The April 24, 2006 issue of the Archives of Internal Medicine published a study from Australia that examined the effects of a twice daily supplement of 600 mg. of calcium carbonate on fracture rates and bone density.
This was a 5 year, double blind, placebo-controlled trial of 1660 women older than 70 years of age.
1.Using an intention-to-treat analysis, supplementation did not significantly reduce fracture rate.
2.But, of the 56.8% of the study participants who actually took the calcium, there was a reduced fracture rate ( hazard ratio 0.66) and improved bone density measurements.
So when viewed from a "public health perspective" it was not effective. However, calcium seems to work if you take the pills.
These results are similar to those of the recently published Woman's Health Study which also demonstrated that pills only work when you take them. Unlike the U.S. study this one did not find an increase in kidney stones. The misread and sometimes mis-reported results of the WHS may have lead some to stop their calcium in the belief that calcium supplemention does not help.
It does seem to decrease risk of fracture and it may even reduce the risk of colon polyps.