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HOBART, Tasmania -- For children who can't or won't get enough calcium from their diets, supplements seem to be an inadequate substitute, a meta-analysis suggested.
HOBART, Tasmania, Sept. 18 -- For children who can't or won't get enough calcium from their diets, supplements seem to be an inadequate substitute, a meta-analysis suggested.
Calcium supplements temporarily increased kids' total bone mineral density by about 1.7%, but the only lasting effect was in upper-limb bone density, reported Tania Winzenberg, Ph.D., of the Menzies Research Institute here, and colleagues.
"This small increase in upper limb bone mineral density is unlikely to result in a clinically important decrease in the risk of fracture" either during childhood or later in life, Dr. Winzenberg and colleagues reported online in the BMJ.
"Importantly, we found no effects at other sites where fracture is common-namely, the femoral neck and lumbar spine," the Australian team added.
The meta-analysis included 19 studies published from 1992 to 2005 and involving more than 2,800 mostly white and Asian children. Only randomized, placebo-controlled trials of calcium supplements in healthy children that lasted at least three months with at least six months of follow-up were included. Eleven of the studies included only girls, one study included only boys, and the rest were roughly equally divided.
Analysis of the pooled data found that, compared with controls, children who took calcium supplements had slightly greater total bone mineral density (standardized mean difference 0.14; 95% confidence interval 0.01 to 0.27) and upper limb bone mineral density (standardized mean difference 0.14; 95% CI=0.04 to 0.24).
"This effect is about the same as an increase in bone mineral density of 6.38 mg/cm2 or about 1.7 percentage points greater in supplemented groups," the investigators said.
The study found no significant effect of calcium supplements on the density of the femoral neck or lumbar spine.
After the children stopped taking calcium supplements, the greater bone density persisted only in upper-limb bone measurements, not the total bone-density measurements, through follow-up periods that ranged from about a year to eight years.
Subgroup analysis found no evidence that sex, baseline calcium intake, pubertal stage, ethnicity, physical activity level, or how long the children took supplements influenced the effect (data not presented).
Calcium supplement doses in the studies ranged from 300 mg/day to 1,200 mg/day. Types of supplements included calcium citrate malate, calcium carbonate, and calcium phosphate as well as so-called "diary calcium supplements" including milk extract or milk minerals. The study found no differences according to the type of supplement used.
The researchers estimated that the 1.7% increase in upper-limb bone density they found would reduce the relative risk of fractures of the wrist and forearm by about 5%.
"If this were applied to the peak incidence of all fractures in childhood (about 3% a year in 15- to 19-year-old boys and 1% in 10- to 14-year-old girls), the decrease in absolute risk would be at most 0.2% a year in boys and 0.1% a year in girls," the authors said.
"Therefore, while it is possible that the small increase in bone mineral density from calcium supplementation could reduce the risk of fracture in childhood, the public health impact of this is likely to be small," they said.
Nor is the effect likely to translate into significant reduced fracture risk during adulthood, they added.
The current study did not assess the impact of dietary calcium on bone health. Nor did it examine the effect of calcium supplements in children with medical conditions affecting bone metabolism, "so the results can not be extrapolated to children with such conditions," the authors said.
The study emphasizes that when trying to make sure kids get enough calcium, "natural foods are the way to go," said Melvin B. Heyman, M.D., of the University of California San Francisco, who helped write the American Academy of Pediatrics guidelines on bone health and calcium intake.
Less than 40% of those ages six to 19 get the recommended intake of calcium, the academy guidelines say. Children one to three years old should be getting 500 mg/day, those four to eight should be getting 800 mg/day, and those nine to 18 should be getting 1,300 mg/day, according to the guidelines.
Calcium obtained from supplements may have a greater tendency to be blocked from absorption in the intestinal tract by competing minerals or excreted in the urine, according to Dr. Heyman.
Non-dairy sources of calcium include salmon (203 mg/three-ounce serving), broccoli (62 mg/cup), collards (266 mg/cup), baked beans (127 mg/cup), as well as calcium-fortified orange juice (300 mg/cup) and breakfast cereals (100 mg/cup), according to the guidelines.
Calcium supplements should be considered as a last resort "for children and adolescents who cannot or will not consume adequate amounts of calcium from preferred dietary sources," the academy guidelines state.
"Decisions about their use must be made on an individual basis, keeping in mind the usual dietary habits of the person, any individual risk factors for osteoporosis, and the likelihood that the use of the supplement will be maintained," the guidelines advise.