Obesity and stress may be associated with precocious puberty

Marcia Herman-Giddens first noticed that something was changing in girls when she was director of the child abuse team at Duke University Medical Center in Durham, North Carolina, in the late 1980s. When she examined girls who had been abused , Herman-Giddes noticed that many of them had started to develop breasts at 6 or 7 years of age.

“Something just didn’t feel right,” commented Herman-Giddes, now a professor at the University of North Carolina’s Gillings School of Global Public Health. She speculated whether girls who developed breasts early were more likely to be sexually abused, but found no data accompanying the onset of puberty in girls in the United States. So she decided to collect this data.

A decade later she published a study of more than 17,000 girls screened in pediatricians’ offices across the country.

The numbers revealed that, on average, girls in the mid-1990s began to develop breasts — usually the first sign of puberty — around age 10, more than a year earlier than the previously recorded age. The phenomenon was even more notable among black girls, who had started to develop breasts at age 9, on average.

The medical community was shocked by the discovery, and many among its members questioned the new and unexpected trend spotted by an unknown medical assistant, recalled Herman-Giddens.

But the study turned out to be a game-changer in the medical understanding of puberty. In the decades since, studies in dozens of countries have confirmed that the age of puberty in girls has declined by three months per decade since the 1970s. A similar, but less pronounced, pattern has been observed among boys.

It is difficult to define what is cause and what is effect, but precocious puberty can have harmful effects, especially for girls.

Girls who enter puberty earlier are at greater risk of depression, anxiety, substance abuse and other psychological problems compared to those who reach puberty later. Girls who start menstruating earlier may also be at increased risk of developing breast or uterine cancer in adulthood.

No one knows which risk factor—or, more likely, what combination of factors—is leading to the drop in the initial age of puberty, nor does anyone know how to explain the sharp differences on a racial and sexual basis. Obesity appears to play a role, but cannot by itself explain the change.

Scientists are also researching other possible influences, including stress and chemicals found in certain plastics. And, for reasons that aren’t clear, doctors around the world have reported an increase in cases of precocious puberty during the coronavirus pandemic.

“We are seeing these dramatic changes in all children and we don’t know how to prevent them,” said Dr. Anders Juul, a pediatric endocrinologist at the University of Copenhagen and author of two recent studies on the phenomenon. “We don’t know what the cause is.”

Obesity

Around the time that Herman-Giddens published his landmark study, Juul’s research group examined breast development in a group of 1,100 girls in Copenhagen.

Unlike American children, the Danish group followed the pattern traditionally described in medical textbooks: Girls started developing breasts when they were 11 years old, on average.

“I was interviewed several times about the puberty boom in America, as we called it,” said Juul. “And I said, ‘This is not happening in Denmark’.”

At the time, Juul suggested that the early onset of puberty in the US was likely related to an increased incidence of childhood obesity, something that had not occurred in Denmark.

Since the 1970s, obesity has been linked to the early onset of menstruation. Numerous studies since then have established that girls who are overweight or obese tend to start menstruating at a younger age than girls of average weight.

“I think few today question that obesity is a major contributor to early puberty,” said Dr. Natalie Shaw, a pediatric endocrinologist at the National Institute of Environmental Health Sciences and a scholar of the effects of obesity on puberty.

Even so, she added, many girls who reach puberty early are not overweight.

“Obesity doesn’t explain everything,” Shaw said. “It’s happening too quickly.”

Exposure to chemicals

Juul has become one of the biggest proponents of an alternative theory: that the explanation lies in exposure to chemicals. He said the girls who had developed breasts earlier in his 2009 study had the highest levels of phthalates in their urine. Phthalates are substances used to increase the durability of plastics. They are found in everything from vinyl flooring to food packaging.

Phthalates are part of a broader class of chemicals known as endocrine disruptors, which can affect the behavior of hormones and which in recent decades have become widespread in the environment. But the evidence that they are driving precocious puberty is unclear.

In a review article published last month, Juul and a team of researchers analyzed hundreds of studies on endocrine disruptors and their effects on puberty.

The methods used in the studies varied widely: some were done with boys, some with girls, and children were tested for many different chemicals at different ages of exposure.

In the end, the analysis included 23 studies that were sufficiently similar to allow comparisons, but failed to prove a clear link between any individual chemical and age at puberty.

“The big takeaway is that there are few publications and data to explore this question in depth,” said Russ Hauser, an environmental epidemiologist at the Harvard T.H. Chan School of Public Health and a co-author of the analysis.

This paucity of data has led many scientists to view the theory with skepticism, said Hauser, who recently published a paper on 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 precocious puberty, at least among girls. Early childhood sexual abuse has been linked to the early onset of puberty. But it is difficult to determine causality.

Stress and trauma can trigger early development, or, as Herman-Giddes theorized decades ago, girls who develop physically earlier may be more vulnerable to abuse.

Girls whose mothers have a history of mood disorders also appear to be likely to start puberty earlier, as do girls who do not live with their biological father. Lifestyle factors such as lack of physical activity have also been linked to changes at the time of puberty.

And during the pandemic, pediatric endocrinologists around the world have seen more cases of precocious puberty among girls.

A study published in Italy in February showed that 328 girls were treated for precocious puberty at five clinics in the country during a seven-month period in 2020, compared to 140 in the same period in 2019. (No change was observed among boys ). According to informal observations, the same thing may be happening in India, Turkey and the United States.

“I’ve asked my colleagues across the country and several of them say they’re seeing a similar trend,” said Dr. Paul Kaplowitz, professor emeritus of pediatrics at National Children’s Hospital in Washington.

It is unclear whether the trend was caused by increased stress, a more sedentary lifestyle, or a closer relationship between parents and children, which would have allowed them to observe early changes.

More likely, several factors are contributing simultaneously. And many of these issues disproportionately impact lower-income families, a fact that researchers say may help explain racial differences at the onset of puberty in the United States.

Translation by Clara Allain