Bone Calcium Balance Research Articles

Moderate consumption of freeze-dried blueberry powder increased net bone calcium retention compared with no treatment in healthy postmenopausal women: a randomized crossover trial

BackgroundPreclinical studies suggest that blueberry consumption is associated with improved bone health. ObjectivesWe conducted a blueberry dose-response study in ovariectomized (OVX)-rats that informed a study in postmenopausal women using the urinary appearance of calcium (Ca) tracers from prelabeled bone to reflect changes in bone balance. We hypothesized that blueberry consumption would reduce bone loss in a dose-dependent manner compared with no treatment. MethodsOVX rats were fed 4 doses of blueberry powder (2.5%, 5%, 10%, and 15%) in randomized order to determine bone 45Ca retention. Fourteen healthy, nonosteoporotic women ≥4 y past menopause were dosed with 50 nCi of 41Ca, a long-lived radioisotope, and equilibrated for 5 mo to allow 41Ca deposition in bone. Following a 6-wk baseline period, participants were assigned to a random sequence of 3 6-wk interventions, a low (17.5 g/d), medium (35 g/d), or high (70 g/d) dose of freeze-dried blueberry powder equivalent to 0.75, 1.5, or 3 cups of fresh blueberries incorporated into food and beverage products. Urinary 41Ca:Ca ratio was measured by accelerator mass spectrometry. Serum bone resorption biomarkers and urinary polyphenols were measured at the end of each control and intervention period. Data were analyzed using a linear mixed model and repeated measures analysis of variance. ResultsIn both OVX rats and postmenopausal women, blueberry interventions benefited net bone calcium balance at lower but not at higher doses. In women, net bone calcium retention increased by 6% with the low (95% CI: 2.50, 8.60; P < 0.01) and 4% with the medium (95% CI: 0.96, 7.90; P < 0.05) dose compared with no treatment. Urinary excretion of hippuric acid increased dose-dependently with blueberry consumption. No significant relationships were found between bone resorption biomarkers, 25-hydroxyvitamin D, and interventions. ConclusionsModerate consumption (<1 cup/d) of blueberries may be an effective strategy to attenuate bone loss in healthy postmenopausal women.This trial was registered at clinicaltrials.gov as NCT02630797.

Natural stable calcium isotope ratios: a new gold standard for bone balance?

Bone calcium balance is the net gain, loss, or equilibrium of calcium moving to and from bone, which reflects bone balance. There are currently no clinically available tools for measuring real-time bone balance. In this issue, Shroff etal. demonstrate the use of natural stable calcium isotope ratios as a novel biomarker of bone balance in children with chronic kidney disease on dialysis that is highly repeatable and associated with radiological and biochemical markers of bone metabolism.

Naturally occurring stable calcium isotope ratios are a novel biomarker of bone calcium balance in chronic kidney disease

Dysregulated calcium homeostasis is common in chronic kidney disease and causally associated with disorders of bone mineralization. However, radiological measures and biomarkers do not allow accurate evaluation of bone calcium balance. Non-radioactive calcium isotopes, 42Ca and 44Ca, are present in our diet and sequestered into body compartments following principles of kinetic isotope fractionation. Isotopically light 42Ca is preferentially incorporated into bone, while heavier 44Ca is excreted. The ratio (44/42Caserum) increases when bone formation exceeds resorption and vice versa, reflecting bone calcium balance. We measured these calcium isotopes by inductively coupled plasma mass-spectrometry in blood, urine and feces of 42 children with chronic kidney disease and 92 receiving dialysis therapy. We compared the isotope ratios with bone biomarkers and determined total bone mineral content by dual-energy x-ray absorptiometry and peripheral quantitative CT expressed as age-adjusted z-scores. The 44/42Caserum ratio positively correlated with serum calcium, 25-hydroxyvitamin D and alkaline phosphatases and inversely with serum parathyroid hormone and other bone resorption markers. The 44/42Caserum ratio positively correlated with age-adjusted z-scores of tibial trabecular bone mineral density and total bone mineral content measured by peripheral quantitative CT, and hip bone mineral density measured by dual-energy X-ray absorptiometry. Significant and independent predictors of total bone mineral content, measured by, were the 44/42Caserum ratio and parathyroid hormone. The44/42Caserum ratio, repeated after four weeks, highly correlated with baseline values. When adjusted for calcium-containing medications and kidney impairment, the 44/42Caserum ratio in patients receiving dialysis was 157% lower than that of age-matched children and 29% lower than levels in elderly women with osteoporosis, implying significantly lower bone mineral content. Thus, calcium isotope ratios may provide a novel, sensitive and non-invasive method of assessing bone calcium balance in chronic kidney disease.

Calcium isotope fractionation by osteoblasts and osteoclasts, across endothelial and epithelial cell barriers, and with binding to proteins.

Timely and accurate diagnosis of osteoporosis is essential for adequate therapy. Calcium isotope ratio (δ44/42Ca) determination has been suggested as a sensitive, noninvasive, and radiation-free biomarker for the diagnosis of osteoporosis, reflecting bone calcium balance. The quantitative diagnostic is based on the calculation of the δ44/42Ca difference between blood, urine, and bone. The underlying cellular processes, however, have not been studied systematically. We quantified calcium transport and δ44/42Ca fractionation during in vitro bone formation and resorption by osteoblasts and osteoclasts and across renal proximal tubular epithelial cells (HK-2), human vein umbilical endothelial cells (HUVECs), and enterocytes (Caco-2) in transwell systems and determined transepithelial electrical resistance characteristics. δ44/42Ca fractionation was furthermore quantified with calcium binding to albumin and collagen. Calcified matrix formed by osteoblasts was isotopically lighter than culture medium by -0.27 ± 0.03‰ within 5 days, while a consistent effect of activated osteoclasts on δ44/42Ca could not be demonstrated. A transient increase in δ44/42Ca in the apical compartment by 0.26‰ occured across HK-2 cells, while δ44/42Ca fractionation was small across the HUVEC barrier and absent with Caco-2 enterocytes, and with binding of calcium to albumin and collagen. In conclusion, δ44/42Ca fractionation follows similar universal principles as during inorganic mineral precipitation; osteoblast activity results in δ44/42Ca fractionation. δ44/42Ca fractionation also occurs across the proximal tubular cell barrier and needs to be considered for in vivo bone mineralization modeling. In contrast, the effect of calcium transport across endothelial and enterocyte barriers on blood δ44/42Ca should be low and is absent with physiochemical binding of calcium to proteins.

Calcium-41: a technology for monitoring changes in bone mineral.

The rare, long-lived radiotracer, 41Ca, measured by accelerator mass spectrometry in the urine or serum following incorporation into the bone provides an ultra-sensitive tool to assess changes in bone calcium balance in response to an intervention. Changes in bone balance can be followed for years with one small dose that is both radiologically and biologically non-invasive. Sequential interventions can be compared, with greater precision than they can with biochemical markers of bone turnover and with greater power than with bone densitometry. This method is especially useful to screen interventions over a period of weeks. The development and validation of this tool and its applications are reviewed. Mini abstract: Use of 41Ca measured in the urine or blood by accelerator mass spectrometry to assess bone balance provides a tool to compare the relative efficacy of multiple interventions. This perspective provides insights in the use of this novel method and comparisons with more traditional methods for evaluating the efficacy of interventions.

Soluble corn fiber increases bone calcium retention in postmenopausal women in a dose-dependent manner: a randomized crossover trial

Background: Dietary soluble corn fiber (SCF) significantly improves calcium absorption in adolescents and the bone strength and architecture in rodent models.Objective: In this study, we aimed to determine the skeletal benefits of SCF in postmenopausal women.Design: We used our novel technology of determining bone calcium retention by following the urinary appearance of 41Ca, a rare long-lived radioisotope, from prelabeled bone to rapidly and sensitively evaluate the effectiveness of SCF in reducing bone loss. A randomized-order, crossover, double-blinded trial was performed in 14 healthy postmenopausal women to compare doses of 0, 10, and 20 g fiber from SCF/d for 50 d.Results: A dose-response effect was shown with 10 and 20 g fiber from SCF/d, whereby bone calcium retention was improved by 4.8% (P < 0.05) and 7% (P < 0.04), respectively. The bone turnover biomarkers N-terminal telopeptide and osteocalcin were not changed by the interventions; however, a significant increase in bone-specific alkaline phosphatase, which is a bone-formation marker, was detected between 0 and 20 g fiber from SCF/d (8%; P = 0.035).Conclusion: Daily SCF consumption significantly increased bone calcium retention in postmenopausal women, which improved the bone calcium balance by an estimated 50 mg/d. This study was registered at clinicaltrials.gov as NCT02416947.

Calcium Accumulation Only during Rapid Growth in Female Rats

AbstractCalcium retention varies with developmental state, which may be partially under the control of insulin-like growth factor 1 (IGF-1). IGF-1 levels can be manipulated through dietary and therapeutic interventions. We investigated the relationship between IGF-1 endogenous production and calcium utilization and bone accretion during growth as well as the effects of IGF-1 treatment on calcium utilization during rapid and slowed growth in intact female Sprague-Dawley rats. In 33 rats killed at 11 time points (n= 3 each) from age 4 to 24 wk, femoral and vertebral bone mass were paralleled by plasma IGF-1 up to 9 wk. Fractional calcium absorption was maximal at 9 wk, reduced by one-half at 12 wk, and there was no further change at 20 wk. From this study, we selected 2 stages of growth, rapid and slow, for a subsequent intervention study. A 4-wk intervention was initiated at 6 or 8 wk when rats (n= 15/group) received either continuous rhIGF-1/IGF binding protein 3 (IGFBP3) infusion (0.3 mg/d) or vehicle (control) by osmotic mini-pumps. In rapidly growing IGF-1/IGFBP3-treated rats compared to controls, but not in slowly growing treated compared to control rats, IGF-1 treatment increased (P< 0.05) calcium absorption (35 vs. 21%), bone calcium balance (0.55 vs. 0.3 mmol/d), and femoral calcium content (31 vs. 24% of dry weight). Exogenous IGF-1/IGFBP3 treatment increased calcium accretion during rapid growth, but rats past rapid growth were no longer as sensitive to this dose of IGF-1/IGFBP3. Thus, interventions designed to improve bone mass through increased IGF-1 will have the greatest impact during rapid growth.

Confusion on the Complexity of Calcium Balance

Calcium balance is an overall assessment of the net calcium taken in minus the net calcium taken out. It can only be assessed when patients are in steady state and requires complicated isotope methods that can simultaneously assess intestinal absorption and endogenous secretion, urinary and stool excretion, bone calcium uptake and removal, and dialysate calcium removal. By virtue of the need for steady state, formal balance studies cannot be accurately carried out in patients on dialysis. However, many of the components of calcium balance have been assessed. Importantly, because 99% of calcium is in bone, studies must accurately assess both the rapidly exchangeable calcium from the bone surface and the net bone calcium balance that results from the difference in bone formation minus resorption. While it is tempting to adjust the dialysate calcium concentration to correct the net positive calcium balance that is likely present in patients who receive calcium-based phosphate binders, the reality is that the highly variable, yet important, role of bone cannot be easily assessed at the bedside. Thus, it is best to prevent the calcium overload in the first place by avoiding high-dose calcium-based phosphate binders and optimizing bone remodeling.

Calcium Metabolism in Health and Disease

This brief review focuses on calcium balance and homeostasis and their relationship to dietary calcium intake and calcium supplementation in healthy subjects and patients with chronic kidney disease and mineral bone disorders (CKD-MBD). Calcium balance refers to the state of the calcium body stores, primarily in bone, which are largely a function of dietary intake, intestinal absorption, renal excretion, and bone remodeling. Bone calcium balance can be positive, neutral, or negative, depending on a number of factors, including growth, aging, and acquired or inherited disorders. Calcium homeostasis refers to the hormonal regulation of serum ionized calcium by parathyroid hormone, 1,25-dihydroxyvitamin D, and serum ionized calcium itself, which together regulate calcium transport at the gut, kidney, and bone. Hypercalcemia and hypocalcemia indicate serious disruption of calcium homeostasis but do not reflect calcium balance on their own. Calcium balance studies have determined the dietary and supplemental calcium requirements needed to optimize bone mass in healthy subjects. However, similar studies are needed in CKD-MBD, which disrupts both calcium balance and homeostasis, because these data in healthy subjects may not be generalizable to this patient group. Importantly, increasing evidence suggests that calcium supplementation may enhance soft tissue calcification and cardiovascular disease in CKD-MBD. Further research is needed to elucidate the risks and mechanisms of soft tissue calcification with calcium supplementation in both healthy subjects and CKD-MBD patients.

Sodium and Bone Health: Impact of Moderately High and Low Salt Intakes on Calcium Metabolism in Postmenopausal Women

High salt intake is a well-recognized risk factor for osteoporosis because it induces calciuria, but the effects of salt on calcium metabolism and the potential impact on bone health in postmenopausal women have not been fully characterized. This study investigated adaptive mechanisms in response to changes in salt and calcium intake in postmenopausal women. Eleven women completed a randomized cross-over trial consisting of four successive 5-wk periods of controlled dietary intervention, each separated by a minimum 4-wk washout. Moderately low and high calcium (518 versus 1284 mg) and salt (3.9 versus 11.2 g) diets, reflecting lower and upper intakes in postmenopausal women consuming a Western-style diet, were provided. Stable isotope labeling techniques were used to measure calcium absorption and excretion, compartmental modeling was undertaken to estimate bone calcium balance, and biomarkers of bone formation and resorption were measured in blood and urine. Moderately high salt intake (11.2 g/d) elicited a significant increase in urinary calcium excretion (p = 0.0008) and significantly affected bone calcium balance with the high calcium diet (p = 0.024). Efficiency of calcium absorption was higher after a period of moderately low calcium intake (p < 0.05) but was unaffected by salt intake. Salt was responsible for a significant change in bone calcium balance, from positive to negative, when consumed as part of a high calcium diet, but with a low calcium intake, the bone calcium balance was negative on both high and low salt diets.

Bone calcium turnover during pregnancy and lactation in women with low calcium diets is associated with calcium intake and circulating insulin-like growth factor 1 concentrations

Few data exist on longitudinal changes in bone calcium turnover rates across pregnancy and lactation. Our aim was to characterize calcium kinetic variables and predictors of these changes across pregnancy and early lactation in women with low calcium intakes. Stable calcium isotopes were administered to 10 Brazilian women during early pregnancy (EP; weeks 10-12 of gestation), late pregnancy (LP; weeks 34-36 of gestation), and early lactation (EL; 7-8 wk postpartum). Multicompartmental modeling was used to assess the rates of bone calcium turnover in relation to calcium intakes and circulating concentrations of parathyroid hormone (PTH), insulin-like growth factor 1, and 1,25-dihydroxyvitamin D. Rates of bone calcium deposition increased significantly from EP to LP (P = 0.001) and were significantly associated with serum PTH during LP (P < or = 0.01). Rates of bone calcium resorption were also higher during LP and EL than during EP (P < or = 0.01) and were associated with both PTH (P < or = 0.01) and IGF-1 (P < or = 0.05) during LP but not during EL. Net balance in bone calcium turnover was positively associated with dietary calcium during EP (P < or = 0.01), LP (P < or = 0.01), and EL (P < or = 0.01). The mean (+/-SD) calcium intake was 463 +/- 182 mg/d and, in combination with insulin-like growth factor 1, explained 68-94% of the variability in net bone calcium balance during pregnancy and lactation. Net deficits in bone calcium balance occurred during pregnancy and lactation. Increased dietary calcium intake was associated with improved calcium balance; therefore, greater calcium intakes may minimize bone loss across pregnancy and lactation in women with habitual intakes of <500 mg calcium/d.

Measurement of 25-Hydroxyvitamin D by the Nichols ADVANTAGE, DiaSorin LIAISON, DiaSorin RIA, and Liquid Chromatography–Tandem Mass Spectrometry

Vitamin D [ergocalciferol (D2) and cholocalciferol (D3)] is 25-hydroxylated by the liver and subsequently hydroxylated by the kidney to form 1,25-vitamin D, the active form of the vitamin. 25-Hydroxyvitamin D (25-OH-vitamin D) and 1,25-dihydroxyvitamin D have important effects on calcium absorption, bone calcium balance, and renal excretion of calcium and phosphorus (1). Assessment of the monohydroxy form of vitamin D is important for identifying insufficient endogenous synthesis disorders that impair gastrointestinal absorption and to identify renal or hepatic abnormalities (2). Here we report on 25-OH-vitamin D as measured by the Nichols ADVANTAGE® 25-OH Vitamin D, DiaSorin LIAISON® 25-OH Vitamin D, DiaSorin 25-OH Vitamin D RIA, …

Calcium supplementation and postmenopausal bone loss.

A series of 103 early postmenopausal women completed a questionnaire about their dietary calcium intake and were then divided into three groups: those with an intake below 550 mg/day, those with an intake between 550 and 1150 mg/day, and those with an intake above 1150 mg/day. Thereafter they were given a daily supplement of 500 mg calcium for two years and had their bone mineral content measured every three months. Any changes found were taken as an estimate of bone calcium balance. All three groups showed a similar fall in bone mineral content over the two years, indicating that a calcium intake of 1000-2000 g daily is ineffective in preventing bone loss in the early menopause.

872 CALCIUM DYNAMICS IN INFANCY

Calcium (Ca) disorders and therapeutic effectiveness can be assessed by measurements of bone dynamics using stable tracer methods. A pulse of IV Ca-46 is followed by a 9-15 day continuous feeding of Ca-48. Ca isotopic abundances in serum, urine, and feces are determined by thermoionization mass spectrometry (0.5% precision). Kinetic parameters (mg/kg/d) are calculated by nonlinear, weighted least squares analysis and growth is compensated for by using expanding pool sizes. Two infants (Inf.) had Ca turnover rates 12 times that of a control adult (Ad); bone Ca deposition (vo+) and resorption (vo-) were determined with 2 to 5% precision. Two infants with osteogenesis imperfecta (OI) were studied before (B) and while taking ascorbic acid (C). Inf show excessive endogenous fecal (vf) to urinary (vu) Ca excretion as compared to adults, suggesting a major role for vf in regulating Ca balance in Inf. An Inf with OI had similar Ca dynamics except for a decrease in bone Ca fluxes. Ascorbic acid, as suggested for clinical use, had no effect on bone calcium balance.

Effects of oestrogen and progestogen therapy on calcium metabolism in post-menopausal women.

The effects of estrogen therapy on calcium metabolism was studied in postmenopausal women. Ethinyl estradiol gradually decreases plasma and urinary calcium and phosphate levels reaching a maximum at about 6 months. This decline is partially reversed by the end of 1 year though values consistently and indefinitely remain lower than control values. Tubular reabsorption of phosphate also shows a similar pattern. Urine calcium levels fall earlier than urine hydroxyproline though bo th appear to remain within the premonpausal range indefinitely. The hyp ophosphatalmic effect of estrogens is in part due to an inhibition of bone resorption but appears primarily due to parathyroid stimulation. The rise in calcium absorption may be explained by the rise in parathyroid hormone. Since the reduction in the rate of new bone formation is not as great as the degree of inhibition of bone resorption the net long-term effect is an enhancement of bone calcium balance. However there is no evidence that estrogens directly stimulate new bone formation. It is not certain to what extent the incidence of forearm fracture spinal osteoporosis and fractured femur of the neck might be reduced by the inhibition of bone resorption nor is it known how estrogens inhibit bone resorption. The comparative doses of estrogen needed to significantly reduce urine calcium excretion at 1 month are 6 mg estriol succinate .025 mg ethinyl estradiol .1 mg estrone sulphate and .65 mg conjugated estrogens. The results indicate that estrogens are capable of inhibiting bone resorption in postmenopausal women for most likely an indefinite period of time.