(HealthScoutNews) -- Are fat children condemned to an adulthood hobbled by osteoporosis?

That's the unsettling conclusion of a study by a New York pediatric endocrinologist who found that childhood fat may compromise bone growth and could lead to a higher risk of osteoporosis in later years.

"If you have two children of the same weight, the one who has more body fat has less bone," says Dr. Mary Horlick, a pediatric endocrinologist at St. Luke's-Roosevelt Hospital Center in New York City. She studied 344 children and adolescents to determine their body fat in relation to their bone mass.

"Because you need to acquire bone mass during the growing years, children with more body fat could be at risk [for osteoporosis] as adults," she says.

Adults who are heavy have a lower risk of osteoporosis because carrying around that extra weight strengthens bones. But the reverse seems to be true in children, Horlick says.

"Their bone development is compromised," she says.

Dr. Charles Billington, associate director of the Minnesota Obesity Center, calls Horlick's findings "intriguing," and adds, "if it is borne out to be true, then it is yet another reason why we should be panicked about the current state of obesity."

The percentage of U.S. children and adolescents defined as overweight has more than doubled since the early 1970s. About 13 percent of children and adolescents are now seriously overweight, according to the Centers for Disease Control and Prevention.

In 1998, 12.3 percent of white children were overweight, up from 8 percent in 1986. Among African-American and Hispanic children, the percentage grew from 10 percent for each group in 1986, to 21.5 percent and 21.8 percent, respectively, by 1998. These findings, from the National Longitudinal Study of Youth, were published in a recent issue of the Journal of the American Medical Association.

Health officials also warn that overweight children are setting themselves up for potential health problems as adults, including diabetes and cardiovascular disease.

For their research, Horlick and her colleagues did a cross-sectional study of healthy children and adolescents between the ages of 5 and 18, whose weights ranged from "underweight" to "normal" to "overweight." They found that when they compared children of the same sex and weight, the child with more body fat typically had lower bone mass. Conversely, children with more lean, largely muscle tissue had more bone mass.

One interesting caveat, though, was that the results were somewhat different for girls and boys, Horlick says.

"Although fat doesn't contribute to bone the same way lean tissue does, the girls' fat contributed to some bone development, but in the boys there was none at all," she says.

One possible explanation, Horlick says, is that females need fat for reproductive purposes, so the body helps balance their fat and bone mass growth.

Still, Horlick says her findings are worrisome because of what they may portend for the children of today.

What's more, heavy adults whose excess weight now lowers their risk for osteoporosis may have had denser bones as children, Horlick says.

"This is purely speculative," she says, "but when the people who are fat now were growing up, they led different kinds of lives," with more exercise and intake of more dairy products, which contain bone-building calcium.

Billington says, "It would be interesting to measure the bone density of these kids [in Horlick's study] into adulthood. Are they going to stay that way or become like heavy adults, for whom the added weight helps prevent osteoporosis?"

Horlick hopes to find that out. She's participating in an ongoing study of 1,500 children and adolescents being conducted by the National Institutes of Health's Institute of Child Health and Human Development.

The study is taking place at five hospital centers throughout the country, including St. Luke's-Roosevelt. It will follow young people, ages six to 16, over a four-year period to measure their body weight, fat and lean tissue content and bone mass, she says.

What To Do

You can learn more about childhood obesity from the American Academy of Family Physicians. And the Centers for Disease Control and Prevention has information on obesity for both children and adults.

For an explanation of osteopororis, visit the National Institutes of Health.

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