The review, by Tania Winzenberg, MD, and colleagues at Australia's Menzies Research Institute, analyzed data from 19 studies of calcium supplements in children aged 3 to 18 years. The researchers selected only studies that tested calcium supplements against inactive placebo and included measurements of . The time frames of the studies were between 8.5 months and seven years.
Pooled data on all 2,859 children in the studies showed that calcium supplements had very little, if any, effect on children's bone density.
"There is 'gold' level evidence that calcium supplements may not help to build stronger bones in children enough to make a difference in the risk of breaking a bone," Winzenberg and colleagues write. "The results of this review do not support the use of calcium supplements in healthy children."
The findings appear in the current issue of The Cochrane Library. It is published by the Cochrane Collaboration, an international effort to evaluate health care research based on stringent criteria.
The studies of calcium supplements included studies of calcium pills as well as calcium extracted from milk and added to foods.
"We found there wasn't much effect at all," Winzenberg told the Health Behavior News Service. "It does challenge what we thought we knew."
Kids Need Calcium
Kids' bone density is a major factor in how easily they fracture bones. But that's small potatoes compared to the lifelong consequences of too-low bone density. From the time people enter puberty until the time they are young adults, they build up essentially all the bone they ever will have. Low bone density during late childhood predictsin later life.
Childhood fracture rates are up -- a sign that kids aren't building strong enough bones. Calcium is a main ingredient for bone building, notes calcium and osteoporosis expert Robert Heaney, MD, professor of medicine at Creighton University in Omaha.
"You have to have calcium or you can't store it as bone," Heaney tells WebMD. "The human body is born with 25 grams of calcium at birth. We have to build that up by diet. The question is how much is enough to do that."
The Winzenberg analysis found that calcium supplements didn't have an effect, even in kids who were getting too little calcium in their diets. But only three of the studies included in the analysis included kids getting less than 500 milligrams of calcium a day.
"If a child is getting up to 600 milligrams to 800 milligrams of calcium a day, giving more will not help," Heaney says. "So if a child is in that range, I would predict a study would not find any improvement from calcium supplements."
Andrew Shao, PhD, is vice president for scientific and regulatory affairs at the Council for Responsible Nutrition, a supplement-industry trade group. He says that though the Winzenberg group did a thorough analysis of the clinical data, its conclusions are based on giving calcium supplements for a relatively short time.
"One thing that hasn't been done in clinical trials is looking at long-term calcium supplements over the years where peak bone mass is achieved," Shao says. "That is the most critical piece of evidence missing here."
Indeed, Winzenberg and colleagues dothe need for long-term studies of calcium supplements in children in their peak bone-building years.
Getting Calcium Naturally
A major source of calcium is dairy foods. In a written statement, the National Dairy Council tells WebMD it isn't surprised by the study findings.
"Supplements don't measure up to milk and dairy foods when it comes to nutrition," the NDC says. "In addition to being an excellent source of calcium, milk provides vitamin D, potassium, and magnesium, all of which are essential for optimal bone health and human development."
Still, some kids don't get enough of these essential nutrients. Might supplements help? Yes, says Heaney.
"Food sources of calcium have to be preferred overwhelmingly," he says. "But that is not to condemn supplements. Well-formulated supplements will allow you to absorb as much calcium in milk or in calcium-fortified orange juice."