American girls are hitting puberty earlier than ever — a change that puts them at higher risk for behavioral problems as adolescents and breast cancer as adults, a new study shows.

About 15% of 1,239 girls studied showed the beginnings of breast development at age 7, according to an article in today's Pediatrics. One in 10 white girls, twice as many as in a 1997 study, showed breast growth by that age, as did 23% of black girls and 15% of Hispanic girls.

The median age of breast development fell from 10.9 years in 1991 to 9.9 in 2006, according to a Danish study published in Pediatrics last year.

The new study doesn't explain why girls are developing earlier, but it did find heavier girls with a higher body-mass index were more likely than others to begin puberty early, says pediatrician Frank Biro, director of adolescent medicine at Cincinnati Children's Hospital Medical Center.

A growing number of researchers also are concerned about hormone-disrupting chemicals in the environment.

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Source: USA Today
http://www.usatoday.com/news/health/2010-08-09-1Apuberty09_ST_N.htm