MONDAY, Aug. 6, 2001 (HealthDayNews) -- Extra weight could spur puberty in young girls, a new study has found.
Using data from a landmark 1997 study on puberty, doctors found that young girls, especially white girls, were much more likely to show early signs of breast development or pubic hair if they were overweight.
For instance, the study found that 7-year-old girls whose weight averaged 60 pounds showed some pubertal development, while girls of the same age whose weight averaged 53 pounds did not, says Dr. Paul Kaplowitz, a pediatric endocrinologist and lead author of the study, which appears in this month's Pediatrics.
"Our hypothesis was that being overweight increases the likelihood that puberty will come earlier. We were pleased but not surprised to see the results of the study bore that out," he says.
One result did surprise him: The weight of African-American girls did not show a significant association with early puberty, despite the fact that black girls, proportionally, are heavier than white girls and start puberty on average a year younger than white girls.
"There may be genetic differences in the African-American population [that cause the earlier puberty]. There are still a lot of unanswered questions," Kaplowitz says.
A 1997 study, based on physical exams of 17,000 girls aged 3 to 12 throughout the country, found the average onset of early puberty, which includes some breast development and/or appearance of pubic hair, was age 10 for white girls and age 9 for African-American girls. That study was done by Marcia Herman-Giddens, an adjunct associate professor of maternal and child health at the University of North Carolina. Previously, pubertal development had been thought to start for all girls at age 11.
The average age of onset of menstruation, however, has not changed, remaining at 12.2 years for African-American girls and 12.8 years for white girls.
Herman-Giddens, who also is an author of the latest study, finds the results "logical" but warns against jumping to conclusions.
"All it shows is that there is an association, some sort of relationship. [Overweight] is not a cause. The why has yet to be figured out," she says.
Dr. Ora Pescovitz, director of pediatric endocrinology at Indiana University School of Medicine, who was critical of some interpretations of Herman-Giddens' 1997 study, says the latest findings are solid.
"The findings are consistent with the data. The concept [of the association between overweight and earlier onset of pubertal development] has been substantiated in the literature and in other places as well. I don't have a problem with it," she says.
"The onset of puberty is correlated with body size. Puberty is delayed in girls who have inadequate body fat. They don't have enough body fat to go through the reproductive process," she says. "Obesity may be the other side of that spectrum; the brain recognizes that when a body is a certain size, it's OK to go into puberty."
In the new study, Kaplowitz, an associate professor of pediatrics at Virginia Commonwealth University School of Medicine, looked at the weight of approximately 5,000 girls, ages 6 to 9, using the body mass index (BMI), a standard based on a formula involving weight and height. He then compared the girls' BMIs to their pubertal development.
He found a "statistically significant" association between the overweight white girls and their earlier pubertal development compared with white girls who were not overweight. "It's extremely unlikely that these characteristics would appear by chance," he says.
Among approximately 400 African-American girls in the study, the association between weight and pubertal development was not statistically significant, he says.
On the question of whether early pubertal development causes overweight rather than the other way around, Kaplowitz says his reviews of the literature showed that the levels of estrogen generally found in young girls with some pubertal development were too low to affect weight gain. More likely overweight is the trigger, he says.
The association between overweight and hormonal development may be that the levels of a protein, called leptin, are high in people with body fat, and the presence of leptin is associated with early puberty, Kaplowitz says.
In the meantime, he says parents should take the new information with a grain of salt.
"We have no evidence that losing weight will slow puberty, but we could inform parents that early puberty may be one of the health consequences of overweight," he says.
What To Do
An explanation of early puberty can be found at American Academy of Family Physicians. Also of interest is a recent press release from the Rand Institute about the general increase in obesity.
The North Carolina study generated much discussion about early puberty. Some endocrinologists say the definitive sign that a girl has reached puberty comes when she menstruates for the first time. Read this joint release from the Endocrine Society and the Lawson Wilkins Pediatric Endocrine Society calling for more research on precocious puberty.
