Girls Reaching Puberty Earlier, Researchers Unsure Why

August 12, 2010

A higher prevalence of onset of breast development was seen in whites, while black girls develop overall at an earlier age. Obesity was indicated as a factor.

Though researchers are unclear about the reasons why, the onset of puberty among adolescent girls is coming at an earlier age than in previous generations. The study, led by researchers at the University of Cincinnati Children’s Hospital Medical Center, “found a higher prevalence of onset of breast development, especially in white girls.”

Weight was a factor, but according to lead investigator Frank Biro, MD’s conversations with the New York Times, researchers are testing the theory that environmental chemicals such as estrogen are tweaking the female biological clock, saying that they are currently investigating the effects of “several different potential factors, including genes and environmental exposures, as well as how those two may interact with each other.”

These concerns are founded as the environmental causes of puberty were thrust into the spotlight over concerns of tainted Chinese infant formula produced by Synutra International. The Chinese Ministry of Health is investigating the cases of four infants who “have shown signs of premature development, including growth of breasts” and elevated hormone levels.

The study also confirmed the findings of a 1997 study which indicated that black and Hispanic girls develop at an even earlier age than white girls. In this case, of the 1239 subjects, “10.4% of white, 23.4% of black non-Hispanic, and 14.9% of Hispanic girls had attained breast stage 2 [Tanner Breast Stages]; at 8 years, 18.3%, 42.9%, and 30.9%, respectively, had attained breast stage 2. The prime determinant of height velocity was pubertal status.”

These findings will renew the debate over what constitutes normal adolescent development, which has trended earlier in developed countries with improvements in access to healthcare and better nutrition, though hopefully future research will more firmly establish the line between healthy and abnormal growth patterns.