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First, weight; next, puberty

Heavier girls tend to develop sooner, but obesity is the real problem, experts say.

March 12, 2007|Mary Beckman | Special to The Times

Girls seem to be growing up faster these days, and not just because they dress to show more skin. Compared with their mothers, they actually have more skin to show -- and that added fat seems to be altering their rate of development.

Pediatric experts had noticed that girls appeared to be developing breasts (the first outward sign of puberty) at earlier ages -- and that they tended to gain weight around puberty. But no one knew which came first: earlier development or weight gain. By tracking girls' weights from early ages, researchers have found that the extra pounds come first.

Because both early puberty and weight gain can affect girls' health, the results add a new dimension to the importance of diet and exercise for girls.

In a study published in the March issue of the journal Pediatrics, a team of scientists monitored hundreds of girls from age 3 to 12 and found the heavier ones hit puberty earlier than their slimmer peers. Of the heaviest 15% of girls, 50% had started developing breasts by age 9. Because girls generally start puberty between the ages of 8 and 14, the researchers considered this "early," though normal, puberty.

In fact, the girls' weight as early as age 3 could predict a younger entrance into puberty, says lead study author Dr. Joyce Lee, a pediatric endocrinologist at the University of Michigan. "I thought, 'Wow, these girls are still toddlers,' " she says.

In addition, the faster girls gained weight between 3 years of age and first grade, the more likely they were to begin to develop breasts by fourth grade.

The shift toward earlier puberty has worried parents and pediatricians because some studies show that girls whose bodies mature younger tend to misbehave in school and suffer from anxiety or depression, Lee says. In addition, longer exposures to sex hormones are thought to put women at greater risk for breast cancer.

But it's the obesity that's more problematic. Health problems such as diabetes, high blood pressure and heart disease due to obesity are better documented, experts say. "Parents should try to prevent excessive weight gain in their children," Lee says.

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What defines puberty?

Confusion over weight's effects on puberty has been fueled in part by the various definitions of puberty in previous studies.

Some have used the development of breasts, others the appearance of pubic hair and still others the start of menstruation. The age at which all of these changes occur has shifted since the Industrial Age, but only changes in breast development have paralleled the obesity epidemic, presenting a challenge for researchers seeking to untangle the connection.

Researchers now largely define budding breasts as the first outward sign of puberty. In the 1960s, a child development expert named Dr. James Tanner created the scale still in use today to determine the extent of a girl's progression into puberty. In his study of almost 200 British girls published in 1969, he found they start puberty at about 11 years. In 1997, Dr. Marcia Herman-Giddens, a doctor of public health at the University of North Carolina in Chapel Hill, found that this age had dropped to about 10 years.

The problem with trying to establish the onset of puberty by breast growth, researchers say, has been that extra weight makes breasts look a little larger than they are, and kids have been getting fatter over the last several decades. Researchers can tell the difference between breast tissue and fat by feeling the breast, but many studies have relied simply on an eye check. So researchers have sometimes mistaken plumpness for puberty.

Many parents think that the appearance of pubic hair signifies puberty, but it doesn't. Pubic hair, along with underarm hair and body odor, is caused by hormones pouring from the adrenal glands, which aren't directly involved in sexual maturation. "Pubic hair before 8 years of age is extremely common," Kaplowitz says. "We see it in about 20% of black girls and 8% of white."

Menarche is much easier to date than breast development, but has been more difficult to link to obesity. "If I asked when a woman had her first period, she could probably tell me to the year and month," says Dr. Frank Biro, an adolescent medicine physician at Cincinnati Children's Hospital Medical Center. He says studies in which people have to recall how old they were at the time of menarche are more accurate than asking a parent when his or her daughter started budding breasts.

But although menarche used to follow on the heels of breast development predictably, that's no longer the case. For women born in the 1940s and 1950s, the age of puberty onset appears to correlate with menarche, but for women born in the 1970s, that connection is gone. For that reason, using menarche as an indication of puberty would not reveal a connection between obesity and sexual maturation.

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