Dr. Frank M. Biro of Cincinnati Children's Hospital Medical Center says the proportion of girls developing breasts at 7 and 8, particularly among white girls, is greater than that reported from studies of girls born 10 to 30 years earlier.
Biro and colleagues collected baseline information on 1,239 girls at ages 6-8 years in three sites: New York's East Harlem, the greater Cincinnati metropolitan area and the San Francisco Bay area.
The study, published in the journal Pediatrics, found by age 8, 27 percent of the girls had begun puberty.
By age 7, 10.4 percent of white girls had reached puberty, 23.4 percent of black non-Hispanics did and 14.9 percent of Hispanic girls reached puberty. However, by age 8, 18.3 percent of whites, 42.9 percent of black non-Hispanics and 30.9 percent of Hispanics had reached puberty.
A study in 1997 found that at age 7, 5 percent of white girls had reached puberty.
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