More than a decade after researchers found that some American girls
were beginning puberty as young as 7, new data show that the average
age for whites and Latinas may still be in flux.
By Shari Roan, Los Angeles Times
August 8, 2010
Doctors and parents were stunned when research published more than a
decade ago found American girls were beginning puberty at much younger
ages, some as early as 7. A new study released Sunday suggests the
average age at which puberty begins may still be falling for white and
According to the paper, which appears in the journal Pediatrics,
almost 25% of African American girls have reached a stage of breast
development marking the onset of puberty by age 7, as had almost 15%
of Latina girls and more than 10% of white girls.
Those percentages are significantly higher than in 1997, when a
landmark study first reported that girls were beginning puberty much
younger than they had in the mid-20th century. In that study, the rate
of girls who had begun puberty at age 7 was, on average, 5% for
whites, compared with 10.4% in the new study.
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In other words, the average age of puberty onset still appears to be
"In 1997, people said, 'That can't be right; there must be something
wrong with the study,' " said Dr. Frank M. Biro, director of
adolescent medicine at Cincinnati Children's Hospital Medical Center
and the lead author of the new study. "But the average age is going
down even further."
Biro's study included 1,238 girls ages 6 to 8 who lived in one of
three regions: Cincinnati, East Harlem, N.Y., or San Francisco.
Puberty was determined by two examiners who worked independently to
assess the girls' breast development. By age 8, 27% of the girls had
begun puberty: 18.3% of whites, 42.9% of blacks and 30.9% of Latinas.
Compared with data from the 1997 study, the age at which puberty
begins did not fall for African American girls, although they still
mature at younger ages than white or Latina girls. It's not clear why
there was no change for black girls. "Perhaps black girls have
approached a biologic minimum," Biro said.
Even for white and Latina girls, it is too early to declare that
puberty age is still falling, said Dr. Joyce Lee, assistant professor
of pediatric endocrinology at C.S. Mott Children's Hospital at the
University of Michigan, who was not involved in the study. The
methodology used in the new study differs somewhat from the one in
1997, making direct comparisons difficult, she said.
But, she added, "it's incredible the difference you see between the
There are numerous potential explanations for why puberty is starting
earlier. Chief among them is the increase in average body weight among
children over the last three decades, Lee said. Excess body weight,
especially body fat, is thought to increase the blood levels of
estrogens that promote breast development. Earlier studies, including
one by Lee, have linked early puberty to higher body mass index as far
back as the toddler years.
But other studies suggest that body fat may not be the only cause. A
Danish study released last year in the journal Pediatrics found
puberty occurring earlier in children regardless of body mass index at
age 7. Factors may include a diet that is increasingly high in sugar
and fat, declining physical activity and exposure to endocrine
disrupters, chemicals in the environment that act on hormones.
"Kids today are exposed to plastic much more than they were 10 or 20
years ago," Lee said.
Biro said that his study would continue to follow the girls'
development, and that blood and urine samples were being collected to
look at biomarkers that reflect potential environmental exposures.
Early development in girls is not inconsequential. Studies have linked
it to various health risks including a poor body image, reduced self-
esteem, higher rates of eating problems, depression and earlier onset
of sexual activity. Early maturation in a large population of girls
may also affect future breast cancer rates. Studies have linked a
younger age at the first menstrual period to a higher risk of breast
cancer after menopause.
Parents may be able to influence the timing of puberty, Biro said,
through such lifestyle decisions as encouraging a healthful diet and
physical activity, and avoiding lotions, shampoos and other products
for children and babies that contain phthalates, which are known
"For younger children and the tweens, they should probably live a
little bit greener," Biro said. "People could eat together as families
— not avoiding fast food, but minimizing it to once a week — and
families could engage in regular physical activity."
Truth resides in every human heart, and one has to search for it there, and to be guided by truth as one sees it. But no one has a right to coerce others to act according to his own view of truth. - Mohandas Gandhi
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