Measurement Of Calcium Absorption Research Articles

Effects of Calcium Source on Calcium-Metabolic Parameters in Healthy Women and Men

Background/Objectives: Calcium and vitamin D are important for bone health. We compared 24-hour urinary calcium-excretion (Uca/24hrs), during dietary calcium steady-state condition, for different calcium-sources and effects of vitamin D, age and sex. Subjects/Methods: Fifty-two healthy pre- and postmenopausal women and men completed the regimens: placebo, calcium carbonate (400mg) +18μg vitamin D, calcium carbonate (400mg) +38μg vitamin D and 400mg calcium phosphate (milk). Uca/24hrs was measured during dietary calcium steady state as a surrogate measure of calcium-absorption. Serum-calcium, parathyroid hormone (PTH), 25-hydroxy-vitamin D, Procollagen Type 1 N-terminal Pro- Peptide (P1NP) and C-terminal Telopeptide of type 1 collagen (CTX) were measured. Results: Mean daily intake of calcium for the study group ± SD was 1105 ±396 mg. Mean-Uca ± SD: placebo 5.19 ± 2.04 mmol/24hrs, milk 5.88 ± 2.39 mmol/24hrs, (CaCO3+D) 6.19 ± 2.34 mmol/24hrs and (CaCO3 + DD) 6.26 ± 2.32 mmol/day. Uca were higher for all regimens compared to placebo (p <0.001), no difference was found between regimens. CTX was lower during all regimens compared to placebo (p <0.001): placebo 450 ± 243 μg/L, Milk 377 ± 248 μg/L, (CaCO3+D) 392 ± 266 μg/L and (CaCO3+DD) 361 ± 232 μg/L. Conclusions: Uca was higher during supplementation with calcium compared to placebo. Supplementation with calcium reduced bone resorption significantly without effecting PTH. Menopausal status, sex and supplement with vitamin d demonstrated no effect on calcium excretion.

Gastrointestinal calcium absorption and dietary calcium load: relationships with bone remodelling in vertebral osteoporosis.

Patients with vertebral osteoporosis have a wide range of bone loss rates, bone remodelling rates and capacities for gastrointestinal (GI) calcium absorption. To test the hypothesis that variations in GI absorptive capacity determine rates of bone loss or remodelling, we have sought relationships between calcium absorption or vitamin D metabolite levels on the one hand and rates of cancellous and cortical bone loss (measured by serial quantitative computed tomography in the radius; n = 25) or indices of bone remodelling in tetracycline-prelabelled transiliac biopsies (n = 41) on the other, in a sequential untreated group. Calcium absorption (net and true) was measured in 18-day balances and by a two-isotope deconvolution method (fractional absorption and maximum absorption rate, MAR). There was no significant seasonal effect on any of these four measures of calcium absorption (variance ratio, F = 0.52-1.61, p > 0.1) or on 1,25-dihydroxyvitamin D levels (F = 0.13, p > 0.1; range 11-69 pg/ml), notwithstanding the expected seasonal effect on 25-hydroxyvitamin D levels (mean 18.7 ng/ml, zenith mid July, semi-amplitude 7.5 ng/ml; F = 6.82, p < 0.01). Neither this metabolite nor 1,25-dihydroxyvitamin D correlated with any index of calcium absorption (p > 0.1). No measure of calcium absorption (or intake) had a significant relationship with radial cortical or cancellous bone loss (p all > 0.1) but cancellous bone loss was associated with the rate of endogenous calcium excretion (r = 0.50, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Unequal Distribution of a Stable Isotopic Calcium Tracer Between Casein and Whey Fractions of Infant Formulas, Human Milk and Cow's Milk

Measurement of calcium absorption with tracers assumes a complete equilibration of tracer with milk calcium. In this study, the equilibration of tracer between the micellar casein and soluble fractions (primarily whey) of infant formulas, human milk and cow's milk was measured in vitro using milk samples enriched with 42Ca and analyzed by thermal ionization mass spectrometry. Incomplete equilibration of tracer occurred with the micellar casein fraction of all milks. The least equilibration with micellar casein was found with premature infant formula, for which the ratio of slopes of the equilibration lines (whey/casein) was 8.5/1. These differences may be due to Ca-casein binding in cow's milk-based formulas. The effects of the lack of tracer equilibration in vivo cannot be determined. However, unequal bioavailability of casein- vs. whey-bound Ca may exist.

Mineral metabolism in diabetes mellitus: changes accompanying treatment with a portable subcutaneous insulin infusion system.

To define abnormalities that might account for the osteopenia of diabetes we investigated mineral metabolism n i seven juvenile-onset diabetic patients. Each wasstudied before and after normal or near-normal plasma glucose levels had been achievedby 7–14 days of treatment with a portable infusion system delivering insulin scMean basal urinary calcium excretion fell from 0.075 ± 0.06 mg/dl glomerular filtrate (GF) on conventional therapy to 0.023 ± 0.02 mg/dl GF during pump therapy (P < 0.025). Serum phosphorus rose from 4.09 ± 0.09 to 5.01 ± 0.8 mgdl (P < 0.001) due to a rise in the renal tubular threshold for phosphate reabsorption from 3.89 ± 1.2 to 5.49 ± 1.1 mg/dl (P < 0.001). Incremental urinary calcium excretion after a standard oral calcium load (a measure of calcium absorption) did not change significantly. Similarly, there wereno significant changes in the immunoreactive parathyroid hormone concentration (61 ± 25 vs. 63 ± 20 μleq/ml) or in nephrogenous cAMP excretion (1.37 ± 0.7 vs. 1.18 ± 0.6 pm...

The measurement of calcium absorption and absorption rate with an external arm radioactivity counter.

1. A large-volume scintillation counter was used to measure calcium absorption from the ratio of forearm uptake of 47Ca after oral 47CaCl2 (administered with milk) to forearm uptake after intravenously administered 47CaCl2. 2. In some subjects serial measurements of both forearm uptake of 47Ca and blood 47Ca radioactivity were also recorded, and by using deconvolution both total calcium absorption and calcium absorption rate were determined. 3. The forearm ratio determination of 47Ca absorption correlated well with that obtained by deconvolution of either serial blood 47Ca or forearm 47Ca measurements provided that the forearm radioactivity measurements were made at least 8 h after the administration of 47CaCL2. 4. Although the two deconvolution techniques gave similar estimates of total calcium absorption there were discrepancies between their measurements of calcium absorption rate. These discrepancies were reduced but not eliminated by the use of additional lead shielding around the Armac counter.

The measurement of calcium absorption using an oral and intravenous tracer. 2. Clinical studies.

The equations derived to measure the calcium flow rates in the gut and blood have been applied to data gathered from 23 subjects. Each subject was given 5 μCi45Ca by intravenous injection and 20 μCi47Ca orally. The specific activities of plasma, urine and faeces were then measured and the absorption and calcium endogenous flow rates found, using both methods described in a previous publication. The measurements based on the calculations of the faecal occupancies, of the two tracers were found to be more satisfactory than the calculations based on plasma occupancy. The measurements on subjects who had gastric surgery gave some information on the site of calcium absorption.

Measurement of calcium absorption by a double isotope method in patients with disorders of calcium metabolism.

Measurement of calcium absorption by a double isotope method in patients with disorders of calcium metabolism.

47Ca Studies in Adult Coeliac Disease and Other Gastrointestinal Conditions with Particular Reference to Osteomalacia

Harris, O. D., Philip, Helen M., Cooke, W. T. & Pover, W. F. R. 1970. 47Ca Studies in Adult Coeliac Disease and Other Gastrointestinal Conditions with Particular Reference to Osteomalacia. Scand. J. Gastroent. 5, 169-175.Following oral administration of 47Ca the early plasma levels and, using a whole body counter, the 6-day retention of the isotope were studied in 31 patients: 17 with adult coeliac disease and 14 with other gastrointestinal disorders. Osteomalacia was present in 19. Though there was significant correlation between 120-minute plasma levels and 6-day retention of 47Ca, the percentage retention at any given plasma level might range between 40 and 70, which precluded the use of the method as a measure of calcium absorption. No correlation between the percentage retention and the presence or absence of osteomalacia was found.

The measurement of calcium absorption by a double-isotope method

The measurement of calcium absorption by a double-isotope method