MONDAY, Nov. 4 (HealthDay News) -- U.S. girls are developing
breasts at a younger age compared to years past, and obesity
appears to explain a large share of the shift, a new study
Researchers found that between 2004 and 2011, American girls
typically started developing breasts around the age of 9. And those
who were overweight or obese started sooner -- usually when they
were about 8 years old.
The numbers are concerning, the researchers said -- especially
since the typical age at breast development is younger now than it
was in a similar study from 1997. The main reason: Girls are
heavier now than they were in the '90s.
"This is another manifestation of America's high body-mass index," said lead researcher Dr. Frank Biro, of Cincinnati Children's Hospital Medical Center. Body-mass index (BMI) is a measure of body fat based on a ratio of height to weight.
The findings, reported online Nov. 4 and in the December print
issue of the journal
Pediatrics, add to evidence that American children are
hitting puberty earlier than in decades past. The rising tide of
childhood obesity has been suspected as a major cause, but the new
study gives more hard data to support the idea.
Biro said, however, that excess pounds do not seem to be the
full explanation. And it's possible that other factors -- such as
diet or chemicals in the environment -- play a role.
Why should people worry that puberty is coming sooner now than
in years past? There is a concern when young kids look older than
they are, and are possibly treated that way, Biro said.
Studies have found that girls who mature early are more likely
to be influenced by older friends, start having sex sooner and have
more problems with low self-esteem and depression. "Just because
you're developing more quickly physically doesn't mean you're
maturing emotionally or socially," Biro said.
Plus, early puberty has been tied to long-term health risks. For
women, an earlier start to menstruation has been linked to a
heightened risk of breast cancer. It's not clear why, but some
researchers suspect that greater lifetime exposure to estrogen
might be one reason.
Biro said earlier puberty also has been tied to increased risks
of high blood pressure, heart disease and diabetes in adulthood.
It's hard, though, to know whether earlier puberty is to blame
since obese kids tend to start puberty earlier, and obese children
often become obese adults, he said.
Dr. Patricia Vuguin, a pediatric endocrinologist at the Steven
and Alexandra Cohen Children's Medical Center in New Hyde Park,
N.Y., said it's not known if it's the earlier development or the
obesity itself that causes the increased risk of those
But it is clear that childhood obesity has consequences, said
Vuguin, who was not involved in the study. "For parents, the
message is to pay more attention to a healthy diet and exercise
even in a child's early years," she said.
The findings are based on 1,200 girls from three U.S. cities who
were followed between 2004 and 2011. Black girls started developing
breasts around age 8, while Hispanic, white and Asian girls
typically started at age 9.
When Biro's team compared their findings with the 1997 study,
they found that white girls were clearly maturing faster in recent
years. Twenty-one percent had started developing breasts before age
9, versus 11 percent in the earlier study, for example.
Black girls seemed to be developing earlier too: 22 percent
started before age 8, versus 15 percent in 1997. But that
difference was not significant in statistical terms, Biro said.
"What seems to be happening is that white girls are 'catching up' with black girls," he said.
From the data, it appeared that increasing body weight accounted
for much of the difference between the two studies, Biro said. But
excess pounds did not tell the whole story, he said.
It's possible that other factors are at work, Biro said,
including various environmental chemicals that can disrupt hormone
activity, such as certain pesticides and plasticizers. Lack of
exercise and childhood diets that are low in fiber and high in meat
and dairy also have been suspected of contributing to earlier
puberty. But none of those suspicions has yet been proven.
Vuguin said research like this is important for doctors because
they need to keep evaluating what "normal" development is. There is
a difference between relatively earlier puberty and what doctors
call "precocious puberty" -- which can have consequences such as
stunted growth because the bones stop maturing earlier than
Traditionally, Vuguin said, precocious puberty has been defined
as signs of puberty -- including breast development -- before the
age of 8 in girls. Doctors may use hormonal medications to treat
"But if you have, for example, an obese African-American girl who is developing breasts at the age of 7, that might be 'normal' now," Vuguin said. "I think there is starting to be a shift in how we're looking at this: Should we treat it, or let it be? It's complicated."
The American Academy of Pediatrics has more on
development during puberty.
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