The study, "Effects of calcium supplementation on bone density in healthy children: meta-analysis of randomized controlled trials", is published in this month's British Medical Journal (doi:10.1136/bmj.38950.561400.55). Researchers from the University of Tasmania's Menzies Research Institute, which carries out epidemiological and population health research, conducted the analysis under the umbrella of osteoporosis prevention.
The findings could bring negative attention to calcium supplements by discrediting their effectiveness in the public eye; however industry advocates are likely to question just how much weight can be given to meta-analyses of studies which may be of varying quality.
Indeed, the researchers themselves highlight several limitations, such as that few of the studies analyzed were conducted on children with low baseline intakes and there were limited numbers of stuidies in purely postpubertal and peribubertal children.
Due to these limitations the review is unlikely to ring an alarm bell for the supplement industry. But dissemination in the media without proper attention to these could detract from sales - as experienced by vitamin E makers following the publication of negative studies at the end of 2004.
Moreover, it comes on the back of negativity caused by the publication earlier this year of the WHI calcium vitamin D study in the New England Journal of Medicine (Vol. 354, pp. 669-683), which reported little fracture risk reduction in a study population where comply with instructions was low.
The Tasmanian study looked at 19 studies involving a total of 2859 children, and calculated a 0.1 percent decrease in absolute risk of all fractures in childhood for girls, and a 0.2 percent decrease for boys. "…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," wrote the study authors led by Tania Winzenberg.
Overall, the study found calcium supplementation had little effect on bone mineral density, except for a small benefit on the upper limb. This represented a 1.7 percentage point increase in bone mineral density - which continued even after supplementation was halted - in the supplement group compared with the control group. The study highlights this increase in density is unlikely to result in signification fracture reduction.
The researchers identified 233 references to potential studies and narrowed them down to 35 references to 19 randomized controlled trials. Of the 2,859 participants aged three to 18, 1367 were randomized to receive calcium supplementation and 1426 to placebo. Sixty-six participants withdrew early from the studies.
The calcium supplementation in the studies ranged between 300 and 1200mg per day from calcium citrate malate, calcium carbonate, calcium phosphate, calcium lactate gluconate, calcium phosphate milk extract or milk minerals. No dairy food supplement studies met the selection criteria.
The study indicated that extending risk calculations for the participants into their adult years is "problematic" in part because the longest follow-up time period of the studies in questions was only seven years.
"Given that calcium accumulation in the skeleton accelerates during puberty, the paucity of data in the peripubertal period is an important gap," the authors noted.
The motivation for finding a public health solution for low bone density is considerable. According to the National Osteoporosis Society (NOS), the combined cost of hospital and social care for patients with hip fractures alone is more than £1.73bn per year in the United Kingdom.
Osteoporosis is a disease resulting in deterioration of bone tissue, increased bone fragility and risk of fracture. NOS says, based on current trends, hip fracture rates in the UK could increase from around 46,000 in 1985 to 117,000 in 2016. Eighty percent of those with the disease arewomen.
Literature surrounding the disease suggests osteoporosis is a preventable disease, avoided through a diet rich in calcium and vitamin D at a young age. For instance, by about age 20, the average woman has attained 98 percent of her skeletal mass and therefore can already have a predisposition towards the disease.