By Amy Norton
HealthDay Reporter
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 suggests.
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 conditions.
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