1. We studied the effect of mineral supplementation and its duration is osteoporosis by analysing the calcium and phosphorus balances of 49 treated osteoporotic patients whose median length of calcium treatment was 19 weeks with a range of 8 days to over 4 years. Forty-four studies satisfied statistical criteria of reproducibility and included 35 women (10 also receiving oestrogen replacement therapy) and nine men.

2. Mean calcium balance was positive in women taking calcium supplements alone, +1.9 ± 2.5 mmol daily (P < 0.002), and was significantly more positive (P < 0.05) in women also taking oestrogens, +4.2 ± 2.1 mmol daily. Calcium balance was not significantly positive in men.

3. Calcium balance correlated negatively with duration of supplementation, but, significantly, only when duration of supplementation was expressed logarithmically (r = −0.401, P < 0.01) giving the regression equation y = 4.2–1.6 log x, where y = calcium balance in mol/day and x = duration of supplementation in weeks. Theoretical net calcium retention, without allowance for dermal loss, could be calculated by integration.

4. Mean phosphorus balance was significantly positive in both groups of women and in the whole population. Although its correlation with duration of supplementation did not reach statistical significance (P < 0.1), the ratio of the regression slopes for calcium and phosphorus, 1.5:1, corresponded to their molar ratio in bone.

5. These statistics are, we believe, the first to describe an exponential decline in calcium balance during mineral treatment of osteoporosis, but they firmly suggest that such treatment, with or without oestrogen therapy, conveys temporary benefit.

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