- freely available
Nutrients 2013, 5(1), 302-327; doi:10.3390/nu5010302
Published: 22 January 2013
Abstract: Through a systematic search in Pubmed for literature, on links between calcium malnutrition and risk of chronic diseases, we found the highest degree of evidence for osteoporosis, colorectal and breast cancer, as well as for hypertension, as the only major cardiovascular risk factor. Low calcium intake apparently has some impact also on cardiovascular events and disease outcome. Calcium malnutrition can causally be related to low activity of the extracellular calcium-sensing receptor (CaSR). This member of the family of 7-TM G-protein coupled receptors allows extracellular Ca2+ to function as a “first messenger” for various intracellular signaling cascades. Evidence demonstrates that Ca2+/CaSR signaling in functional linkage with vitamin D receptor (VDR)-activated pathways (i) promotes osteoblast differentiation and formation of mineralized bone; (ii) targets downstream effectors of the canonical and non-canonical Wnt pathway to inhibit proliferation and induce differentiation of colorectal cancer cells; (iii) evokes Ca2+ influx into breast cancer cells, thereby activating pro-apoptotic intracellular signaling. Furthermore, Ca2+/CaSR signaling opens Ca2+-sensitive K+ conductance channels in vascular endothelial cells, and also participates in IP3-dependent regulation of cytoplasmic Ca2+, the key intermediate of cardiomyocyte functions. Consequently, impairment of Ca2+/CaSR signaling may contribute to inadequate bone formation, tumor progression, hypertension, vascular calcification and, probably, cardiovascular disease.
Calcium malnutrition can be linked to the pathogenesis of various chronic diseases (for review, [1,2,3,4]). Apart from intestinal dysfunctions causing impaired calcium absorption from the gut lumen, e.g., inflammatory bowel disease or lactase deficiency, today’s inadequate habitual calcium nutrition is the main reason for a low calcium status in millions of people worldwide .
Table 1 provides an update on levels of calcium intake in different population groups, in selected countries, in different geographical regions. As recommended dietary allowances (RDA) according to the 2011 report on Dietary Reference Intakes for Calcium and Vitamin D of the Institute of Medicine (USA) range from 1000 to 1300 mg calcium per day, depending on age and gender . Data in Table 1 suggest that worldwide, many populations are at risk for a nutritional calcium deficit (for details, see ). However, one has to acknowledge that the interpretation of the evidence for calcium malnutrition is not always straightforward because of the great difference between studies with respect to design, methodology, and cohort size. However, the data collated in Table 1 confirm the long-standing assumption that, in many countries, certain population groups, such as the elderly, ingest significantly less calcium than the recommended amount, which is currently 1300 mg per day for this age group . In addition, the extent of nutritional calcium insufficiency in schoolchildren, adolescents, and young women of childbearing age is of serious concern, particularly in South-East Asian countries, although daily calcium requirements in this region may be lower for ethnic reasons (see Section 4.9 in ref. ).
|Table 1. Actual and recommended dietary calcium intake in different population groups of selected countries.|
|Country||Age (years)||RDA a (mg/day)||Calcium intake (mg/day)||Study|
|Austria||19–79||1000–1300||561 (±290) b||576 (±309) b||Kudlacek et al. |
|Belgium||75–80||1300||748 (324–1166) e||676 (287–1101) e||Amorim Cruz et al. |
|Denmark||70–75||1300||544 (127–1812) e||Andersen et al. |
|France||75–80||1300||620 (402–1010) e||635 (428–944) e||Amorim Cruz et al. |
|Germany||18–79||1000–1300||1181 (902–1535) e||1082 (849–1379) e||Hintzpeter et al. |
|Netherlands||75–80||1300||1036 (725–1447) e||1010 (612–1616) e||Amorim Cruz et al. |
|Poland||70–75||1300||325 (86–851) e||Andersen et al. |
|Lebanon||10–16||1300||873 (793–952) d||673 (595–750) d||Salamoun et al. |
|Canada||18–35||1000||562 (0–2630) e||Rubin et al. |
|USA||31–50||1000||1118 (±25) b||864 (±20) b||Bailey et al. |
|USA||>55||1300||611 (381–892) e||Lappe et al. |
|Brazil||16–20||1300||659 (596–721) d||881 (730–1032) d||Peters et al. |
|Bangladesh||16–40||1000||180 c||Islam et al. |
|Indonesia||18–40||1000||270 (239–302) d||Green et al. |
|Malaysia||18–40||1000||386 (353–420) d||Green et al. |
|China||>55||1300||485 (±253) b||Kruger et al. |
|Japan||65–75||1300||527 (±195) b||Nakamura et al. |
|Australia||20–94||1000–1300||643 (±340) b||Pasco et al. |
a RDA, recommended daily allowance according to the 2011 report on Dietary Reference Intakes for Calcium and Vitamin D of the Institute of Medicine, National Academy of Sciences USA ; b mean (±SD); c median (90% CI); d median (95% CI); e mean (range).
2. Calcium Malnutrition and Disease Incidence: Epidemiological Evidence
Over the years, a great number of observational and interventional studies indicated that chronic calcium malnutrition is associated with various diseases and pathologic conditions of unrelated etiology (for review, see [1,2,3,4]). These include osteoporosis and risk of falls and fractures, periodontal disease and age-related tooth loss, several types of cancer, hypertension, and cardiovascular disease. It is therefore not surprising that low calcium intake is associated with a significant increase in all-cause mortality as can be implied from a study by Rejnmark et al. . These authors performed a patient level pooled analysis of eight major vitamin D trials and found a significant (p < 0.01) reduction of mortality when calcium was co-administered with vitamin D, while vitamin D alone had no effect. Furthermore, evidence mainly from animal studies suggests a link between low calcium status and disease incidence for autoimmune diseases such as inflammatory bowel disease and multiple sclerosis [23,24]. Although there is reason to believe that maintenance of adequate serum calcium levels is a prerequisite for normal function of the innate immune system [25,26], a link between a negative calcium balance and a specific infectious or chronic inflammatory disease has not yet been established in humans.
There is ample evidence that, in addition to calcium malnutrition, vitamin D insufficiency is a significant risk factor for a number of chronic diseases. These are in particular osteoporosis and related pathologies, as well as colorectal and breast cancer (for review, see ). Calcium and vitamin D reduce disease risks by activating different molecular and cellular mechanisms. Therefore, for efficient disease prevention, requirements for both calcium and vitamin D must be met. This is important in view of the high prevalence of combined calcium and vitamin D insufficiency worldwide .
2.1. Bone Diseases
2.1.1. Calcium Deficiency and Rickets
Nutritional rickets is not only a sequel of vitamin D deficiency, but can also be caused by deficits in phosphate  or calcium . There is evidence that in Nigeria, South Africa, Northern India, and Bangladesh a form of rickets occurs in older toddlers and children, which is only partially amenable to vitamin D, but can be fully resolved by calcium supplements alone [29,30]. The partial ineffectiveness of vitamin D could be due to the fact that two-thirds of the children with rickets had serum 25-(OH)D concentrations well above the rachitic range . It has been suggested that, in this case, rickets is attributable to low dietary calcium intake, which is characteristic of cereal-based diets with limited variety and little access to dairy products . According to De Lucia et al. , low dietary calcium intake after weaning is another reason for rickets with normal circulating 25-(OH)D, which is occasionally seen in the United States.
2.1.2. Osteoporosis, Falls and Fractures
In 1998, Riggs et al.  had proposed a unitary model for involutional osteoporosis, in which, apart from hormonal imbalances, calcium malnutrition and calcium malabsorption are considered to be of great significance in the development of the disease in both genders. Consequently, nutrient and supplemental calcium has been widely used for the prevention and treatment of osteoporosis (e.g., [33,34,35,36,37,38,39]). A meta-analysis of randomized controlled trials by Boonen et al.  emphasized the need to co-administer calcium with vitamin D to significantly (p < 0.025) reduce the risk of hip fractures. Likewise, a patient level pooled analysis of seven major trials conducted in the USA and Europe, with fractures as endpoint  found that vitamin D alone is not effective in preventing fractures, but that calcium and vitamin D together significantly (p < 0.025) reduce the rate of total fractures, including hip and probably vertebral fractures as well. Tang and colleagues  provided further evidence that in people aged 50 years or older, daily doses of 1200 mg calcium in combination with 800 IU vitamin D have the best therapeutic effect to prevent fractures and osteoporotic bone loss. It is interesting to note that adult, though not elderly, African Americans experience less fragility fractures despite lower serum 25-(OH)D concentrations than whites in the same age range. Aloia  suggested that this seeming paradox can be explained by, among others, differences between African Americans and other populations in “calcium economy”. In other words, increased calcium absorption and superior calcium conservation might compensate, in African Americans, for the negative effect of vitamin D insufficiency on bone health.
A lower incidence of fractures could be partially due to the positive effect of calcium and vitamin D supplementation on neuro-musculoskeletal functions  leading to a reduction in the number of falls in the elderly . Taken together, calcium in combination with vitamin D is the “gold standard” for treating older persons with decreased bone mineral density, increased propensity to falls, and osteoporotic fractures (for review, see ).
There is evidence that poor calcium nutrition is a significant risk factor for total cancer incidence , and, in particular, for colorectal and breast cancer. Low calcium intake may contribute to the development of renal, gastric, pancreatic, ovarian, endometrial, and lung cancer as well as multiple myeloma, though conclusive evidence is missing (for review, see ).
2.2.1. Colorectal Cancer
Already in 1985, Garland et al.  had reported results of a 19 year prospective trial, which allowed the identification of low dietary calcium as an independent risk factor for colon cancer. Additional findings by Garland et al.  on an inverse association between nutritional calcium levels and colon cancer risk seem to indicate that the incidence of colon cancer can be reduced by approximately 70% if daily calcium intake is raised from 800 to 1400 mg. Since then, many other observational studies reported a strong association between incidence of colorectal cancer and low calcium intake: for example, Huncharek et al.  performed a meta-analysis of 60 epidemiological studies, and showed that high calcium intake, regardless of whether it is dietary or supplemental, had a significant protective effect against tumor development in the distal colon and rectum. Wu et al.  analyzed data from two large prospective trials, which had involved more than 80,000 women and 40,000 men. They reported a significant risk reduction for distal colon cancer for subjects whose dietary calcium intake was ≥1250 mg compared to those who ingested 500 mg or less. Cho et al.  analyzed pooled primary data from 10 cohort studies, in which more than half a million individuals were followed up for six to 16 years. They found a significant (p < 0.001 for trend) inverse relation between total calcium intake and colorectal cancer incidence. Comparable findings were reported by Jenab et al. , who had conducted a nested case-control study within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort of more than 520,000 participants from 10 western European countries.
It should be noted that the efficiency of calcium in reducing the risk of colorectal cancer depends very much on the vitamin D status of an individual, so that optimal prevention of the disease necessitates high intake levels of both vitamin D and calcium [52,53,54,55]. Notably, Fedirko et al.  reported a significant interaction (p < 0.01) between dietary calcium and vitamin D on reduction of colorectal cancer-related mortality in a nested case–control study within the EPIC cohort.
2.2.2. Breast Cancer
From their studies on fat-induced carcinogenesis in mice, Lipkin and Newmark suggested that low dietary calcium could also promote breast cancer in humans .This notion gained strong support from multiple observations of an inverse relation between calcium intake and disease incidence in both pre-menopausal and post-menopausal women: Lin et al.  studied the effects of calcium intake from nutrient sources and supplements on breast cancer risk in a large cohort of premenopausal women. They found that higher intakes of total calcium were associated with a lower risk of premenopausal breast cancer (RR = 0.61; 95% CI: 0.40–0.92). Shin et al.  reported that in premenopausal women, dairy calcium (>800 mg/day versus ≤200 mg/day; RR = 0.69) had inverse associations with premenopausal breast cancer risk. McCullough et al.  analyzed data from nearly 70,000 postmenopausal women participating in the Cancer Prevention Study II Nutrition Cohort and found a moderately lower risk of breast cancer with intake of dietary calcium >1250 mg/day compared to <500 mg/day ((RR = 0.80, p [trend] = 0.02). This association was even stronger (RR = 0.67) in women with estrogen receptor-positive tumors. Consumption of dairy products was also inversely associated with risk (RR = 0.81; 95% CI, 0.69–0.95; p [trend] = 0.002) in this study. In a recent case-control study conducted among Chinese women by Zhang et al. , no significant association was found between dairy product intake and breast cancer risk, but a statistically significant inverse association of dietary calcium intake with breast cancer risk was observed with the adjusted OR (95% CI) of 0.35 (0.22–0.56) comparing the highest with the lowest quartile. Chen et al.  performed a meta-analysis of 15 studies on calcium intake and breast cancer risk: an inter-quantile comparison showing that high calcium consumption was associated with overall relative risk of 0.81 (95% CI = 0.72–0.90) adds to the evidence that calcium has a chemopreventive effect against breast cancer.
Bérubé et al.  found that combined intake of calcium and vitamin D by pre-menopausal women was superior to separate intakes in reducing mammographic breast density, a surrogate marker of breast cancer incidence. This notion is valid also for breast cancer incidence as shown by Abbas et al.  in a population-based case-control study in Germany (for discussion, see ).
2.2.3. Prostate Cancer
Rather conflicting data have been reported with respect to the effect of calcium intake on the incidence of prostate cancer. In 1998, a study by Giovannucci et al.  found a positive association between calcium intake from food sources and supplements and risk of prostate cancer. Later, Gao et al.  analyzed 12 prospective studies published from 1966 to 2005. Dose-response analyses suggested that dairy product and calcium intakes were each positively associated with the risk of prostate cancer (p [trend] = 0.029 and 0.014, respectively). It was, however, not clear whether calcium intake itself was an independent risk factor for prostate cancer. This issue seemed to be clarified by Allen et al. , who analyzed data from almost the entire EPIC study cohort. They found that calcium from dairy products was positively associated with risk (p [trend] = 0.02), but not calcium from other foods. The situation elsewhere in the world appears to be less clear. Huncharek et al.  performed a meta-analysis of 45 observational studies, the majority of which were conducted in the United States. Results from 23 cohort studies and 26 case-control studies did not support an association between dairy product use and an increased risk of prostate cancer. While calcium data from cohort studies were heterogeneous and could not be used for the analyses, and respective data from case-control studies demonstrated no association with increased risk of prostate cancer. The results of this meta-analysis  should be seen with some caution because, as pointed out by the authors, “much of the reviewed literature predated the widespread use of PSA screening in the United States, and only few studies provided information on proportion of cases (controls) screened for prostate cancer and the stage distribution of cancer cases included in individual analyses”. When this information was available, somewhat different results were obtained: For example, Kristal et al.  examined nutritional risk factors for prostate cancer among nearly 10,000 participants in the Prostate Cancer Prevention Trial (United States and Canada, 1994–2003) and found that dietary calcium was positively associated (p [trend] = 0.165) with low-grade cancer but inversely associated (p [trend] = 0.034) with high-grade cancer. A preventive effect of high calcium intake against high-grade cancers was also found in a recent case-control study conducted by Williams et al.  among US veterans.
2.3. Cardiovascular Disease
Calcium insufficiency has been correlated not only with cardiovascular risk factors, such as obesity, metabolic syndrome, diabetes mellitus type 2 and hypertension, but also with incident cardiovascular symptoms and stroke, as well as with greater mortality from chronic cardiovascular disease. However, the extent to which patients with high cardiovascular risk will benefit from calcium supplements is still under debate [71,72].
2.3.1. Cardiovascular Risk Factors
Obesity: A clinical study of calcium intake with a skeletal endpoint showed a significant correlation between low calcium intake and increased body weight in women aged 30–80 years . Findings from two studies that were conducted in the USA [73,74] suggested that high calcium intake significantly reduces the risk of obesity. In contrast, Puntus et al.  found no association between calcium intake and body mass index in a well controlled, large cohort study on healthy adult Austrians.
Dyslipidemia and glucose intolerance are, apart from hypertension and obesity, constituents of the so-called metabolic syndrome and of non-insulin-dependent diabetes mellitus. A link between low calcium and the metabolic syndrome and type 2 diabetes mellitus has been reported in observational studies (reviewed by ). The available evidence is limited because most observational studies were cross-sectional and did not adjust for important confounders.
Hypertension: Evidence from a large number of observational studies and randomized clinical trials indicates that low dietary calcium constitutes a significant risk factor for primary hypertension (for review, see ). Calcium appears to be particularly effective in reducing the age-related increase in blood pressure. Dobnig et al.  conducted a randomized, double-blind, multi-center study on the effect of daily high-dose calcium supplements in healthy, elderly adults and observed a substantial reduction of systolic and diastolic blood pressure after one year of treatment in individuals who were in the upper third of pre-study blood pressure values. No further improvement was seen with calcium plus vitamin D supplementation. It seems that, apart from hypertension, none of the classical risk factors of cardiovascular disease are significantly associated with low calcium intake.
2.3.2. Cardiovascular Disease: Incidence and Mortality
In 1999, Bostick et al.  had published results from a prospective cohort study of more than 30,000 Iowa women, suggesting that a higher intake of calcium is associated with reduced ischemic heart disease mortality in postmenopausal women. However, as mentioned previously, it is still a matter of debate whether higher intake of calcium also has a benefit on incident cardiovascular symptoms such as ischemic heart disease, myocardial infarction, and stroke [71,72]. For example, in a large cohort study of Japanese women and men, Umesawa et al.  found a significant inverse association of calcium intake with risk of stroke, particularly of the ischemic subtype, but did not detect any correlation with the risk of ischemic heart disease. The results of a 12 year follow-up of approximately 40,000 male health professionals in USA by Al-Delaimy et al.  suggested that neither dietary nor supplemental intakes of calcium were appreciably associated with the risk of ischemic heart disease among men. Lewis et al.  conducted a randomized placebo-controlled trial on the effect of calcium supplementation on the risk of atherosclerotic vascular disease in postmenopausal women. Patient-level analysis after a five year follow up period indicated that in patients with pre-existing atherosclerotic cardiovascular disease, calcium therapy reduced the risk of hospitalization and was associated with significantly fewer heart failure death events.
Lewis et al.  interpreted their study that it “supplies compelling evidence that calcium supplementation does not have any adverse effect on myocardial function.” This statement refers to studies by Pentti et al.  and Bolland et al. [84,85], who had claimed that high calcium intake promotes calcification of coronary arteries and subsequent myocardial infarction. This notion, that was heavily debated in recent years, and particularly the studies by Bolland et al. [84,85] were heavily criticized (cf. [86,87]). In addition, Samelson et al.  most recently published the results of their prospective observational study on a cohort within the Framingham offspring study: The authors found no evidence that calcium intake from dietary sources, or from supplements, had any effect on coronary artery calcification. They also concluded from their study that there is no need “to modify current recommendations for calcium intake to protect skeletal health with respect to vascular calcification risk”. It should be noted that vascular calcifications develop secondary to vascular damage, which frequently results from vitamin D insufficiency and associated secondary hyperparathyroidism [89,90,91,92], whereas high calcium has been shown to prevent vascular damage and calcification through activation of the CaSR on vascular smooth muscle cells (for details, see Section 3.3.3).
3. Principles of Extracellular Calcium Sensing
Although the inverse relationship between dietary calcium intake and risk of multiple chronic diseases was known for years, it was not apparent how low levels of calcium intake could generate signals that were transduced to organs and cell systems distant from the intestinal lumen. Also, it is well known that the impact even of large variations in calcium intake on extracellular calcium concentrations [Ca2+]o is attenuated by the systemic actions of calcium-regulating hormones, 1,25-dihydroxyvitamin D3 and parathyroid hormone (PTH). This allows physiological variations in [Ca2+]o to occur only within a narrow range. How these can be translated into modulation of cellular functions became clear, when Brown and colleagues  cloned and characterized an extracellular calcium-sensing receptor (CaSR) from the bovine parathyroid gland. The CaSR, which was identified as a member of family C of G protein-coupled receptors, transduces small changes in [Ca2+]o, i.e., in the range of 0.05 mM , along various intracellular signaling pathways (Figure 1).
Human cells that express this receptor include parathyroid chief, thyroid C and kidney cells , osteoblasts , gastric , and large intestinal epithelial cells , mammary gland , ovarian , prostate gland , pancreatic duct  and islet cells  as well as monocytes, macrophages, and dendritic cells . The CaSR was also detected in arterial smooth muscle and endothelial cells . Furthermore, in many regions of the brain, neuronal and glial cells express CaSR . Expression of a functional CaSR allows extracellular Ca2+ to act as a “first messenger” for various intracellular signaling pathways that play an important role in control of cellular proliferation, differentiation, and function (for review, see [94,107,108]).
3.1. The Extracellular Calcium-Sensing Receptor (CaSR): General Properties and Function
The CaSR plays an important role in the maintenance of systemic calcium homeostasis mainly by modulating PTH secretion from the parathyroid gland . It is known that, under physiological conditions, serum Ca2+ concentrations oscillate continuously within a narrow range. Amplitude and frequency of these oscillations are determined by the activity and cell-specific function of the CaSR on parathyroid gland chief cells. When, for example, due to reduced Ca2+ transfer from the intestine, the serum Ca2+ concentration falls to the lower physiological limit, this will change the activity of the parathyroid CaSR and thereby cause the release of PTH. When, as a consequence of PTH action on bone and kidney, serum Ca2+ reaches the upper physiological limit, activation of the CaSR leads to inhibition of PTH secretion, PTH gene expression, and parathyroid cell proliferation. Other effects of the CaSR that are relevant for systemic Ca2+ homeostasis include regulation of renal synthesis of 1,25-(OH)2D3  and of calcitonin secretion from C cells in the thyroid gland . The important role of the CaSR in systemic Ca2+ homeostasis is highlighted by results of a genome-wide association study, which showed that serum calcium in European and Asian Indian populations is significantly associated with single nucleotide polymorphisms near the CaSR gene, whereas no other locus reached genome-wide significance .
Expression of a functional CaSR allows cell-specific responses to physiological changes in [Ca2+] in the plasma and in other extracellular fluid compartments. Hence, the CaSR plays a key role not only in systemic Ca2+ homeostasis but also in local control of cellular functions, such as cartilage and bone formation [112,113,114,115], or growth limitation of normal and neoplastic cells [116,117]. While low calcium intake from diet can thus be linked to the development of osteoporosis and of various malignancies, involvement of the CaSR in the pathogenesis of other calcium insufficiency-related chronic diseases, such as hypertension and cardiovascular disease, is not yet fully understood.
3.2. The Extracellular Calcium-Sensing Receptor (CaSR): Molecular Properties
The human CaSR has a 612 amino acid extracellular domain, which is followed by 7 transmembrane helices built from 250 amino acids, and, finally, by a 216 residue carboxy terminal. The CaSR has a homodimeric structure with at least two high-affinity binding sites for Ca2+ in the extracellular domain of each monomer, which exhibit high positive cooperativity (Figure 1). This enables the CaSR to amplify the intensity of the otherwise minute signals from extracellular Ca2+ [108,118]. By coupling to stimulatory or inhibitory heterotrimeric G proteins the CaSR channels signals from extracellular fluid Ca2+ to various “second messenger”-generating systems, which include adenylate cyclase/cAMP, phospholipase A2 (PLA2)/arachidonic acid (AA) as well as phospholipase C (PLC)/diacylglycerol (DG) and inositoltrisphosphate (IP3). The latter is an important intermediate in CaSR-evoked Ca2+ influx through a non-selective cation channel  (Figure 1).
3.3. The Extracellular Calcium-Sensing Receptor (CaSR): Cell-Specific Actions
The concept of an important role of the CaSR in regulation of bone formation and mineralization as developed earlier [112,120], is fully supported by recent findings from a study in a CaSR knock-out mouse model . As osteoblastic lineage cells are endowed with a functional CaSR (e.g., [121,122,123]), changes in [Ca2+]o can be directly transduced into control of osteoblast proliferation, differentiation and function during any phase of mineralized bone formation (Figure 2). This process, in which the canonical Wnt/β-catenin signaling cascade plays a key role,  is coordinated by separate receptor-mediated effects of [Ca2+]o and 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) [112,115,125]: As illustrated in Figure 2, activation of the Wnt/β-catenin pathway initiates “osteogenic differentiation” of pluripotent mesenchymal stem cells into osteoprogenitor cells, which characteristically express the osteoblast-specific transcription factor, Core-binding factor-1 (Cbfa1). Signaling from the CaSR in conjunction with the non-canonical Wnt5a/Ca2+ pathway  increases the expression of Cbfa. This causes osteoprogenitor cells to proliferate and to produce collagen . Subsequently, signaling from 1,25(OH)2D3/VDR inhibits proliferation and matrix deposition and at the same time promotes osteoblast differentiation through phases of matrix maturation and mineralization . Independent of vitamin D, activation of the CaSR increases the expression of osteoblast-specific differentiation markers, such as alkaline phosphatase (ALP), osteocalcin (OC) and osteopontin (OP). Finally, the CaSR plays an important role in orderly bone formation by regulating crystal growth and by preventing excessive mineralization .
3.3.2. Cancer Cells
Colorectal cancer: The CaSR is expressed in normal human colonic epithelium, mainly in the upper half of the crypt, and is absent from the crypt base . Thus, expression of the CaSR correlates with a [Ca2+]o gradient that, according to Whitfield , decreases in the direction from top to base of the crypt. Pluripotent stem cells at the bottom of the crypt can thus proliferate without restraints from anti-mitotic signaling from the CaSR. Daughter cells, however, while migrating to the crypt top undergo differentiation under the influence of increasing CaSR expression and activity . The assumption of an important role of the CaSR, in control of crypt cell homeostasis, is supported by findings in an intestinal-specific CaSR knockout mouse, which shows changes in crypt structure, expansion of the proliferative zone, and hyperproliferation of colonic epithelial cells . There is suggestive evidence that the CaSR, on the luminal aspect of human colonocytes, reacts to ingestion of calcium-rich food by rapid activation of anti-mitogenic intracellular pathways .
The CaSR on human colon carcinoma cells has high sequence homology with the parathyroid CaSR [98,132], and is expressed as long as the cancer cells retain a certain degree of differentiation [128,133]. Epigenetic silencing of the CaSR could be one reason for reduced expression of the receptor in more advanced cancers and in nearly all lymph node metastases . From the evidence that expression of the CaSR is highest in well differentiated cancers and declines during tumor progression [128,133], it can be implied that calcium acting via the CaSR is a chemopreventive rather than a chemotherapeutic agent.
The sequence of events downstream of CaSR activation that actually link CaSR to cell cycle control in colon carcinoma cells starts with inhibition of phospholipase A2 activity  (Figure 1 and Figure 3), which would reduce the amount of arachidonic acid available for the synthesis of proliferation-stimulating prostaglandins. Subsequent down-regulation of c-myc proto-oncogene expression , activation of the cyclin-dependent kinase inhibitor p21  and inhibition of cyclin D1 finally leads to cell cycle arrest at the G1/S-phase transition. CaSR-activated pro-differentiating signaling in colonocytes involves inhibition of the Wnt/β-catenin pathway by down-regulation of the T-cell transcription factor (TCF)-4 with subsequent induction of E-cadherin expression [137,138,139]. Interestingly, part of the anti-proliferative action of 1,25(OH)2D3 has been traced to a VDR-mediated, negative effect on TCF-4 [137,140] (Figure 3). These findings illustrate that Ca2+ and vitamin D independently inhibit colorectal cancer cell proliferation. Therefore, a combination of both agents is well suited to reduce the risk of colorectal cancer.
Breast cancer: A role for a functional CaSR in breast cancer can be inferred from the fact that in premenopausal women serum calcium levels vary inversely with breast cancer risk in a concentration-dependent manner . Both normal and malignant mammary gland epithelial cells are endowed with the CaSR . However, little is known of the role played by the CaSR in mediating changes in ambient Ca2+ to regulate cellular growth in mammary gland cells. In MCF-7 breast cancer cells, activation of the CaSR is transduced via the PI-PLC pathway into generation of IP3, which not only causes the release of Ca2+ from endoplasmic reticulum, but also evokes Ca2+ influx across the plasma membrane through non-selective cation channels (Figure 1; for details, [108,142]). The rise in intracellular Ca2+ may conceivably activate pro-apoptotic intracellular signaling , particularly through involvement of different plasma membrane calcium ATPase isoforms . In addition, the CaSR can inhibit breast cancer cell growth through its functional linkage with the tumor-suppressor BRCA1: Promkan et al.  reported that BRCA1 up-regulates the expression of the CaSR and, at the same time, functions through the receptor in suppressing the expression of survivin, an anti-apoptotic protein that is present in most cancer cells.
An apparent cross-talk between Ca2+/CaSR and 1,25(OH)2D3/VDR signaling  on cytosolic Ca2+ may explain, at least in part, how vitamin D and calcium together efficiently inhibit mammary gland cell growth in vivo (cf. Section 2.2.2).
Activation of the CaSR could have dual effects on disease outcome: On the one hand, activation of the CaSR in human MCF-7 breast cancer cells by extracellular calcium concentrations that are detected in bone at tumor metastasis, enhances expression of the estrogen receptor-alpha . An improved estrogen receptor status is considered a good prognostic factor. On the other hand, the CaSR has also been shown to stimulate synthesis and secretion of parathyroid hormone-related peptide, which is thought to play a key role in osteolytic metastases .
Prostate cancer: The CaSR is expressed on human prostate cancer cell lines [101,149,150]. Unlike colorectal and breast cancer cells, prostate cancer cells respond to high calcium with increased proliferation. This may be due to transactivation by the CaSR of the epidermal growth factor receptor (EGFR) and subsequent activation of ERK1/2 (cf. Figure 1) and release of PTHrP [101,149]. This can explain why prostate cancers expressing high levels of the CaSR are more likely to metastasize to bone than those poorly expressing the CaSR. Stimulation of PTHrP release from bone metastatic prostate cancer cells induces osteoclastic bone resorption, whereby the Ca2+ concentration in the resorptive lacunae of osteoclasts rises to eight to 40 mM . High calcium, acting through the CaSR, causes malignant prostate cells to proliferate and to release even more PTHrP, leading to increased osteolytic activity and enhanced survival of metastatic cells in the bony microenvironment . The relevance of CaSR expression for metastases development, and for disease outcome, is underscored by the recent findings of Shui et al.  that common genetic variants of the CaSR are significantly associated with prostate cancer mortality.
3.3.3. Cardiac, Vascular, Renal Juxtaglomerular and Epithelial Cells
Because current literature on expression of the CaSR in human arterial and cardiac cells is rather limited, inference on the function of the receptor in the human cardiovascular system has to be made from the wealth of information on the expression and function of the CaSR in the vasculature (heart and blood vessels and associated structures) of rodents and other experimental animals. In addition, a substantial role of the CaSR in maintaining normal blood pressure and cardiovascular functions is supported by studies on the effect of so-called calcimimetics, i.e., synthetic allosteric activators of the CaSR, in various animal models  and patients with chronic kidney disease . It is now very clear that the CaSR is part of an intricate network of calcium channels, pumps, and exchangers, which is involved in the control of intracellular calcium concentration ([Ca2+]i) and thereby in modulation of cardiovascular functions [154,155].
Cardiomyocytes: The CaSR is functionally expressed on rat neonatal and adult cardiomyocytes [154,156,157]. Upon activation by [Ca2+]o the receptor transduces signals preferentially along the PLC pathway causing intracellular accumulation of IP3 (cf. Figure 1) and, in turn, a rise in [Ca2+]i, the classic “second messenger” in cardiac physiology. Thus, the CaSR has been implicated in regulating cardiac development, function, and homeostasis . Apart from regulating [Ca2+]i, the CaSR may be involved in excitation-contraction coupling through a unique feedback mechanism. Hofer et al.  observed that intracellular signaling events can produce changes in [Ca2+]o that are detected by the CaSR on cells in close proximity. According to Tfelt-Hansen et al. , the CaSR on cardiomyocytes may therefore change its activity with every heart contraction.
Endothelial and smooth muscle cells of human arteries express a functional CaSR . The receptor was detected also in endothelial cells from rat mesenteric and porcine coronary arteries , and in rat aortic smooth muscle cells . Indeed, the CaSR is functionally expressed on all cells of the vascular wall-adventitia, fibroblast, vascular smooth muscle cells (VSMC), and endothelium. It is closely involved in the regulation of vascular tone and arterial blood pressure (for review, see ). In a hypothetical model proposed by Weston et al.  the CaSR plays a key role in myo-endothelial coupling in the vasculature. Activation of the CaSR induces endothelium-dependent hyperpolarization in neighboring myocytes. In short, activation of the endothelial CaSR is associated with the opening of a Ca2+-sensitive K+ conductance channel. K+ released into the intercellular space is taken up by the myocyte Na+/K+-ATPase. This contributes to a reversal of spasminogen-induced depolarization of vascular myocytes and, consequently, to vascular relaxation. This can explain, at least in part, the well documented hypotensive effect of dietary Ca2+ (see section 2.3.1).
The CaSR has also been shown to be involved in vascular repair and maintenance of vascular integrity . Normal expression of the receptor on VSMC seems to be important for prevention of vascular calcification, since calcification is associated with reduced expression of the CaSR in blood vessels : large and small arteries of normal subjects and of patients with advanced chronic kidney disease express the CaSR, although the expression is lower in epigastric arteries of patients with advanced renal impairment, compared with healthy transplant donors. Analysis of epigastric arteries, taken from chronic kidney disease patients, showed that a decrease in CaSR expression was accompanied by progressive calcification of VSMC areas . Moreover, there is increasing evidence from in vitro and in vivo studies that calcimimetic compounds upregulate the CaSR in vascular cells and thereby attenuate vascular mineralization associated with reduced kidney function (for review, see ).
Juxtaglomerular cells: According to Atchison and Beierwaltes , signaling from Ca2+/CaSR in juxtaglomerular cells inhibits a calcium-inhibitable isoform of adenylate cyclase (cf. Figure 1), which is associated with formation of renin. Reduced activity of the renin-angiotensin II-aldosterone system could partially account for a CaSR mediated hypotensive effect of dietary and supplemental calcium.
Renal epithelial cells: Activation of the basolateral CaSR in the thick ascending limb of Henle’s (TAL) mediates the anti-hypertensive effect of elevated extracellular calcium in two ways: (i) CaSR signaling via PKC results in up-regulation of COX-2 and enhanced synthesis of the natriuretic prostaglandin E2 [162,163]; (ii) by activation of PLA2, CaSR signaling targets apical electrolyte transporters and channels participating in the control of electrolyte reabsorption from the lumen . The importance of the CaSR in this process has been proven by identification of activating mutations in the CaSR gene, which cause Bartter syndrome type 5, a human disease characterized by excessive wasting of NaCl and other electrolytes . Taken together, signaling from the basolateral CaSR in the TAL induces natriuresis and thereby causes reduction of plasma volume. This can partially explain the blood pressure-lowering effect of elevated extracellular calcium
There is no doubt that the CaSR plays an important role in local control of cellular homeostasis and function in many tissues and organs. Impaired or malfunctioning signaling from Ca2+/CaSR may therefore contribute to the adverse health effects of low habitual calcium intake. Because of the synergistic action of Ca2+/CaSR-activated and vitamin D receptor-mediated signaling cascades, one should bear in mind that, for optimal health outcome, restoration of both an adequate calcium and vitamin D status is necessary. There is evidence that efficient disease prevention does not require intake of more calcium and vitamin D than currently recommended for maintaining optimal bone health .
Work in EK’s laboratory was supported by grants from the European Commission “Multifaceted CaSR”, project No. FP7-264663, Austrian Science Fund, project No. P22200-B11, and Herzfeldersche Familienstiftung.
Conflict of Interest
The authors declare no conflict of interest.
- Peterlik, M.; Cross, H.S. Vitamin D and calcium deficits predispose for multiple chronic diseases. Eur. J. Clin. Investig. 2005, 35, 290–304, doi:10.1111/j.1365-2362.2005.01487.x.
- Peterlik, M.; Cross, H.S. Vitamin D and calcium insufficiency-related chronic diseases: Molecular and cellular pathophysiology. Eur. J. Clin. Nutr. 2009, 63, 1377–1386, doi:10.1038/ejcn.2009.105.
- Peterlik, M.; Grant, W.B.; Cross, H.S. Calcium, vitamin D and cancer. Anticancer Res. 2009, 29, 3687–3698.
- Ward, B.K.; Magno, A.L.; Walsh, J.P.; Ratajczak, T. The role of the calcium-sensing receptor in human disease. Clin. Biochem. 2012, 45, 943–953, doi:10.1016/j.clinbiochem.2012.03.034.
- Peterlik, M.; Boonen, S.; Cross, H.S.; Lamberg-Allardt, C. Vitamin D and calcium insufficiency-related chronic diseases: An emerging world-wide public health problem. Int. J. Environ. Res. Public Health 2009, 6, 2585–2607, doi:10.3390/ijerph6102585.
- Ross, A.C.; Manson, J.E.; Abrams, S.A.; Aloia, J.F.; Brannon, P.M.; Clinton, S.K.; Durazo-Arvizu, R.A.; Gallagher, J.C.; Gallo, R.L.; Jones, G.; et al. The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: What clinicians need to know. J. Clin. Endocrinol. Metab. 2011, 96, 53–58, doi:10.1210/jc.2010-2704.
- FAO/WHO. Human Vitamin and Mineral Requirements; FAO/WHO non-series publication: Rome, Italy, 2002.
- Kudlacek, S.; Schneider, B.; Peterlik, M.; Leb, G.; Klaushofer, K.; Weber, K.; Woloszczuk, W.; Willvonseder, R. Assessment of vitamin D and calcium status in healthy adult Austrians. Eur. J. Clin. Investig. 2003, 33, 323–331, doi:10.1046/j.1365-2362.2003.01127.x.
- Amorim Cruz, J.A.; Moreiras, O.; Brzozowska, A. Longitudinal changes in the intake of vitamins and minerals of elderly Europeans. Eur. J. Clin. Nutr. 1996, 50, S77–S85.
- Andersen, R.; Molgaard, C.; Skovgaard, L.T.; Brot, C.; Cashman, K.D.; Chabros, E.; Charzewska, J.; Flynn, A.; Jakobsen, J.; Karkkainen, M.; et al. Teenage girls and elderly women living in northern Europe have low winter vitamin D status. Eur. J. Clin. Nutr. 2005, 59, 533–541, doi:10.1038/sj.ejcn.1602108.
- Hintzpeter, B.; Mensink, G.B.; Thierfelder, W.; Muller, M.J.; Scheidt-Nave, C. Vitamin D status and health correlates among German adults. Eur. J. Clin. Nutr. 2008, 62, 1079–1089, doi:10.1038/sj.ejcn.1602825.
- Salamoun, M.M.; Kizirian, A.S.; Tannous, R.I.; Nabulsi, M.M.; Choucair, M.K.; Deeb, M.E.; El-Hajj Fuleihan, G.A. Low calcium and vitamin D intake in healthy children and adolescents and their correlates. Eur. J. Clin. Nutr. 2005, 59, 177–184, doi:10.1038/sj.ejcn.1602056.
- Rubin, L.A.; Hawker, G.A.; Peltekova, V.D.; Fielding, L.J.; Ridout, R.; Cole, D.E. Determinants of peak bone mass: Clinical and genetic analyses in a young female Canadian cohort. J. Bone Miner. Res. 1999, 14, 633–643, doi:10.1359/jbmr.19126.96.36.1993.
- Bailey, R.L.; Dodd, K.W.; Goldman, J.A.; Gahche, J.J.; Dwyer, J.T.; Moshfegh, A.J.; Sempos, C.T.; Picciano, M.F. Estimation of total usual calcium and vitamin D intakes in the United States. J. Nutr. 2010, 140, 817–822, doi:10.3945/jn.109.118539.
- Lappe, J.M.; Davies, K.M.; Travers-Gustafson, D.; Heaney, R.P. Vitamin D status in a rural postmenopausal female population. J. Am. Coll. Nutr. 2006, 25, 395–402.
- Peters, B.S.; dos Santos, L.C.; Fisberg, M.; Wood, R.J.; Martini, L.A. Prevalence of vitamin D insufficiency in Brazilian adolescents. Ann. Nutr. Metab. 2009, 54, 15–21.
- Islam, M.Z.; Lamberg-Allardt, C.; Karkkainen, M.; Ali, S.M. Dietary calcium intake in premenopausal Bangladeshi women: Do socio-economic or physiological factors play a role? Eur. J. Clin. Nutr. 2003, 57, 674–680, doi:10.1038/sj.ejcn.1601597.
- Green, T.J.; Skeaff, C.M.; Rockell, J.E.; Venn, B.J.; Lambert, A.; Todd, J.; Khor, G.L.; Loh, S.P.; Muslimatun, S.; Agustina, R.; et al. Vitamin D status and its association with parathyroid hormone concentrations in women of child-bearing age living in Jakarta and Kuala Lumpur. Eur. J. Clin. Nutr. 2008, 62, 373–378, doi:10.1038/sj.ejcn.1602696.
- Kruger, M.C.; Ha, P.C.; Todd, J.M.; Kuhn-Sherlock, B.; Schollum, L.M.; Ma, J.; Qin, G.; Lau, E. High-calcium, vitamin D fortified milk is effective in improving bone turnover markers and vitamin D status in healthy postmenopausal Chinese women. Eur. J. Clin. Nutr. 2012, 66, 856–861.
- Nakamura, K.; Saito, T.; Yoshihara, A.; Ishikawa, M.; Tsuchiya, Y.; Oshiki, R.; Kobayashi, R.; Maruyama, K.; Hyodo, K.; Nashimoto, M.; et al. Low calcium intake is associated with increased bone resorption in postmenopausal Japanese women: Yokogoshi study. Public Health Nutr. 2009, 12, 2366–2370, doi:10.1017/S1368980009005084.
- Pasco, J.A.; Henry, M.J.; Nicholson, G.C.; Brennan, S.L.; Kotowicz, M.A. Behavioural and physical characteristics associated with vitamin D status in women. Bone 2009, 44, 1085–1091, doi:10.1016/j.bone.2009.02.020.
- Rejnmark, L.; Avenell, A.; Masud, T.; Anderson, F.; Meyer, H.E.; Sanders, K.M.; Salovaara, K.; Cooper, C.; Smith, H.E.; Jacobs, E.T.; et al. Vitamin D with calcium reduces mortality: Patient level pooled analysis of 70,528 patients from eight major vitamin D trials. J. Clin. Endocrinol. Metab. 2012, 97, 2670–2681, doi:10.1210/jc.2011-3328.
- Zhu, Y.; Mahon, B.D.; Froicu, M.; Cantorna, M.T. Calcium and 1α,25-dihydroxyvitamin D3 target the TNF-α pathway to suppress experimental inflammatory bowel disease. Eur. J. Immunol. 2005, 35, 217–224, doi:10.1002/eji.200425491.
- Cantorna, M.T.; Humpal-Winter, J.; DeLuca, H.F. Dietary calcium is a major factor in 1,25-dihydroxycholecalciferol suppression of experimental autoimmune encephalomyelitis in mice. J. Nutr. 1999, 129, 1966–1971.
- Mathieu, C.; van Etten, E.; Gysemans, C.; Decallonne, B.; Kato, S.; Laureys, J.; Depovere, J.; Valckx, D.; Verstuyf, A.; Bouillon, R. In vitro and in vivo analysis of the immune system of vitamin D receptor knockout mice. J. Bone Miner. Res. 2001, 16, 2057–2065, doi:10.1359/jbmr.2001.16.11.2057.
- Olszak, I.T.; Poznansky, M.C.; Evans, R.H.; Olson, D.; Kos, C.; Pollak, M.R.; Brown, E.M.; Scadden, D.T. Extracellular calcium elicits a chemokinetic response from monocytes in vitro and in vivo. J. Clin. Investig. 2000, 105, 1299–1305, doi:10.1172/JCI9799.
- Tiosano, D.; Hochberg, Z. Hypophosphatemia: The common denominator of all rickets. J. Bone Miner. Metab. 2009, 27, 392–401, doi:10.1007/s00774-009-0079-1.
- Pettifor, J.M. Nutritional rickets: Deficiency of vitamin D, calcium, or both? Am. J. Clin. Nutr. 2004, 80, 1725S–1729S.
- Thacher, T.D.; Fischer, P.R.; Pettifor, J.M.; Lawson, J.O.; Isichei, C.O.; Reading, J.C.; Chan, G.M. A comparison of calcium, vitamin D, or both for nutritional rickets in Nigerian children. N. Engl. J. Med. 1999, 341, 563–568, doi:10.1056/NEJM199908193410803.
- Balasubramanian, K.; Rajeswari, J.; Gulab; Govil, Y.C.; Agarwal, A.K.; Kumar, A.; Bhatia, V. Varying role of vitamin D deficiency in the etiology of rickets in young children vs. adolescents in northern India. J. Trop. Pediatr. 2003, 49, 201–206, doi:10.1093/tropej/49.4.201.
- DeLucia, M.C.; Mitnick, M.E.; Carpenter, T.O. Nutritional rickets with normal circulating 25-hydroxyvitamin D: A call for reexamining the role of dietary calcium intake in North American infants. J. Clin. Endocrinol. Metab. 2003, 88, 3539–3545, doi:10.1210/jc.2002-021935.
- Riggs, B.L.; Khosla, S.; Melton, L.J., III. A unitary model for involutional osteoporosis: Estrogen deficiency causes both type I and type II osteoporosis in postmenopausal women and contributes to bone loss in aging men. J. Bone Miner. Res. 1998, 13, 763–773, doi:10.1359/jbmr.19188.8.131.523.
- Heaney, R.P. Calcium in the prevention and treatment of osteoporosis. J. Intern. Med. 1992, 231, 169–180, doi:10.1111/j.1365-2796.1992.tb00520.x.
- Dawson-Hughes, B.; Dallal, G.E.; Krall, E.A.; Sadowski, L.; Sahyoun, N.; Tannenbaum, S. A controlled trial of the effect of calcium supplementation on bone density in postmenopausal women. N. Engl. J. Med. 1990, 323, 878–883, doi:10.1056/NEJM199009273231305.
- Elders, P.J.; Lips, P.; Netelenbos, J.C.; van Ginkel, F.C.; Khoe, E.; van der Vijgh, W.J.; van der Stelt, P.F. Long-term effect of calcium supplementation on bone loss in perimenopausal women. J. Bone Miner. Res. 1994, 9, 963–970.
- Recker, R.R.; Hinders, S.; Davies, K.M.; Heaney, R.P.; Stegman, M.R.; Lappe, J.M.; Kimmel, D.B. Correcting calcium nutritional deficiency prevents spine fractures in elderly women. J. Bone Miner. Res. 1996, 11, 1961–1966.
- Dawson-Hughes, B.; Harris, S.S.; Krall, E.A.; Dallal, G.E. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N. Engl. J. Med. 1997, 337, 670–676.
- Chapuy, M.C.; Arlot, M.E.; Duboeuf, F.; Brun, J.; Crouzet, B.; Arnaud, S.; Delmas, P.D.; Meunier, P.J. Vitamin D3 and calcium to prevent hip fractures in the elderly women. N. Engl. J. Med. 1992, 327, 1637–1642, doi:10.1056/NEJM199212033272305.
- Larsen, E.R.; Mosekilde, L.; Foldspang, A. Vitamin D and calcium supplementation prevents osteoporotic fractures in elderly community dwelling residents: A pragmatic population-based 3-year intervention study. J. Bone Miner. Res. 2004, 19, 370–378.
- Boonen, S.; Lips, P.; Bouillon, R.; Bischoff-Ferrari, H.A.; Vanderschueren, D.; Haentjens, P. Need for additional calcium to reduce the risk of hip fracture with vitamin D supplementation: Evidence from a comparative metaanalysis of randomized controlled trials. J. Clin. Endocrinol. Metab. 2007, 92, 1415–1423, doi:10.1210/jc.2006-1404.
- Abrahamsen, B.; Masud, T.; Avenell, A.; Anderson, F.; Meyer, H.E.; Cooper, J.C.; Smith, H.; LaCroix, A.Z.; Torgerson, D.; Johansen, A.; et al. Patient level pooled analysis of 68,500 patients from seven major vitamin D fracture trials in US and Europe. BMJ 2010, 340, b5463.
- Tang, B.M.; Eslick, G.D.; Nowson, C.; Smith, C.; Bensoussan, A. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: A meta-analysis. Lancet 2007, 370, 657–666, doi:10.1016/S0140-6736(07)61342-7.
- Aloia, J.F. African Americans, 25-hydroxyvitamin D, and osteoporosis: A paradox. Am. J. Clin. Nutr. 2008, 88, 545S–550S.
- Pfeifer, M.; Begerow, B.; Minne, H.W.; Abrams, C.; Nachtigall, D.; Hansen, C. Effects of a short-term vitamin D and calcium supplementation on body sway and secondary hyperparathyroidism in elderly women. J. Bone Miner. Res. 2000, 15, 1113–1118, doi:10.1359/jbmr.2000.15.6.1113.
- Pfeifer, M.; Begerow, B.; Minne, H.W.; Suppan, K.; Fahrleitner-Pammer, A.; Dobnig, H. Effects of a long-term vitamin D and calcium supplementation on falls and parameters of muscle function in community-dwelling older individuals. Osteoporos. Int. 2009, 20, 315–322, doi:10.1007/s00198-008-0662-7.
- Lips, P.; Bouillon, R.; van Schoor, N.M.; Vanderschueren, D.; Verschueren, S.; Kuchuk, N.; Milisen, K.; Boonen, S. Reducing fracture risk with calcium and vitamin D. Clin. Endocrinol. 2010, 73, 277–285, doi:10.1111/j.1365-2265.2009.03701.x.
- Park, Y.; Leitzmann, M.F.; Subar, A.F.; Hollenbeck, A.; Schatzkin, A. Dairy food, calcium, and risk of cancer in the NIH-AARP diet and health study. Arch. Intern. Med. 2009, 169, 391–401, doi:10.1001/archinternmed.2008.578.
- Garland, C.; Shekelle, R.B.; Barrett-Connor, E.; Criqui, M.H.; Rossof, A.H.; Paul, O. Dietary vitamin D and calcium and risk of colorectal cancer: A 19-year prospective study in men. Lancet 1985, 1, 307–309.
- Garland, C.F.; Garland, F.C.; Gorham, E.D. Can colon cancer incidence and death rates be reduced with calcium and vitamin D? Am. J. Clin. Nutr. 1991, 54, 193S–201S.
- Huncharek, M.; Muscat, J.; Kupelnick, B. Colorectal cancer risk and dietary intake of calcium, vitamin D, and dairy products: A meta-analysis of 26,335 cases from 60 observational studies. Nutr. Cancer 2009, 61, 47–69, doi:10.1080/01635580802395733.
- Wu, K.; Willett, W.C.; Fuchs, C.S.; Colditz, G.A.; Giovannucci, E.L. Calcium intake and risk of colon cancer in women and men. J. Natl. Cancer Inst. 2002, 94, 437–446, doi:10.1093/jnci/94.6.437.
- Cho, E.; Smith-Warner, S.A.; Spiegelman, D.; Beeson, W.L.; van den Brandt, P.A.; Colditz, G.A.; Folsom, A.R.; Fraser, G.E.; Freudenheim, J.L.; Giovannucci, E.; et al. Dairy foods, calcium, and colorectal cancer: A pooled analysis of 10 cohort studies. J. Natl. Cancer Inst. 2004, 96, 1015–1022, doi:10.1093/jnci/djh185.
- Jenab, M.; Bueno-de-Mesquita, H.B.; Ferrari, P.; van Duijnhoven, F.J.; Norat, T.; Pischon, T.; Jansen, E.H.; Slimani, N.; Byrnes, G.; Rinaldi, S.; et al. Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations:A nested case-control study. BMJ 2010, 340, b5500.
- Mizoue, T.; Kimura, Y.; Toyomura, K.; Nagano, J.; Kono, S.; Mibu, R.; Tanaka, M.; Kakeji, Y.; Maehara, Y.; Okamura, T.; et al. Calcium, dairy foods, vitamin D, and colorectal cancer risk: The Fukuoka colorectal cancer study. Cancer Epidemiol. Biomarkers Prev. 2008, 17, 2800–2807, doi:10.1158/1055-9965.EPI-08-0369.
- Ishihara, J.; Inoue, M.; Iwasaki, M.; Sasazuki, S.; Tsugane, S. Dietary calcium, vitamin D, and the risk of colorectal cancer. Am. J. Clin. Nutr. 2008, 88, 1576–1583, doi:10.3945/ajcn.2008.26195.
- Fedirko, V.; Riboli, E.; Tjonneland, A.; Ferrari, P.; Olsen, A.; Bueno-de-Mesquita, H.B.; van Duijnhoven, F.J.; Norat, T.; Jansen, E.H.; Dahm, C.C.; et al. Prediagnostic 25-hydroxyvitamin D, VDR and CaSR polymorphisms, and survival in patients with colorectal cancer in western European populations. Cancer Epidemiol. Biomarkers Prev. 2012, 21, 582–593, doi:10.1158/1055-9965.EPI-11-1065.
- Lipkin, M.; Newmark, H.L. Vitamin D, calcium and prevention of breast cancer: A review. J. Am. Coll. Nutr. 1999, 18, 392S–397S.
- Lin, J.; Manson, J.E.; Lee, I.M.; Cook, N.R.; Buring, J.E.; Zhang, S.M. Intakes of calcium and vitamin D and breast cancer risk in women. Arch. Intern. Med. 2007, 167, 1050–1059.
- Shin, M.H.; Holmes, M.D.; Hankinson, S.E.; Wu, K.; Colditz, G.A.; Willett, W.C. Intake of dairy products, calcium, and vitamin D and risk of breast cancer. J. Natl. Cancer. Inst. 2002, 94, 1301–1311, doi:10.1093/jnci/94.17.1301.
- McCullough, M.L.; Rodriguez, C.; Diver, W.R.; Feigelson, H.S.; Stevens, V.L.; Thun, M.J.; Calle, E.E. Dairy, calcium, and vitamin D intake and postmenopausal breast cancer risk in the cancer prevention study II nutrition cohort. Cancer Epidemiol. Biomarkers Prev. 2005, 14, 2898–2904, doi:10.1158/1055-9965.EPI-05-0611.
- Zhang, C.X.; Ho, S.C.; Fu, J.H.; Cheng, S.Z.; Chen, Y.M.; Lin, F.Y. Dairy products, calcium intake, and breast cancer risk: A case-control study in China. Nutr. Cancer 2011, 63, 12–20.
- Chen, P.; Hu, P.; Xie, D.; Qin, Y.; Wang, F.; Wang, H. Meta-analysis of vitamin D, calcium and the prevention of breast cancer. Breast Cancer Res. Treat. 2010, 121, 469–477, doi:10.1007/s10549-009-0593-9.
- Berube, S.; Diorio, C.; Masse, B.; Hebert-Croteau, N.; Byrne, C.; Cote, G.; Pollak, M.; Yaffe, M.; Brisson, J. Vitamin D and calcium intakes from food or supplements and mammographic breast density. Cancer Epidemiol. Biomarkers Prev. 2005, 14, 1653–1659.
- Abbas, S.; Linseisen, J.; Chang-Claude, J. Dietary vitamin D and calcium intake and premenopausal breast cancer risk in a German case-control study. Nutr. Cancer 2007, 59, 54–61, doi:10.1080/01635580701390223.
- Giovannucci, E.; Rimm, E.B.; Wolk, A.; Ascherio, A.; Stampfer, M.J.; Colditz, G.A.; Willett, W.C. Calcium and fructose intake in relation to risk of prostate cancer. Cancer Res. 1998, 58, 442–447.
- Gao, X.; LaValley, M.P.; Tucker, K.L. Prospective studies of dairy product and calcium intakes and prostate cancer risk: A meta-analysis. J. Natl. Cancer Inst. 2005, 97, 1768–1777, doi:10.1093/jnci/dji402.
- Allen, N.E.; Key, T.J.; Appleby, P.N.; Travis, R.C.; Roddam, A.W.; Tjonneland, A.; Johnsen, N.F.; Overvad, K.; Linseisen, J.; Rohrmann, S.; et al. Animal foods, protein, calcium and prostate cancer risk: The European prospective investigation into cancer and nutrition. Br. J. Cancer 2008, 98, 1574–1581, doi:10.1038/sj.bjc.6604331.
- Huncharek, M.; Muscat, J.; Kupelnick, B. Dairy products, dietary calcium and vitamin D intake as risk factors for prostate cancer: A meta-analysis of 26,769 cases from 45 observational studies. Nutr. Cancer 2008, 60, 421–441.
- Kristal, A.R.; Arnold, K.B.; Neuhouser, M.L.; Goodman, P.; Platz, E.A.; Albanes, D.; Thompson, I.M. Diet, supplement use, and prostate cancer risk: Results from the prostate cancer prevention trial. Am. J. Epidemiol. 2010, 172, 566–577, doi:10.1093/aje/kwq148.
- Williams, C.D.; Whitley, B.M.; Hoyo, C.; Grant, D.J.; Schwartz, G.G.; Presti, J.C., Jr.; Iraggi, J.D.; Newman, K.A.; Gerber, L.; Taylor, L.A.; et al. Dietary calcium and risk for prostate cancer: A case-control study among US veterans. Prev. Chronic Dis. 2012, 9, E39.
- Wang, L.; Manson, J.E.; Song, Y.; Sesso, H.D. Systematic review: Vitamin D and calcium supplementation in prevention of cardiovascular events. Ann. Intern. Med. 2010, 152, 315–323.
- Wang, L.; Manson, J.E.; Sesso, H.D. Calcium intake and risk of cardiovascular disease: A review of prospective studies and randomized clinical trials. Am. J. Cardiovasc. Drugs 2012, 12, 105–116, doi:10.2165/11595400-000000000-00000.
- Davies, K.M.; Heaney, R.P.; Recker, R.R.; Lappe, J.M.; Barger-Lux, M.J.; Rafferty, K.; Hinders, S. Calcium intake and body weight. J. Clin. Endocrinol. Metab. 2000, 85, 4635–4638, doi:10.1210/jc.85.12.4635.
- Zemel, M.B.; Shi, H.; Greer, B.; Dirienzo, D.; Zemel, P.C. Regulation of adiposity by dietary calcium. FASEB J. 2000, 14, 1132–1138.
- Puntus, T.; Schneider, B.; Meran, J.; Peterlik, M.; Kudlacek, S. Influence of age and gender on associations of body mass index with bone mineral density, bone turnover markers and circulating calcium-regulating and bone-active sex hormones. Bone 2011, 49, 824–829, doi:10.1016/j.bone.2011.06.003.
- Pittas, A.G.; Lau, J.; Hu, F.B.; Dawson-Hughes, B. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis. J. Clin. Endocrinol. Metab. 2007, 92, 2017–2029, doi:10.1210/jc.2007-0298.
- McCarron, D.A.; Reusser, M.E. Finding consensus in the dietary calcium-blood pressure debate. J. Am. Coll. Nutr. 1999, 18, 398S–405S.
- Dobnig, H.; Pfeifer, M.; Begerow, B.; Suppan, K. Calcium, Not Vitamin D Decreases Blood Pressure Effectively in Elderly Subjects with Low Vitamin D Levels: A Randomized, Double-blind, Multi-center Study. In Abstracts of the 87th Annual Meeting of the Endocrine Society, San Diego, California, USA, 4–7 June 2005.
- Bostick, R.M.; Kushi, L.H.; Wu, Y.; Meyer, K.A.; Sellers, T.A.; Folsom, A.R. Relation of calcium, vitamin D, and dairy food intake to ischemic heart disease mortality among postmenopausal women. Am. J. Epidemiol. 1999, 149, 151–161, doi:10.1093/oxfordjournals.aje.a009781.
- Umesawa, M.; Iso, H.; Ishihara, J.; Saito, I.; Kokubo, Y.; Inoue, M.; Tsugane, S. Dietary calcium intake and risks of stroke, its subtypes, and coronary heart disease in Japanese: The JPHC study cohort I. Stroke 2008, 39, 2449–2456, doi:10.1161/STROKEAHA.107.512236.
- Al-Delaimy, W.K.; Rimm, E.; Willett, W.C.; Stampfer, M.J.; Hu, F.B. A prospective study of calcium intake from diet and supplements and risk of ischemic heart disease among men. Am. J. Clin. Nutr. 2003, 77, 814–818.
- Lewis, J.R.; Calver, J.; Zhu, K.; Flicker, L.; Prince, R.L. Calcium supplementation and the risks of atherosclerotic vascular disease in older women: Results of a 5-year RCT and a 4.5-year follow-up. J. Bone Miner. Res. 2011, 26, 35–41, doi:10.1002/jbmr.176.
- Pentti, K.; Tuppurainen, M.T.; Honkanen, R.; Sandini, L.; Kroger, H.; Alhava, E.; Saarikoski, S. Use of calcium supplements and the risk of coronary heart disease in 52–62-year-old women: The Kuopio osteoporosis risk factor and prevention study. Maturitas 2009, 63, 73–78, doi:10.1016/j.maturitas.2009.03.006.
- Bolland, M.J.; Barber, P.A.; Doughty, R.N.; Mason, B.; Horne, A.; Ames, R.; Gamble, G.D.; Grey, A.; Reid, I.R. Vascular events in healthy older women receiving calcium supplementation: Randomised controlled trial. BMJ 2008, 336, 262–266, doi:10.1136/bmj.39440.525752.BE.
- Bolland, M.J.; Bacon, C.J.; Horne, A.M.; Mason, B.H.; Ames, R.W.; Wang, T.K.; Grey, A.B.; Gamble, G.D.; Reid, I.R. Vitamin D insufficiency and health outcomes over 5 y in older women. Am. J. Clin. Nutr. 2010, 91, 82–89.
- Nordin, B.E.; Nakane, M.; Ma, J.; Metcalfe, A.V. Effects of a weak case. BMJ 2006, 186, 20–28.
- Burckhardt, P. Potential negative cardiovascular effects of calcium supplements. Osteoporos. Int. 2011, 22, 1645–1647, doi:10.1007/s00198-011-1602-5.
- Samelson, E.J.; Booth, S.L.; Fox, C.S.; Tucker, K.L.; Wang, T.J.; Hoffmann, U.; Cupples, L.A.; O’Donnell, C.J.; Kiel, D.P. Calcium intake is not associated with increased coronary artery calcification: The Framingham study. Am. J. Clin. Nutr. 2012, 96, 1274–1280, doi:10.3945/ajcn.112.044230.
- De Boer, I.H.; Kestenbaum, B.; Shoben, A.B.; Michos, E.D.; Sarnak, M.J.; Siscovick, D.S. 25-hydroxyvitamin D levels inversely associate with risk for developing coronary artery calcification. J. Am. Soc. Nephrol. 2009, 20, 1805–1812, doi:10.1681/ASN.2008111157.
- Mathew, S.; Lund, R.J.; Chaudhary, L.R.; Geurs, T.; Hruska, K.A. Vitamin D receptor activators can protect against vascular calcification. J. Am. Soc. Nephrol. 2008, 19, 1509–1519, doi:10.1681/ASN.2007080902.
- Wu-Wong, J.R.; Nakane, M.; Ma, J.; Ruan, X.; Kroeger, P.E. Effects of vitamin D analogs on gene expression profiling in human coronary artery smooth muscle cells. Atherosclerosis 2006, 186, 20–28, doi:10.1016/j.atherosclerosis.2005.06.046.
- Watson, K.E.; Abrolat, M.L.; Malone, L.L.; Hoeg, J.M.; Doherty, T.; Detrano, R.; Demer, L.L. Active serum vitamin D levels are inversely correlated with coronary calcification. Circulation 1997, 96, 1755–1760, doi:10.1161/01.CIR.96.6.1755.
- Brown, E.M.; Gamba, G.; Riccardi, D.; Lombardi, M.; Butters, R.; Kifor, O.; Sun, A.; Hediger, M.A.; Lytton, J.; Hebert, S.C. Cloning and characterization of an extracellular Ca2+-sensing receptor from bovine parathyroid. Nature 1993, 366, 575–580.
- Tfelt-Hansen, J.; Brown, E.M. The calcium-sensing receptor in normal physiology and pathophysiology: A review. Crit. Rev. Clin. Lab. Sci. 2005, 42, 35–70, doi:10.1080/10408360590886606.
- Brown, E.M.; Pollak, M.; Hebert, S.C. Sensing of extracellular Ca2+ by parathyroid and kidney cells: Cloning and characterization of an extracellular Ca2+-sensing receptor. Am. J. Kidney Dis. 1995, 25, 506–513, doi:10.1016/0272-6386(95)90118-3.
- Shalhoub, V.; Grisanti, M.; Padagas, J.; Scully, S.; Rattan, A.; Qi, M.; Varnum, B.; Vezina, C.; Lacey, D.; Martin, D. In vitro studies with the calcimimetic, cinacalcet HCl, on normal human adult osteoblastic and osteoclastic cells. Crit. Rev. Eukaryot. Gene Expr. 2003, 13, 89–106, doi:10.1615/CritRevEukaryotGeneExpr.v13.i24.20.
- Hebert, S.C.; Cheng, S.; Geibel, J. Functions and roles of the extracellular Ca2+-sensing receptor in the gastrointestinal tract. Cell Calcium 2004, 35, 239–247, doi:10.1016/j.ceca.2003.10.015.
- Kallay, E.; Kifor, O.; Chattopadhyay, N.; Brown, E.M.; Bischof, M.G.; Peterlik, M.; Cross, H.S. Calcium-dependent c-myc proto-oncogene expression and proliferation of Caco-2 cells: A role for a luminal extracellular calcium-sensing receptor. Biochem. Biophys. Res. Commun. 1997, 232, 80–83, doi:10.1006/bbrc.1997.6225.
- Cheng, I.; Klingensmith, M.E.; Chattopadhyay, N.; Kifor, O.; Butters, R.R.; Soybel, D.I.; Brown, E.M. Identification and localization of the extracellular calcium-sensing receptor in human breast. J. Clin. Endocrinol. Metab. 1998, 83, 703–707, doi:10.1210/jc.83.2.703.
- McNeil, L.; Hobson, S.; Nipper, V.; Rodland, K.D. Functional calcium-sensing receptor expression in ovarian surface epithelial cells. Am. J. Obstet. Gynecol. 1998, 178, 305–313, doi:10.1016/S0002-9378(98)80017-3.
- Sanders, J.L.; Chattopadhyay, N.; Kifor, O.; Yamaguchi, T.; Brown, E.M. Ca2+-sensing receptor expression and PTHrP secretion in PC-3 human prostate cancer cells. Am. J. Physiol. Endocrinol. Metab. 2001, 281, E1267–E1274.
- Racz, G.Z.; Kittel, A.; Riccardi, D.; Case, R.M.; Elliott, A.C.; Varga, G. Extracellular calcium sensing receptor in human pancreatic cells. Gut 2002, 51, 705–711, doi:10.1136/gut.51.5.705.
- Squires, P.E.; Harris, T.E.; Persaud, S.J.; Curtis, S.B.; Buchan, A.M.; Jones, P.M. The extracellular calcium-sensing receptor on human beta-cells negatively modulates insulin secretion. Diabetes 2000, 49, 409–417, doi:10.2337/diabetes.49.3.409.
- Yamaguchi, T.; Olozak, I.; Chattopadhyay, N.; Butters, R.R.; Kifor, O.; Scadden, D.T.; Brown, E.M. Expression of extracellular calcium (Ca2+)o-sensing receptor in human peripheral blood monocytes. Biochem. Biophys. Res. Commun. 1998, 246, 501–506, doi:10.1006/bbrc.1998.8648.
- Molostvov, G.; James, S.; Fletcher, S.; Bennett, J.; Lehnert, H.; Bland, R.; Zehnder, D. Extracellular calcium-sensing receptor is functionally expressed in human artery. Am. J. Physiol. Renal Physiol. 2007, 293, F946–F955, doi:10.1152/ajprenal.00474.2006.
- Yano, S.; Brown, E.M.; Chattopadhyay, N. Calcium-sensing receptor in the brain. Cell Calcium 2004, 35, 257–264, doi:10.1016/j.ceca.2003.10.008.
- Chattopadhyay, N.; Brown, E.M. Calcium-Sensing Receptor; Kluwer Academic Publishers: Boston, MA, USA, 2003.
- Chakravarti, B.; Chattopadhyay, N.; Brown, E.M. Signaling through the extracellular calcium-sensing receptor (CaSR). Adv. Exp. Med. Biol. 2012, 740, 103–142, doi:10.1007/978-94-007-2888-2_5.
- Maiti, A.; Hait, N.C.; Beckman, M.J. Extracellular calcium-sensing receptor activation induces vitamin D receptor levels in proximal kidney HK-2G cells by a mechanism that requires phosphorylation of p38 alpha MAPK. J. Biol. Chem. 2008, 283, 175–183.
- Garrett, J.E.; Tamir, H.; Kifor, O.; Simin, R.T.; Rogers, K.V.; Mithal, A.; Gagel, R.F.; Brown, E.M. Calcitonin-secreting cells of the thyroid express an extracellular calcium receptor gene. Endocrinology 1995, 136, 5202–5211, doi:10.1210/en.136.11.5202.
- Kapur, K.; Johnson, T.; Beckmann, N.D.; Sehmi, J.; Tanaka, T.; Kutalik, Z.; Styrkarsdottir, U.; Zhang, W.; Marek, D.; Gudbjartsson, D.F.; et al. Genome-wide meta-analysis for serum calcium identifies significantly associated SNPs near the calcium-sensing receptor (CaSR) gene. PLoS Genet. 2010, 6, e1001035, doi:10.1371/journal.pgen.1001035.
- Dvorak, M.M.; Siddiqua, A.; Ward, D.T.; Carter, D.H.; Dallas, S.L.; Nemeth, E.F.; Riccardi, D. Physiological changes in extracellular calcium concentration directly control osteoblast function in the absence of calciotropic hormones. Proc. Natl. Acad. Sci. USA 2004, 101, 5140–5145.
- Chang, W.; Tu, C.; Chen, T.H.; Bikle, D.; Shoback, D. The extracellular calcium-sensing receptor (CaSR) is a critical modulator of skeletal development. Sci. Signal. 2008, 1, ra1, doi:10.1126/scisignal.1159945.
- Brown, E.M.; Lian, J.B. New insights in bone biology: Unmasking skeletal effects of the extracellular calcium-sensing receptor. Sci. Signal. 2008, 1, pe40, doi:10.1126/scisignal.135pe40.
- Dvorak-Ewell, M.M.; Chen, T.H.; Liang, N.; Garvey, C.; Liu, B.; Tu, C.; Chang, W.; Bikle, D.D.; Shoback, D.M. Osteoblast extracellular Ca2+-sensing receptor regulates bone development, mineralization, and turnover. J. Bone Miner. Res. 2011, 26, 2935–2947, doi:10.1002/jbmr.520.
- Rodland, K.D. The role of the calcium-sensing receptor in cancer. Cell Calcium 2004, 35, 291–295.
- Saidak, Z.; Mentaverri, R.; Brown, E.M. The role of the calcium-sensing receptor in the development and progression of cancer. Endocr. Rev. 2009, 30, 178–195, doi:10.1210/er.2008-0041.
- Brown, E.M.; Yang, J.J. Biochemistry and biology of the extracellular calcium-sensing receptor. Bone 2009, 44, S201–S202, doi:10.1016/j.bone.2009.03.011.
- Magno, A.L.; Ward, B.K.; Ratajczak, T. The calcium-sensing receptor: A molecular perspective. Endocr. Rev. 2011, 32, 3–30, doi:10.1210/er.2009-0043.
- Dvorak, M.M.; Riccardi, D. Ca2+ as an extracellular signal in bone. Cell Calcium 2004, 35, 249–255.
- Yamaguchi, T.; Kifor, O.; Chattopadhyay, N.; Brown, E.M. Expression of extracellular calcium (Ca2+)o-sensing receptor in the clonal osteoblast-like cell lines, UMR-106 and SAOS-2. Biochem. Biophys. Res. Commun. 1998, 243, 753–757, doi:10.1006/bbrc.1998.8178.
- Yamaguchi, T.; Chattopadhyay, N.; Kifor, O.; Butters, R.R., Jr.; Sugimoto, T.; Brown, E.M. Mouse osteoblastic cell line (MC3T3-E1) expresses extracellular calcium (Ca2+)o-sensing receptor and its agonists stimulate chemotaxis and proliferation of MC3T3-E1 cells. J. Bone Miner. Res. 1998, 13, 1530–1538.
- Yamaguchi, T.; Chattopadhyay, N.; Kifor, O.; Brown, E.M. Extracellular calcium (Ca2+)o-sensing receptor in a murine bone marrow-derived stromal cell line (ST2): Potential mediator of the actions of (Ca2+)o on the function of ST2 cells. Endocrinology 1998, 139, 3561–3568, doi:10.1210/en.139.8.3561.
- Baron, R.; Rawadi, G. Targeting the Wnt/beta-catenin pathway to regulate bone formation in the adult skeleton. Endocrinology 2007, 148, 2635–2643, doi:10.1210/en.2007-0270.
- Krause, C.; de Gorter, D.J.J.; Karperien, M.; ten Dijke, P. Signal transduction cascades controlling osteoblast differentiation. In Primer of the Metabolic Bone Diseases, 7th ed.; American Society of Bone Mineral Research: Washington, DC, USA, 2008; pp. 10–14.
- Kohn, A.D.; Moon, R.T. Wnt and calcium signaling: β-catenin-independent pathways. Cell Calcium 2005, 38, 439–446, doi:10.1016/j.ceca.2005.06.022.
- Owen, T.A.; Aronow, M.S.; Barone, L.M.; Bettencourt, B.; Stein, G.S.; Lian, J.B. Pleiotropic effects of vitamin D on osteoblast gene expression are related to the proliferative and differentiated state of the bone cell phenotype: Dependency upon basal levels of gene expression, duration of exposure, and bone matrix competency in normal rat osteoblast cultures. Endocrinology 1991, 128, 1496–1504, doi:10.1210/endo-128-3-1496.
- Sheinin, Y.; Kallay, E.; Wrba, F.; Kriwanek, S.; Peterlik, M.; Cross, H.S. Immunocytochemical localization of the extracellular calcium-sensing receptor in normal and malignant human large intestinal mucosa. J. Histochem. Cytochem. 2000, 48, 595–602, doi:10.1177/002215540004800503.
- Whitfield, J.F. Calcium, calcium-sensing receptor and colon cancer. Cancer Lett. 2009, 275, 9–16, doi:10.1016/j.canlet.2008.07.001.
- Bhagavathula, N.; Kelley, E.A.; Reddy, M.; Nerusu, K.C.; Leonard, C.; Fay, K.; Chakrabarty, S.; Varani, J. Upregulation of calcium-sensing receptor and mitogen-activated protein kinase signalling in the regulation of growth and differentiation in colon carcinoma. Br. J. Cancer 2005, 93, 1364–1371, doi:10.1038/sj.bjc.6602852.
- Rey, O.; Chang, W.; Bikle, D.; Rozengurt, N.; Young, S.H.; Rozengurt, E. Negative cross-talk between calcium-sensing receptor and beta-catenin signaling systems in colonic epithelium. J. Biol. Chem. 2012, 287, 1158–1167.
- Gama, L.; Baxendale-Cox, L.M.; Breitwieser, G.E. Ca2+-sensing receptors in intestinal epithelium. Am. J. Physiol. 1997, 273, C1168–C1175.
- Kallay, E.; Bajna, E.; Wrba, F.; Kriwanek, S.; Peterlik, M.; Cross, H.S. Dietary calcium and growth modulation of human colon cancer cells: Role of the extracellular calcium-sensing receptor. Cancer Detect. Prev. 2000, 24, 127–136.
- Hizaki, K.; Yamamoto, H.; Taniguchi, H.; Adachi, Y.; Nakazawa, M.; Tanuma, T.; Kato, N.; Sukawa, Y.; Sanchez, J.V.; Suzuki, H.; et al. Epigenetic inactivation of calcium-sensing receptor in colorectal carcinogenesis. Mod. Pathol. 2011, 24, 876–884, doi:10.1038/modpathol.2011.10.
- Kallay, E.; Bonner, E.; Wrba, F.; Thakker, R.V.; Peterlik, M.; Cross, H.S. Molecular and functional characterization of the extracellular calcium-sensing receptor in human colon cancer cells. Oncol. Res. 2003, 13, 551–559.
- Kallay, E.; Bises, G.; Bajna, E.; Bieglmayer, C.; Gerdenitsch, W.; Steffan, I.; Kato, S.; Armbrecht, H.J.; Cross, H.S. Colon-specific regulation of vitamin D hydroxylases—A possible approach for tumor prevention. Carcinogenesis 2005, 26, 1581–1589, doi:10.1093/carcin/bgi124.
- Chakrabarty, S.; Wang, H.; Canaff, L.; Hendy, G.N.; Appelman, H.; Varani, J. Calcium sensing receptor in human colon carcinoma: Interaction with Ca2+ and 1,25-dihydroxyvitamin D3. Cancer Res. 2005, 65, 493–498.
- MacLeod, R.J.; Hayes, M.; Pacheco, I. Wnt5a secretion stimulated by the extracellular calcium-sensing receptor inhibits defective Wnt signaling in colon cancer cells. Am. J. Physiol. Gastrointest. Liver Physiol. 2007, 293, G403–G411, doi:10.1152/ajpgi.00119.2007.
- Bhagavathula, N.; Hanosh, A.W.; Nerusu, K.C.; Appelman, H.; Chakrabarty, S.; Varani, J. Regulation of E-cadherin and β-catenin by Ca2+ in colon carcinoma is dependent on calcium-sensing receptor expression and function. Int. J. Cancer 2007, 121, 1455–1462, doi:10.1002/ijc.22858.
- Palmer, H.G.; Gonzalez-Sancho, J.M.; Espada, J.; Berciano, M.T.; Puig, I.; Baulida, J.; Quintanilla, M.; Cano, A.; de Herreros, A.G.; Lafarga, M.; et al. Vitamin D3 promotes the differentiation of colon carcinoma cells by the induction of E-cadherin and the inhibition of β-catenin signaling. J. Cell. Biol. 2001, 154, 369–387, doi:10.1083/jcb.200102028.
- Almquist, M.; Manjer, J.; Bondeson, L.; Bondeson, A.G. Serum calcium and breast cancer risk: Results from a prospective cohort study of 7847 women. Cancer Causes Control 2007, 18, 595–602, doi:10.1007/s10552-007-9001-0.
- El Hiani, Y.; Ahidouch, A.; Roudbaraki, M.; Guenin, S.; Brule, G.; Ouadid-Ahidouch, H. Calcium-sensing receptor stimulation induces nonselective cation channel activation in breast cancer cells. J. Membr. Biol. 2006, 211, 127–137, doi:10.1007/s00232-006-0017-2.
- Roderick, H.L.; Cook, S.J. Ca2+ signalling checkpoints in cancer: Remodelling Ca2+ for cancer cell proliferation and survival. Nat. Rev. Cancer 2008, 8, 361–375, doi:10.1038/nrc2374.
- Curry, M.C.; Luk, N.A.; Kenny, P.A.; Roberts-Thomson, S.J.; Monteith, G.R. Distinct regulation of cytoplasmic calcium signals and cell death pathways by different plasma membrane calcium ATPase isoforms in MDA-MB-231 breast cancer cells. J. Biol. Chem. 2012, 287, 28598–28608.
- Promkan, M.; Liu, G.; Patmasiriwat, P.; Chakrabarty, S. BRCA1 suppresses the expression of survivin and promotes sensitivity to paclitaxel through the calcium sensing receptor (CaSR) in human breast cancer cells. Cell Calcium 2011, 49, 79–88, doi:10.1016/j.ceca.2011.01.003.
- Mathiasen, I.S.; Sergeev, I.N.; Bastholm, L.; Elling, F.; Norman, A.W.; Jaattela, M. Calcium and calpain as key mediators of apoptosis-like death induced by vitamin D compounds in breast cancer cells. J. Biol. Chem. 2002, 277, 30738–30745.
- Leclercq, G. Calcium-induced activation of estrogen receptor α—New insight. Steroids 2012, 77, 924–927, doi:10.1016/j.steroids.2012.01.012.
- Sanders, J.L.; Chattopadhyay, N.; Kifor, O.; Yamaguchi, T.; Butters, R.R.; Brown, E.M. Extracellular calcium-sensing receptor expression and its potential role in regulating parathyroid hormone-related peptide secretion in human breast cancer cell lines. Endocrinology 2000, 141, 4357–4364, doi:10.1210/en.141.12.4357.
- Yano, S.; Macleod, R.J.; Chattopadhyay, N.; Tfelt-Hansen, J.; Kifor, O.; Butters, R.R.; Brown, E.M. Calcium-sensing receptor activation stimulates parathyroid hormone-related protein secretion in prostate cancer cells: Role of epidermal growth factor receptor transactivation. Bone 2004, 35, 664–672, doi:10.1016/j.bone.2004.04.014.
- Liao, J.; Schneider, A.; Datta, N.S.; McCauley, L.K. Extracellular calcium as a candidate mediator of prostate cancer skeletal metastasis. Cancer Res. 2006, 66, 9065–9073, doi:10.1158/0008-5472.CAN-06-0317.
- Shui, I.M.; Mucci, L.A.; Wilson, K.M.; Kraft, P.; Penney, K.L.; Stampfer, M.J.; Giovannucci, E. Common genetic variation of the calcium sensing receptor and lethal prostate cancer risk. Cancer Epidemiol. Biomarkers Prev. 2012, 22, 118–126.
- Smajilovic, S.; Yano, S.; Jabbari, R.; Tfelt-Hansen, J. The calcium-sensing receptor and calcimimetics in blood pressure modulation. Br. J. Pharmacol. 2011, 164, 884–893, doi:10.1111/j.1476-5381.2011.01317.x.
- Torres, P.A.; de Broe, M. Calcium-sensing receptor, calcimimetics, and cardiovascular calcifications in chronic kidney disease. Kidney Int. 2012, 82, 19–25, doi:10.1038/ki.2012.69.
- Tfelt-Hansen, J.; Hansen, J.L.; Smajilovic, S.; Terwilliger, E.F.; Haunso, S.; Sheikh, S.P. Calcium receptor is functionally expressed in rat neonatal ventricular cardiomyocytes. Am. J. Physiol. Heart Circ. Physiol. 2006, 290, H1165–H1171.
- Weston, A.H.; Geraghty, A.; Egner, I.; Edwards, G. The vascular extracellular calcium-sensing receptor: An update. Acta Physiol. 2011, 203, 127–137, doi:10.1111/j.1748-1716.2010.02249.x.
- Wang, R.; Xu, C.; Zhao, W.; Zhang, J.; Cao, K.; Yang, B.; Wu, L. Calcium and polyamine regulated calcium-sensing receptors in cardiac tissue. Eur. J. Biochem. 2003, 270, 2680–2688, doi:10.1046/j.1432-1033.2003.03645.x.
- Zhong, X.; Liu, J.; Lu, F.; Wang, Y.; Zhao, Y.; Dong, S.; Leng, X.; Jia, J.; Ren, H.; Xu, C.; et al. Calcium sensing receptor regulates cardiomyocyte function through nuclear calcium. Cell Biol. Int. 2012, 36, 937–943, doi:10.1042/CBI20110594.
- Hofer, A.M.; Curci, S.; Doble, M.A.; Brown, E.M.; Soybel, D.I. Intercellular communication mediated by the extracellular calcium-sensing receptor. Nat. Cell Biol. 2000, 2, 392–398, doi:10.1038/35017020.
- Molostvov, G.; Bland, R.; Zehnder, D. Expression and role of the calcium-sensing receptor in the blood vessel wall. Curr. Pharm. Biotechnol. 2009, 10, 282–288, doi:10.2174/138920109787847466.
- Alam, M.U.; Kirton, J.P.; Wilkinson, F.L.; Towers, E.; Sinha, S.; Rouhi, M.; Vizard, T.N.; Sage, A.P.; Martin, D.; Ward, D.T.; et al. Calcification is associated with loss of functional calcium-sensing receptor in vascular smooth muscle cells. Cardiovasc. Res. 2009, 81, 260–268.
- Atchison, D.K.; Beierwaltes, W.H. The influence of extracellular and intracellular calcium on the secretion of renin. Pflugers Arch. 2012, doi:10.1007/s00424-012-1107-x.
- Wang, D.; An, S.J.; Wang, W.H.; McGiff, J.C.; Ferreri, N.R. CaR-mediated COX-2 expression in primary cultured MTAl cells. Am. J. Physiol. Renal Physiol. 2001, 281, F658–F664.
- Abdullah, H.I.; Pedraza, P.L.; McGiff, J.C.; Ferreri, N.R. Calcium-sensing receptor signaling pathways in medullary thick ascending limb cells mediate COX-2-derived PGE2 production: Functional significance. Am. J. Physiol. Renal Physiol. 2008, 295, F1082–F1089, doi:10.1152/ajprenal.90316.2008.
- Gamba, G.; Friedman, P.A. Thick ascending limb: The Na+:K+:2Cl− co-transporter, NKCC2, and the calcium-sensing receptor, CasR. Pflugers Arch. 2009, 458, 61–76, doi:10.1007/s00424-008-0607-1.
- Vargas-Poussou, R.; Huang, C.; Hulin, P.; Houillier, P.; Jeunemaitre, X.; Paillard, M.; Planelles, G.; Dechaux, M.; Miller, R.T.; Antignac, C. Functional characterization of a calcium-sensing receptor mutation in severe autosomal dominant hypocalcemia with a Bartter-like syndrome. J. Am. Soc. Nephrol. 2002, 13, 2259–2266, doi:10.1097/01.ASN.0000025781.16723.68.
- Peterlik, M. Vitamin D insufficiency and chronic diseases: Hype and reality. Food Funct. 2012, 3, 784–794, doi:10.1039/c2fo10262e.
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