In the last decade, the number of girls in the US reaching puberty at the age of 7 has doubled. The cause has not been confirmed, but obesity and exposure to chemicals that mimic the female hormone estrogen are the prime suspects, according to an article in New Scientist magazine.
The figures come from a study of 1200 girls in three US cities. Of the girls studied, 10.4 percent of white 7-year-olds had breast development consistent with the onset of puberty, compared to 5 percent in a 1997 study, earlier studies had identified early puberty mainly in black girls. The new study is being published on Monday in the journal Pediatrics.
Marcia Herman-Giddens of the University of North Carolina at Chapel Hill, who led the 1997 study, expressed shock at the increases. “To find the girls are starting breast development earlier and earlier is extremely concerning,” she says. “To have that much change in such a short time, it has to be the environment.”
Frank Biro of the Cincinnati Children’s Hospital Medical Center in Ohio, head of the new study, suggests that “Part of it is the increase in overweight and obese girls.” Hormones released by the extra fat cells could play a role. His team is also checking blood and urine samples for chemicals that mimic oestrogen, from plastics in the environment, for example, to soy in the diet.