman-Giddens noticed that many of them started developing breasts as young as 6 or 7 years old.

“It didn’t seem normal,” said the D^D Herman-Giddens, who is now a professor at the Gillings School of Global Public Health at the University of North Carolina. She wondered if girls with early breast development were more likely to be sexually abused, but found no data to track the onset of puberty in girls in the US . So she decided to collect them herself.

Ten years later, she published a study of more than 17,000 girls who underwent physical examinations in pediatricians’ offices nationwide. The figures revealed that, on average, girls in the mid-1990s started developing breasts – usually the first sign of puberty – around the age of 10, more than a year earlier than had been previously recorded. The decline was even more striking among black girls, who began developing their breasts, on average, at age 9.

The medical community was shocked by these results, and many of these doctors had their doubts about this dramatic new trend spotted by an unknown medical assistant, recalls Ms.^me Herman-Giddens. “They were caught off guard,” she says.

But the study proved to be a watershed moment in the medical understanding of puberty. Research over the following decades confirmed, in dozens of countries, that the age of puberty among girls had fallen by about three months per decade since the 1970s. A similar, but less extreme, trend has was observed in boys.

Although it is difficult to separate cause and effect, early puberty can have adverse consequences, especially for girls.

Girls who experience early puberty are at higher risk for depression, anxiety, substance abuse and other psychological problems, compared to their peers who reach puberty later. Girls who menstruate earlier may also have a higher risk of developing breast or uterine cancer as adults.

No one knows what risk factor – or, more likely, what combination of factors – is driving age decline or why there are stark differences between races and genders. Obesity seems to play a role, but it cannot fully explain this change. Researchers are also investigating other potential influences, including chemicals found in certain plastics and stress. And for reasons not very obvious, doctors around the world have reported an increase in cases of precocious puberty during the pandemic.

“We see these marked changes in all of our children, and we don’t know how to prevent them, even if we wanted to,” Dr.^r Anders Juul, a pediatric endocrinologist at the University of Copenhagen, who published two recent studies on the phenomenon. “We don’t know what caused it. »

Obesity

About the time the D^D Herman-Giddens published its landmark study, the research group of Dr.^r Juul examined breast development in a cohort of 1100 girls in Copenhagen, Denmark. Unlike American children, the Danish group fit the pattern long described in medical textbooks: Girls began developing their breasts at the average age of 11.

At the time, the D^r Juul suggested that the earlier onset of puberty in the United States was likely linked to an increase in childhood obesity, which had not happened in Denmark.

Obesity has been linked to earlier periods in girls since the 1970s. Numerous studies have since established that overweight or obese girls tend to have their periods earlier than average-weight girls.

“I don’t think there’s a big controversy today about obesity being a big factor in precocious puberty,” Dr.^D Natalie Shaw, a pediatric endocrinologist at the National Institute of Environmental Health Sciences, who has studied the effects of obesity on puberty.

Yet, she added, many girls who go through precocious puberty are not overweight.

“Obesity can’t explain all of this,” said Dr.^D Shaw. Everything just happened too fast. »

Chemical products

The D^r Juul has become one of the strongest proponents of another theory, that exposure to chemicals is responsible. According to him, the girls whose breasts developed the earliest in his 2009 study had the highest urinary levels of phthalates, substances used to make plastics more durable and found in everything from coatings to vinyl flooring to food packaging.

Phthalates belong to a broader class of chemicals called “endocrine disruptors,” which can affect the behavior of hormones and have become ubiquitous in the environment over the past few decades. But the evidence that they cause precocious puberty is murky.

In a review article published last month, Dr.^r Juul and a team of researchers analyzed hundreds of studies on endocrine disruptors and their effects on puberty. The methods used in these studies vary considerably; some were done on boys, some on girls, and they tested many different chemicals at various ages of exposure. Ultimately, the analysis looked at 23 studies similar enough to compare, but it failed to find an association between any individual chemical and the age of puberty.

“The main finding is that there are few publications and a dearth of data to explore this question,” said Dr.^r Russ Hauser, environmental epidemiologist at Harvard TH Chan School of Public Health and co-author of the analysis.

This lack of data has led many scientists to be skeptical of the theory, said Dr.^r Hauser, who recently published a report on how endocrine disruptors affect puberty in boys^⁠1. “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 precocious puberty, at least in girls. Sexual abuse in early childhood has been linked to an earlier onset of puberty. However, causal links are difficult to establish. Stress and trauma could promote earlier development or, as the D^D Herman-Giddens decades ago, girls who develop physically earlier might be more vulnerable to abuse.

Girls whose mothers have a history of mood disorders also seem more likely to reach early puberty, as do girls who do not live with their biological father. Lifestyle factors, such as lack of physical activity, have also been associated with changes in pubertal rhythm.

And during the pandemic, pediatric endocrinologists around the world have noticed that the number of cases of precocious puberty in girls is increasing.

A study published in Italy in February showed that 328 girls were referred to 5 clinics in the country during a 7-month period in 2020, compared to 140 during the same period in 2019. (No difference was found among boys. ) Incidentally, the same could happen in India, Turkey and the United States.

“I’ve asked my colleagues across the country and a number of them are saying, yes, we’re seeing a similar trend,” the D said.^r Paul Kaplowitz, professor emeritus of pediatrics at Children’s National Hospital in Washington. It’s unclear whether this trend is due to increased stress, a more sedentary lifestyle, or parents being close enough to their children to notice early changes.

It is highly likely that several factors are contributing at the same time. And many of these problems have a disproportionate effect on low-income families, which may partly explain racial differences in the onset of puberty in the United States, the researchers said.

This article was originally published in The New York Times.