Circulating Calcium Concentrations Research Articles

Serum Calcium Concentrations and Risk of All-Cause and Cause-Specific Mortality: Results From 2 Prospective Cohorts.

Calcium plays a critical role in various physiological activities. However, the association between circulating calcium concentrations and mortality in a general healthy population remains undetermined. To examine the association of serum calcium concentrations with all-cause and cause-specific mortality. Leveraging data from the UK Biobank (n = 361 662) and the US National Health and Nutrition Examination Survey (NHANES, n = 36 985), we prospectively examined the association of serum calcium concentrations with all-cause and cause-specific mortality using Cox proportional hazard and restricted cubic spline models. During a median follow-up of 12.0 years, UK Biobank documented 18 327 deaths, including 3119 (17.0%) from cardiovascular disease (CVD) and 9599 (52.4%) from cancer. We found a U-shaped relationship of albumin-adjusted calcium concentrations with all-cause and CVD mortality. Compared with participants with moderate calcium levels (the third quintile, Q3), those with low and high levels had an increased risk of all-cause (hazard ratio [HR] 1.02 for Q1 vs Q3; 1.10 for Q5 vs Q3) and CVD mortality (HR 1.11 for Q1 vs Q3; 1.25 for Q5 vs Q3). In contrast, there was a linear positive relationship with cancer mortality (HR 1.09 for Q5 vs Q1). Similar results for all-cause, CVD, and cancer mortality were observed in US NHANES. Our findings provide novel insights into the association between serum calcium concentrations and mortality in the general healthy population.

Prediagnostic serum calcium concentrations and risk of colorectal cancer development in 2 large European prospective cohorts

BackgroundHigher dietary calcium consumption is associated with lower colorectal cancer (CRC) risk. However, little data are available on the association between circulating calcium concentrations and CRC risk. ObjectivesTo explore the association between circulating calcium concentrations and CRC risk using data from 2 large European prospective cohort studies. MethodsConditional logistic regression models were used to calculate multivariable-adjusted ORs and 95% CIs in case-control studies nested within the European Prospective Investigation into Cancer and Nutrition (EPIC; n-cases = 947, n-controls = 947) and the UK Biobank (UK-BB; n-cases = 2759, n-controls = 12,021) cohorts. ResultsIn EPIC, nonalbumin-adjusted total serum calcium (a proxy of free calcium) was not associated with CRC (OR: 0.94; 95% CI: 0.85, 1.03; modeled as continuous variable, per 1 mg/dL increase), colon cancer (OR: 0.93; 95% CI: 0.82, 1.05) or rectal cancer (OR: 1.01; 95% CI: 0.84, 1.20) risk in the multivariable adjusted model. In the UK-BB, serum ionized calcium (free calcium, most active form) was inversely associated with the risk of CRC (OR: 0.85; 95% CI: 0.76, 0.95; per 1 mg/dL) and colon cancer (OR: 0.78; 95% CI: 0.68, 0.90), but not rectal cancer (OR: 1.02; 95% CI: 0.83, 1.24) in multivariable adjusted models. Meta-analysis of EPIC and UK-BB CRC risk estimates showed an inverse risk association for CRC in the multivariable adjusted model (OR: 0.90; 95%CI: 0.84, 0.97). In analyses by quintiles, in both cohorts, higher levels of serum calcium were associated with reduced CRC risk (EPIC: ORQ5vs.Q1: 0.69; 95% CI: 0.47, 1.00; P-trend = 0.03; UK-BB: ORQ5vs.Q1: 0.82; 95% CI: 0.72, 0.94; P-trend < 0.01). Analyses by anatomical subsite showed an inverse cancer risk association in the colon (EPIC: ORQ5vs.Q1: 0.63, 95% CI: 0.39, 1.02; P-trend = 0.05; UK-BB: ORQ5vs.Q1: 0.75; 95% CI: 0.64, 0.88; P-trend < 0.01) but not the rectum. ConclusionsIn UK-BB, higher serum ionized calcium levels were inversely associated with CRC, but the risk was restricted to the colon. Total serum calcium showed a null association in EPIC. Additional prospective studies in other populations are needed to better investigate these associations.

Molecular dynamics study of tropical calcific pancreatitis (TCP) associated calcium-sensing receptor single nucleotide variation.

Tropical Calcific Pancreatitis (TCP) is a chronic non-alcoholic pancreatitis characterised by extensive calcification. The disease usually appears at a younger age and is more common in tropical regions. This disease’s progression can lead to pancreatic diabetes, which can subsequently lead to pancreatic cancer. The CASR gene encodes a calcium-sensing receptor (CaSR), which is a GPCR protein of class C. It is expressed in the islets of Langerhans, the parathyroid gland, and other tissues. It primarily detects small gradients in circulating calcium concentrations and couples this information to intracellular signalling, which helps to regulate PTH (parathyroid hormone) secretion and mineral ion homeostasis. From co-leading insulin release, CaSR modulates ductal HCO3− secretion, Ca2+ concentration, cell-cell communication, β-cell proliferation, and intracellular Ca2+ release. In pancreatic cancer, the CaSR limits cell proliferation. TCP-related four novel missense mutations P163R, I427S, D433H and V477A, found in CaSR extracellular domain (ECD) protein, which were reported in the mutTCPdb Database (https://lms.snu.edu.in/mutTCPDB/index.php). P163R mutation occurs in ligand-binding domain 1 (LBD-1) of the CaSR ECD. To investigate the influence of these variations on protein function and structural activity multiple in-silico prediction techniques such as SIFT, PolyPhen, CADD scores, and other methods have been utilized. A 500 ns molecular dynamic simulation was performed on the CaSR ECD crystal structure and the corresponding mutated models. Furthermore, Principal Component Analysis (PCA) and Essential Dynamics analysis were used to forecast collective motions, thermodynamic stabilities, and the critical subspace crucial to CaSR functions. The results of molecular dynamic simulations showed that the mutations P163R, I427S, D433H, and V477A caused conformational changes and decreased the stability of protein structures. This study also demonstrates the significance of TCP associated mutations. As a result of our findings, we hypothesised that the investigated mutations may have an effect on the protein’s structure and ability to interact with other molecules, which may be related to the protein’s functional impairment.

Association of famine exposure and the serum calcium level in healthy Chinese adults.

ObjectiveFamine exposure and higher serum calcium levels are related with increased risk of many disorders, including Alzheimer’s disease, atherosclerosis, diabetes, and osteoporosis. Whether famine exposure has any effect on serum calcium level is unclear. Besides, the normal reference range of serum calcium is variable among different populations. Our aims are 1) determining the reference interval of calcium in Chinese adults; 2) exploring its relationship with famine exposure.MethodsData in this study was from a cross-sectional study of the epidemiologic investigation carried out during March-August 2010 in Jiading district, Shanghai, China. Nine thousand and two hundred eleven participants with estimated glomerular filtration rate (eGFR) ≥60ml/min/1.73m2 were involved to calculate reference interval of total calcium from 10569 participants aged 40 years or older. The analysis of famine exposure was conducted in 9315 participants with complete serum biochemical data and birth year information.ResultsAfter rejecting outliers, the 95% reference interval of total serum calcium was 2.122~2.518 mmol/L. The equation of albumin-adjusted calcium was: Total calcium + 0.019* (49-Albumin), with a 95% reference interval of 2.151~2.500 mmol/L. Compared to the age-balanced control group, there was an increased risk of being at the upper quartile of total serum calcium (OR=1.350, 95%CI=1.199-1.521) and albumin-adjusted calcium (OR=1.381, 95%CI=1.234-1.544) in subjects experienced famine exposure in childhood. Females were more vulnerable to this impact (OR= 1.621, 95%CI= 1.396-1.883 for total serum calcium; OR=1.722, 95%CI= 1.497-1.980 for albumin-adjusted calcium).ConclusionsFamine exposure is an important environmental factor associated with the changes in circulating calcium concentrations, the newly established serum calcium normal range and albumin-adjusted calcium equation, together with the history of childhood famine exposure, might be useful in identifying subjects with abnormal calcium homeostasis and related diseases, especially in females.

Association of Albumin-Corrected Serum Calcium Levels with Colorectal Cancer Survival Outcomes.

In epidemiological studies, higher calcium intake has been associated with decreased colorectal cancer (CRC) incidence. However, whether circulating calcium concentrations are associated with CRC prognosis is largely unknown. In this retrospective cohort analysis, we identified 498 patients diagnosed with stage I–IV CRC between the years of 2000 and 2018 in whom calcium and albumin level measurements within 3 months of diagnosis had been taken. We used the Kaplan–Meier method for survival analysis. We used multivariate Cox proportional hazards regression to identify associations between corrected calcium levels and CRC survival outcomes. Corrected calcium levels in the highest tertile were associated with significantly lower progression-free survival rates (hazard ratio (HR) 1.85; 95% confidence interval (CI) 1.28–2.69; p = 0.001) and overall survival (HR 1.86; 95% CI 1.26–2.74, p = 0.002) in patients with stage IV or recurrent CRC, and significantly lower disease-free survival rates (HR 1.44; 95% confidence interval (CI) 1.02–2.03; p = 0.040) and overall survival rates (HR 1.72; 95% CI 1.18–2.50; p = 0.004) in patients with stage I–III disease. In conclusion, higher corrected calcium levels after the diagnosis of CRC were significantly associated with decreased survival rates. Prospective trials are necessary to confirm this association.

Peripartal treatment with low-dose sertraline accelerates mammary gland involution and has minimal effects on maternal and offspring bone.

Women mobilize up to 10% of their bone mass during lactation to provide milk calcium. About 8%–13% of mothers use selective serotonin reuptake inhibitors (SSRI) to treat peripartum depression, but SSRIs independently decrease bone mass. Previously, peripartal use of the SSRI fluoxetine reduced maternal bone mass sustained post‐weaning and reduced offspring bone length. To determine whether these effects were fluoxetine‐specific or consistent across SSRI compounds, we examined maternal and offspring bone health using the most prescribed SSRI, sertraline. C57BL/6 mice were given 10 mg/kg/day sertraline, from the beginning of pregnancy through the end of lactation. Simultaneously, we treated nulliparous females on the same days as the primiparous groups, resulting in age‐matched nulliparous groups. Dams were euthanized at lactation day 10 (peak lactation, n = 7 vehicle; n = 9 sertraline), lactation day 21 (weaning, n = 9 vehicle; n = 9 sertraline), or 3m post‐weaning (n = 10 vehicle; n = 10 sertraline) for analysis. Offspring were euthanized at peak lactation or weaning for analysis. We determined that peripartum sertraline treatment decreased maternal circulating calcium concentrations across the treatment period, which was also seen in nulliparous treated females. Sertraline reduced the bone formation marker, procollagen 1 intact N‐terminal propeptide, and tended to reduce maternal BV/TV at 3m post‐weaning but did not impact maternal or offspring bone health otherwise. Similarly, sertraline did not reduce nulliparous female bone mass. However, sertraline reduced immunofluorescence staining of the tight junction protein, zona occludens in the mammary gland, and altered alveoli morphology, suggesting sertraline may accelerate mammary gland involution. These findings indicate that peripartum sertraline treatment may be a safer SSRI for maternal and offspring bone rather than fluoxetine.

Short communication: Circulating serotonin is related to the metabolic status and lactational performance at the onset of lactation in dairy cows

Serotonin (5-hydroxytryptamine, 5-HT) affects many physiological functions because it is involved in glucose and lipid metabolism, calcium homeostasis, and regulation of lactation in dairy cows. This study aimed to examine physiological differences in serum 5-HT concentrations (high vs. low) and their association with metabolic status and milk production at the onset of lactation. Twelve multiparous Holstein dairy cows were milked within 4 h of calving, and blood and milk samples were collected at the first 6 subsequent milkings after parturition and at the evening milkings on d 5, 8, 10, and 14. Cows were retrospectively divided into 2 groups (6 cows/group): low serum 5-HT (LSS) and high serum 5-HT (HSS) according to their calculated areas under the curve (AUC) for serum 5-HT for the entire experimental period (cut-off: 46,000 ng/mL × 324 h). Concentrations of 5-HT, free fatty acids (FFA), β-hydroxybutyrate (BHB), glucose, calcium, and IGF-1 were measured in blood. Milk was analyzed for fat, protein, lactose, and 5-HT concentrations. Milk yield was recorded at each milking and energy-corrected milk yield was calculated. Serum 5-HT concentrations were higher in HSS than in LSS [AUC (ng/mL × 324 h): 57,830 ± 4,810 vs. 25,005 ± 5,930]. The amount of energy-corrected milk was lower in HSS than in LSS. The HSS group produced less colostrum and had decreased milk yield, specifically during the first 6 milkings. Concentrations of FFA, BHB, and glucose in plasma did not differ between groups. Concentrations of IGF-1 in serum were elevated in HSS compared with LSS throughout the experiment. Total circulating calcium concentrations in serum tended to be higher in HSS than in LSS. Milk fat and protein yields were decreased in HSS compared with LSS. Milk 5-HT decreased overall during the experimental period, with LSS maintaining higher 5-HT concentrations than HSS until d 14 of lactation. In conclusion, cows with high serum 5-HT concentrations showed a reduced metabolic load at the onset of lactation, concomitantly lower milk yield, and a reduced energy output via milk.

PO-102 Pre-diagnostic serum calcium concentrations and risk of colorectal cancer development in a prospective european cohort

IntroductionHigher intake levels of dietary calcium have been shown to be associated with decreased risk of colorectal cancer (CRC) development in several prospective studies. However, very little information is available on the CRC risk association of circulating calcium concentrations, particularly since elevated serum calcium has been associated in some settings with metabolic dysfunction and diabetes, factors which appear to be related to higher CRC risk.Material and methodsIn order to explore this question, we conducted a case-control study nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort to investigate the association between serum calcium levels and the risk of colorectal cancer (CRC) development. 975 first incident CRC cases were matched to 975 matched controls from within the cohort by sex, age, study centre, length of follow-up and some additional relevant variables. Serum calcium levels were measured using reflection X-ray fluorescence spectrometry on the pre-diagnostically-collected serum samples from cases and matched controls.Conditional logistic regression was used to calculate multivariable-adjusted odds ratios (OR) and 95% confidence intervals (CIs).Results and discussionsHigher levels of serum calcium were associated with reduced risk of CRC (OR Q5vs.Q1=0.69, 95% CI: 0.48–0.99; p trend=0.02). Sub-group analyses by anatomical sub-site suggest that the observed inverse cancer risk association is apparent in the colon (OR Q5vs.Q1=0.61, 95% CI: 0.38–0.98; p trend=0.04) and not in the rectum (OR Q5vs.Q1=0.99, 95% CI: 0.53–1.85; p trend=0.54) where the association appeared to be non-linear. The magnitude of the association in the colon is similar to that observed with dietary calcium at the same anatomical site. Stratified analysis by sex is suggestive of a stronger association for men than women.ConclusionIn conclusion, elevated serum calcium levels are inversely associated with risk of CRC development, with some evidence for heterogeneity by anatomical sub-site and sex. Additional studies are necessary to confirm these findings and to further investigate potential underlying mechanisms for the role of serum calcium in CRC development.

PO-103 Can we eat to prevent colorectal cancer?

IntroductionHigher intake levels of dietary calcium have been shown to be associated with decreased risk of colorectal cancer (CRC) development in several prospective studies. However, very little information is available on the CRC risk association of circulating calcium concentrations, particularly since elevated serum calcium has been associated in some settings with metabolic dysfunction and diabetes, factors which appear to be related to higher CRC risk.Material and methodsIn order to explore this question, we conducted a case-control study nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort to investigate the association between serum calcium levels and the risk of colorectal cancer (CRC) development. 975 first incident CRC cases were matched to 975 matched controls from within the cohort by sex, age, study centre, length of follow-up and some additional relevant variables. Serum calcium levels were measured using reflection X-ray fluorescence spectrometry on the pre-diagnostically-collected serum samples from cases and matched controls.Conditional logistic regression was used to calculate multivariable-adjusted odds ratios (OR) and 95% confidence intervals (CIs).Results and discussionsHigher levels of serum calcium were associated with reduced risk of CRC (OR Q5vs.Q1=0.69, 95% CI: 0.48–0.99; p trend=0.02). Sub-group analyses by anatomical sub-site suggest that the observed inverse cancer risk association is apparent in the colon (OR Q5vs.Q1=0.61, 95% CI: 0.38–0.98; p trend=0.04) and not in the rectum (OR Q5vs.Q1=0.99, 95% CI: 0.53–1.85; p trend=0.54) where the association appeared to be non-linear. The magnitude of the association in the colon is similar to that observed with dietary calcium at the same anatomical site. Stratified analysis by sex is suggestive of a stronger association for men than women.ConclusionIn conclusion, elevated serum calcium levels are inversely associated with risk of CRC development, with some evidence for heterogeneity by anatomical sub-site and sex. Additional studies are necessary to confirm these findings and to further investigate potential underlying mechanisms for the role of serum calcium in CRC development.

Interaction of 5-hydroxy-l-tryptophan and negative dietary cation-anion difference on calcium homeostasis in multiparous peripartum dairy cows

Hypocalcemia affects almost 50% of all dairy cows. Our laboratory has previously demonstrated that infusions of the serotonin precursor 5-hydroxy-l-tryptophan (5-HTP) increase circulating calcium concentrations in the Holstein transition cow. It is unknown whether feeding a negative dietary cation-anion difference (DCAD) diet alters the relationship between 5-HTP and hypocalcemia. The main objective of this study was to determine whether feeding a negative DCAD (-DCAD) diet before calving in conjunction with 5-HTP treatment could further diminish the magnitude of hypocalcemia at the time of calving. We used a randomized complete block design with a 2 × 2 factorial arrangement. Thirty-one multiparous Holstein cows were fed either a positive (+13 mEq/100 g) or negative (-13 mEq/100 g) DCAD diet 21 d before parturition and were intravenously infused daily with saline or 5-HTP (1 mg/kg) starting 7 d before the estimated date of parturition. Cows were blocked by parity and were randomly assigned to 1 of 4 treatment groups: positive DCAD plus saline, positive DCAD plus 5-HTP, negative DCAD plus saline, and negative DCAD plus 5-HTP, resulting in n = 8 per group. Total calcium (tCa), ionized calcium (iCa), and feed intake were recorded. The iCa was elevated prepartum in the -DCAD/5-HTP group compared with the other treatment groups as well as on d 0 and 1 postpartum. Although differences in tCa were not significant across the pre- or postpartum periods, tCa was numerically higher on d 0 and significantly higher on d 1 in -DCAD/5-HTP cows compared with all other groups. Prepartum the -DCAD/5-HTP treatment group ate less than the other treatment groups; however, postpartum dry matter intake differences were not significant. These findings demonstrate that feeding a -DCAD diet in conjunction with 5-HTP prepartum can increase postpartum circulating iCa concentrations and therefore diminish the magnitude of hypocalcemia at the time of parturition.

Circulating calcium concentrations, vascular disease and mortality: a systematic review.

Associations between serum calcium and vascular disease have been reported, but the consistency of these findings is unknown. We conducted a systematic review to determine whether circulating calcium concentrations are associated with risks of cardiovascular disease and death in normocalcaemic populations. We conducted PubMed searches up to 18 December 2014 and scrutinized reference lists of papers. Eligible studies related serum calcium to mortality or cardiovascular events in humans. A follow-up of at least one year was required for longitudinal studies. Studies in populations selected on the basis of renal disease or abnormal serum calcium were excluded. Two investigators performed independent data extraction. The results were tabulated and, where possible, meta-analysed. Five of 11 studies reported a statistically significant positive association between serum calcium and mortality. Meta-analysis of eight of these studies showed a hazard ratio of death of 1.13 (1.09, 1.18) per standard deviation of serum calcium. Eight of 13 studies reported a statistically significant positive association between serum calcium and cardiovascular disease. Meta-analysis of eight studies showed a hazard ratio of cardiovascular disease of 1.08 (1.04, 1.13) per standard deviation of serum calcium. For two studies reporting odds ratios, the pooled odds ratio per standard deviation was 1.22 (1.11, 1.32). When hazard ratios adjusted for cardiovascular risk factors were meta-analysed, the pooled hazard ratio was 1.04 (1.01, 1.08). Other studies demonstrated associations between serum calcium and stroke and between serum calcium and direct measurements of arterial disease and calcification. These observational data indicate that serum calcium is associated with vascular disease and death, but they cannot determine causality.

The role of gastro-intestinal tract in the calcium absorption

Calcium is associated with various functions of clinical importance. Its unique distribution;low intracellular and high extracellular concentration, is crucial for the neuro-muscular function. Calcium is also indispensable for the vascular contraction and blood coagulation. Thus, circulating calcium concentration must be strictly maintained within a narrow range, for which parathyroid hormone(PTH), vitamin D, and calcitonin contribute. Food-derived protein-bound calcium must be first released in the acidic condition. Thus, gastric acid is essential for the effective calcium absorption. Intestinal calcium absorption occurs via both active transport and passive transport. For the former, such molecules as transient receptor potential vanilloid type 6(TRPV6), calbindin 9k, and Ca²⁺-ATPase contribute. In the adult, calcium absorption rate is approximately 30% under the ordinary condition. Lower calcium intake is associated with increased calcium absorption and decreased urinary excretion. In the Dietary Reference Intakes for Japanese, calcium requirement is determined based on factorial method. Recommended Dietary Allowance(RDA)for calcium ranges from 600-800 mg/day for adult. However, the average calcium intake is far lower than Estimated Average Requirement(EAR). Thus, an effort to increase the calcium intake, rather than considering the detailed calcium absorption rate, is most essential in Japan.

Bone Is a Major Target of PTH/PTHrP Receptor Signaling in Regulation of Fetal Blood Calcium Homeostasis.

The blood calcium concentration during fetal life is tightly regulated within a narrow range by highly interactive homeostatic mechanisms that include transport of calcium across the placenta and fluxes in and out of bone; the mechanisms of this regulation are poorly understood. Our findings that endochondral bone-specific PTH/PTHrP receptor (PPR) knockout (KO) mice showed significant reduction of fetal blood calcium concentration compared with that of control littermates at embryonic day 18.5 led us to focus on bone as a possibly major determinant of fetal calcium homeostasis. We found that the fetal calcium concentration of Runx2 KO mice was significantly higher than that of control littermates, suggesting that calcium flux into bone had a considerable influence on the circulating calcium concentration. Moreover, Runx2:PTH double mutant fetuses showed calcium levels similar to those of Runx2 KO mice, suggesting that part of the fetal hypocalcemia in PTH KO mice was caused by the increment of the mineralized bone mass allowed by the formation of osteoblasts. Finally, Rank:PTH double mutant mice had a blood calcium concentration even lower than that of the either Rank KO or PTH KO mice alone at embryonic day 18.5. These observations in our genetic models suggest that PTH/PTHrP receptor signaling in bones has a significant role of the regulation of fetal blood calcium concentration and that both placental transport and osteoclast activation contribute to PTH's hypercalcemic action. They also show that PTH-independent deposition of calcium in bone is the major controller of fetal blood calcium level.

Serotonin regulates calcium homeostasis in lactation by epigenetic activation of hedgehog signaling.

Calcium homeostasis during lactation is critical for maternal and neonatal health. We previously showed that nonneuronal/peripheral serotonin [5-hydroxytryptamine (5-HT)] causes the lactating mammary gland to synthesize and secrete PTHrP in an acute fashion. Here, using a mouse model, we found that genetic inactivation of tryptophan hydroxylase 1 (Tph1), which catalyzes the rate-limiting step in peripheral 5-HT synthesis, reduced circulating and mammary PTHrP expression, osteoclast activity, and maternal circulating calcium concentrations during the transition from pregnancy to lactation. Tph1 inactivation also reduced sonic hedgehog signaling in the mammary gland during lactation. Each of these deficiencies was rescued by daily injections of 5-hydroxy-L-tryptophan (an immediate precursor of 5-HT) to Tph1-deficient dams. We used immortalized mouse embryonic fibroblasts to demonstrate that 5-HT induces PTHrP through a sonic hedgehog-dependent signal transduction mechanism. We also found that 5-HT altered DNA methylation of the Shh gene locus, leading to transcriptional initiation at an alternate start site and formation of a variant transcript in mouse embryonic fibroblasts in vitro and in mammary tissue in vivo. These results support a new paradigm of 5-HT-mediated Shh regulation involving DNA methylation remodeling and promoter switching. In addition to having immediate implications for lactation biology, identification and characterization of a novel functional regulatory relationship between nonneuronal 5-HT, hedgehog signaling, and PTHrP offers new avenues for the study of these important factors in development and disease.

Skeletal and nonskeletal effects of vitamin D: is vitamin D a tonic for bone and other tissues?

The vitamin D endocrine system is critical for the maintenance of circulating calcium concentrations, but recently, there has been advocacy for the widespread use of vitamin D supplements to improve skeletal and nonskeletal health. Recent studies of tissue-selective vitamin D receptor knockout mice indicate that the principal action of vitamin D responsible for the maintenance of calcium homoeostasis is the regulation of intestinal calcium absorption. High levels of vitamin D can increase bone resorption and impair mineralization, consistent with its role in maintaining circulating calcium concentrations. These findings suggest that circumspection is appropriate in its clinical use. There is now substantial clinical trial data with vitamin D supplements, which fails to establish their efficacy on bone density or the prevention of falls or fractures. However, some trials in frail and/or vitamin D-deficient populations have produced positive outcomes. Where there are positive effects of vitamin D supplementation on skeletal outcomes, these are mainly seen in cohorts with baseline circulating 25-hydroxyvitamin D (25(OH)D) levels in the range 25-40 nmol/L or lower. A great diversity of nonskeletal conditions have been associated with low 25(OH)D, but there is little evidence for efficacy of vitamin D supplementation for such end-points. At present, supplements should be advised for populations with risk factors (e.g., lifestyle, skin color, and frailty) for having serum 25(OH)D levels in the 25- to 40-nmol/L range or below. A dose of ≤800 IU/day is adequate. This approach will maintain 25(OH)D levels well above the threshold for osteomalacia and makes allowance for the poor accuracy and precision of some 25(OH)D assays.

Cardiovascular Effects of Calcium Supplements

Calcium supplements reduce bone turnover and slow the rate of bone loss. However, few studies have demonstrated reduced fracture incidence with calcium supplements, and meta-analyses show only a 10% decrease in fractures, which is of borderline statistical and clinical significance. Trials in normal older women and in patients with renal impairment suggest that calcium supplements increase the risk of cardiovascular disease. To further assess their safety, we recently conducted a meta-analysis of trials of calcium supplements, and found a 27%–31% increase in risk of myocardial infarction, and a 12%–20% increase in risk of stroke. These findings are robust because they are based on pre-specified analyses of randomized, placebo-controlled trials and are consistent across the trials. Co-administration of vitamin D with calcium does not lessen these adverse effects. The increased cardiovascular risk with calcium supplements is consistent with epidemiological data relating higher circulating calcium concentrations to cardiovascular disease in normal populations. There are several possible pathophysiological mechanisms for these effects, including effects on vascular calcification, vascular cells, blood coagulation and calcium-sensing receptors. Thus, the non-skeletal risks of calcium supplements appear to outweigh any skeletal benefits, and are they appear to be unnecessary for the efficacy of other osteoporosis treatments.

The Calcium-Sensing Receptor as a Regulator of Cellular Fate in Normal and Pathological Conditions

The calcium-sensing receptor (CaSR) belongs to the evolutionarily conserved family of plasma membrane G protein-coupled receptors (GPCRs). Early studies identified an essential role for the CaSR in systemic calcium homeostasis through its ability to sense small changes in circulating calcium concentration and to couple this information to intracellular signaling pathways that influence parathyroid hormone secretion. However, the presence of CaSR protein in tissues is not directly involved in regulating mineral ion homeostasis points to a role for the CaSR in other cellular functions including the control of cellular proliferation, differentiation and apoptosis. This position at the crossroads of cellular fate designates the CaSR as an interesting study subject is likely to be involved in a variety of previously unconsidered human pathologies, including cancer, atherosclerosis and Alzheimer's disease. Here, we will review the recent discoveries regarding the relevance of CaSR signaling in development and disease. Furthermore, we will discuss the rational for developing and using CaSR-based therapeutics.

The Calcium-Sensing Receptor as a Regulator of Cellular Fate in Normal and Pathological Conditions

The calcium-sensing receptor (CaSR) belongs to the evolutionarily conserved family of plasma membrane G protein-coupled receptors (GPCRs). Early studies identified an essential role for the CaSR in systemic calcium homeostasis through its ability to sense small changes in circulating calcium concentration and to couple this information to intracellular signaling pathways that influence parathyroid hormone secretion. However, the presence of CaSR protein in tissues is not directly involved in regulating mineral ion homeostasis points to a role for the CaSR in other cellular functions including the control of cellular proliferation, differentiation and apoptosis. This position at the crossroads of cellular fate designates the CaSR as an interesting study subject is likely to be involved in a variety of previously unconsidered human pathologies, including cancer, atherosclerosis and Alzheimer’s disease. Here, we will review the recent discoveries regarding the relevance of CaSR signaling in development and disease. Furthermore, we will discuss the rational for developing and using CaSR-based therapeutics. Keywords: Apoptosis, calcium-sensing receptor, differentiation, proliferation, signaling, cancer, parathyroid hormone, G protein-coupled receptor, homeostasis, systemic calcium, calcium resorption, calcitonin, bone resorption, gene expression, inflammation.

Circulating vitamin D, calcium and risk of cerebrovascular disease: a systematic review and meta-analysis

Available literature suggests that both vitamin D and calcium may be associated with a wide range of non-skeletal outcomes. However, epidemiological evidence supporting their individual associations with incident cerebrovascular disease is scarce. We conducted a systematic review and meta-analysis of prospective cohort studies, published before February 2012 and sought from MEDLINE, EMBASE, BIOSIS and the Science Citation Index databases, and reported cerebrovascular disease (defined as any fatal or non-fatal ischemic stroke, hemorrhagic stroke, cerebrovascular accident or transient ischemic attack) by circulating vitamin D (25-hydroxy vitamin D [25(OH)D] as active metabolite) and calcium levels. Two independent investigators abstracted information on 25(OH)D and calcium, cerebrovascular outcomes and other characteristics from selected studies. Relative risks (RRs) were pooled by both random and fixed effects meta-analyses and were further examined under different study-level characteristics. Publication bias was assessed with funnel plots and Egger's asymmetry test. From 5,778 initial references, nine unique prospective cohort studies met our inclusion criteria. Seven studies (involving 47,809 participants and 926 cerebrovascular events) focused on circulating 25(OH)D and 3 reported on circulating calcium (22,577 participants and 727 events). For 25(OH)D, in a comparison of individuals in the top third versus those in the bottom third at baseline, the combined RR for cerebrovascular disease, adjusted for several conventional risk factors, was 0.60 (95% CI 0.48, 0.72). The corresponding RR in the prospective studies that reported on baseline circulating calcium levels for cerebrovascular disease was 1.40 (95% CI 1.19, 1.64). There was no apparent evidence of heterogeneity or publication bias among included studies. Available data indicate that higher circulating level of vitamin D is associated with a decreased risk of cerebrovascular disease. Conversely, higher circulating calcium concentration is associated with an increased risk of cerebrovascular disease.

Cardiovascular effects of calcium supplementation

Trials in normal older women and in patients with renal impairment suggest that calcium supplements increase the risk of cardiovascular disease. To further assess their safety, we recently conducted a meta-analysis of trials of calcium supplements, and found a 27-31% increase in risk of myocardial infarction and a 12-20% increase in risk of stroke. These findings are robust because they are based on pre-specified analyses of randomized, placebo-controlled trials and show consistent risk across the trials. The fact that cardiovascular events were not primary endpoints of any of these studies will introduce noise but not bias into the data. A recent re-analysis of the Women's Health Initiative suggests that co-administration of vitamin D with calcium does not lessen these adverse effects. The increased cardiovascular risk with calcium supplements is consistent with epidemiological data relating higher circulating calcium concentrations to cardiovascular disease in normal populations. There are several possible pathophysiological mechanisms for these effects, including effects on vascular calcification, on the function of vascular cells, and on blood coagulation. Calcium-sensing receptors might mediate some of these effects. Because calcium supplements produce small reductions in fracture risk and a small increase in cardiovascular risk, there may be no net benefit from their use. Food sources of calcium appear to produce similar benefits on bone density, although their effects on fracture are unclear. Since food sources have not been associated with adverse cardiovascular effects, they may be preferable. Available evidence suggests that other osteoporosis treatments are still effective without calcium co-administration.