Dietary supplementation with 1,200 mg/d calcium carbonate didn't prevent fractures in an ambulatory elderly population because compliance was low. Those who took it, however, benefited.  

The findings come from a 5-year, double-blind, placebo-controlled study of almost 1,500 women over the age of 70. The authors found that while calcium supplementation did not significantly reduce fracture risk (hazard ratio 0.87; 95% CI; 0.67–1.12), it was because almost half the women (43%) didn't comply with the treatment regimen. In the 56.8% of women who took at least 80% of their tablets (calcium or placebo), the women who were receiving calcium had a hazard ratio for fracture of 10.2% versus 15.4% in the women receiving placebo (0.66; 95% CI; 0.45–0.97). The calcium-treated patients also had better quantitative ultrasonography findings of the heel, better femoral neck and whole-body dual x-ray absorptiometry data, and better bone strength.  

The only adverse event that was increased in the treated group versus the placebo group was constipation.  

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Dietary supplementation with 1,200 mg/d calcium carbonate didn't prevent fractures in an ambulatory elderly population because compliance was low. Those who took it, however, benefited.