Girls have always gone through puberty at varying ages. When I was 11 years old, I looked like a flat-chested scrawny little girl. Meanwhile, my best friend Judy at that age looked like a grown woman, basically the same as when she graduated from high school. This was a real problem for large-chested Judy because older men frequently hit on her, probably having no idea that she was only 11 years old and unprepared to cope with their advances.
Early maturation in girls is associated with lower self-esteem, less favorable body image, and greater rates of eating problems, depression, suicide attempts and risky behavior. Beyond the emotional issues, girls that go through puberty early are also at higher risk for some medical problems such as breast cancer, endometrial cancer, pre-diabetes and elevated blood pressure. These emotional and health concerns appear to worsen as the age of puberty onset lowers.
Although the timing of puberty always varies between different girls, the average age when girls enter puberty has fallen in the past two decades. A lot of reports and controversy have surrounded this finding, starting with a study published in 1997 in Pediatrics. Why this is happening is not fully understood. Ongoing studies are trying to determine whether this trend is continuing or whether the age of puberty onset for girls has stabilized.
The results of a new study on the timing of breast development in girls were just reported in Pediatrics by a research team led by Dr. Frank Biro, director of adolescent medicine at Cincinnati Children’s Hospital Medical Center. Dr. Biro and his colleagues studied 1239 girls ages 6 to 8 who were recruited from 3 diverse sites: East Harlem in New York, Cincinnati metropolitan area, and San Francisco Bay Area. The recruited group was 34% white, 31% black, 30% Hispanic, and 5% Asian. The data came from interviews with caregivers and physical examinations of the girls. Great care was taken to ensure that the examinations were performed by only well-trained certified staff, using identical well-established guidelines for determining the onset of puberty.
The researchers found that more girls are starting puberty at the age of 7 or 8 than previously reported 10 to 30 years earlier. At 7 years, 10.4% of white, 23.4% of black, and 14.9% of Hispanic girls had enough breast development to indicate the beginning of puberty. At 8 years, 18.3% of white, 42.9% of black and 30.9% of Hispanic girls had sufficient breast development. In comparison, the 1997 study found only 5% of white girls and 15.4% of black girls to have entered puberty at the age of 7.
So the new study shows that the age of entering puberty is continuing to fall for young girls, especially white girls. However, black and Hispanic girls still mature at younger ages than white girls. The cause of this concerning trend is not fully understood. Increased rates of obesity are thought to play a significant role, because body fat can produce sex hormones. Environmental chemicals are also suspected, since they might mimic effects of estrogen and speed up puberty, but this is still under study. Genetics may also play a role.
Breast Cancer and the Environmental Research Centers (BCERC) were established in 2003 as a consortium to study some of these issues, in partnership with the National Institute of Environmental Health Science (NIEHS) and National Cancer Institute (NCI). As Dr. Biro summarizes, “I think we need to think about the stuff we’re exposing our bodies to and the bodies of our kids. This is a wake-up call, and I think we need to pay attention to it.”