With more children and adolescents taking part in sports activities, it's even more important for them to learn how to properly condition and warm-up to prevent injuries and decrease the risk of long-term knee problems.The sound of crunching football helmets; the speed of a hockey player racing down the ice to score; and the twisting and turning of a gymnast moving across a floor mat bring cheers from the crowd at any sports event.

The harder kids play, the harder they fall. The fact is, broken bones, or fractures, are common in childhood and often happen when kids are playing or participating in sports. Most fractures occur in the upper extremities: the wrist, the forearm, and above the elbow. Why? When children fall, it's a natural instinct for them to throw their hands out in an attempt to stop it.

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Recent studies indicate that eating foods rich in calcium helps lower body fat levels. But do calcium supplements work just as well as dietary sources ?

While calcium supplements have been touted to prevent broken bones in adults, providing them to children may not help prevent fractures as they age, Australian researchers report.

"At two of the areas where we worry about fractures in later life -- the spine and the hip -- the giving of calcium supplements had no effect on bone health in children," said study lead author Dr. Tania Winzenberg, a musculoskeletal epidemiologist at the Menzies Research Institute, in Tasmania.

"It had been thought that calcium supplements would be more helpful than that in children," she said. "So, giving calcium supplements to children has little effect on fractures, and fractures is what we worry about."

In their review, the researchers analyzed data collected from 19 different studies. The studies included nearly 2,900 children between three and 18 years of age, and focused on the benefits of calcium supplementation lasting at least three months. The studies tracked bone outcomes after at least six months of follow-up.

Winzenberg's team found only a small effect of supplementation on total-body bone mineral content and upper arm bone density. Children taking the supplements only had 1.7 percent better bone density in their upper arms compared to kids not taking the supplements.

The team also found no effect on the rate of fractures seen later in life among people given calcium supplements as children. This was particularly true for common fracture sites, such as the hip and lumbar spine.

Based on the findings, Winzenberg's group recommends other approaches to improving kids' bone health, especially increasing vitamin D intake and eating more fruit and vegetables. Vitamin D is sourced mainly from exposure to sunlight, and is essential to the intestinal absorption of calcium.

The findings don't apply to children who may have significant problems with their bones or who can't eat dairy products, Winzenberg said. For healthy children, calcium remains an important part of the diet, she noted.

One expert agreed that calcium supplementation probably doesn't benefit healthy children.

"Healthy children, with an adequate diet, may have all the calcium they need to build bone," said Dr. David L. Katz, an associate professor of public health and director of the Prevention Research Center at Yale University School of Medicine. "Growing bone might need a combination of materials, such as calcium combined with vitamin D, to grow stronger," he said.

This study does not exclude a possible benefit of calcium supplementation for children with low intake of dietary calcium, or children with certain health problems, Katz said.

"But it does indicate that calcium supplementation in healthy children is a questionable practice," he said. "For now, the tried-and-true approach to the early prevention of osteoporosis remains a healthful, balanced diet, and plenty of exercise," Katz said.