Puberty starting earlier for many girls: study

Girls are reaching puberty in life earlier than ever, research shows.

About 15 percent of American girls now begin puberty by age 7, according to a study of 1,239 girls published last year in the journal Pediatrics. One in 10 white girls begin developing breasts by that age - twice the rate seen in a 1997 study. Among black girls, 23 percent hit puberty by age 7.

Special Section: Dr. Jennifer Ashton

On "The Early Show" CBS News Medical Correspondent Dr. Jennifer Ashton, an OB-GYN who specializes in adolescent care, said "early puberty," also known as "precocious puberty," has risks for girls.

"You have to remember, this is occurring at a time of childhood development where all girls and children want to do is fit in and look like the person sitting next to them," Ashton said. "It can generate a lot of fear. It's not cute. Adults can look at it and say, 'Oh, how cute.' It's really an adult body, a developing adult body in a child's age.'"

Ashton said the effects on girls can be emotional as well as physical.

"We know that girls of that age can suffer from low self-esteem," she said. "They can be subjected to more peer pressure, increased risks of eating disorder, even depression. They are known to participate in sexual activity in an earlier age because of this. Also, they can be shorter because we know that estrogen is one of the key hormones in puberty closes off the growth plates and girls will not be as tall as if they went to puberty in a later age."

So why is this happening?

It's not clearly understood why this occurs, Ashton said, but some point to the rise in obesity.

"Body fat generates the hormone estrogen, partially," Ashton said. "Estrogen is part of the hormones that triggers puberty. A lot more children are overweight and obese. Environmental exposures, things like BPA (Bisphenol A) that are ubiquitous in our environment can have hormone-like activity and research is ongoing as to whether that plays a role. And your family history - if your mother went through early puberty, you have a greater chance of going through early puberty, as well."

Early puberty could affect girls as they get older, Ashton said. They have an increased risk of breast cancer and uterine cancer, she said, because these girls have more time to be exposed to the estrogen hormone.

"It's not a trivial thing by any means," Ashton said.

She recommends talking to a pediatrician if parents notice signs of puberty at a young age.

"This could be a very frightening process for a child as well as a parent," Ashton said.

Ashton is the author of "The Body Scoop for Girls."