Estrogen reduction after menopause causes a small negative calcium balance. Increasing calcium intake, which has been shown to have a positive impact on bone mineral density in postmenopausal women, may reduce this negative balance. It is unclear if the effect size is large enough to reduce the incidence of fractures. To reduce the risk of fractures in the general population, the use of calcium supplementation needs to be addressed through a public health initiative. Prince and colleagues evaluated the use of calcium supplementation in a relatively healthy, vitamin D–sufficient, ambulatory, older population of women. In addition, they assessed the biochemical and structural effects of calcium supplementation.

The study was a longitudinal, double-blind, placebo-controlled trial of women 70 years and older who were selected from a broad-based population in Western Australia. Data on prevalence of fractures caused by minimal trauma; years since menopause; smoking history; and daily intake of protein, calcium, and alcohol were collected at baseline. Bone structure was assessed using dual radiographic absorptiometry of the hip and whole body, quantitative ultrasonography of the heel, and peripheral quantitative computed tomography of the distal radius. Participants were randomized to receive 600 mg of calcium carbonate twice per day or placebo. Incidence fractures, adverse events, and bone measures were recorded throughout the study.

A total of 1,460 women completed the five-year study; of those, 16.2 percent developed osteoporotic fractures. Calcium supplementation did not reduce the risk for these fractures compared with placebo. However, there was a significant reduction in fracture risk in those who were compliant (i.e., those who took 80 percent or more of the calcium tablets). Calcium supplementation did show an improvement in all bone structure measurements compared with placebo at the end of the five years. The only significant adverse event that was higher in the calcium supplement group than the placebo group was the incidence of constipation.

The authors conclude that calcium supplementation in healthy older women is ineffective in preventing osteoporotic fractures because of poor compliance. They add that it is effective in women who are compliant with the regimen.