Calcium requirement—a reappraisal of the methods used in its determination and their application to patients with osteoporosis

Abstract

The accepted practice of calculating the dietary calcium requirement from the relationship between calcium balance and intake was recently criticized on mathematical grounds. To try to determine the appropriate calcium intake in patients with osteoporosis, I examined the relationships between calcium intake, output, and balance in a group of such patients. Calcium-balance studies were performed on 25 patients with untreated osteoporosis: intake (x +/- SEM) was 30.34 +/- 3.02 mmol/d, output was 30.59 +/- 2.69 mmol/d, and calcium balance was -0.25 +/- 0.64 mmol/d. There was a significant correlation between intake and both output and balance (r = 0.98, P < 0.001 and r = 0.61, P < 0.01, respectively). Intake and output became equal at 31.7 (95% CI 27.9, 35.5) mmol/d. This value is the same as that obtained when the conventional method of calculation is used. Furthermore, if random values for calcium output are assigned to the observed values of intake it can be demonstrated that the same values will always be obtained by both methods The only difference is that the calculation based on balance and intake results in a narrower confidence interval.