A growing body of research indicates puberty is starting earlier among girls in the United States and Europe, raising new questions about the roles of obesity and exposure to chemicals in accelerating development.
More girls in the United States are showing some breast development by the time they are 7 or 8 years old than past generations, according to new research published this week in the journal Pediatrics.
The findings are in line with previous studies showing breast development is not uncommon at a young age in the United States, including a 1997 study from the University of North Carolina that first raised alarm about early puberty rates. A study published in 2009 also found that breast development in Denmark is beginning in girls at an average age of 9 years and 10 months, a year earlier than in 1991.
Obesity is considered a major contributing factor to early puberty, but there is also growing concern among some researchers that environmental exposure to chemicals commonly used in plastics and consumer goods, like BPA or phthalates, could be playing a role.
For the Pediatrics paper, researchers at the Cincinnati Children’s Hospital Medical Center studied 1,239 girls from New York, San Francisco and Cincinnati. They found that while a larger proportion of all 7-and 8-year-old girls have breast development now, the increase was especially pronounced in Caucasian girls, where the rates of early breast development doubled since the early 1990s.
“The results definitely indicate that the age of puberty, the beginning of breast development, is decreasing in girls in the United States,” said Susan Pinney, one of the paper’s co-authors.
About 10 percent of Caucasian girls, 15 percent of Hispanic participants and 23 percent of black girls in the study showed some breast development by the age of 7, and the rates climbed to 18 percent, 31 percent and 43 percent respectively by the age of 8. The study did not include data on the beginning of menstruation.
“Our data clearly show that in girls that are overweight and obese they are definitely more likely to go into puberty earlier,” Pinney said, but for chemical exposure there are no definitive studies that show a connection between the two. The researchers did collect blood and urine samples from the girls and plan to test them for levels of certain environmental chemicals in future research as they continue to follow the participants.
“I think [obesity] is contributing to the decrease of the age of puberty but I’m not convinced it’s the whole story,” said Paul Kaplowitz, chief of endocrinology at Children’s National Medical Center.
“I think that something else may be going on, and I think we simply don’t have the answers right now — nobody has come up with a solid study for BPA or phthalates.”
BPA has been shown to mimic estrogen in animals, but studies in humans are limited.
Kaplowitz says earlier puberty is not only seen in Western countries and has been reported around the world, but has been “observed to different degrees.” Socioeconomic status certainly plays a role, he said, in poorer countries where there is a shortage of food, as malnutrition can delay puberty.
He said the Cincinnati study reaffirms a lot of what was already known in the field, but warns parents not to read too much into these results.
“I don’t think it’s fair to assume that every child who has early breast development is going to rapidly progress through puberty and have early periods,” he said.
Pinney said the study has raised many questions about chemical exposure that still need to be answered, but that she hopes parents can focus on what is a known contributing factor.
“As a society we really need to pay attention to the relationship we see between obesity and early puberty,” Pinney said. “It’s not easy to tackle, but we know by reducing childhood obesity that will have many positive effects.”