Some girls are developing breasts and entering puberty earlier than they did even just a decade ago - increasingly at age 7 and 8.
The new reality is troubling parents and educators, who wonder what effects early maturity will have on the girls' lives.
"Earlier maturation in girls is associated with lower self-esteem and less favourable body image, as well as greater rates of eating problems, depression and suicide attempts. They were more likely to be influenced by deviant peers, with earlier onset of sexual intercourse," write the authors of a new study on early onset puberty that suggests obesity rates factor heavily in the shift.
The study, published Monday in the journal Pediatrics, looked at 1,239 girls aged 6 to 8. At age 7, 15 per cent had started developing breasts; by age 8, that number had ballooned to 27 per cent.
The numbers are significantly higher than a landmark 1997 U.S. study led by Marcia Herman-Giddens that looked at puberty in 17,077 girls. The authors of that study discovered that far more seven- and eight-year-olds had pubic hair and breasts than doctors had realized. It showed that 5 per cent of white girls and 15.4 per cent of black girls had those signs of puberty at age 7.
The latest surge has alarmed the authors of the newest study. Although they don't know if the age has stabilized or will continue dropping, they warn that early onset puberty has consequences.
"Here's a girl whose body appears to the world to be much more mature than her psychological age or her cognitive age. She has to cope with that disconnect," said co-author Susan Pinney, an associate professor of environmental health at the University of Cincinnati College of Medicine.
"It makes you odd - it makes you different," said Linda Cameron, associate professor at the University of Toronto's Ontario Institute for Studies in Education. "It's a less favourable body image for a little girl."
Overweight and obese girls were significantly more likely to grow breasts earlier, and the authors hypothesize that's because body fat can produce sex hormones. Black girls were also found to develop earlier than other girls: Some 23 per cent had begun puberty at age 7, compared to 10 per cent of white girls and 15 per cent of Hispanic girls. By age 8, the numbers grew to 43 per cent in blacks, 31 per cent in Hispanics and 18 per cent in whites.
Although breasts may be growing earlier, the average age of first menstrual period still sits largely unchanged between 12 and 13, a point that should placate panicked parents, says Sari Kives, who works in the department of pediatric gynecology at Toronto's Hospital for Sick Children.
"It doesn't mean that their daughters' periods will start earlier, which is a source of a lot of the angst," said Dr. Kives, adding, "I've dealt with scenarios where the parents were very, very overwrought by the onset of puberty, particularly in kids with special needs. The parents have even more angst because they think the kid isn't going to be able to cope."
Prof. Cameron thinks parents should be "sensitized" not to treat their children like young women, just because they might be starting to look like it.
"You're balancing. It's like the fulcrum between wanting them to feel comfortable, normal and natural with this situation that has happened to their body, but also doing things that will ameliorate: proper food, clothing [that fits] making sure that exercise is a possibility and that they are not put into situations where sexual play can happen beyond the normal."
Said Dr. Pinney: "The worst thing is for a girl is to find this happening to her and nobody will talk about it."
Most concerning to her is the link between early sexual maturation and weight. Likewise for Dr. Kives, who sees many affected girls - many of whom are on the "heavier side."
"We need to educate our patients that being overweight is associated with health concerns, and this is just one of many."