Association of calcitriol and blood pressure in normotensive men

Vitamin d and stage 5 chronic kidney disease: a new paradigm?

Vitamin D receptor agonists (VDRA) are currently recommended for the treatment of secondary hyperparathyroidism in stage 5 CKD. They are considered to be contraindicated in the presence of low or normal (for a dialysis patient) levels of PTH due to the risk of developing adynamic bone disease, with consequent vascular calcification. However, these recommendations are increasingly at odds with the epidemiological evidence, which consistently shows a large survival advantage for patients treated with low-dose VDRAs, regardless of plasma calcium, phosphate, or PTH. A large number of pleiotropic effects of vitamin D have been described, including inhibition of renin activity, anti-inflammation, and suppression of vascular calcification stimulators and stimulation of vascular calcification inhibitors present in the uremic milieu. Laboratory studies suggest that a normal cellular vitamin D level is necessary for normal cardiomyocyte and vascular smooth muscle function. While pharmacological doses of VDRA can be harmful, the present evidence suggests that the level of 1,25-dihydroxycholecalciferol should also be more physiological in stage 5 CKD, and that widespread use of low-dose VDRA would be beneficial. A randomized controlled trial to test this hypothesis is warranted.

Vitamin D status is not related to development of atrial fibrillation in the community

BACKGROUND

Atrial fibrillation (AF) is common and is an important cause of cardiovascular morbidity and mortality. Vitamin D is an emerging risk factor in cardiovascular disease, and vitamin D status is modifiable. Thus, we sought to investigate whether vitamin D status predisposed to the development of AF in a community-based sample.

METHODS

We evaluated the relation between vitamin D status and development of AF in 2,930 participants of the Framingham Heart Study, Massachusetts, USA, without prevalent AF. The mean age was 65 ± 11 years, and 56% were women. Vitamin D status was assessed by measuring 25-hydroxyvitamin D (25[OH]D) concentrations. Multivariable Cox regression models were adjusted for AF risk factors and season.

RESULTS

During a mean follow-up of 9.9 years, 425 participants (15%) developed AF. In Cox proportional hazards models, 25(OH)D was not associated with development of AF, with a multivariable-adjusted hazard ratio of 0.99 per SD increment in 25(OH)D levels (95% CI 0.88-1.10, P = .81). Also, no relation was found in models including 25(OH)D as a dichotomous variable (above and below the cohort-specific 20th percentile; P = .59).

CONCLUSION

In our community-based sample, vitamin D status was not related to incident AF. Our data suggest that vitamin D deficiency does not promote the development of AF in the ambulatory setting.

Shining D' light on chronic kidney disease: mechanisms that may underpin the cardiovascular benefit of vitamin D

Hypovitaminosis D is a significant health-care burden worldwide, particularly in susceptible populations such as those with chronic kidney disease (CKD). Recent epidemiological studies have identified that both higher serum vitamin D concentrations and use of vitamin D supplements may confer a survival benefit both in terms of all-cause and cardiovascular mortality. There is potential to investigate this inexpensive therapy for the CKD population, which suffers excessive cardiovascular events, although the mechanisms explaining this link have yet to be fully elucidated. This review discusses potential mechanisms identified in the basic science literature that may provide important insights into how vitamin D may orchestrate a change in cardiovascular risk profile through such diverse mechanisms as inflammation, atherogenesis, glucose homeostasis, vascular calcification, renin-angiotensin regulation and alterations in cardiac physiology. Where available, the clinical translation of these concepts to intervention trials in the CKD population will be reviewed.

Vitamin d therapy and cardiovascular health

Vitamin D belongs to the family of nuclear steroid hormones, which has pleiotropic effects on several organ systems. Different vitamin D compounds have been studied as potential cardioprotective agents over the past 20 years. The results of these clinical studies vary based on the form and dosage of vitamin D administered during the trial. In the past 5 years, many have described an association of vitamin D compounds and cardiovascular health through reduction in blood pressure, reduction in inflammatory biomarkers, improved insulin sensitivity, and reduction in cardiovascular disease complications and death. Because there are several vitamin D compounds, it is important to consider the full breadth of the literature when examining vitamin D and cardiovascular health, to assist in hypothesis generation and understanding of the current state of the science. Although a growing body of evidence suggests that nutritional vitamin D supplementation and potentially even treatment with synthetic analogues of vitamin D may be cardioprotective, relatively few studies have examined either of these compounds in a randomized, controlled fashion. Studies examining the benefit of vitamin D supplementation are now beginning, but future studies considering calcitriol and analogue therapy also seem warranted.

Vitamin D insufficiency is associated with impaired vascular endothelial and smooth muscle function and hypertension in young rats

Increasing evidence links vitamin D deficiency and cardiovascular dysfunction in human adults. There is a worldwide increase in the prevalence of vitamin D deficiency in women of reproductive age, particularly dark-skinned and/or veiled women and their infants. We used a rat model to determine the functional impact of vitamin D deficiency during intra uterine and early life on resistance artery reactivity and blood pressure in the offspring as young adults. Rat dams were maintained on vitamin D deficient or replete chow before and during pregnancy and lactation. The offspring were maintained on the same chow until studied at 7-8 weeks of age. Conscious blood pressure was measured. Endothelial and smooth muscle function were tested in mesenteric arteries on a pressure myograph. Vitamin D deficient male and female offspring had a 10-fold lower serum 25-hydroxyvitamin D (P < 0.0001) and markedly elevated blood pressures (11-20 mmHg, P < 0.001) and heart rates (21-40 beats min(-1), P < 0.02) than control fed offspring. Serum calcium was unchanged. Mesenteric artery myogenic tone was doubled in vitamin D deficiency. Endothelium-derived nitric oxide-evoked dilation was halved in arteries from vitamin D deficient males and dioestrous females. Dilation attributed to endothelium-derived hyperpolarizing factor was all but abolished in vitamin D deficient oestrous females. Nitroprusside-evoked dilation was unaltered in arteries from males, but was markedly reduced in vessels of vitamin D deplete females. In conclusion, early life vitamin D deficiency is associated with endothelial vasodilator dysfunction, and this is likely to contribute to the accompanying elevation in blood pressure and an increased cardiovascular disease risk.

Vitamin D and cardiovascular outcomes: a systematic review and meta-analysis

CONTEXT

Several studies found association between vitamin D levels and hypertension, coronary artery calcification, and heart disease.

OBJECTIVE

The aim of this study was to summarize the evidence on the effect of vitamin D on cardiovascular outcomes.

DESIGN AND METHODS

We searched electronic databases from inception through August 2010 for randomized trials. Reviewers working in duplicate and independently extracted study characteristics, quality, and the outcomes of interest. Random-effects meta-analysis was used to pool the relative risks (RR) and the weighted mean differences across trials.

RESULTS

We found 51 eligible trials with moderate quality. Vitamin D was associated with nonsignificant effects on the patient-important outcomes of death [RR, 0.96; 95% confidence interval (CI), 0.93, 1.00; P = 0.08], myocardial infarction (RR, 1.02; 95% CI, 0.93, 1.13; P = 0.64), and stroke (RR, 1.05; 95% CI, 0.88, 1.25; P = 0.59). These analyses were associated with minimal heterogeneity. There were no significant changes in the surrogate outcomes of lipid fractions, glucose, or diastolic or systolic blood pressure. The latter analyses were associated with significant heterogeneity, and the pooled estimates were trivial in absolute terms.

CONCLUSIONS

Trial data available to date are unable to demonstrate a statistically significant reduction in mortality and cardiovascular risk associated with vitamin D. The quality of the available evidence is low to moderate at best.

Relations of serum phosphorus levels to echocardiographic left ventricular mass and incidence of heart failure in the community

AIMS

To evaluate the association of serum phosphorus with cardiac structure/function and incident heart failure.

METHODS AND RESULTS

We related serum phosphorus to echocardiographic left ventricular (LV) measurements cross-sectionally, and to incident heart failure prospectively in 3300 participants (mean age 44 years, 51% women) free of heart failure, myocardial infarction, and chronic kidney disease (estimated glomerular filtration rate [eGFR]<60 mL/min/1.73 m(2)). Cross-sectionally, serum phosphorus was related positively to LV mass, internal dimensions, and systolic dysfunction. On follow-up (mean 17.4 years), 157 individuals developed heart failure. In models adjusting for established risk factors as time-varying covariates, each mg/dL increment in serum phosphorus was associated with a 1.74-fold risk of heart failure [95% confidence intervals (CI) 1.17-2.59]. Individuals in the highest serum phosphorus quartile experienced a two-fold (95% CI 1.28-3.40) risk of heart failure compared with participants in the lowest quartile. These relations were maintained upon additional adjustment for LV mass/dimensions and systolic dysfunction. In analyses restricted to individuals with eGFR >90 mL/min/1.73 m(2), no proteinuria and serum phosphorus <4.5 mg/dL, the association of serum phosphorus with heart failure remained robust.

CONCLUSION

In our community-based sample, higher serum phosphorus was associated with greater LV mass cross-sectionally, and with an increased risk of heart failure prospectively.

Serum 25-hydroxyvitamin D, calcium, phosphorus, and electrocardiographic QT interval duration: findings from NHANES III and ARIC

CONTEXT

Disturbances in 25-hydroxyvitamin D, calcium, and phosphorus concentrations have been associated with increased risks of total and cardiovascular mortality. It is possible that changes in electrocardiographic QT interval duration may mediate these effects, but the association of 25-hydroxyvitamin D, phosphorus, and calcium concentrations with QT interval duration has not been evaluated in general population samples.

OBJECTIVE

The objective of the study was to evaluate the association of 25-hydroxyvitamin D, phosphorus, and calcium concentrations with QT interval duration in two large samples of the U.S. general population.

DESIGN

This study included cross-sectional analyses the Third National Health and Nutrition Survey (NHANES III) and the Atherosclerosis Risk in Communities (ARIC) study.

SETTING

The study was conducted in the general community.

PATIENTS OR OTHER PARTICIPANTS

Patients included 7,312 men and women from NHANES III and 14,825 men and women from the ARIC study.

INTERVENTIONS

Serum 25-hydroxyvitamin D, total and ionized calcium, and inorganic phosphorus were measured in NHANES III, and serum total calcium and inorganic phosphorus were measured in ARIC.

MAIN OUTCOME MEASURE

QT interval duration was obtained from standard 12-lead electrocardiograms.

RESULTS

In NHANES III, the multivariate adjusted differences in average QT interval duration comparing the highest vs. the lowest quartiles of serum total calcium, ionized calcium, and phosphorus were -3.6 msec (-5.8 to -1.3; P for trend = 0.005), -5.4 msec (-7.4 to -3.5; P for trend <0.001), and 3.9 msec (2.0-5.9; P for trend <0.001), respectively. The corresponding differences in ARIC were -3.1 msec (-4.3 to -2.0; P for trend <0.001), -2.9 msec (-3.8 to -1.9; P for trend <0.001), and 2.3 msec (1.3-3.3; P for trend <0.001). No association was found between 25-hydroxyvitamin D concentrations and QT interval duration.

CONCLUSIONS

In two large samples of the general population, QT interval duration was inversely associated with the serum total and ionized calcium and positively associated with serum phosphorus.

Role of vitamin D in arterial hypertension

Vitamin D deficiency is highly prevalent and may contribute to arterial hypertension. The antihypertensive effects of vitamin D include suppression of renin and parathyroid hormone levels and renoprotective, anti-inflammatory and vasculoprotective properties. Low 25-hydroxyvitamin D levels, which are used to classify the vitamin D status, are an independent risk factor for incident arterial hypertension. Meta-analyses of randomized controlled trials showed that vitamin D supplementation reduces systolic blood pressure by 2-6 mmHg. However, further studies are needed before drawing a final conclusion on the effect of vitamin D therapy on blood pressure and cardiovascular risk. In our current clinical practice we should take into account the high prevalence of vitamin D deficiency, the easy, cheap and safe way by which it can be supplemented and the promising clinical data suggesting that vitamin D might be useful for the treatment of arterial hypertension as well as other chronic diseases. Therefore, we recommend that testing for and treating vitamin D deficiency in patients with arterial hypertension should be seriously considered.

Markers of bone metabolism in premature myocardial infarction (≤ 40 years of age)

INTRODUCTION

Acute myocardial infarction (AMI) at young age is a rare disease with a poor prognosis. Bone metabolism parameters such as 1,25 (OH)₂ vitamin D₃, 25 (OH) vitamin D₃ and osteocalcin have been recently implicated in the development of coronary heart disease (CHD). We evaluated the role of these serum markers in a study population of very young AMI survivors (≤ 40 years).

METHODS AND RESULTS

We prospectively enrolled 302 subjects into our multi-center case control study, including 102 young myocardial infarction patients (≤ 40 years) and 200 control subjects who were frequency-matched on gender and age in an approximate 2:1 ratio per case patient. In the adjusted logistic regression analysis, we used baseline laboratory measurements for the first analysis (acute phase analysis) and measurements from one-year follow-up visits (stable phase analysis). In both, elevated levels of 25 (OH) vitamin D₃ (acute phase: OR per IQR 2.02, 95% CI 1.13-3.58, p = 0.017; stable phase: OR 4.07, 95% CI 1.8-9.21, p = 0.001) and 1,25 (OH)₂ vitamin D₃ (acute phase: OR 2.82, 95% CI 1.7-4.7, p < 0.001; stable phase: OR 4.57, 95% CI 2.31-9.05, p < 0.001) were associated with premature AMI. Conversely, osteocalcin was inversely associated with premature myocardial infarction (acute phase: OR 0.53, 95% CI 0.28-1.03, p = 0.059; stable phase: OR 0.26, 95% CI 0.12-0.6, p < 0.001). The observed associations were independent of the acute phase of myocardial infarction.

CONCLUSION

In our study, elevated levels of 25 (OH) vitamin D₃ and 1,25 (OH)₂ vitamin D₃, as well as decreased levels of osteocalcin were associated with myocardial infarction in very young patients. The precise mechanism and implications of these findings will have to be elucidated in future studies.

Is the vitamin d receptor found in muscle?

The active form of vitamin D, 1α,25-dihydroxyvitamin D(3), is critical for the regulation of serum calcium and phosphorus levels that in turn support bone mineralization and neuromuscular activity. It is well known that vitamin D deficiency causes rachitic/osteomalacic myopathy and cardiac disorder and the provision of vitamin D can reverse the symptoms. However, the underlying mechanisms remain unclear. The question of whether the vitamin D receptor is found in muscle has been debated but not settled. We recently studied all available antibodies against the vitamin D receptor and found that most antibodies used detect proteins other than the vitamin D receptor, and therefore, the utility of these antibodies may generate the false-positive results. Using antibodies that do not detect proteins in tissues from vitamin D receptor null mice, we have developed a specific and sensitive immunohistochemical assay. The results from this investigation show that the vitamin D receptor is undetectable in skeletal, cardiac, and smooth muscle, suggesting that the function of vitamin D on muscle is either of an indirect nature or does not involve the known receptor.

The metabolic syndrome and carotid intima-media thickness in relation to the parathyroid hormone to 25-OH-D(3) ratio in a general population

BACKGROUND

Parathyroid hormone (PTH) and vitamin D interactively regulate calcium fluxes across membranes, and thereby modulate insulin sensitivity, blood pressure, and arterial calcification. We hypothesized that lower calcium intake as reflected by circulating PTH and 25-OH-D₃ might be associated with the metabolic syndrome (MS) and arterial calcification.

METHODS

In a random population sample (n = 542; 50.5% women; mean age, 49.8 ± 13.1 years), we measured MS prevalence (International Diabetes Federation (IDF) and American Heart Association (AHA) criteria), PTH and 25-OH-D₃, serum and 24-h urinary calcium, MS components, carotid intima-media thickness (CIMT), and calcium intake from dairy products. We assessed associations in multivariable-adjusted analyses, using linear and logistic regressions.

RESULTS

The prevalence of MS was 21.0% (IDF criteria) and 23.6% (AHA criteria). MS prevalence, blood pressure, waist circumference, body mass index, fasting blood glucose, insulin and triglycerides, and CIMT increased (P ≤ 0.042) across quartiles of the PTH/25-OH-D₃ ratio, whereas serum and 24-h urinary calcium decreased (P ≤ 0.029). Waist circumference and fasting blood glucose decreased across quartiles of habitual calcium intake (P ≤ 0.04). In models that included MS (IDF) and PTH/25-OH-D₃, the regression coefficients relating CIMT to PTH/25-OH-D₃ ratio and MS were +51 µm (P = 0.013) and +19 µm (P = 0.45), respectively. Multivariable-adjusted analyses were confirmatory.

CONCLUSIONS

MS prevalence and CIMT were positively associated with PTH/25-OH-D₃. CIMT was not associated with MS. Prospective studies and intervention trials should address the causality of these associations.

Should vitamin D status be assessed in patients with congestive heart failure?

For decades the vitamin D biological system has been considered almost exclusively as the master integrator of calcium-phosphate homeostasis and bone metabolism. More recently, the discovery that many human tissues and cells, which do not directly participate in mineral ion homeostasis, express the vitamin D receptor (VDR) and are able to convert the circulating pro-hormone 25-hydroxyvitamin D in its active form, 1,25-dihydroxyvitamin D, has provided new insights into the biological function of this peculiar endocrine system. Several reports have highlighted a variety of human diseases possibly related to vitamin D insufficiency or deficiency (respectively defined as 25-hydroxyvitamin D serum levels lower than 30 or lower than 20 ng/ml). In particular, experimental and observational studies, including those published in this journal issue, support the concept that vitamin D deficiency is involved in the pathogenesis of congestive heart failure, a disabling condition affecting over 15 million of patients worldwide. Considering that circulating levels of 25-hydroxyvitamin D represent the accepted clinical indicator of individual vitamin D status, the measurement of this pro-hormone can be regarded as an appropriate and cost-effective screening tool in patients with chronic heart failure.

Drug off-target effects predicted using structural analysis in the context of a metabolic network model

Recent advances in structural bioinformatics have enabled the prediction of protein-drug off-targets based on their ligand binding sites. Concurrent developments in systems biology allow for prediction of the functional effects of system perturbations using large-scale network models. Integration of these two capabilities provides a framework for evaluating metabolic drug response phenotypes in silico. This combined approach was applied to investigate the hypertensive side effect of the cholesteryl ester transfer protein inhibitor torcetrapib in the context of human renal function. A metabolic kidney model was generated in which to simulate drug treatment. Causal drug off-targets were predicted that have previously been observed to impact renal function in gene-deficient patients and may play a role in the adverse side effects observed in clinical trials. Genetic risk factors for drug treatment were also predicted that correspond to both characterized and unknown renal metabolic disorders as well as cryptic genetic deficiencies that are not expected to exhibit a renal disorder phenotype except under drug treatment. This study represents a novel integration of structural and systems biology and a first step towards computational systems medicine. The methodology introduced herein has important implications for drug development and personalized medicine.

Pharmaceutical science is only beginning to scratch the surface on the exact mechanisms of drug action that lead to a drug's breadth of patient responses, both intended and side effects. Decades of clinical trials, molecular studies, and more recent computational analysis have sought to characterize the interactions between a drug and the cell's molecular machinery. We have devised an integrated computational approach to assess how a drug may affect a particular system, in our study the metabolism of the human kidney, and its capacity for filtration of the contents of the blood. We applied this approach to retrospectively investigate potential causal drug targets leading to increased blood pressure in participants of clinical trials for the drug torcetrapib in an effort to display how our approach could be directly useful in the drug development process. Our results suggest specific metabolic enzymes that may be directly responsible for the side effect. The drug screening framework we have developed could be used to link adverse side effects to particular drug targets, discover new uses for old drugs, identify biomarkers for metabolic disease and drug response, and suggest genetic or dietary risk factors to help guide personalized patient care.

Role of vitamin D in cardiovascular health

Observational studies strongly associate vitamin D deficiency with a variety of cardiovascular diseases beyond defects in bone and calcium metabolism. Vitamin D has multiple mechanisms that potentially may affect cardiovascular health. Because vitamin D deficiency is common, therapies directed at the replacement of vitamin D may be beneficial. To date however, studies evaluating vitamin D supplementation are few and have not consistently shown benefit. It is possible that the lack of benefit in these studies may have arisen from suboptimal levels of vitamin D supplementation or other unknown factors. Nevertheless, the growing body of observational data and consistent findings of relatively high rates of low vitamin D serum levels warrant further well-designed studies to investigate the relation between vitamin D and cardiovascular health. In conclusion, vitamin D is now recognized as important for cardiovascular health and its deficiency as a potential risk factor for several cardiovascular disease processes.

Chronic treatment with vitamin D lowers arterial blood pressure and reduces endothelium-dependent contractions in the aorta of the spontaneously hypertensive rat

Vitamin D has cardiovascular protective effects besides regulating calcium homeostasis. To examine the chronic in vivo effect of a physiological dose of 1,25-dihydroxyvitamin D(3) on the occurrence of endothelium-dependent contractions, spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) were treated with the vitamin D derivative for 6 wk. The serum 1,25-dihydroxyvitamin D(3) level of both treated WKY and SHR was significantly higher than in untreated rats while the mean arterial blood pressure of the treated SHR was significantly lower than that of control SHR. Aortic rings with or without endothelium were studied in conventional organ chambers for isometric force measurement. Confocal microscopy was used to measure the cytosolic free calcium concentration (with the fluorescent dye fluo 4) and reactive oxygen species (ROS; with dichlorodihydrofluorescein diacetate). Reverse transcription PCR and Western blotting were used to determine the mRNA and protein expression level of cyclooxygenase-1 (COX-1), prostacyclin synthase, and thromboxane synthase. The endothelium-dependent concentration-contraction curves to both acetylcholine- and A-23187-induced contractions were shifted to the right in aortas from treated SHR but not from treated WKY. The chronic treatment normalized the relaxations of contracted preparations to acetylcholine. There were no significant differences in the increases in cytosolic free calcium concentration evoked by acetylcholine and A-23187 between control and treated groups. The endothelial ROS level was higher in SHR than WKY aortas and reduced by the chronic treatment. The gene and protein expression studies indicated that the overexpression of COX-1 observed in SHR aorta was reduced by the chronic treatment. These results demonstrate that chronic treatment with 1,25-dihydroxyvitamin D(3) modulates vascular tone and this modulation is accompanied by a lowered blood pressure, reduced expression of COX-1 mRNA and protein, and reduced ROS level in SHR. The reduction in endothelium-dependent contractions does not involve the surge in endothelial cytosolic calcium concentration that initiates the contractions.

1,25-dihydroxyvitamin D3 reduces systolic blood pressure in hypertensive adults: a pilot feasibility study

Vitamin D has been reported to lower blood pressure in vivo by regulating the renin-angiotensin system; however, there are limited clinical studies to support this finding in humans. We investigated the effect of vitamin D treatment on hypertension in a three-arm randomized placebo controlled pilot and feasibility study. We tested placebo with two forms of vitamin D: cholecalciferol (vitamin D(3)) and the active form of vitamin D, calcitriol. Subjects were recruited from the Atlanta Veterans Affairs Medical Center in Decatur, GA between April and August 2008. Subjects received 200,000IU of vitamin D(3) (n=3) weekly for 3 weeks or matching placebo (n=3) weekly for 3 weeks (n=3) or 0.5mug calcitriol (n=2) taken twice daily for one week. Our primary endpoint was blood pressure measured by 24h ambulatory blood pressure monitor. Subjects receiving calcitriol experienced a 9% decrease in mean systolic blood pressure (SBP) compared placebo (p<0.001). One week after conclusion of calcitriol therapy SBP returned to pre-treatment levels. There was no reduction in blood pressure in the placebo or vitamin D(3) groups. Results from this pilot study suggests that active vitamin D therapy may be an effective short-term intervention for reducing blood pressure and needs to be explored further in larger controlled studies.

The impact of vitamin D deficiency on diabetes and cardiovascular risk

PURPOSE OF REVIEW

To review the association between vitamin D deficiency and diabetes and cardiovascular risk.

RECENT FINDINGS

Vitamin D deficiency is newly recognized as a common condition of increasing prevalence worldwide. Clinically, vitamin D has an established role in calcium and bone metabolism and has recently been shown to be associated with increased risk of developing type 1 and type 2 diabetes mellitus and cardiovascular disease (CVD), as well as with cardiovascular risk factors such as hypertension and obesity. The molecular mechanisms of these associations remain incompletely understood. The active metabolite of vitamin D regulates transcription of multiple gene products with antiproliferative, prodifferentiative, and immunomodulatory effects. Although vitamin D deficiency is frequently unrecognized clinically, laboratory measurement is easy to perform and treatment of vitamin D deficiency is relatively well tolerated and inexpensive. Limited, yet promising, results of proof-of-concept intervention studies of using vitamin D in diabetes will be presented.

SUMMARY

The high prevalence of vitamin D deficiency and plausible molecular mechanisms linking this to diabetes and cardiovascular risk suggest treatment of vitamin D deficiency to prevent and/or treat diabetes is a promising field to explore.

Vitamin D and cardiovascular disease

Vitamin D insufficiency/deficiency has been observed worldwide at all stages of life. It has been characterized as a public health problem, since low concentrations of this vitamin have been linked to the pathogenesis of several chronic diseases. Several studies have suggested that vitamin D is involved in cardiovascular diseases and have provided evidence that it has a role in reducing cardiovascular disease risk. It may be involved in regulation of gene expression through the presence of vitamin D receptors in various cells, regulation of blood pressure (through renin-angiotensin system), and modulation of cell growth and proliferation including vascular smooth muscle cells and cardiomyocytes. Identifying correct mechanisms and relationships between vitamin D and such diseases could be important in relation to patient care and healthcare policies.

Cholecalciferol supplementation in hemodialysis patients: effects on mineral metabolism, inflammation, and cardiac dimension parameters

BACKGROUND AND OBJECTIVES

Vitamin D deficiency is highly prevalent in chronic kidney disease. The aim of this study was to evaluate the effects of oral cholecalciferol supplementation on mineral metabolism, inflammation, and cardiac dimension parameters in long-term hemodialysis (HD) patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This 1-year prospective study included 158 HD patients. Serum levels of 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)(2)D], intact parathyroid hormone, and plasma brain natriuretic peptide as well as circulating bone metabolism and inflammation parameters were measured before and after supplementation. Baseline 25(OH)D and 1,25(OH)(2)D levels were measured twice (end of winter and of summer, respectively). Therapy with paricalcitol, sevelamer, and darbepoietin was evaluated.

RESULTS

There was an increase in serum 25(OH)D and 1,25(OH)(2)D levels after supplementation. Conversely, serum calcium, phosphorus, and intact parathyroid hormone were decreased. There was a reduction in the dosage and in the number of patients who were treated with paricalcitol and sevelamer. Darbepoietin use was also reduced, with no modification of hemoglobin values. Serum albumin increased and C-reactive protein decreased during the study. Brain natriuretic peptide levels and left ventricular mass index were significantly reduced at the end of the supplementation.

CONCLUSIONS

Oral cholecalciferol supplementation in HD patients seems to be an easy and cost-effective therapeutic measure. It allows reduction of vitamin D deficiency, better control of mineral metabolism with less use of active vitamin D, attenuation of inflammation, reduced dosing of erythropoiesis-stimulating agents, and possibly improvement of cardiac dysfunction.

Is vitamin D the fountain of youth?

OBJECTIVE

To review the role of vitamin D deficiency for both classic and "nonclassic" effects and raise the caution that association does not prove causation.

METHODS

The pertinent literature regarding vitamin D and its effects on bone, muscle function, immune function, glucose tolerance, cancer risk, and development of cardiovascular disease and other conditions is reviewed. In addition, the limitations of observational studies are discussed.

RESULTS

Vitamin D inadequacy is common worldwide and classically causes osteomalacia and rickets. More recently, the contribution of low vitamin D status to increased falls and fracture risk has become appreciated. Additionally, nonclassic effects of vitamin D inadequacy are being recognized, and low vitamin D status is being potentially associated with a multitude of conditions (including Alzheimer disease, osteoarthritis, multiple sclerosis, and hypertension) and higher overall mortality. It is important to recognize that associations in observational studies can be due to chance, bias, or confounders or may be indicative of causality.

CONCLUSION

Because vitamin D deficiency has been established to have adverse musculoskeletal consequences, optimization of vitamin D status, for both the individual patient and the overall population, is indicated.

Cholecalciferol supplementation alters calcitriol-responsive monocyte proteins and decreases inflammatory cytokines in ESRD

In vitro, monocyte 1alpha-hydroxylase converts 25-hydroxyvitamin D [25(OH)D] to 1,25-dihydroxyvitamin D to regulate local innate immune responses, but whether 25(OH)D repletion affects vitamin D-responsive monocyte pathways in vivo is unknown. Here, we identified seven patients who had 25(OH)D insufficiency and were undergoing long-term hemodialysis and assessed changes after cholecalciferol and paricalcitol therapies in both vitamin D-responsive proteins in circulating monocytes and serum levels of inflammatory cytokines. Cholecalciferol therapy increased serum 25(OH)D levels four-fold, monocyte vitamin D receptor expression three-fold, and 24-hydroxylase expression; therapy decreased monocyte 1alpha-hydroxylase levels. The CD16(+) "inflammatory" monocyte subset responded to 25(OH)D repletion the most, demonstrating the greatest increase in vitamin D receptor expression after cholecalciferol. Cholecalciferol therapy reduced circulating levels of inflammatory cytokines, including IL-8, IL-6, and TNF. These data suggest that nutritional vitamin D therapy has a biologic effect on circulating monocytes and associated inflammatory markers in patients with ESRD.

Vitamin D metabolites as clinical markers in autoimmune and chronic disease

Recent research has implicated vitamin D deficiency (serum levels of 25-hydroxyvitamin D <50 nmol/L) with a number of chronic conditions, including autoimmune conditions such as multiple sclerosis, lupus, and psoriasis, and chronic conditions such as osteoporosis, osteoarthritis, metabolic syndrome, fibromyalgia and chronic fatigue syndrome. It has been assumed that low levels of 25-hydroxyvitamin D (25-D) accurately indicate vitamin D storage and vitamin D receptor (VDR)-mediated control of calcium metabolism and innate immunity. To evaluate this assumption, 25-D and 1,25-dihydroxyvitamin D3 (1,25-D) levels were measured in 100 Canadian patients with these conditions. Additionally, other inflammatory markers (CK, CRP) were measured. Results showed a strong positive association between these autoimmune conditions and levels of 1,25-D >110 pmol/L. However, there was little association with vitamin D deficiency or the other inflammatory markers, meaning that the results challenge the assumption that serum levels of 25-D are a sensitive measure of the autoimmune disease state. Rather, these findings support the use of 1,25-D as a clinical marker in autoimmune conditions. High levels of 1,25-D may result when dysregulation of the VDR by bacterial ligands prevents the receptor from expressing enzymes necessary to keep 1,25-D in a normal range.

Vitamin D status and arterial hypertension: a systematic review

Vitamin D deficiency is common and is primarily caused by a lack of ultraviolet-B (UVB) radiation from reduced sun exposure, and the consequent limiting of vitamin D production in the skin. The vitamin D endocrine system regulates about 3% of the human genome. Observational data support the concept that vitamin D is involved in the pathogenesis of cardiovascular diseases and arterial hypertension. The antihypertensive properties of vitamin D include renoprotective effects, suppression of the renin-angiotensin-aldosterone system, direct effects on vascular cells, and effects on calcium metabolism, including prevention of secondary hyperparathyroidism. The results of clinical studies largely, but not consistently, favor the hypothesis that vitamin D sufficiency promotes lowering of arterial blood pressure. Randomized, placebo-controlled trials are greatly needed to clarify and definitively prove the effect of vitamin D on blood pressure. In general, the antihypertensive effects of vitamin D seem to be particularly prominent in vitamin-D-deficient patients with elevated blood pressure. Thus, in view of the relatively safe and inexpensive way in which vitamin D can be supplemented, we believe that vitamin D supplementation should be prescribed to patients with hypertension and 25-hydroxyvitamin D levels below target values.

A new role for vitamin D receptor activation in chronic kidney disease

Vitamin D has proven to be much more than a simple "calcium hormone." The fact that the vitamin D receptor has been found in cells not related to mineral metabolism supports that statement. The interest of nephrologists in vitamin D and its effects beyond mineral metabolism has increased over the last few years, evidencing the importance of this so-called "sunshine hormone." In the present review, we highlight the most recent developments in the traditional use of vitamin D in chronic kidney disease (CKD) patients, namely, the control of secondary hyperparathyroidism (sHPT). Furthermore, we also explore the data available regarding the new possible therapeutic uses of vitamin D for the treatment of other complications present in CKD patients, such as vascular calcification, left ventricular hypertrophy, or proteinuria. Finally, some still scarce but very promising data regarding a possible role of vitamin D in kidney transplant patients also are reviewed. The available data point to a potential beneficial effect of vitamin D in CKD patients beyond the control of mineral metabolism.

The role of vitamin D in the development of cardiac failure

A krónikus szívelégtelenség leginkább az időseket érintő népbetegség, amelyben a D-vitamin-hiány rendkívül gyakori. A legtöbb D-vitamin a bőrben képződik, ezért a szívelégtelenségben szenvedő betegek életmódja részben magyarázhatja a D-vitamin-hiány gyakoriságát. Azonban egyre több adat támasztja alá azt az elképzelést, hogy a D-vitamin-hiány nemcsak következménye, hanem oka is lehet a krónikus szívelégtelenség kialakulásának. A D-vitaminnak közvetlen hatása van a szívre és indirekt hatása a szívelégtelenséghez vezető legfőbb rizikófaktorokra. A közvetlen szívhatás a szívizomsejtek kontraktilitásában, a natriureticus fehérjék elválasztásában, az extracelluláris mátrix és a gyulladásos citokinek változásában nyilvánul meg. Emellett a D-vitamin hatással van a szívelégtelenség legfontosabb rizikófaktoraira, a vérnyomásra, a renin-angiotenzin rendszerre és az érelmeszesedésre is. A sok kísérletes adat ellenére csupán néhány megfigyelés igazolja a D-vitamin kedvező hatását a krónikus szívelégtelenségre. További nagy esetszámú, randomizált vizsgálat szükséges annak megerősítésére, hogy a D-vitamin-hiányban adott D-vitamin-pótlás előnyös hatású a krónikus szívelégtelenségre és a halálozási kockázatra.

Milk intake and the risk of type 2 diabetes mellitus, hypertension and prostate cancer

Milk intake is widely recommended for a healthy diet. Recent evidences suggest that milk/dairy products are associated with a lower risk of type 2 diabetes and hypertension. On the other hand, high calcium intake has been associated with a higher risk of prostate cancer. The calcium and vitamin D content in dairy foods could have beneficial effects on glucose metabolism and renin/angiotensin system as well regulates body weight. The association between high dairy/calcium consumption and prostate cancer risk are related to the presence of estrogens and insulin like growth factor (IGF-I) in milk. Based on the current evidence, it is possible that milk/dairy products, when consumed in adequate amounts and mainly with reduced fat content, has a beneficial effect on the prevention of hypertension and diabetes. Its potential role in the pathogenesis of prostate cancer is not well supported and requires additional study.

The use of vitamin D analogues in chronic kidney diseases: possible mechanisms beyond bone and mineral metabolism

Chronic kidney disease (CKD) is a common and costly medical condition, and currently available therapeutic options remain unsatisfactory. Vitamin D analogues are widely used for the bone and mineral disorder associated with CKD. However, accumulating evidence suggests that vitamin D analogues may have actions other than their effects on bone and mineral metabolism. In this article, we review the following aspects on the use of vitamin D analogues for the treatment of CKD: (1) epidemiological studies showing that patients with late-stage CKD have better survival than untreated patients; (2) animal studies showing that vitamin D analogues may retard the progression of CKD; (3) human studies on the anti-proteinuric and possibly renal protecting effects of vitamin D analogues in CKD and (4) the potential mechanisms of its therapeutic benefit. Nonetheless, definitive proof of the clinical benefits by randomized control trial would be necessary before one could advocate the routine use of vitamin D analogues for the treatment of CKD patients.

Dairy product consumption and the metabolic syndrome

The metabolic syndrome is an important risk factor for type 2 diabetes mellitus and CVD. Epidemiological studies have now suggested protective effects of dairy product consumption on the development of this syndrome. Here we review the physiological effects and possible mechanisms involved of three main dairy constituents (Ca, protein, fat) on important components of the metabolic syndrome. Ca supplements improve the serum lipoprotein profile, particularly by decreasing serum total and LDL-cholesterol concentrations. They also lower systolic and diastolic blood pressure. Insufficient evidence exists for a significant role of Ca supplements or dairy in body-weight management. Effects of Ca may be related to intestinal binding to fatty acids or bile acids, or to changes in intracellular Ca metabolism by suppressing calciotropic hormones. Dietary proteins may increase satiety in both the short and longer term, which may result in a reduced energy intake. They have also been reported to improve the serum lipoprotein profile as compared with carbohydrates. Dairy proteins are precursors of angiotensin-I-converting enzyme-inhibitory peptides, which may lower blood pressure. Such effects, however, have inconsistently been reported in human studies. Finally, conjugated linoleic acid, which effectively lowers body weight in animals, has no such effect in humans in the quantities provided by dairy products. To reduce the intake of SFA, the consumption of low-fat instead of high-fat dairy products is recommended. In conclusion, more research is warranted to better understand the physiological effects and the mechanisms involved of dairy products in the prevention and treatment of the metabolic syndrome.

Vitamin D and the vasculature: can we teach an old drug new tricks?

BACKGROUND

Vitamin D is a steroid hormone known for its role in regulating levels of calcium and phosphorus. Vitamin D has important autocrine/paracrine roles and it is involved in vascular biology. Clinical studies have shown a relationship between vitamin D levels and cardiovascular health, and low levels of vitamin D metabolites have been associated with higher incidence of congestive heart failure and increases in mortality.

OBJECTIVE

To summarise the effect of vitamin D on cardiovascular pathology, the leading cause of death in chronic kidney disease patients.

CONCLUSIONS

All results indicate a potential effect of vitamin D on cardiovascular health. Therefore, maintaining optimum levels of circulating vitamin D is critical for a healthy cardiovascular system. In patients with low vitamin D status, like renal patients, supplementation with vitamin D metabolites has shown beneficial cardiovascular effects.

Long-term effect of calcium-vitamin D(3) fortified milk on blood pressure and serum lipid concentrations in healthy older men

BACKGROUND/OBJECTIVES

Some epidemiological and clinical studies have shown that increased dairy consumption or calcium and/or vitamin D supplementation can have a beneficial effect on blood pressure, and lipid and lipoprotein concentrations. The aim of this study was to assess the long-term effects of calcium-vitamin D(3) fortified milk on blood pressure and lipid-lipoprotein concentrations in community-dwelling older men.

SUBJECTS/METHODS

This is a substudy of a 2-year randomized controlled trial in which 167 men aged >50 years were assigned to receive either 400 ml per day of reduced fat (approximately 1%) milk fortified with approximately 1000 mg of calcium and 800 IU of vitamin D(3) or to a control group receiving no additional fortified milk. Weight, blood pressure, lipid and lipoprotein concentrations were measured every 6 months. Participants on lipid-lowering (n=32) or antihypertensive medication (n=39) were included, but those who commenced, increased or decreased their medication throughout the intervention were excluded (n=27).

RESULTS

In the 140 men included in this study (milk, n=73; control, n=67), there were no significant effects of the calcium-vitamin D(3) fortified milk on weight, systolic or diastolic blood pressure, total cholesterol, high-density lipoprotein or low-density lipoprotein cholesterol or triglyceride concentrations at any time throughout the intervention. Similar results were observed after excluding men taking antihypertensive or lipid-lowering medication or limiting the analysis to those with baseline calcium intakes <1000 mg per day and/or with hypovitaminosis D (25(OH)D <75 nmol/l).

CONCLUSIONS

Supplementation with reduced-fat calcium-vitamin D(3) fortified milk did not have a beneficial (nor detrimental) effect on blood pressure, lipid or lipoprotein concentrations in healthy community-dwelling older men.

Vitamin D: current status and perspectives

The role of vitamin D in maintaining bone health has been known for decades. Recently, however, the discovery that many tissues expressed the vitamin D receptor and were able to transform the 25-OH vitamin D into its most active metabolite, 1,25-(OH)

Clin Chem Lab Med 2009;47:120–7.

Association of serum phosphate with vascular and valvular calcification in moderate CKD

Within the normal range, higher serum phosphate concentrations are associated with cardiovascular events and mortality in individuals with chronic kidney disease (CKD) and in those with normal kidney function. Experimental models suggest that phosphate has a direct calcifying effect on vascular smooth muscle. We examined associations of serum phosphate concentrations with vascular and valvular calcification in 439 participants from the Multi-Ethnic Study of Atherosclerosis who had moderate CKD and no clinical cardiovascular disease. Serum phosphate concentrations were within the normal range (2.5 to 4.5 mg/dl) in 95% of study participants. The prevalence of calcification in the coronary arteries, descending thoracic aorta, aortic valve, and mitral valve was 67, 49, 25, and 20%, respectively, measured by electron-beam or multi-detector row computed tomography. After adjustment for demographics and estimated GFR, each 1-mg/dl increment in serum phosphate concentration was associated with a 21% (P = 0.002), 33% (P = 0.001), 25% (P = 0.16), and 62% (P = 0.007) greater prevalence of coronary artery, thoracic, aortic valve, and mitral valve calcification, respectively. Adjustment for traditional risk factors for atherosclerosis, parathyroid hormone, or 1,25-dihydroxyvitamin D levels did not alter these associations. In conclusion, higher serum phosphate concentrations, although still within the normal range, are associated with a greater prevalence of vascular and valvular calcification in people with moderate CKD. It remains to be determined whether lowering phosphate concentrations will impact calcification risk in the setting of kidney disease.

Maternal plasma 25-hydroxyvitamin D concentrations and the risk for gestational diabetes mellitus

Background

Evidence is accumulating for a role of vitamin D in maintaining normal glucose homeostasis. However, studies that prospectively examined circulating concentrations of 25-hydroxyvitamin D (25-[OH] D) in relation to diabetes risk are limited. Our objective is to determine the association between maternal plasma 25-[OH] D concentrations in early pregnancy and the risk for gestational diabetes mellitus (GDM).

Methods

A nested case-control study was conducted among a prospective cohort of 953 pregnant women. Among them, 57 incident GDM cases were ascertained and 114 women who were not diagnosed with GDM were selected as controls. Controls were frequency matched to cases for the estimated season of conception of the index pregnancy.

Results

Among women who developed GDM, maternal plasma 25-[OH] D concentrations at an average of 16 weeks of gestation were significantly lower than controls (24.2 vs. 30.1 ng/ml, P<0.001). This difference remained significant (3.62 ng/ml lower on average in GDM cases than controls (P value = 0.018)) after the adjustment for maternal age, race, family history of diabetes, and pre-pregnancy BMI. Approximately 33% of GDM cases, compared with 14% of controls (P<0.001), had maternal plasma 25-[OH] D concentrations consistent with a pre-specified diagnosis of vitamin D deficiency (<20 ng/ml). After adjustment for the aforementioned covariates including BMI, vitamin D deficiency was associated with a 2.66-fold (OR (95% CI): 2.66 (1.01–7.02)) increased GDM risk. Moreover, each 5 ng/ml decrease in 25-[OH] D concentrations was related to a 1.29-fold increase in GDM risk (OR (95% CI): 1.29 (1.05–1.60)). Additional adjustment for season and physical activity did not change findings substantially.

Conclusions

Findings from the present study suggest that maternal vitamin D deficiency in early pregnancy is significantly associated with an elevated risk for GDM.

Vitamin D and human health: lessons from vitamin D receptor null mice

The vitamin D endocrine system is essential for calcium and bone homeostasis. The precise mode of action and the full spectrum of activities of the vitamin D hormone, 1,25-dihydroxyvitamin D [1,25-(OH)(2)D], can now be better evaluated by critical analysis of mice with engineered deletion of the vitamin D receptor (VDR). Absence of a functional VDR or the key activating enzyme, 25-OHD-1alpha-hydroxylase (CYP27B1), in mice creates a bone and growth plate phenotype that mimics humans with the same congenital disease or severe vitamin D deficiency. The intestine is the key target for the VDR because high calcium intake, or selective VDR rescue in the intestine, restores a normal bone and growth plate phenotype. The VDR is nearly ubiquitously expressed, and almost all cells respond to 1,25-(OH)(2)D exposure; about 3% of the mouse or human genome is regulated, directly and/or indirectly, by the vitamin D endocrine system, suggesting a more widespread function. VDR-deficient mice, but not vitamin D- or 1alpha-hydroxylase-deficient mice, and man develop total alopecia, indicating that the function of the VDR and its ligand is not fully overlapping. The immune system of VDR- or vitamin D-deficient mice is grossly normal but shows increased sensitivity to autoimmune diseases such as inflammatory bowel disease or type 1 diabetes after exposure to predisposing factors. VDR-deficient mice do not have a spontaneous increase in cancer but are more prone to oncogene- or chemocarcinogen-induced tumors. They also develop high renin hypertension, cardiac hypertrophy, and increased thrombogenicity. Vitamin D deficiency in humans is associated with increased prevalence of diseases, as predicted by the VDR null phenotype. Prospective vitamin D supplementation studies with multiple noncalcemic endpoints are needed to define the benefits of an optimal vitamin D status.

Vitamin D, the renin-angiotensin system, and insulin resistance

Insulin resistance is characterized by the systemic impairment of insulin action and is usually the result of aging, obesity, chronic inflammation, or another factor that may contribute to the inhibition of the insulin signaling pathway. Insulin resistance is accompanied by defects in lipid metabolism and blood coagulation, hypertension, obesity, and vascular inflammation in a syndrome called syndrome X or metabolic syndrome. Metabolic syndrome is involved in the development of atherosclerosis with consequent cardiovascular complications including acute myocardial infarction, stroke, and vascular disease. Recent data have shown that vitamin D acts as a negative regulator of the renin gene and that vitamin D deficiency is followed by increased renin-angiotensin II expression. The link between the insulin signaling pathway/insulin resistance and the renin-angiotensin system has been well documented in previous studies. The present review focuses on disorders characterized by a reduction in vitamin D concentration or its receptor function and the development of insulin resistance or metabolic syndrome, and discusses also possible therapeutic interventions.

Calcitriol blunts pro-atherosclerotic parameters through NFkappaB and p38 in vitro

BACKGROUND

Disturbances in vitamin D(3) metabolism are associated with an increased cardiovascular morbidity and mortality. The aim of this study was to assess the effects of calcitriol, the active metabolite of vitamin D3, on pro-atherosclerotic parameters in human umbilical vein cord endothelial cells (HUVEC).

MATERIALS AND METHODS

Calcitriol at 10(-10) and/or 10(-9) mol L(-1) was given to cultured HUVEC which were either non-stimulated or lipopolysaccharide (LPS) stimulated. Inter cellular adhesion molecule-1 and platelet-endothelial cell adhesion molecule-1, were determined by flow cytometry analysis. The receptor of advanced glycation end product (RAGE) and interleukin-6 (IL-6) mRNA expressions by RT-PCR and IL-6 secretion by enzyme-linked immunosorbent assay (ELISA). Nuclear p65 DNA-binding activity was measured by transcription factor assay kit and the inhibitor-kappaBalpha (IkappaBalpha), phosphorylated-IkappaBalpha (P-IkappaBalpha) and phosphorylated-p38 mitogen-activated protein kinase (MAPK) protein levels were determined by Western blot. Results Calcitriol decreased the adhesion molecules expression, as well as the LPS-induced mRNA expressions of RAGE and IL-6 and LPS induced IL-6 secretion. Furthermore, the LPS induced nuclear factor kappaB (NFkappaB)-p65 DNA-binding activity was also decreased by calcitriol. IkappaBalpha levels were increased and p-IkappaBalpha levels decreased after calcitriol treatment. The increased levels of activated p38 MAPK after LPS treatment were also decreased due to pre-incubation with calcitriol.

CONCLUSIONS

The decreased NFkappaB and p38 activities followed by calcitriol treatment may explain the anti-inflammatory/atherosclerotic properties of calcitriol that were observed previously and were emphasized in this study, demonstrating the inhibitory effect of calcitriol on the pro-inflammatory parameters: adhesion molecules, RAGE and IL-6.

Vitamin D derivatives acutely reduce endothelium-dependent contractions in the aorta of the spontaneously hypertensive rat

The available evidence suggests that vitamin D has cardiovascular effects besides regulating calcium homeostasis. To examine the effect of 1,25-dihydroxyvitamin D(3), the major metabolite of vitamin D, on endothelium-dependent contractions, aortic rings of spontaneously hypertensive rats (SHR) were suspended in organ chambers for isometric force measurements. Rings were incubated with N(omega)-nitro-l-arginine methyl ester (l-NAME) and then exposed to increasing concentrations of acetylcholine, ATP, or the calcium ionophore to trigger contractions. This was done in the absence or presence of 1,25-dihydroxyvitamin D(3). The release of prostacyclin after acetylcholine or A-23187 stimulation was also measured. The cytosolic-free calcium concentration was measured by confocal microscopy after incubation with the fluorescent dyes fluo-4 and fura red. The presence of vitamin D receptors was confirmed using immunohistochemistry. Acetylcholine- and ATP-induced endothelium-dependent contractions were significantly reduced compared with those obtained in the absence of the drug. This effect was not present if A-23187 was used as an agonist. The acetylcholine- but not the A-23187-induced release of prostacyclin was reduced by the acute administration of 1,25-dihydroxyvitamin D(3). Exposure to 1,25-dihydroxyvitamin D(3) reduced the increase in cytosolic-free calcium concentration caused by acetylcholine but not by A-23187 in cells. Vitamin D receptors were densely distributed in the endothelium. Inecalcitol (19-nor-14-epi-23-yne-1,25-dihydroxyvitamin D(3)), a synthetic analog of vitamin D, caused a comparable depression of endothelium-dependent contractions as 1,25-dihydroxyvitamin D(3). These results demonstrate that vitamin D(3) modulates vascular tone by reducing calcium influx into the endothelial cells and hence decreasing the production of endothelium-derived contracting factors.

Calcium-independent and 1,25(OH)2D3-dependent regulation of the renin-angiotensin system in 1alpha-hydroxylase knockout mice

To determine whether the cardiovascular effect of 1,25(OH)(2)D is dependent on calcium and/or phosphorus, mice with targeted deletion of the 25(OH)D 1alpha-hydroxylase and their wild-type littermates were fed a normal diet or a diet to rescue the ambient serum calcium and phosphorus levels. Mice on the normal diet were treated daily with vehicle or 1,25(OH)(2)D(3) while mice on the rescue diet received vehicle, captopril or losartan. After four weeks the vehicle-treated knockout mice developed hypertension, cardiac hypertrophy and impaired cardiac function along with an up-regulation of the renin-angiotensin system in both renal and cardiac tissues. Although the serum calcium and phosphorus levels were normalized in knockout mice on the rescue diet, abnormalities in blood pressure, cardiac structure-function and the renin-angiotensin system remained. In contrast, 1,25(OH)(2)D(3) not only normalized serum calcium and phosphorus levels but also normalized blood pressure, cardiac structure-function and the renin-angiotensin system. Treatment of the knockout mice with either captopril or losartan normalized blood pressure and cardiac structure and function although renin expression remained elevated. This study shows that 1,25(OH)2D plays a protective role in the cardiovascular system by repressing the renin-angiotensin system independent of extracellular calcium or phosphorus.

Vitamin D, glucose, insulin, and insulin sensitivity

This review examines available evidence of links between abnormalities of glucose and insulin metabolism and vitamin D deficiency. Possible mechanisms of action of vitamin D include stimulation of insulin secretion and effects on insulin sensitivity. Sun exposure usually implies greater outdoor physical activity, which in itself may have beneficial effects on insulin sensitivity, unrelated to serum 25-hydroxyvitamin D concentrations. The observed associations in humans among vitamin D, insulin, and glucose metabolism have not yet been confirmed by intervention studies and, hence, a causal association has not been established. Clinical trials are needed to determine whether vitamin D treatment of vitamin D-deficient individuals is able to prevent or treat diabetes mellitus.

The association between vitamin D and inflammation with the 6-minute walk and frailty in patients with heart failure

OBJECTIVES

To identify relationships between anabolic hormones, inflammatory markers, and physical function.

DESIGN

Cross-sectional.

SETTING

Outpatient university heart failure program in Connecticut.

PARTICIPANTS

Sixty patients with an ejection fraction of 40% or less.

MEASUREMENTS

The 6-minute walk distance and frailty phenotype were measured. The relationship between physical measures of hormones and inflammatory mediators were examined. Linear and ordinal logistic regression analyses were performed for the physical measures.

RESULTS

Forty-three men (mean age 77 +/- 9) and 17 women (mean age 78 +/- 12) participated. Longer 6-minute walk distance was correlated with higher 25-hydroxyvitamin D (25OHD) level, and a shorter walk was correlated with higher cortisol: dehydroepiandrosterone sulphate (DHEAS) ratio, high-sensitivity C-reactive protein (hsCRP), interleukin-6 (IL6), and intact parathyroid hormone (PTH) (all P<.05). Percentage of free testosterone, DHEAS alone, and N-terminal pro-brain natriuretic peptide (NTpro-BNP) did not correlate with 6-minute walk distance. Higher frailty phenotype score (more frail) was correlated with higher high-sensitivity CRP, higher IL6, and lower 25OHD levels (all P<.05). Linear regression with the 6-minute walk distance as the dependent variable and independent variables of age, sex, percentage of free testosterone, DHEAS, 25OHD, intact PTH, hsCRP, IL6, cortisol/DHEAS ratio, and NTpro-BNP, revealed age, sex, 25OHD and hsCRP to be significant (coefficient of determination=53.5%). Ordinal logistic regression with the frailty phenotype and hormonal levels revealed that age, 25OHD, and hsCRP also predicted frailty status.

CONCLUSION

Twenty-five-hydroxyvitamin D and hsCRP levels may contribute to lower aerobic capacity and frailty in patients with heart failure. A longitudinal study will further define the role of 25OHD and hsCRP on muscle strength and functional decline.

Effects of angiotensin-converting enzyme gene polymorphism and serum vitamin D levels on ambulatory blood pressure measurement and left ventricular mass in Turkish hypertensive population

INTRODUCTION

Regulation of angiotensin converting enzyme (ACE) and angiotensin II (ang-II) levels is under genetic control. 1,25(OH)2 vitamin D3 treatment has been shown to reduce the ang-II level, reduce myocardial hypertrophy and to decrease blood pressure. This study was designed to examine the effect of ACE gene polymorphisms on 24-h ambulatory blood pressure measurement (24 h) values, vitamin D levels and target organ damage in hypertensive patients.

METHODS

This study was carried on 118 patients with essential hypertension (female/male: 70/48, mean age: 49.1+/-7.6 years, hypertension duration: 56+/-40.5 months). All patients were assessed for target organ damage; the eye by retinal examination, the heart with echocardiography and the kidney with blood and 24-h urine analysis. 24-h ambulatory blood pressure measurement was performed in all patients. PCR amplification was employed to detect ACE genotypes.

RESULTS

ACE genotypes were as follows: DD (n=49) 41.5%; ID (n=37) 31.4% and II (n=32) 27.1%. No difference was present between groups of ACE polymorphism when 24-h ambulatory blood pressure measurement values, retinal vascular changes and microalbuminuria were taken into account. Statistically significant left ventricular mass index levels were obtained in the DD group when compared with the non-DD (ID+II) group (P : 0.009). Positive correlations have been noted between left ventricular mass index and day/night and early morning systolic pressures. A negative correlation exists between serum 25 (OH) vitamin D levels and 24-h ambulatory blood pressure measurement values (P<0.05).

CONCLUSIONS

The presence of the D allele is linked with a higher risk for left ventricular mass index in the Turkish hypertensive population.