(Agencies)
Updated: 2007-11-27 11:16

Kalkwarf's hospital recently found that kids who break an arm have lower bone density than their playmates who don't. That suggests the fracture rise isn't due solely to newer forms of risky play, like inline skates.

And last year, government researchers found overweight children were more likely to suffer a fracture, even though theoretically their bones should be hardier from carrying more weight. Maybe they have poorer balance; maybe they fall harder. Kalkwarf says there even are hints that fat itself may produce bone-harming substances.

Doctors have long known that less than a quarter of adolescents get enough calcium.

But strong bones require more than calcium alone. Exercise is at least as important. Consider: The dominant arm of a tennis player has 35 percent more bone than the non-dominant arm.

And Canadian researchers recently reported that postmenopausal women who had exercised more as teens had 8 percent stronger bone decades later than their more sedentary counterparts.

Yet childhood exercise is dropping as obesity rises.

Likewise, the body can't absorb calcium and harden bones without vitamin D. By some estimates, 30 percent of teens get too little.

It's not just that they don't drink fortified milk. Bodies make vitamin D with sunlight. With teen computer use, urban youngsters without safe places to play outdoors and less school P.E., it's no wonder D levels are low. Because skin pigment alters sun absorption, black children are particularly at risk.

Rickets marks the worst deficiency, where bones become so soft that legs literally bow. Rickets was once thought to have been eradicated with milk fortification, but "I am now treating rickets in a way that I never treated it 20 years ago," says Tosi, who diagnoses rickets or super-low D levels in children every month at a bone clinic she runs for mostly inner-city children.

Doctors who've never seen rickets can miss it. Charlene Bullock repeatedly asked her 5-year-old's doctor why his leg was bending inward and he could no longer run with his playmates. It took a trip to Tosi's special clinic to learn Na-shun had rickets -- the once energetic child had quit running because his bones ached like an old man's.

Fortunately, rickets caught early is easily cured with high-dose infusions of vitamin D and calcium, and Bullock's son quickly rebounded. "He's doing everything with that little leg."

It's the kids whose low vitamin D hasn't gotten quite bad enough for symptoms that Tosi most worries about. They may never get treated.

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