Oakland, Calif. (August 9, 2010) -- Girls are starting puberty
early, according to new research from the Breast Cancer and the Environment
Research Centers (BCERCs). More girls are experiencing the onset of breast
development at age 7 and 8, compared to those in a study conducted more than 10
years ago and another study conducted 30 years earlier. The change was
especially notable for white girls.
The research published online in the Aug. 9, 2010, issue of
Pediatrics, shows that 10% of white girls, 23% of black girls, 15% of Hispanics
girls and 2% of Asian girls in the BCERC study had started breast development
by age 7. Previous studies found that
5% of white girls and 15% of black girls had started breast development at age
7. The current study is one of the first
to report on age of onset of puberty for Hispanic and Asian girls.
The age of onset of puberty in girls has fallen in the past
two decades and it is continuing to fall in white but not black girls, although
black girls still mature at younger ages than white girls. The researchers used
well-established criteria of pubertal maturation, including the five stages of
breast development known as the Tanner Breast Stages.
There were 1,239 girls between the ages of 6 and 8 from the
San Francisco Bay Area, the Cincinnati
area, and East Harlem, N.Y. who participated in the study. Some regional differences were found—the
girls in the Bay Area were less likely to have experienced onset of puberty at
age 7 or 8 years than the girls in Cincinnati
or New York.
“This study is an initial description of maturation status
of girls in the BCERC Epidemiology Studies, including the Bay Area's CYGNET
Study that demonstrates that girls appear to be maturing earlier than previous
studies have shown. These differences
over time were most striking for white girls, whereas the proportion of African
American girls who started puberty at age 8 years were similar to a survey
conducted in the mid-1990's,” said Dr. Lawrence H. Kushi, associate director
for epidemiology at the Kaiser Permanente Division of Research in Oakland,
CA and a co-author of the study.
Dr. Louise C. Greenspan, a pediatric endocrinologist at
Kaiser Permanente in San Francisco and a co-author of the study said,
“Pediatricians have been using age 8 as the minimum age for normal breast
development. The data from this study suggest that there is a true trend to
earlier puberty in girls. Obesity and ethnic differences are contributing, and
further analysis of our longitudinal data will allow us to investigate the root
causes, including differences in nutritional intake, built environment, and
Other research has established a clear link between an
earlier age of menarche (first menstrual period) and an increased risk of
breast cancer in adult life.
“Understanding the role of environment in adult breast cancer may best
come from these types of detailed studies of early development. Ultimately, we hope that our increased
understanding about the role of the environment in early development can be
turned into methods for breast cancer prevention,” said Dr. Robert A. Hiatt,
Director of the Bay Area Breast Cancer and the Environment Research Center and
Deputy Director of the UCSF Helen Diller Family Comprehensive Cancer Center.