Previous research has suggested that girls who get their first period at a young age are more likely to be overweight adults. But a new study shows this may not be true and that others factors may be involved.

It turns out that a girl’s weight at the time of her first period is a much better indicator of her weight as an adult, write Aviva Must, PhD, and colleagues in Pediatrics.

Kids' Weight Can Forecast Adult Obesity

Earlier Periods More Common

Girls in the U.S. now start their periods around age 12.5, Must told reporters in a conference call. Must is an associate professor of public health and family medicine at Tufts University’s medical school.

Early first period is usually defined as happening before age 12, says Must. In 1965, 14 percent of U.S. girls fell into that category. In 1991, the figure had risen to 18 percent. Over the same time frame, the percentage of girls who got their first period before age 11 stayed rare but quadrupled from 1 to 4 percent.

“It has been known for some time that girls who are overweight are more likely to have their first period at a young age. It’s not absolutely certain why this is, says Must.

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FYI for Parents

“For parents of an overweight girl, she may develop breasts or get her first period before other girls of her same age. That early maturity is an expected consequence of childhood overweight,” says Must.

“I should say that precocious puberty, which is going into puberty by around age six or seven, is not something that we expect. If a parent sees that, the [girl] should have a medical evaluation,” says Must.

“For parents of a normal-weight girl, if she does mature early, it does not mean that she is at any increased risk of being an overweight adult,” says Must.

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Overweight Youngsters

Must and colleagues followed up on 448 women who had participated in a health study 30 years earlier.

The long-ago study meticulously tracked the height, weight, and age at first menstrual period of about 700 fourth-grade girls living near Boston, most of whom were white. Decades later, Must’s team contacted as many of the participants as possible.

By then, the women were around 42 years old. About 28 percent were overweight and 9 percent were obese. The findings:

—Girls who were overweight before their first period were nearly eight times as likely to be overweight as adults.

—Girls who started menstruating at an early age — but who were not overweight — were not any more likely to have weight problems as adults.

Other studies may not have had data that was as thorough, says Must.

Since kids’ weight problems often carry over into adulthood, it’s important to make a healthy weight a priority “well before adolescence,” the researchers note.

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By Miranda Hitti, reviewed by Michael W. Smith, MD

SOURCES: Must, A. Pediatrics, September 2005; vol 116: pp 620-627. News release, American Medical Association.