Researchers from the University of California at Berkeley surveyed 444 girls aged 6 to 8 years in northern California. Over two years, scientists charted symptoms indicating an onset of puberty, defined as breast development and appearance of pubic hair. They also noted differences in the girls' ethnic backgrounds, body mass index and family income.
Eighty of the girls didn't live with their biological fathers, though some had stepfathers or other male role models living at home. Researchers saw earlier breast development in that group, but only among those who were also from higher income families, defined as households earning more than $50,000 a year. Earlier onset of pubic hair was also found in that group, but only among African American girls.
The study appears in this month's issue of the Journal of Adolescent Health, and has been excerpted by several news outlets.
Early puberty has previously been linked to emotional problems, substance abuse and earlier sexual activity, as well as higher risks of breast cancer and reproductive diseases later in life, Business Week reported. Previous studies have also linked childhood obesity to early maturation.
"It's possible that in lower income families, it is more normative to rely upon a strong network of alternative caregivers," the study's lead author, Julianna Deardorff, an assistant professor of maternal and child health at UC Berkeley, told Medical News Today. "Higher income families without fathers are more likely to have a single mother who works long hours and is not as available for care giving."
"In some ways, our study raises more questions than it answers," Deardorff said.