Several studies have documented earlier onset of puberty in girls over the past few decades. In a longitudinal study following more than 1,200 girls for seven years, researchers found those with higher BMI had earlier onset of puberty, as measured by breast development, and that white girls are entering puberty at younger ages than previously reported. The study, “Onset of Breast Development in a Longitudinal Cohort,” in the December 2013 Pediatrics (published online Nov. 4), tracked girls in San Francisco, Cincinnati and New York City. The age at onset of breast development varied by race, BMI, and geographic location. In white, non-Hispanic girls, breast development began at a median age of 9.7 years, which is earlier than previously documented, according to the study authors. Black girls continue to experience breast development earlier than white girls, at a median age of 8.8 years, compared to 9.3 years for Hispanic girls and 9.7 years for Asian girls. However, BMI was a stronger predictor of puberty onset than race or ethnicity. Study authors conclude the earlier onset of puberty in white girls is likely due to greater obesity.