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

WASHINGTON -- Too little milk, sunshine and exercise: It's an anti-bone trifecta. And for some kids, shockingly, it's leading to rickets, the soft-bone scourge of the 19th century.

Malik McDonald, aged 6, holds a milk container included in the food bag he carried to the car from the Second Harvest food bank of Greater New Orleans Saturday, Nov. 17, 2007, in New Orleans. [Agencies]

But cases of full-blown rickets are just the red flag: Bone specialists say possibly millions of seemingly healthy children aren't building as much strong bone as they should -- a gap that may leave them more vulnerable to bone-cracking osteoporosis later in life than their grandparents are.

"This potentially is a time-bomb," says Dr. Laura Tosi, bone health chief at Children's National Medical Center in Washington.

Now scientists are taking the first steps to track kids' bone quality and learn just how big a problem the anti-bone trio is causing, thanks to new research that finally shows just what "normal" bone density is for children of different ages.

Dr. Heidi Kalkwarf of the Cincinnati Children's Hospital led a national study that gave bone scans to 1,500 healthy children ages 6 to 17 to see how bone mass is accumulated. The result, published last summer: The first bone-growth guide, just like height-and-weight charts, for pediatricians treating children at high risk of bone problems.

Next, the government-funded study is tracking those 1,500 children for seven more years, to see how their bones turn out. Say a 7-year-old is in the 50th percentile for bone growth. Does she tend to stay at that level by age 14, or catch up to kids with denser bones? If not, if she more prone to fractures?

Ultimately, the question is what level is cause for concern.

"I don't know if we're raising a population that's going to be at risk" for osteoporosis, Kalkwarf cautions. "It's really hard to know what the cutoff is, how low is too low."

But almost half of peak bone mass develops during adolescence, and the concern is that missing out on the strongest possible bones in childhood could haunt people decades later. By the 30s, bone is broken down faster than it's rebuilt. Then it's a race to maintain bone and avoid the thin bones of osteoporosis in old age.

"There's some early data showing that even a 10 percent deficit in your bone mass when you finish your adolescent years can increase your potential risk of having osteoporosis and fractures as much as 50 percent," says Dr. James Beaty, president of the American Academy of Orthopaedic Surgeons.

Already there's evidence that US children break their arms more often today than four decades ago -- girls 56 percent more, and boys 32 percent more, according to a Mayo Clinic study.

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