Why are American girls hitting puberty early?

According to the findings of a new study, American girls seem to be growing up faster, kicking the puberty process at a much younger age.
Early onset of puberty (breast development) is witnessed in girls of all races, particularly white girl with research suggesting that obesity was behind the worrying national trend.
A landmark study in 1997, the first documenting early puberty in American girls was four months later than the average age found by the new study, which is 9.7 years old.
Girls who mature earlier are more susceptible to a host of health complications including elevated risk of cancer, hypertension and depression. It can also lower self-esteem and impact academic achievement.
The study researcher Dr. Frank Biro, a doctor in the Division of Adolescent Medicine at Cincinnati Children’s Hospital Medical Center stated, “The impact of earlier maturation in girls has important clinical implications involving psychosocial and biologic outcomes. The current study suggests clinicians may need to redefine the ages for both early and late maturation in girls.”
Details of the study
In order to get some insight into whether obesity was a major contributing factor to this shift, the researchers conducted a study. They analyzed a group of 1200 girls in New York, the San Francisco Bay area and the greater Cincinnati area, as part of the government funded Breast Cancer and the Environment Research Program.
The subjects aged between 6 to 8 years at the onset of the study in 2004 were monitored for multiple years. Experts kept track of signs of maturation, through well established measures including the five stages of breast development known as the Tanner Breast Stages.
Revelations of the study
According to the findings which appear in the journal Pediatrics, the average age at which the girls developed breasts was 8.8 for African American girls, 9.3 for Hispanic girls, 9.7 for white non-Hispanic girls and 9.7 for Asian girls. It was noted that girls with higher body mass indexes were more likely to have reached puberty at younger ages.
Biro stated, “The influence of BMI on the age of puberty is now greater than the impact of race and ethnicity. These girls were born and raised in the midst of an obesity epidemic. This is yet another impact of obesity epidemic in this country.”