RENEE MONTAGNE, host:
Girls in the United States are entering puberty at younger ages than 30 years ago, according to studies, and part of the reason for earlier puberty is that more girls are overweight, some by the time they're three years old. That's the finding of a new study in the journal Pediatrics.
NPR's Patti Neighmond reports.
PATTI NEIGHMOND: Dr. Joyce Lee is a pediatric endocrinologist at the University of Michigan. She says it's been known for some time that overweight girls tend to go through puberty earlier than their normal weight counterparts. What wasn't known was which came first. Did puberty stimulate weight gain or did the weight gain cause puberty?
In Lee's study, 354 girls were weighed at three years old and at four and a half, then they were examined for signs of puberty in grades one, four, five and six. Dr. Lee...
Dr. JOYCE LEE (University of Michigan): We looked at body mass index, which is a measure of body fat calculated from weight and height. And we found that girls with a higher body mass index at 36 months of age were more likely to have earlier puberty. And we also found that girls who had a higher increase in their body mass index between 36 months and first grade were also more likely to have earlier puberty.
NEIGHMOND: About one in four girls were considered overweight or at risk of overweight. Of those girls about two-thirds of them reached puberty by age nine, which means their breasts were beginning to develop. The range for normal puberty is between eight and 14. The average is about 10 to 12 years old. And when girls go through early puberty, Lee says, they're more likely to experience problems as teenagers.
Dr. LEE: Girls who have earlier onset of puberty may have more behavioral problems and psychosocial stress, can have earlier initiation of alcohol use and sexual intercourse, and can also have increased rates of adult obesity and reproductive cancers.
NEIGHMOND: While extremely rare, some studies have shown an increase in breast and endometrial cancer among women who went through early puberty. Also rare, there is some evidence that early puberty inhibits a child's growth later on. Dr. Lee is concerned more girls will go through early puberty because more children today are overweight. Dr. Paul Kaplowitz is chief of endocrinology at Children's National Medical Center in Washington, D.C.
Dr. PAUL KAPLOWITZ (Children's National Medical Center, Washington, D.C): A high BMI in girls is highly associated with increased body fat. And so what we suspect but have no proof of is that girls with a higher BMI and greater body fat, we know that they have higher levels in the blood of a protein called leptin, which is made in fat cells.
NEIGHMOND: Leptin produces hormones which stimulates the production of egg follicles and estrogen in the ovaries. From an evolutionary point of view, Kaplowitz says, it makes sense that fat is linked to reproduction. When food was scarce due to drought or too many animals, it was not a good time to reproduce. Low body weight, and therefore low levels of leptin, made it harder to have children, which at the time was a good thing. Today it's a different story. Food is abundant and so apparently is fat.
Dr. KAPLOWITZ: Everyone knows that there is a trend for both children and adults to be more overweight now than they were 30 years ago. A number of studies have shown that the rate of obesity in young girls has tripled since the late '60s. And many of us contend that this is the single most important reason why we're seeing early maturation in girls.
NEIGHMOND: Kaplowitz adds that early puberty is not the most harmful consequence of increased obesity. The dramatic increase in diabetes among children, he says, is far more dangerous.
Patti Neighmond, NPR News.
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