Daily supplements of calcium may reduce the risk of fractures in a healthy population by 72 per cent, according to results of a randomised placebo-controlled trial.
Emphasising the importance of the supplements, researchers from University Hospital Zurich and Dartmouth Medical School in New Hampshire report that the benefits were no longer observed when supplementation was stopped.
The results are published in this month's American Journal of Clinical Nutrition.
The use of calcium, usually in combination with vitamin D, has long been recommended to reduce the risk of bone fracture for older people, and the use of these supplements is widely accepted by the general public. Calcium is reported to be the biggest seller in the US supplements industry. Annual sales were about $993m (€836m) in 2004, according to the Nutrition Business Journal.
The new study adds to this body of evidence, showing that among the 930 healthy participants in the study, fewer fractures were recorded in the group receiving a daily calcium carbonate supplement, than those receiving placebo.
Heike Bischoff-Ferrari and co-workers recruited the healthy individuals with an average age of 61, and randomly assigned them to receive the calcium supplement (1,200 mg of elemental calcium) or placebo, for four years. After the supplementation period had ended the participants were followed for a further 10.8 years.
Measures of the primary outcomes of all fractures and minimal trauma fractures, showed that people in the calcium group experienced 46 fractures, 15 of which were from minimal trauma, while 54 fractures were documented in the placebo group, 29 of which were from minimal trauma. A minimal trauma fracture is defined as being caused by a falling from a sitting, standing, or walking position and height.
Bischoff-Ferrari and co-workers calculated that calcium supplements reduced the risk of fracture by 72 per cent, but no difference between the groups was observed during the follow-up period when no supplements were consumed.
"Calcium supplementation reduced the risk of all fractures and of minimal trauma fractures among healthy individuals," concluded the researchers. "The benefit appeared to dissipate after treatment was stopped."
The results are at odds with a meta-analysis published last year in the same journal and authored by Bischoff-Ferrari. According to the meta-analysis of 12 prospective cohort studies and nine clinical trials, no statistically significant benefit for 300 mg per day calcium intakes from seven prospective cohort studies involving 170 991 women and with 2954 documented hip fractures, and five prospective cohort studies involving 68 606 men and with 214 documented hip fractures.
Moreover, clinical trials involving supplementation with 800 to 1600 mg per day of calcium did not show any benefits with respect to non-vertebral fractures and hip fracture, compared to placebo.
Commenting independently on the meta-analysis, Jeri Nieves and Robert Lindsay from New York's Columbia University and the Clinical Research Center, Helen Hayes Hospital wrote: "Perhaps these data suggest that calcium supplementation, to be effective, requires the addition of vitamin D supplementation.
"Bone is not just calcium, and calcium does not function in isolation."
Source: American Journal of Clinical Nutrition
June 2008, Volume 87, Number 6, Pages 1945-1951
"Effect of calcium supplementation on fracture risk: a double-blind randomized controlled trial"
Authors: Heike A Bischoff-Ferrari, Judy R Rees, Maria V Grau, Elizabeth Barry, Jiang Gui, and John A Baron