The effect of calcium supplementation on bone loss in 32 controlled trials in postmenopausal women

In 32 controlled trials of calcium supplementation (700-2000 mg) in 3,169 postmenopausal women, mean bone loss in the controls was -1.07% p.a. and in the treated subjects -0.27% p.a. (P for difference < 0.001). The effect was similar at all measured sites and at all doses of 700 mg or more but became weaker after 4 years. We have reviewed 32 trials of calcium supplementation in 3,169 postmenopausal women. We found 24 publications reporting 32 controlled trials lasting at least 1 year, which provided annual percentage changes in bone mass or density at one or more sites in the calcium-treated and control subjects. The median calcium supplement was 1,000 mg, median duration of the trials 2 years and total number of sites measured 79. The average of the mean rates of change in bone mass or density was -1.07% p.a. (P < 0.001) in the controls and -0.27% p.a. (ns) in the treated subjects (P for difference < 0.001). The effect of calcium was much the same at all measured sites (forearm/hand, proximal femur, spine, and total body and others). Supplements of less than 700 mg were not effective, but there was no significant beneficial effect of higher doses. There was significantly faster bone loss at total calcium intakes below 1,150 mg than on intakes over 1,350 mg. The effect of calcium appeared to be lost after 4 years of treatment. Calcium supplementation of about 1,000 mg daily has a significant preventive effect on bone loss in postmenopausal women for at least 4 years.