Compared to the 1997 findings from girls across the U.S., girls in the current study - especially white girls - were more developed at a younger age. As previous research has shown, there were also large differences in development based on race.
At age 7, approximately 10 percent of white girls and 23 percent of black girls had started developing breasts - compared to 5 percent of white girls and 15 percent of black girls in 1997, the authors write.
Among 8-year-olds in the study, 18 percent of white girls and 43 percent of black girls had entered puberty - an increase from around 11 percent of white girls from 1997, but the same as black girls in that year.
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