Meta-analysis of calcium supplementation for the prevention of postmenopausal osteoporosis

Objective: To summarize controlled trials examining the effect of calcium on bone density and fractures in postmenopausal women. Data Source: We searched MEDLINE and EMBASE up to 1998 and the Cochrane Controlled Register up to 2000, and we examined citations of relevant articles and proceedings of international meetings. We contacted osteoporosis investigators to identify additional studies, and primary authors for unpublished data. Study Selection: We included 15 trials (1806 patients) that randomized postmenopausal women to calcium supplementation or usual calcium intake in the diet and reported bone mineral density of the total body, vertebral spine, hip, or forearm, or recorded the number of fractures, and followed patients for at least 1 yr. Data Extraction: For each trial, three independent reviewers assessed the methodological quality and extracted data. Data Synthesis: We found calcium to be more effective than placebo in reducing rates of bone loss after two or more years of treatment. The pooled difference in percentage change from baseline was 2.05% [95% confidence interval (CI) 0.24-3.86] for total body bone density, 1.66% (95% CI 0.92-2.39) for the lumbar spine, 1.64% (95% CI 0.70-2.57) for the hip, and 1.91% (95% CI 0.33-3.50) for the distal radius. The relative risk (RR) of fractures of the vertebrae was 0.77, with a wide CI (95% CI 0.54-1.09); the RR for nonvertebral fractures was 0.86 (95% CI 0.43-1.72). Conclusions: Calcium supplementation alone has a small positive effect on bone density. The data show a trend toward reduction in vertebral fractures, but do not meaningfully address the possible effect of calcium on reducing the incidence of nonvertebral fractures.