OBJECTIVES: To evaluate the validity of a leg-to-leg bioimpedance analysis (BIA) system in predicting body composition as measured by dual-energy X-ray absorptiometry (DXA) in postmenopausal women. SUBJECTS AND METHODS: Body fat mass (FM), %Fat and fat free mass (FFM) were measured in 124 postmenopausal women (age: 51 ± 63 y, body mass index (BMI): 17 ± 38 kgam 2 ) ®rst by the leg-to-leg BIA system, and then by DXA as reference method. Bland-Altman analysis was used to determine the bias and 95% limits of agreement between the two methods for the assessment of the individual. Precision error (CV%) of the BIA system was obtained by repeated measurements with intermediate repositioning.RESULTS: The leg-to-leg BIA system had a high reproducibility with within-day CVs being 0.6% for FFM and 1.1% for FM, and between-day CVs about twice that. The impedance index (Ht 2 aZ) obtained by the leg-to-leg BIA was moderately correlated to FFM measured by DXA (r 0.66). A signi®cant, systematic bias was observed between the two methods. The BIA system overestimated FM by a mean of 3.1 kg, and underestimated FFM by 2.7 kg. The analysis of 95% limits of agreement showed that for most individuals, %Fat estimated by the BIA might differ from that measured by DXA by 12% below to 45% above, indicating the lack of agreement between the two methods for the assessment of the individual. CONCLUSIONS: The leg-to-leg BIA system can provide simple, rapid and highly reproducible measurements of body composition for groups, but it has limited accuracy for the assessment of the individual. Population-speci®c equations will be needed to improve its accuracy in estimating body composition in postmenopausal women.

Synthetic porcine calcitonin (\g=a\-calcitonin) and its methionine-sulphoxide derivative (\g=b\-calcitonin) were given by intravenous infusion to conscious male rats. \g=a\-Calcitonininactivated by performic acid oxidation was used as a control.Microgram doses of \g=a\-calcitonin produced a dose-dependent decrease in the renal excretion of magnesium. The effect was not due to a secondary release of parathyroid hormone since it was also seen in parathyroidectomized animals.A marked increase in the renal excretion of inorganic phosphate, sodium and potassium preceded the change in magnesium excretion in parathyroidectomized rats. It is concluded that the phosphaturia and natriuresis previously described after administration of extracted calcitonin preparations are true effects of the hormone.The effect of \g=b\-calcitonin was indistinguishable from that of \g=a\-calcitonin.

Subcutaneous injection of 300 μmol magnesium raised the serum magnesium to 4.00 mmol/l after 30 min in 150 g male rats and reduced the serum calcium concentration by 0.17 mmol/l after 60 min. Magnesium also acutely diminished the serum concentration of 45Ca given three weeks previously. The administration of magnesium did not reduce the serum concentration of 45Ca and did not increase the rate of disappearance of 45Ca from the serum, when subcutaneous or intravenous labelling took place 180–210 min before the magnesium injection. The magnesium-induced hypocalcaemia therefore cannot be explained by an increased removal of calcium from the circulation. The results are compatible with the hypothesis that the magnesium-induced hypocalcaemia is caused by the release of calcitonin. Injections of 300 μmol magnesium chloride at 12 h intervals for 72 h trebled the 24 h renal excretion of both 40Ca and 45Ca given three weeks previously. The 24 h renal excretion of hydroxyproline was unaltered. Thus there was no indication that the intermittent magnesium injections produced any long-term inhibition of the turnover of bone matrix and bone mineral.

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