FRIDAY, April 6 (HealthScout) -- Girls who reach puberty early are twice as likely to be overweight as their average peers, says a new study.
　　For young black girls, the study says, the odds are even greater.

The finding, by researchers at the University of North Carolina at Chapel Hill, adds to a growing body of research that suggests a connection between weight and the onset of puberty.

"There's an increased risk of overweight in girls who mature early, and given the tendency to be overweight in the United States, we should really be aware of this association and, in particular, efforts should be directed at overweight prevention in minority girls, who are at highest risk," says Linda S. Adair, an associate professor of nutrition at North Carolina.

The causes of early puberty today -- with some girls as young as 8 or 9 developing breasts -- have prompted considerable debate, says Dr. Paul Kaplowitz, a pediatric endocrinologist at Virginia Commonwealth University in Richmond.

"Many people have accepted that weight is part of the story," Kaplowitz says. "But many people are trying to find another reason." Some, he says, have targeted estrogens in the environment and chemicals in pesticides and plastics.

This study won't eliminate those possibilities, he says, but it helps build a strong case against them.

The researchers analyzed data from participants in the National Longitudinal Study of Adolescent Health. Of 6,507 girls, 54.8 percent were white, 21 percent black, 17 percent Hispanic and 7.1 percent Asian.

The girls who menstruated soonest -- before they were 11 -- were about twice as likely to be overweight as the girls who started menstruating later. The researchers considered a normal start of menstruation as between 11 and 13 years of age. They considered girls overweight if their body mass index, or height-weight ratio, was above the 85th percentile for their age group. For instance, a 16-year-old girl who is 5 feet 3 inches tall would weigh more than 139 pounds if she were above the 85th percentile for her age group. If she were 5 feet 6 inches tall, she would need to weigh more than 153 pounds.

But just how likely a girl who reached puberty sooner was to be overweight depended on her race, the study says.

Black girls were 2.57 times more likely to be overweight if they'd reached puberty sooner, the study says. In fact, 12.3 percent of the black girls who participated had matured early, and 57.5 percent of them were overweight.

By comparison, white girls were 1.91 times as likely to be overweight if they reached puberty early. Only 7.8 percent of them had matured early, and 36.4 percent were overweight, the study says.

Hispanics were 1.93 times as likely to be overweight if they'd reached puberty early, similar to white girls. And Asian girls were 1.79 times as likely. Details appear in the April issue of the American Journal of Public Health.

The precise connection between weight and puberty onset remains elusive, Adair says. But some evidence, she says, suggests that adding body fat at an early age creates estrogen-like compounds in the body, which may fool the body into thinking puberty is beginning.

In her own research, Adair says, she's found that very young girls who are overweight end up reaching puberty sooner, suggesting that weight may actually cause earlier menstruation. She says those results will be published soon.

Kaplowitz says he, too, has soon-to-be-published research showing that girls who become overweight early also develop breasts sooner.

The link between weight and puberty onset goes back to studies done in the '60s and '70s, he says, but much of that research focused on girls at the extremes, particularly those who were very overweight. By contrast, Adair's study examines girls considered more normal, he says.

But why the link seems stronger in black girls remains a puzzle, Adair says.

The numbers are particularly worrying, she says, because black girls are much heavier today on average than they were 40 years ago. In the 1960s, the study says, 12 percent of black girls were overweight, but that number had increased to nearly 31 percent by the mid-1990s.

One possible explanation is that body mass index numbers aren_t equal, Adair says. For example, two girls with the same ratios may have weight that's distributed differently, with one having a lot of fat in her abdomen and the other elsewhere on her body.

Just where the fat is located may affect girls in different ways, Adair says.

What we do know, experts say, is that early maturation leads to earlier sexual activity, which carries with it many risks, including exposure to sexually transmitted diseases. And being overweight as a child increases the odds a person will be overweight as an adult, which carries other health risks. Also, very early maturation can carry social costs for young girls, as well.

"They can be subject to teasing by their peers," Adair says. "It puts them psychologically at risk as well."

　　From HealthScout