Effect of calcium supplementation on forearm bone mineral content in postmenopausal women: a prospective, sequential controlled trial.

Three hundred ten normal postmenopausal volunteers were invited to enter a controlled trial of the effects of calcium supplementation on forearm mineral content (FMC); 269 entered the study and 210 completed it. Of those who completed the study, 158 were allocated to one of three calcium-supplemented treatment regimes and 52 were allocated to a control group. Twenty-two of the subjects allocated to the treatment group were unable to take supplementary calcium but agreed to remain in the study as additional controls. There were therefore 136 treated subjects, 52 strict controls and 74 controls altogether. During the initial observation period of 9 mo, there was a highly significant loss of bone in all groups (P less than 0.001). During the 9-mo period of treatment, there was a highly significant reduction in the rate of bone loss in the treated subjects (P less than 0.001), a just significant reduction in the strict controls (P less than 0.05) and a nonsignificant reduction in the rate of loss in all controls. The difference between the treated and strict controls in the second period was not significant but the difference between the treated and all controls in the second period was significant (P less than 0.025). When the analysis was applied only to women within 10 yr of menopause, the difference between the treated and strict control groups in period 2 was significant (P less than 0.025) and the difference between the treated and all controls was highly significant (P less than 0.001).