A systematic review 1 including 33 studies on premenopausal women and men aged 18 to 50 years was abstracted in DARE. There were 27 cross-sectional studies (3,227 women and 384 men), 2 longitudinal studies (n=396) and 4 intervention studies (n=193). The cross-sectional studies in females showed a significant correlation coefficient (r=0.13, 95% CI 0.09 to 0.16, weighted for sample size). The results for the three cross-sectional studies in men showed a non-significant correlation coefficient (r=0.01, weighted for sample size). The four intervention studies in premenopausal women showed that the percentage of bone loss per year in the calcium-supplemented group was less than that of the control group: the weighted value was 1.32 (95% CI 1.21 to 1.42)
Another systematic review 2 including 9 RCTs with a total of 999 subjects was abstracted in DARE.
The rate of bone loss was significantly less in the first year after randomisation than in the second year. By contrast, the rate of loss in the control group was less in the second year than in the first, although this was not significant. At the spine, femoral neck, trochanter, intertrochanteric, midtibia and upper tibia the effect of calcium in reducing bone loss was statistically significant compared to the control only in the first year after randomisation; there was no difference in rates between groups in the second year.
A third systematic review 3 including 14 studies of calcium supplements (including 4 RCTs with 3638 participants, and 3 non-randomised trials with 141 participants), 18 studies of dietary calcium and hip fracture (no RCTs) and 5 studies of dietary calcium and other fracture sites (no RCTs) in subjects aged 57 - 84 years was abstracted in DARE. For calcium supplements, the 4 RCTs reported risk ratios between 0.3 and 0.7, a reduced fracture risk among women randomised to receive calcium supplements. The 3 non-randomised trials found a lower risk of new vertebral fractures in women given calcium supplements than in untreated women. The observational studies had inconsistent findings. Pooling the results of all 16 studies of dietary calcium gave an OR for hip fracture of 0.96 (95% CI 0.93 to 0.99) per 300 mg/day increase in dietary calcium.
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