(RxWiki News) It might seem as though young girls are growing up faster than ever these days. But there may be some truth in that beyond just casual observations.
A recent study found that young girls may be reaching the early stages of puberty sooner than they used to.
Girls' breast development was among the earliest signs of their puberty development.
White girls reached this stage sooner than they did 10 to 20 years ago.
Black girls, however, reached it at about the same rate, though sooner than white girls.
The biggest factor in when a girl began puberty appeared to be her weight.
"Help your daughter maintain a healthy weight."
This study, led by Frank M. Biro, MD, of the Division of Adolescent Medicine at Cincinnati Children's Hospital Medical Center, aimed to learn more about whether girls have been reaching puberty sooner than in the past in the US.
The researchers started following 1,239 girls, aged 6 to 8 years old, in the San Francisco Bay Area, Greater Cincinnati and New York City.
The group consisted of 39 percent black girls, 44 percent Hispanic girls, 26 percent white girls and 12 percent Asian girls.
They were followed for an average of 4.3 years to see when their breasts matured to assess their typical ages at the early stages of puberty.
Girls reached "stage 2" of breast development — when the breast bud forms and the nipple begins to enlarge — at different typical ages depending on the girls' weight and race/ethnicity.
Black girls reached stage 2 of breast development at an average of 8.8 years old, while Hispanic girls reached it at an average of 9.3 years old.
White and Asian girls reached stage 2 of breast development at an average of 9.7 years.
The higher a girl's body mass index (BMI) was, the earlier she tended to reach stage 2 in breast development.
BMI is a ratio of a person's height to weight. It is used to determine whether a person is a healthy weight or is over- or underweight.
These ages were different from findings on girls' breast development in studies one to two decades ago.
While black girls were reaching puberty at similar ages in those past studies, white girls were reaching puberty at later ages in the past.
The biggest influence on a girl's age when she began developing her breasts appeared to be her BMI, or her weight.
"Higher BMI was the strongest predictor of earlier age at breast stage 2 in our study," the researchers wrote. "Similar findings have been reported that noted the association between BMI and body fat with earlier timing of puberty in girls."
This finding remained true even when the researchers took into account differences among the girls' socioeconomic status.
"We observed the onset of breast development in white girls at younger ages than reported in previous publications, suggesting a continued trend to earlier ages of breast development," the researchers wrote. "Black girls continue to experience breast development earlier than white girls."
Although weight appeared to be a major factor, the researchers could not state what actually caused girls to develop at earlier ages.
This study was published November 4 in the journal Pediatrics. The authors declared no conflicts of interest.
The research was funded by the Breast Cancer and the Environment Research Program at the National Institute of Environmental Health Sciences. Funding also came from The National Cancer Institute, the National Center for Research Resources, the Molecular Epidemiology in Children’s Environmental Health training grant and the Avon Foundation.