There's little question that most kids get too little calcium, but a new review of evidence casts doubt on the value of supplements and calcium-fortified foods to build stronger bones.
"The review shows that supplementing the diet with calcium in healthy children has little benefit for bone health," said lead author Tania Winzenberg.
As a result, calcium supplementation should not be pursued as a public health policy for healthy children, the review concludes. But calcium tablets and fortified foods could be valuable for populations of children under-represented in the reviewed studies, Winzenberg said.
"Such foods may have a role in children with medical conditions affecting their bones or their ability to absorb calcium, or in children with very low dietary calcium intake; for example in children who do not consume any dairy products at all," she said.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates research in all aspects of health care. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing trials on a topic.
Winzenberg's team gathered results from 19 studies that added extra calcium to the diets of girls and boys ranging in age from 3 to 18. The calcium boost was delivered in different ways including tablets and by extracting minerals from milk and then adding it to food.
"We found there wasn't much effect at all," said Winzenberg, a family physician and epidemiologist who studies muscle and bone development at the Menzies Research Institute, Australia. "It does challenge what we thought we knew."
In the United States, many packaged foods marketed to children are fortified with calcium, including orange juice, graham crackers and chocolate drinks.
Pediatricians and parents are concerned with calcium intake because they want to ensure that boys and girls achieve peak bone strength in childhood, a time when kids build bone at an accelerated pace.
The link between calcium intake in childhood and osteoporosis risk in adulthood is not clear. But the idea is that the more bone mass a child starts with the more she will end up with later in life, even with the inevitable bone loss that comes with old age.
The Cochrane review gauged the effect of calcium supplementation on bone health by measuring children's bone mineral density and bone mineral content.
The reviewers found few significant increases in bone mass. And none of the build-up was in two bones commonly vulnerable to fracture, the lower spine and the upper end of the thigh bone.
Taking the supplements did increase bone density in the arm slightly, reducing the risk of fracture by at most 0.2 percent a year, and only in the arm did the increase remain after the calcium was stopped, Winzenberg and her colleagues said.
University of Wisconsin Medical School professor Frank R. Greer said the Cochrane review echoes previous calcium supplementation studies in adults. "You can get some short term improvements, but as soon as you stop the supplements it goes right back to where it was," he said.
Greer, who serves on the American Academy of Pediatrics' committee on nutrition, said the questions surrounding supplements are valid, but he said the Cochrane results have little bearing on calcium guidelines from the academy and the federal government.
"Those recommendations are for adequate daily calcium intake, not supplement intake," Greer said.
"In fruits and vegetables and dairy products the calcium is incorporated in the protein. If you absorb the calcium with the protein, you are going to absorb most of the calcium, rather than have it slip through the intestine, and then be excreted," Greer said.
Beginning at age 9, children need about 1,300 milligrams of calcium each day, according to the National Academy of Sciences. But a 1994 survey from the U.S. Department of Agriculture found that children typically get less than 1,000 mg a day, and the average calcium deficiency in girls is even greater.
Greer said genetics matters most in determining whether a child achieves peak bone mass. But scientists are beginning to study other factors -- weight-bearing exercise, fruit and vegetable consumption, even vitamin D intake -- to learn more about their effect on bone strength.
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