Comparison of the effects of calcium loading with calcium citrate or calcium carbonate on bone turnover in postmenopausal women

Effect of Denosumab on Bone Density in Postmenopausal Osteoporosis: A Comparison with and without Calcium Supplementation in Patients on Standard Diets in Korea

The side effects and safety issues tied to calcium supplementation raise questions about its necessity in osteoporosis treatment. We retrospectively evaluated 189 postmenopausal osteoporosis patients treated with denosumab for 12 months. Patients exhibited neither renal dysfunction nor compromised general dietary intake. Patients were divided into three groups as follows: group A, weekly vitamin D 7000 IU; group B, daily vitamin D 1000 IU with elemental calcium 100 mg; and group C, daily vitamin D 1000 IU with elemental calcium 500 mg. All groups showed significant increases in bone density: +6.4 ± 4.7% for the lumbar spine, +2.2 ± 3.5% for the femoral neck, and +2.4 ± 3.8% for the total hip in group A; +7.0 ± 10.9% for the lumbar spine, +2.3 ± 5.2% for the femoral neck, and +2.4 ± 3.8% for the total hip in group B; and + 6.7 ± 8.7% for the lumbar spine, +2.5 ± 8.4% for the femoral neck, and +2.3 ± 4.0% for the total hip in group C. Serum calcium levels increased over time in all three groups with no significant difference. Changes in CTX and P1NP levels did not differ between the groups (all p > 0.05). With regular dietary intake, calcium supplementation levels showed no significant effect on bone density, bone marker changes, or hypocalcemia incidence during denosumab treatment.

Nanoscale mineralization of cell-laden methacrylated gelatin hydrogels using calcium carbonate-calcium citrate core-shell microparticles

Conventional biomaterials developed for bone regeneration fail to fully recapitulate the nanoscale structural organization and complex composition of the native bone microenvironment. Therefore, despite promoting osteogenic differentiation of stem cells, they fall short of providing the structural, biochemical, and mechanical stimuli necessary to drive osteogenesis for bone regeneration and function. To address this, we have recently developed a novel strategy to engineer bone-like tissue using a biomimetic approach to achieve rapid and controlled nanoscale mineralization of a cell-laden matrix in the presence of osteopontin, a non-collagenous protein, and a supersaturated solution of calcium and phosphate medium. Here, we build on this approach to engineer bone regeneration scaffolds comprising methacrylated gelatin (GelMA) hydrogels incorporated with calcium citrate core-shell microparticles as a sustained and reliable source of calcium ions for in situ mineralization. We demonstrate successful biomineralization of GelMA hydrogels by embedded calcium carbonate-calcium citrate core-shell microparticles with the resultant mineral chemistry, structure, and organization reminiscent of that of native bone. The biomimetic mineralization was further shown to promote osteogenic differentiation of encapsulated human mesenchymal stem cells even in the absence of other exogenous osteogenic induction factors. Ultimately, by combining the superior biological response engendered by biomimetic mineralization with the intrinsic tissue engineering advantages offered by GelMA, such as biocompatibility, biodegradability, and printability, we envision that our system offers great potential for bone regeneration efforts.

A novel degradable tricalcium silicate/calcium polyphosphate/polyvinyl alcohol organic-inorganic composite cement for bone filling

In this study, tricalcium silicate (C₃S) calcium/polyphosphate/polyvinyl alcohol organic-inorganic self-setting composites were successfully designed. A variety of tests were conducted to characterize their self-setting properties, mechanical properties, degradation properties, and related biological properties. The composite bone cements showed a short setting time (5.5-37.5 min) with a 5:5-6:4 ratio of C₃S/CPP to maintain a stable compressive strength (28 MPa). In addition, PVA effectively reduced the brittleness of the inorganic phase. Degradation experiments confirmed the sustainable surface degradation of bone cement. A maximum degradation rate of 49% was reached within 56 days, and the structure remained intact without collapse. Culturing MC3T3 cells with bone cement extracts revealed that the composite bone cements had excellent biological properties in vitro. The original extract showed a proliferation promotion effect on cells, whereas most of the other original extracts of degradable bone cements were toxic to the cells. Meanwhile, extracellular matrix mineralization and alkaline phosphatase expression showed remarkable effects on cell differentiation. In addition, a good level of adhesion of cells to the surfaces of materials was observed. Taken together, these results indicate that C₃S/CPP/PVA composite bone cements have great potential in bone defect filling for fast curing.

Citrate Supplementation Restores the Impaired Mineralisation Resulting from the Acidic Microenvironment: An In Vitro Study

Chronic metabolic acidosis leads to bone-remodelling disorders based on excessive mineral matrix resorption and inhibition of bone formation, but also affects the homeostasis of citrate, which is an essential player in maintaining the acid-base balance and in driving the mineralisation process. This study aimed to investigate the impact of acidosis on the osteogenic properties of bone-forming cells and the effects of citrate supplementation in restoring the osteogenic features impaired by the acidic milieu. For this purpose, human mesenchymal stromal cells were cultured in an osteogenic medium and the extracellular matrix mineralisation was analysed at the micro- and nano-level, both in neutral and acidic conditions and after treatment with calcium citrate and potassium citrate. The acidic milieu significantly decreased the citrate release and hindered the organisation of the extracellular matrix, but the citrate supplementation increased collagen production and, particularly calcium citrate, promoted the mineralisation process. Moreover, the positive effect of citrate supplementation was observed also in the physiological microenvironment. This in vitro study proves that the mineral matrix organisation is influenced by citrate availability in the microenvironment surrounding bone-forming cells, thus providing a biological basis for using citrate-based supplements in the management of bone-remodelling disorders related to chronic low-grade acidosis.

Role of Citrate in Pathophysiology and Medical Management of Bone Diseases

Citrate is an intermediate in the “Tricarboxylic Acid Cycle” and is used by all aerobic organisms to produce usable chemical energy. It is a derivative of citric acid, a weak organic acid which can be introduced with diet since it naturally exists in a variety of fruits and vegetables, and can be consumed as a dietary supplement. The close association between this compound and bone was pointed out for the first time by Dickens in 1941, who showed that approximately 90% of the citrate bulk of the human body resides in mineralised tissues. Since then, the number of published articles has increased exponentially, and considerable progress in understanding how citrate is involved in bone metabolism has been made. This review summarises current knowledge regarding the role of citrate in the pathophysiology and medical management of bone disorders.

Calcium citrate: from biochemistry and physiology to clinical applications

Adequate daily calcium intake should normally be achieved by dietary sources. Since low calcium diets are quite common in subjects that do not reach the recommended intake and particularly those at risk of fractures, calcium supplements may become necessary. Different forms of calcium salts are available, but products containing calcium citrate and calcium carbonate complexes are the most frequently used. Although only limited evidence on the efficacy and long-term safety of calcium citrate is available, these supplements may represent a valuable product for the management of different chronic pathological conditions. The aim of this review was to evaluate the current and potential clinical applications of calcium citrate. In particular, we focused on the use of calcium citrate supplementation in subjects with osteoporosis or in bariatric patients. Other pathological conditions that could benefit calcium citrate supplementation may include achloridria, chronic hypoparathyroidism and hypocitraturic subjects with moderate/high risk of nephrolithiasis. Indeed, citrate salts are widely used in the treatment of nephrolithiasis, since they have shown an inhibitory effect on kidney stone formation and recurrence.

The Influence of Different Cholecalciferol Supplementation Regimes on 25(OH) Cholecalciferol, Calcium and Parathyroid Hormone after Bariatric Surgery

Background and objectives: Vitamin D is an essential vitamin that plays a key role in maintaining physiological calcium balance, and is also a pivotal element in the formation of bone structure. Vitamin D deficiency is associated with a wide array of clinical symptoms. Vitamin and mineral deficiencies are quite common prior to and after bariatric surgery, and therefore we have evaluated the effects of two different cholecalciferol supplementation regimes on serum calcium, 25(OH) cholecalciferol, and parathyroid hormone (PTH). Materials and Methods: In this retrospective matched cohort study, two different cholecalciferol supplementation regimes were compared. Group A consisted of 50 patients who had 1000 mg calcium and 800 IU cholecalciferol. In Group B, 50 patients had 1000 mg calcium and 800 IU cholecalciferol with an additional 1 mL liquid cholecalciferol (50,000 IU) monthly. The primary outcome was the effects on blood serum levels of calcium, 25(OH) cholecalciferol, and PTH. Results: In group A and group B, there were significant increases in 25(OH) cholecalciferol, with a higher delta in favor of group B (for all three p < 0.001). A decrease was seen in PTH (p < 0.001), and no differences were measured in calcium levels in both groups. Conclusion: Our study suggests that an additional 1 mL cholecalciferol (50,000 IU) monthly can result in less biochemically 25(OH) cholecalciferol deficient patients after bariatric surgery. No effects were seen on the calcium balance. However, larger randomized clinical trials need to be done to assess the effects on clinical outcomes like bone health and fracture risk.

Vitamin D and Metabolic Supplementation in Orthopedic Trauma

Active assessment and management of hypovitaminosis D among orthopedic patients is low-risk and low-cost while retaining significant potential to improve patient care. Vitamin D has an established role in musculoskeletal development and calcium homeostasis, and vitamin D deficiency is pervasive in orthopedic trauma populations. Clinical guidelines for screening and supplementation for hypovitaminosis D are lacking. Literature on the effects of vitamin K on bone health is limited. Anabolic hormone analogues may have a future role in delayed union or nonunion treatment. Vitamin D deficiency and other endocrine abnormalities should be considered in orthopedic trauma patients presenting with fracture nonunion of uncertain cause.

Comparing the calcium bioavailability from two types of nano-sized enriched milk using in-vivo assay

Calcium bioavailability from two types of enriched (calcium citrate and calcium carbonate) milks homogenized to a nano-sized particle distribution has been studied among 48 female Sprauge-dawley rats. Skim milk powder was enriched with some essential nutrients (Inulin, DHA & EPA, vitamins B6, K1, and D3) as enhancers of calcium bioavailability according to recommended dietary allowances of the West European and North American. Ovariectomized and ovariectomized-osteoporosis rats were used as a menopause and menopause-osteoporosis model, respectively. Although, nano-sized enriched milk powders had the greatest calcium bioavailability among the groups, but bioavailability of nano-sized calcium carbonate-enriched-milk was significantly (P<0.05) better than nano-sized calcium citrate-enriched-milk. Moreover, the trends were similar for bone calcium, strength and morphology. Therefore, based on the current results the calcium carbonate nano-sized enriched milk could be an effective enriched milk powder in ovariectomized-osteoporosis and ovariectomized rats as a model of menopause-osteoporosis and menopause women.

Calcium revisited: part II calcium supplements and their effects

Calcium supplements were tested in pregnancy and lactation, in childhood and adolescence, in pre- and postmenopausal women and in elderly persons with various effects on bone density and fracture incidence. They must be properly chosen and adequately used. In this case, the reported minor negative side-effects do not restrict their use. All these aspects are reviewed here.

Calcium and vitamin D supplementation: state of the art for daily practice

BACKGROUND

Calcium and vitamin D play an essential role in bone metabolism but deficiency and/or inadequate intake are common.

OBJECTIVES

To describe a practical approach based on the literature regarding clinically important aspects of calcium and vitamin D supplementation.

METHODS

A systematic evaluation of relevant literature in Medline was conducted. We included physiological studies, publications on relevant guidelines, meta-analysis, randomized clinical trials, and cohort studies.

RESULTS

An adequate calcium intake and vitamin D supplementation is recommended in most guidelines xon fracture prevention. Daily supplementation with 800 IU is advocated in most guidelines, appears to be safe, and with this approach it is generally not necessary to determine vitamin D levels. There are no data on additional effects of loading doses of vitamin D on fracture or fall prevention. Calcium supplementation should be tailored to the patient's need: usually 500 mg per day is required. The intestinal absorption of calcium citrate is approximately 24% better than that of calcium carbonate independent of intake with meals. Data on difference between calcium absorption with calcium carbonate compared to calcium citrate with simultaneous use of proton pump inhibitors are lacking. Concern has arisen about a possible link between calcium supplementation and an increased risk of myocardial infarction. Probably only well-designed prospective randomized controlled trials will be able to allow definite conclusions on this subject.

CONCLUSION

Daily supplementation with 800 IU vitamin D is a practical and safe strategy without the need for prior determination of vitamin D levels. Calcium supplementation should be tailored to the patient's need based on total daily dietary calcium intake. In most patients 500 mg per day is required to achieve a total intake of 1,200 mg, or in some 1,000 mg per day. More calcium is absorbed from calcium citrate compared to calcium carbonate.

Vitamin D supplementation for prevention of mortality in adults

BACKGROUND

Available evidence on the effects of vitamin D on mortality has been inconclusive. In a recent systematic review, we found evidence that vitamin D3 may decrease mortality in mostly elderly women. The present systematic review updates and reassesses the benefits and harms of vitamin D supplementation used in primary and secondary prophylaxis of mortality.

OBJECTIVES

To assess the beneficial and harmful effects of vitamin D supplementation for prevention of mortality in healthy adults and adults in a stable phase of disease.

SEARCH METHODS

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index-Expanded and Conference Proceedings Citation Index-Science (all up to February 2012). We checked references of included trials and pharmaceutical companies for unidentified relevant trials.

SELECTION CRITERIA

Randomised trials that compared any type of vitamin D in any dose with any duration and route of administration versus placebo or no intervention in adult participants. Participants could have been recruited from the general population or from patients diagnosed with a disease in a stable phase. Vitamin D could have been administered as supplemental vitamin D (vitamin D3 (cholecalciferol) or vitamin D2 (ergocalciferol)) or as an active form of vitamin D (1α-hydroxyvitamin D (alfacalcidol) or 1,25-dihydroxyvitamin D (calcitriol)).

DATA COLLECTION AND ANALYSIS

Six review authors extracted data independently. Random-effects and fixed-effect meta-analyses were conducted. For dichotomous outcomes, we calculated the risk ratios (RRs). To account for trials with zero events, we performed meta-analyses of dichotomous data using risk differences (RDs) and empirical continuity corrections. We used published data and data obtained by contacting trial authors.To minimise the risk of systematic error, we assessed the risk of bias of the included trials. Trial sequential analyses controlled the risk of random errors possibly caused by cumulative meta-analyses.

MAIN RESULTS

We identified 159 randomised clinical trials. Ninety-four trials reported no mortality, and nine trials reported mortality but did not report in which intervention group the mortality occurred. Accordingly, 56 randomised trials with 95,286 participants provided usable data on mortality. The age of participants ranged from 18 to 107 years. Most trials included women older than 70 years. The mean proportion of women was 77%. Forty-eight of the trials randomly assigned 94,491 healthy participants. Of these, four trials included healthy volunteers, nine trials included postmenopausal women and 35 trials included older people living on their own or in institutional care. The remaining eight trials randomly assigned 795 participants with neurological, cardiovascular, respiratory or rheumatoid diseases. Vitamin D was administered for a weighted mean of 4.4 years. More than half of the trials had a low risk of bias. All trials were conducted in high-income countries. Forty-five trials (80%) reported the baseline vitamin D status of participants based on serum 25-hydroxyvitamin D levels. Participants in 19 trials had vitamin D adequacy (at or above 20 ng/mL). Participants in the remaining 26 trials had vitamin D insufficiency (less than 20 ng/mL).Vitamin D decreased mortality in all 56 trials analysed together (5,920/47,472 (12.5%) vs 6,077/47,814 (12.7%); RR 0.97 (95% confidence interval (CI) 0.94 to 0.99); P = 0.02; I(2) = 0%). More than 8% of participants dropped out. 'Worst-best case' and 'best-worst case' scenario analyses demonstrated that vitamin D could be associated with a dramatic increase or decrease in mortality. When different forms of vitamin D were assessed in separate analyses, only vitamin D3 decreased mortality (4,153/37,817 (11.0%) vs 4,340/38,110 (11.4%); RR 0.94 (95% CI 0.91 to 0.98); P = 0.002; I(2) = 0%; 75,927 participants; 38 trials). Vitamin D2, alfacalcidol and calcitriol did not significantly affect mortality. A subgroup analysis of trials at high risk of bias suggested that vitamin D2 may even increase mortality, but this finding could be due to random errors. Trial sequential analysis supported our finding regarding vitamin D3, with the cumulative Z-score breaking the trial sequential monitoring boundary for benefit, corresponding to 150 people treated over five years to prevent one additional death. We did not observe any statistically significant differences in the effect of vitamin D on mortality in subgroup analyses of trials at low risk of bias compared with trials at high risk of bias; of trials using placebo compared with trials using no intervention in the control group; of trials with no risk of industry bias compared with trials with risk of industry bias; of trials assessing primary prevention compared with trials assessing secondary prevention; of trials including participants with vitamin D level below 20 ng/mL at entry compared with trials including participants with vitamin D levels equal to or greater than 20 ng/mL at entry; of trials including ambulatory participants compared with trials including institutionalised participants; of trials using concomitant calcium supplementation compared with trials without calcium; of trials using a dose below 800 IU per day compared with trials using doses above 800 IU per day; and of trials including only women compared with trials including both sexes or only men. Vitamin D3 statistically significantly decreased cancer mortality (RR 0.88 (95% CI 0.78 to 0.98); P = 0.02; I(2) = 0%; 44,492 participants; 4 trials). Vitamin D3 combined with calcium increased the risk of nephrolithiasis (RR 1.17 (95% CI 1.02 to 1.34); P = 0.02; I(2) = 0%; 42,876 participants; 4 trials). Alfacalcidol and calcitriol increased the risk of hypercalcaemia (RR 3.18 (95% CI 1.17 to 8.68); P = 0.02; I(2) = 17%; 710 participants; 3 trials).

AUTHORS' CONCLUSIONS

Vitamin D3 seemed to decrease mortality in elderly people living independently or in institutional care. Vitamin D2, alfacalcidol and calcitriol had no statistically significant beneficial effects on mortality. Vitamin D3 combined with calcium increased nephrolithiasis. Both alfacalcidol and calcitriol increased hypercalcaemia. Because of risks of attrition bias originating from substantial dropout of participants and of outcome reporting bias due to a number of trials not reporting on mortality, as well as a number of other weaknesses in our evidence, further placebo-controlled randomised trials seem warranted.

The role of the gastrointestinal tract in calcium homeostasis and bone remodeling

While skeletal biology was approached in a rather isolated fashion in the past, an increasing understanding of the interplay between extraskeletal organs and bone remodeling has been obtained in recent years. This review will discuss recent advances in the field that have shed light on how the gastrointestinal tract and bone relate to each other. In particular, the importance of the GI tract in maintaining calcium homeostasis and skeletal integrity will be reviewed as impaired gastric acid production represents a major public health problem with possible implications for sufficient calcium absorption. Osteoporosis, the most prevalent bone disease worldwide, is caused not only by intrinsic defects affecting bone cell differentiation and function but also by a large set of extrinsic factors including hormonal disturbances, malnutrition, and iatrogenic drug application. Given the skeletal requirements of calcium, amino acids, and energy for bone turnover and renewal, it is not surprising that the gastrointestinal (GI) tract is of major importance for skeletal integrity.

Effects of extracellular calcium on viability and osteogenic differentiation of bone marrow stromal cells in vitro

Bone marrow stromal cells (BMSCs) have been extensively used for tissue engineering. However, the effect of Ca(2+) on the viability and osteogenic differentiation of BMSCs has yet to be evaluated. To determine the dose-dependent effect of Ca(2+) on viability and osteogenesis of BMSCs in vitro, BMSCs were cultured in calcium-free DMEM medium supplemented with various concentrations of Ca(2+) (0, 1, 2, 3, 4, and 5 mM) from calcium citrate. Cell viability was analyzed by MTT assay and osteogenic differentiation was evaluated by alkaline phosphatase (ALP) assay, Von Kossa staining, and real-time PCR. Ca(2+) stimulated BMSCs viability in a dose-dependent manner. At slightly higher concentrations (4 and 5 mM) in the culture, Ca(2+) significantly inhibited the activity of ALP on days 7 and 14 (P < 0.01 or P < 0.05), significantly suppressed collagen synthesis (P < 0.01 or P < 0.05), and significantly elevated calcium deposition (P < 0.01) and mRNA levels of osteocalcin (P < 0.01 or P < 0.05) and osteopontin (P < 0.01 or P < 0.05). Therefore, elevated concentrations of extracellular calcium may promote cell viability and late-stage osteogenic differentiation, but may suppress early-stage osteogenic differentiation in BMSCs.

Vitamin D dose response is underestimated by Endocrine Society's Clinical Practice Guideline

OBJECTIVE

The recommended daily intakes of vitamin D according to the recent Clinical Practice Guideline (CPG) of the Endocrine Society are three- to fivefold higher than the Institute of Medicine (IOM) report. We speculated that these differences could be explained by different mathematical approaches to the vitamin D dose response.

METHODS

Studies were selected if the daily dose was ≤2000 IU/day, the duration exceeded 3 months, and 25-hydroxyvitamin D (25OHD) concentrations were measured at baseline and post-therapy. The rate constant was estimated according to the CPG approach. The achieved 25OHD result was estimated according to the following: i) the regression equation approach of the IOM; ii) the regression approach of the Vitamin D Supplementation in Older Subjects (ViDOS) study; and iii) the CPG approach using a rate constant of 2.5 (CPG2.5) and a rate constant of 5.0 (CPG5.0). The difference between the expected and the observed 25OHD result was expressed as a percentage of observed and analyzed for significance against a value of 0% for the four groups.

RESULTS

Forty-one studies were analyzed. The mean (95% CI) rate constant was 5.3 (4.4-6.2) nmol/l per 100 IU per day, on average twofold higher than the CPG rate constant. The mean (95% CI) for the difference between the expected and observed expressed as a percentage of observed was as follows: i) IOM, -7 (-16,+2)% (t=1.64, P=0.110); ii) ViDOS, +2 (-8,+12)% (t=0.40, P=0.69); iii) CPG2.5, -21 (-27,-15)% (t=7.2, P<0.0001); and iv) CPG5.0+3 (-4,+10)% (t=0.91, P=0.366).

CONCLUSION

The CPG 'rule of thumb' should be doubled to 5.0 nmol/l (2.0 ng/ml) per 100 IU per day, adopting a more risk-averse position.

Intake of dehydrated nopal (Opuntia ficus indica) improves bone mineral density and calciuria in adult Mexican women

Background

The intake of dehydrated nopal (DN) at a high stage of maturity along with high calcium content could improve bone mineral density (BMD) and calciuria and thus prevent osteoporosis.

Objective

To evaluate the effect of calcium intake from a vegetable source (DN) on BMD and calciuria covering a 2-year period in menopausal and non-menopausal women with low bone mass (LBM).

Methods

The study was quasi-experimental, blinded, and randomized, and included 131 Mexican women aged 35–55. Urinary calcium/creatinine index (CCI) was determined; BMD was analyzed on lumbar spine and total hip regions. Four groups were studied: Control group (CG), women with normocalciuria and a minimum dose of DN; experimental group 1 (EG1), women with hypercalciuria and a minimum dose of DN; experimental group 2 (EG2), women with hypercalciuria, and a maximum dose of DN; and normal group (NG) for reference in BMD.

Results

After the first semester of treatment, calciuria levels in women from both experimental groups returned to normal, remaining constant for the rest of the treatment. The percentage difference in BMD increased in the total hip region in the CG (pre 4.5% and post 2.1%) and EG2 (pre 1.8% and post 2.5%) groups significantly in comparison to NG and EG1, which exhibited a significant decrease in their BMD. BMD increased only for the lumbar region in the EG2 group (premenopausal).

Conclusion

The use of a vegetable calcium source such as nopal improves BMD in women with LBM in the total hip and lumbar spine regions principally in the premenopausal women, maintaining constant and normal calciuria levels.

Enhancement of bone formation with a synthetic matrix containing bone morphogenetic protein-2 by the addition of calcium citrate

PURPOSE

The aim of the study was to test whether calcium citrate combined with rhBMP-2 was able to enhance bone regeneration compared with a matrix containing only rhBMP-2.

METHODS

In each of experimental mice, one cylinder of calcium citrate-rhBMP-2 or rhBMP-2 alone was implanted into the thigh muscle pouches of the mouse. The following two treatment modalities were randomly allocated: (1) empty control with rhBMP-2 alone in a gelatin matrix and (2) a gelatin matrix including both calcium citrate and BMP-2. After several weeks, bone granules were obtained by histological analysis.

RESULTS

Histomorphometric analysis showed the greatest amount of newly formed bone was observed in the group that contained 10.0 mg calcium citrate with 2.0 mg rhBMP-2 (p < 0.05). Quantitative histomorphometry revealed in the calcium citrate-rhBMP-2 group an obvious increase in the fractional area and the average new bone mineral density of newly formed bone at 2, 4 and 6 weeks than in the rhBMP-2 group (p < 0.05). At 2 weeks time-point, the mature cancellous bone had formed in the calcium citrate-rhBMP-2 group.

CONCLUSIONS

From this study, it can be concluded that calcium citrate combined with rhBMP-2 significantly enhances bone regeneration in muscle. This synthetic gelatin matrix containing calcium citrate/gelatin granules fulfils a number of criteria required for an ideal carrier system for rhBMP-2. The calcium ions that calcium citrate releases into the surrounding environment can activate bone formation when used as part of a combination of calcium citrate and BMP-2.

Relevance of the sterilization-induced effects on the properties of different hydroxyapatite nanoparticles and assessment of the osteoblastic cell response

Hydroxyapatite (Hap) is a calcium phosphate with a chemical formula that closely resembles that of the mineral constituents found in hard tissues, thereby explaining its natural biocompatibility and wide biomedical use. Nanostructured Hap materials appear to present a good performance in bone tissue applications because of their ability to mimic the dimensions of bone components. However, bone cell response to individual nanoparticles and/or nanoparticle aggregates lost from these materials is largely unknown and shows great variability. This work addresses the preparation and characterization of two different Hap nanoparticles and their interaction with osteoblastic cells. Hap particles were produced by a wet chemical synthesis (WCS) at 37°C and by hydrothermal synthesis (HS) at 180°C. As the ultimate in vivo applications require a sterilization step, the synthesized particles were characterized 'as prepared' and after sterilization (autoclaving, 120°C, 20 min). WCS and HS particles differ in their morphological (size and shape) and physicochemical properties. The sterilization modified markedly the shape, size and aggregation state of WCS nanoparticles. Both particles were readily internalized by osteoblastic cells by endocytosis, and showed a low intracellular dissolution rate. Concentrations of WCS and HS particles less than 500 μg ml(-1) did not affect cell proliferation, F-actin cytoskeleton organization and apoptosis rate and increased the gene expression of alkaline phosphatase and BMP-2. The two particles presented some differences in the elicited cell response. In conclusion, WCS and HS particles might exhibit an interesting profile for bone tissue applications. Results suggest the relevance of a proper particle characterization, and the interest of an individual nanoparticle targeted research.

Effect of calcium citrate on bone integration in a rabbit femur defect model

OBJECTIVE

To explore effect of calcium citrate on bone integration in a rabbit femur defect model, and to compare the bone formation with different sizes by radiological and histological study.

METHODS

Twenty-four male Japanese white rabbits were randomly divided into three groups (Group A, B, C) in this study. Under anesthesia, defects of four sizes (1.2, 1.5, 2.0 and 2.5 mm) were created in each of the rabbits. Commercially pure calcium citrate powder was placed inside the medullary compartment of the femur (Experimental), while in the contralateral femur (Control) nothing was implanted. The defects were analyzed using radiography and histological analysis by using Imagepro-Plus 6.0 software after animal was sacrificed at 4th(Group A), 6th(Group B) and 8th(Group C) weeks postoperatively. Four samples were analyzed for each size of defect and each healing period.

RESULTS

The histological and the radiologic evaluation were performed after sacrification of all rabbits on postoperative 4th and 6th weeks, It showed significant difference between the experimental group and the control group when these defects were less than or equal to 2.0 mm. No statistical difference was observed when these defects were larger than 2.0 mm at all healing periods except at the 4th week.

CONCLUSIONS

Calcium citrate affects the early periods of bone defects healing mechanism in Japanese white rabbits positively, especially when the defect is not too large. We suggest further studies on calcium citrate to determine the effects of various dosages, administration ways and the experimental time on the bone defects.

Systemic effects of conjugated equine estrogen vaginal cream on bone turnover markers in postmenopausal women

OBJECTIVE

To evaluate the systemic effect of therapy with conjugated equine estrogen (CEE) vaginal cream on bone turnover markers in postmenopausal women.

METHODS

This study was conducted in 40 spontaneously menopausal women aged 40-60 years who complained of vulvovaginal symptoms. Subjects were instructed to self-administer 1 g CEE vaginal cream (CEE 0.625 mg) once daily for 12 weeks (continuous phase), then twice weekly for the next 12 consecutive weeks (intermittent phase). Serum levels of bone turnover markers and estradiol and the vaginal maturation index were evaluated at baseline, 12 and 24 weeks after treatment initiation.

RESULTS

Levels of C-terminal cross-linked telopeptide of type I collagen (CTx) were significantly decreased at 12 weeks and 24 weeks when compared to baseline values (median (range) 0.435 (0.171-0.859) and 0.391 (0.122-0.714) vs. 0.562 (0.250-1.290) ng/ml (p < 0.001 and < 0.001), respectively), but there was no significant difference between the levels at 12 and 24 weeks. Levels of procollagen type I N-terminal propeptide (P1NP) and osteocalcin levels were significantly decreased after 24 weeks when compared to pretreatment levels (mean (standard deviation) 41.74 (11.76) vs. 50.02 (17.71) ng/ml (p = 0.002) for P1NP and 23.91 (7.11) vs. 27.54 (8.67) ng/ml (p < 0.001) for osteocalcin, respectively). Estradiol levels were significantly increased and the vaginal maturation index was significantly improved after 12 and 24 weeks when compared to baseline.

CONCLUSIONS

CEE vaginal cream significantly decreased the bone resorption marker (CTx) in postmenopausal women after completion of the continuous-treatment phase. There was no significant further decrease after the intermittent phase. The effects on the markers of bone formation and bone turnover (P1NP and osteocalcin) were apparent only at 24 weeks. The two treatment phases moderately increased serum estradiol levels and significantly improved the vaginal maturation index.

Magnesium supplementation through seaweed calcium extract rather than synthetic magnesium oxide improves femur bone mineral density and strength in ovariectomized rats

Commercially available seaweed calcium extract can supply high amounts of calcium as well as significant amounts of magnesium and other microminerals. The purpose of this study was to investigate the degree to which the high levels of magnesium in seaweed calcium extract affects the calcium balance and the bone status in ovariectomized rats in comparison to rats supplemented with calcium carbonate and magnesium oxide. A total of 40 Sprague-Dawley female rats (7 weeks) were divided into four groups and bred for 12 weeks: sham-operated group (Sham), ovariectomized group (OVX), ovariectomized with inorganic calcium and magnesium supplementation group (OVX-Mg), and ovariectomized with seaweed calcium and magnesium supplementation group (OVX-SCa). All experimental diets contained 0.5% calcium. The magnesium content in the experimental diet was 0.05% of the diet in the Sham and OVX groups and 0.1% of the diet in the OVX-Mg and OVX-SCa groups. In the calcium balance study, the OVX-Mg and OVX-SCa groups were not significantly different in calcium absorption compared to the OVX group. However, the femoral bone mineral density and strength of the OVX-SCa group were higher than those of the OVX-Mg and OVX groups. Seaweed calcium with magnesium supplementation or magnesium supplementation alone did not affect the serum ALP and CTx levels in ovariectomized rats. In summary, consumption of seaweed calcium extract or inorganic calcium carbonate with magnesium oxide demonstrated the same degree of intestinal calcium absorption, but only the consumption of seaweed calcium extract resulted in increased femoral bone mineral density and strength in ovariectomized rats. Our results suggest that seaweed calcium extract is an effective calcium and magnesium source for improving bone health compared to synthetic calcium and magnesium supplementation.

Effects of calcium-fortified ice cream on markers of bone health

Premenopausal women with low calcium intakes consumed calcium-fortified ice cream daily for 28 days. Bone markers, NTX, CTX and PTH decreased significantly by 7 days, with some evidence of a calcium dose-dependent effect. Bone marker responses were observed within 1 h of consuming ice cream. Body weight remained constant over 28 days.

INTRODUCTION

Dietary calcium is important for lifelong bone health. Milk is a good source of bioavailable calcium, but consumption has declined among young adults. The aims were to determine whether calcium-fortified ice cream, a palatable source of calcium, produces significant, sustainable changes in bone turnover markers and parathyroid hormone (PTH) in premenopausal women with calcium intake below recommended UK levels.

METHODS

Eighty women, ages 20-39 years (calcium intake <750 mg/day) were randomised to consume lower saturated fat/sugar ice cream containing 96, 244, 459 or 676 mg calcium daily for 28 days. Urinary NTX/Cr, serum CTX, PINP, 1,25D and PTH were measured (baseline, days 1, 7 and 28). Acute changes in CTX and PTH were measured over 5 h (n = 29 women).

RESULTS

There were significant mean decreases by 7 days in NTX/Cr, CTX, PTH and 1,25D and increases in PINP (one sample t tests), with a significant dose-dependent effect on CTX analysis of covariance. Only CTX remained suppressed at 28 days. Serum CTX and PTH decreased within 1 h. Body weight did not change significantly between baseline and 28 days.

CONCLUSIONS

Daily consumption of calcium-fortified ice cream by premenopausal women may significantly reduce levels of the bone resorption marker serum CTX, without stimulating weight gain. The ice cream could be incorporated into the diet to replace low-calcium snacks and thus help individuals with habitually low calcium intakes to meet recommended intakes. The 244 mg calcium preparation would provide more than a quarter of the UK daily recommended nutrient intake for premenopausal women.

Vitamin D supplementation for prevention of mortality in adults

BACKGROUND

The available evidence on vitamin D and mortality is inconclusive.

OBJECTIVES

To assess the beneficial and harmful effects of vitamin D for prevention of mortality in adults.

SEARCH STRATEGY

We searched The Cochrane Library, MEDLINE, EMBASE, LILACS, the Science Citation Index Expanded, and Conference Proceedings Citation Index-Science (to January 2011). We scanned bibliographies of relevant publications and asked experts and pharmaceutical companies for additional trials.

SELECTION CRITERIA

We included randomised trials that compared vitamin D at any dose, duration, and route of administration versus placebo or no intervention. Vitamin D could have been administered as supplemental vitamin D (vitamin D(3) (cholecalciferol) or vitamin D(2) (ergocalciferol)) or an active form of vitamin D (1α-hydroxyvitamin D (alfacalcidol) or 1,25-dihydroxyvitamin D (calcitriol)).

DATA COLLECTION AND ANALYSIS

Six authors extracted data independently. Random-effects and fixed-effect model meta-analyses were conducted. For dichotomous outcomes, we calculated the risk ratios (RR). To account for trials with zero events, meta-analyses of dichotomous data were repeated using risk differences (RD) and empirical continuity corrections. Risk of bias was considered in order to minimise risk of systematic errors. Trial sequential analyses were conducted to minimise the risk of random errors.

MAIN RESULTS

Fifty randomised trials with 94,148 participants provided data for the mortality analyses. Most trials included elderly women (older than 70 years). Vitamin D was administered for a median of two years. More than one half of the trials had a low risk of bias. Overall, vitamin D decreased mortality (RR 0.97, 95% confidence interval (CI) 0.94 to 1.00, I(2) = 0%). When the different forms of vitamin D were assessed separately, only vitamin D(3) decreased mortality significantly (RR 0.94, 95% CI 0.91 to 0.98, I(2) = 0%; 74,789 participants, 32 trials) whereas vitamin D(2), alfacalcidol, or calcitriol did not. Trial sequential analysis supported our finding regarding vitamin D(3), corresponding to 161 individuals treated to prevent one additional death. Vitamin D(3) combined with calcium increased the risk of nephrolithiasis (RR 1.17, 95% CI 1.02 to 1.34, I(2) = 0%). Alfacalcidol and calcitriol increased the risk of hypercalcaemia (RR 3.18, 95% CI 1.17 to 8.68, I(2) = 17%). Data on health-related quality of life and health economics were inconclusive.

AUTHORS' CONCLUSIONS

Vitamin D in the form of vitamin D(3) seems to decrease mortality in predominantly elderly women who are mainly in institutions and dependent care. Vitamin D(2), alfacalcidol, and calcitriol had no statistically significant effect on mortality. Vitamin D(3) combined with calcium significantly increased nephrolithiasis. Both alfacalcidol and calcitriol significantly increased hypercalcaemia.

Acute effects of calcium carbonate, calcium citrate and potassium citrate on markers of calcium and bone metabolism in young women

Both K and Ca supplementation may have beneficial effects on bone through separate mechanisms. K in the form of citrate or bicarbonate affects bone by neutralising the acid load caused by a high protein intake or a low intake of alkalising foods, i.e. fruits and vegetables. Ca is known to decrease serum parathyroid hormone (S-PTH) concentration and bone resorption. We compared the effects of calcium carbonate, calcium citrate and potassium citrate on markers of Ca and bone metabolism in young women. Twelve healthy women aged 22-30 years were randomised into four controlled 24 h study sessions, each subject serving as her own control. At the beginning of each session, subjects received a single dose of calcium carbonate, calcium citrate, potassium citrate or a placebo in randomised order. The diet during each session was identical, containing 300 mg Ca. Both the calcium carbonate and calcium citrate supplement contained 1000 mg Ca; the potassium citrate supplement contained 2250 mg K. Markers of Ca and bone metabolism were followed. Potassium citrate decreased the bone resorption marker (N-terminal telopeptide of type I collagen) and increased Ca retention relative to the control session. Both Ca supplements decreased S-PTH concentration. Ca supplements also decreased bone resorption relative to the control session, but this was significant only for calcium carbonate. No differences in bone formation marker (bone-specific alkaline phosphatase) were seen among the study sessions. The results suggest that potassium citrate has a positive effect on the resorption marker despite low Ca intake. Both Ca supplements were absorbed well and decreased S-PTH efficiently.

Comparison of the absorption of calcium carbonate and calcium citrate after Roux-en-Y gastric bypass

INTRODUCTION

Roux-en-Y gastric bypass (RYGB) restricts food intake. Consequently, patients consume less calcium. In addition, food no longer passes through the duodenum, the main site of calcium absorption. Therefore, calcium absorption is significantly impaired. The goal of this study is to compare two common calcium supplements in gastric bypass patients.

METHOD

Nineteen patients were enrolled in a randomized, double-blinded, crossover study comparing the absorption of calcium from calcium carbonate and calcium citrate salts. Serum and urine calcium levels were assessed for peak values (C (max)) and cumulative calcium increment (area under the curve [AUC]). Serum PTH was assessed for minimum values (PTH(min)) and cumulative PTH decrement (AUC). Statistical analysis was performed using a repeated analysis of variance model.

RESULTS

Eighteen subjects completed the study. Calcium citrate resulted in a significantly higher serum C (max) (9.4 + 0.4 mg/dl vs. 9.2 + 0.3 mg/dl, p = 0.02) and serum AUC (55 + 2 mg/dl vs. 54 + 2 mg/dl, p = 0.02). Calcium citrate resulted in a significantly lower PTH(min) (24 + 11 pg/ml vs. 30 + 13 pg/ml, p = 0.01) and a higher AUC (-32 + 51 pg/ml vs. -3 + 56 pg/ml, p = 0.04). There was a non-significant trend for higher urinary AUC in the calcium citrate group (76.13 + 36.39 mg/6 h vs. 66.04 + 40.82, p = 0.17).

CONCLUSION

Calcium citrate has superior bioavailability than calcium carbonate in RYGB patients.

Suppression of parathyroid hormone and bone resorption by calcium carbonate and calcium citrate in postmenopausal women

This study was conducted to compare the suppressive effects of calcium carbonate and calcium citrate on bone resorption in early postmenopause. Calcium citrate is thought to be better absorbed. We therefore tested the hypothesis that calcium as citrate is more effective than calcium as carbonate in suppressing parathyroid hormone (PTH) and C-terminal telopeptide. Twenty-five healthy postmenopausal women were recruited in this double blind crossover study. The subjects were randomly allocated to receive either 1,000 mg of elemental calcium as carbonate or 500 mg of calcium as citrate. They were given the alternate calcium dose 1 week later. Serum measurements of total and ionized calcium, phosphate, PTH, and CrossLaps were repeated 12 hours after each dose. Analysis of variance found no significant difference between measures for the two salts. Tests for equivalence indicated that 500 mg of calcium citrate may be superior to 1,000 mg of calcium carbonate in raising serum total and ionized calcium (P = 0.04 and 0.05, respectively). For all parameters measured, 500 mg of calcium citrate was at least as beneficial as 1,000 mg of calcium carbonate. Calcium citrate is at least as effective as calcium carbonate in suppressing PTH and C-terminal telopeptide cross-links, at half the dose. This may be because calcium as citrate is better absorbed than calcium as carbonate. If calcium citrate can be used in lower doses, it may be better tolerated than calcium carbonate.

Effect of dolomite oral exposure in Wistar rats during organogenesis period of pregnancy

The potential of oral exposure to dolomite, a natural product that contains calcium and magnesium, to initiate teratogenesis was analyzed in Wistar rats. Animals received dolomite oral dosages of 500 and 1500mg/kg during the period of gestation from day 6-15 post conceptionem (p.c.). Maternal, embryo and fetal toxicity were evaluated. Dolomite exposure did not produce maternal toxicity assessed by clinical observations, body weight gain, hematology parameters and relative organs weight. Signs of embryo-fetal toxicity were not observed. Skeletal malformations and visceral variations were similar in control and dolomite-treated groups. On the other hand, slight increase was observed in fetal body weight in the dolomite-treated group. Treatment with dolomite resulted in significantly decreased incidences of unossified xiphisternum, incomplete ossification of xiphisternum and sternebrae. These effects could be caused by a beneficial influence of calcium and magnesium salts present in dolomite on ossification process. In conclusion, in this study we found that the oral exposure to rats of up to 1500mg/kg of dolomite during organogenesis did not induce significant maternal and embryo-fetal toxicity.

Calcium supplementation and bone mineral accretion in adolescent girls: an 18-mo randomized controlled trial with 2-y follow-up

BACKGROUND

A recent meta-analysis raised doubt as to whether calcium supplementation in children benefits spine and hip bone mineral density (BMD).

OBJECTIVE

We used state-of-the-art measures of bone (fan-beam dual-energy X-ray absorptiometry and 4 bone turnover markers) to determine whether girls with low habitual calcium intake benefited from supplementation with a soluble form of calcium (calcium citrate malate dissolved in a fruit drink).

DESIGN

The trial was an 18-mo randomized trial of calcium supplementation (792 mg/d) with follow-up 2 y after supplement withdrawal. Subjects were 96 girls (mean age: 12 y) with low calcium intakes (mean: 636 mg/d). The main outcome measure was change in total-body, lumbar spine, and total hip bone mineral content (BMC) during supplementation and 2 y after supplement withdrawal. Changes in BMD and bone turnover markers were secondary outcome measures.

RESULTS

The mean additional calcium intake in the supplemented group was 555 mg/d. Compared with the control group, the supplemented group showed significantly (P < 0.05) greater gains in BMC (except at the total hip site) over the 18-mo study. BMD change was significantly (P < 0.05) greater for all skeletal sites, and concentrations of bone resorption markers and parathyroid hormone were significantly (P < 0.01) lower in the supplemented group than in the control group after 18 mo. After 42 mo, gains in BMC and BMD and differences in bone resorption were no longer evident.

CONCLUSIONS

Calcium supplementation enhances bone mineral accrual in teenage girls, but the effect is short-lived. The likely mechanism for the effect of the calcium is suppression of bone turnover, which is reversed upon supplement withdrawal.

Combined calcium and vitamin D supplementation is not superior to calcium supplementation alone in improving disturbed bone metabolism in patients with congestive heart failure

OBJECTIVES

To clarify the potential role of vitamin D supplementation on bone metabolism in congestive heart failure (CHF) patients with low vitamin D status and insufficient dietary calcium intake.

SUBJECTS/METHODS

One hundred and two ambulatory male CHF patients were recruited, of whom the majority was treated with loop diuretics. Nine patients died during follow-up. Additional 14 participants dropped out prematurely because their health status worsened markedly. Five patients had to be excluded due to lack of compliance. A daily vitamin D3 supplement plus 500 mg calcium (CaD group) or a placebo plus 500 mg calcium (Ca group) was given for 9 months. Biochemical parameters of vitamin D and bone metabolism were analyzed at baseline and after 9 months.

RESULTS

Median 25-hydroxyvitamin D concentrations increased from 41.7 to 103.0 nmol/l (P < 0.001) in the CaD group and remained constant in the Ca group, while median calcium intake increased above 1200 mg/day in both groups. The percentage of patients with elevated parathyroid hormone levels (> 60 pg/ml), as well as the serum concentration of undercarboxylated osteocalcin, an indicator of osteoporotic fracture risk and the bone resorption marker C-telopeptide fell significantly in both study groups (P < 0.025-0.001). At the end of the study period, biomarkers of bone turnover did not differ between groups.

CONCLUSIONS

A vitamin D3 supplement of 50 microg/day has no additional beneficial effects on markers of bone metabolism in CHF patients with low initial 25-hydroxyvitamin D concentrations if an adequate daily calcium intake is guaranteed.

A method for evaluating the fluctuations in the intensity of substance transport between blood and bones in the predominant direction

The dynamics of fluctuations in the intensity of the blood-bone flow of substances in the predominant and opposite directions was evaluated using the percent radioactivity difference coefficient and its graphic presentation. The technology of calculating this coefficient is described.

An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans

Human, animal, and in vitro research indicates a beneficial effect of appropriate amounts of omega-3 (n-3) polyunsaturated fatty acids (PUFA) on bone health. This is the first controlled feeding study in humans to evaluate the effect of dietary plant-derived n-3 PUFA on bone turnover, assessed by serum concentrations of N-telopeptides (NTx) and bone-specific alkaline phosphatase (BSAP). Subjects (n = 23) consumed each diet for 6 weeks in a randomized, 3-period crossover design: 1) Average American Diet (AAD; [34% total fat, 13% saturated fatty acids (SFA), 13% monounsaturated fatty acids (MUFA), 9% PUFA (7.7% LA, 0.8% ALA)]), 2) Linoleic Acid Diet (LA; [37% total fat, 9% SFA, 12% MUFA, 16% PUFA (12.6% LA, 3.6% ALA)]), and 3) alpha-Linolenic Acid Diet (ALA; [38% total fat, 8% SFA, 12% MUFA, 17% PUFA (10.5% LA, 6.5% ALA)]). Walnuts and flaxseed oil were the predominant sources of ALA. NTx levels were significantly lower following the ALA diet (13.20 +/- 1.21 nM BCE), relative to the AAD (15.59 +/- 1.21 nM BCE) (p < 0.05). Mean NTx level following the LA diet was 13.80 +/- 1.21 nM BCE. There was no change in levels of BSAP across the three diets. Concentrations of NTx were positively correlated with the pro-inflammatory cytokine TNFalpha for all three diets. The results indicate that plant sources of dietary n-3 PUFA may have a protective effect on bone metabolism via a decrease in bone resorption in the presence of consistent levels of bone formation.

Severe hypercalcemia after transition from calcium carbonate to calcium citrate in an elderly woman treated with ergocalciferol 50,000 IU per day

BACKGROUND

Absorption of calcium carbonate in the fasting state has been reported to be significantly compromised in subjects with achlorhydria. Although calcium carbonate malabsorption in the fasting state cannot be predicted, it might be corrected if the compound is administered with meals. However, administering calcium carbonate with meals is logistically challenging in long-term care facilities.

OBJECTIVE

The aim of this study was to report the case of a woman who was transitioned to calcium citrate and subsequently experienced symptomatic severe hypercalcemia.

METHODS

An 89-year-old female resident of the Wisconsin Veterans Home, a skilled nursing facility in King, Wisconsin, was receiving long-term treatment with ergocalciferol (vitamin D2) 50,000 IU/d. The patient also was receiving calcium carbonate supplements in the morning, and she rarely ate breakfast (fasting state). The patient was transitioned from 2000 mg/d of elemental calcium as carbonate to 1230 mg/d as citrate.

RESULTS

After being switched from calcium carbonate to calcium citrate, the patient developed severe symptomatic hypercalcemia (16.8 mg/dL), the primary cause of which was the administration of an inappropriately high dose of vitamin D.

CONCLUSIONS

We report a case of symptomatic severe hypercalcemia in a skilled nursing facility resident treated with an inappropriately high daily dose of vitamin D. Hypercalcemia manifested when calcium carbonate was replaced with calcium citrate.

Surgical treatment of obesity

The surgical treatment of obesity has existed for over 50 yr. Surgical options have evolved from high-risk procedures infrequently performed, to safe, effective procedures increasingly performed. The operations used today provide significant durable weight loss, resolution or marked improvement of obesity-related comorbidities, and enhanced quality of life for the majority of patients. The effect of bariatric surgery on the neurohormonal regulation of energy homeostasis is not fully understood. Despite its effectiveness, less than 1% of obese patients are treated surgically. The perception that obesity surgery is unsafe remains a deterrent to care.

Potential use of biochemical markers of bone turnover for assessing the effect of calcium supplementation and predicting fracture risk

BACKGROUND

Biochemical markers of bone remodeling have been extensively used (independent of bone mass measurements) to document the efficacy of various anticatabolic and anabolic bone-modifying medications in reducing fracture risk. Nonetheless, their usefulness in determining the effectiveness of osteoporosis prevention and treatment, particularly calcium supplementation, has not been well established.

OBJECTIVE

This article reviews the use of biochemical markers of bone remodeling as a measure of the effect of calcium supplementation and the implications for prediction of fracture risk.

METHODS

A generalized search of MEDLINE from 1966 through April 2004 using the terms osteoporosis, fracture risk, and the specific bone biomarkers of interest was conducted to identify articles relating to these biomarkers and their relationship to prediction of fracture risk. A second MEDLINE search for the same period used the terms calcium, biological markers, and fracture risk to identify studies of calcium supplementation and bone biomarkers. In both cases, the reference lists of identified review articles were searched for additional publications.

RESULTS

: Several biochemical markers of bone remodeling have been shown to be positively correlated with bone mineral density and fracture risk. Furthermore, calcium supplementation has been shown to have a significant correlation with levels of a number of these biomarkers (P < 0.05): the markers of bone formation procollagen type I carboxy and amino terminal peptides and serum bone-specific alkaline phosphatase, and the markers of bone resorption urinary hydroxyproline, urinary pyridinoline, urinary deoxypyridinoline, urinary amino terminal crosslinked telopeptide, and urinary and serum carboxy terminal crosslinked telopeptide.

CONCLUSIONS

Calcium supplementation has a significant effect on a number of biomarkers of bone remodeling, an effect that is, in turn, correlated with decreased fracture risk. Most studies of the efficacy of calcium supplementation in reducing bone remodeling and influencing bone mineral density and fracture risk have involved calcium carbonate, although a few studies have found that other calcium salts may produce similar results.