Vitamin D: roles in renal and cardiovascular protection

The benefits of Vitamin D in the COVID-19 pandemic: biochemical and immunological mechanisms

In December 2019, a new infectious complication called CoronaVirus Infectious Disease-19, briefly COVID-19, caused by SARS-COV-2, is identified in Wuhan, China. It spread all over the world and became a pandemic. In many individuals who had suffered SARS-COV-2 infection, cytokine storm starts through cytokine overproduction and leads to Acute Respiratory Syndrome (ARS), organ failure, and death. According to the obtained evidence, Vitamin D (VitD) enhances the ACE2/Ang(1-7)/MasR pathway activity, and it also reduces cytokine storms and the ARS risk. Therefore, VitD intake may be beneficial for patients with SARS-COV-2 infection exposed to cytokine storm but do not suffer hypotension. In the present review, we have explained the effects of VitD on the renin-angiotensin system (RAS) function and angiotensin-converting enzyme2 (ACE2) expression. Furthermore, we have reviewed the biochemical and immunological effects of VitD on immune function in the underlying diseases and its role in the COVID-19 pandemic.

Cognitive Function and Vitamin D Status in the Chinese Hemodialysis Patients

OBJECTIVE

Vitamin D insufficiency and the cognitive function decline are both common in patients receiving hemodialysis (HD). The present study evaluated the relation between cognitive function and circulating vitamin D levels in HD patients in Wannan Medical College Affiliated Yijishan Hospital, China.

METHODS

This study was conducted in 80 patients receiving HD in Wannan Medical College Affiliated Yijishan Hospital. To measure cognitive function, Montreal Cognitive Assessment-Basic (MoCA-B) Chinese Version was used. The 25-hydroxyvitamin D [25(OH)D], which is applied to assess vitamin D status, was tested. One-way ANOVA, Tukey post hoc test, and the correlation and regression analysis were used in this study.

RESULTS

Based on the MoCA-B, cognitive function decline (the scores below 26) was present in 28 HD patients, accounting for 35% (28/80). The mean age of these patients is 50.5 ± 10.9 years old. The mean level of 25(OH)D was 16.1 ± 7.3 ng/ml in 80 HD patients. In univariate analysis, there was a significant relationship between MoCA-B score and serum 25(OH)D level (p < 0.05). The level of 25(OH)D was positively correlated with MoCA-B score (r = 0.312, p = 0.023), and the association was independent of demographic and clinical features.

CONCLUSIONS

Vitamin D insufficiency may contribute to cognitive function decline in HD patients. Serum level of 25(OH)D is an independent protective factor of cognitive function in the HD patients.

New progress in drugs treatment of diabetic kidney disease

Diabetic kidney disease (DKD) is not only one of the main complications of diabetes, but also the leading cause of the end-stage renal disease (ESRD). The occurrence and development of DKD have always been a serious clinical problem that leads to the increase of morbidity and mortality and the severe damage to the quality of life of human beings. Controlling blood glucose, blood pressure, blood lipids, and improving lifestyle can help slow the progress of DKD. In recent years, with the extensive research on the pathological mechanism and molecular mechanism of DKD, there are more and more new drugs based on this, such as new hypoglycemic drugs sodium-glucose cotransporter 2 (SGLT2) inhibitors, glucagon-like peptide-1 (GLP-1) inhibitors, and dipeptidyl peptidase-4 (DPP-4) inhibitors with good efficacy in clinical treatment. Besides, there are some newly developed drugs, including protein kinase C (PKC) inhibitors, advanced glycation end product (AGE) inhibitors, aldosterone receptor inhibitors, endothelin receptor (ETR) inhibitors, transforming growth factor-β (TGF-β) inhibitors, Rho kinase (ROCK) inhibitors and so on, which show positive effects in animal or clinical trials and bring hope for the treatment of DKD. In this review, we sort out the progress in the treatment of DKD in recent years, the research status of some emerging drugs, and the potential drugs for the treatment of DKD in the future, hoping to provide some directions for clinical treatment of DKD.

MicroRNA-122 contributes to lipopolysaccharide-induced acute kidney injury via down-regulating the vitamin D receptor in the kidney

BACKGROUND

Our previous studies showed that vitamin D receptor (VDR) depletion promotes lipopolysaccharide (LPS)-induced acute kidney injury (AKI) in mice, and renal VDR is down-regulated in AKI, but the mechanism of VDR down-regulation is unclear.

METHODS

Nutritional vitamin D deficiency was induced by feeding mice a vitamin D-deficient (VD-D) diet. Mice were injected intraperitoneally with LPS (20 mg/kg) to establish LPS-induced AKI. Levels of VDR and miR-122 were measured both in vivo and in vitro. The associations between VDR and miR-122 were analysed by dual-luciferase reporter assays.

RESULTS

Compared with vitamin D-sufficient (VD-S) mice, VD-D mice developed more severe renal injury following LPS challenge. LPS induced a dramatic decrease in VDR expression and marked induction of miR-122 both in vivo and in vitro. Furthermore, miR-122 hairpin inhibitor alleviated LPS-induced VDR down-regulation whereas miR-122 mimic directly suppressed VDR expression in HK-2 cells. In luciferase reporter assays, miR-122 mimic was able to suppress luciferase activity in 293T cells co-transfected with a luciferase reporter that contains a putative miR-122 target site from 3'UTR of the VDR transcript, but not when this site was mutated. Moreover, miR-122 mimic significantly blocked paricalcitol-induced luciferase activity in 293T cells co-transfected with a VDRE-driven luciferase reporter, whereas miR-122 hairpin inhibitor enhanced paricalcitol's activity to suppress PUMA and caspase 3 activation induced by LPS in HK-2 cells.

CONCLUSIONS

Collectively, these studies provide evidence that miR-122 directly targets VDR in renal tubular cells, which strongly suggest that miR-122 up-regulation in the kidney under LPS challenge contributes to kidney injury by down-regulating VDR expression.

Vitamin D Effects on Bone Homeostasis and Cardiovascular System in Patients with Chronic Kidney Disease and Renal Transplant Recipients

Poor vitamin D status is common in patients with impaired renal function and represents one main component of the complex scenario of chronic kidney disease-mineral and bone disorder (CKD-MBD). Therapeutic and dietary efforts to limit the consequences of uremia-associated vitamin D deficiency are a current hot topic for researchers and clinicians in the nephrology area. Evidence indicates that the low levels of vitamin D in patients with CKD stage above 4 (GFR < 15 mL/min) have a multifactorial origin, mainly related to uremic malnutrition, namely impaired gastrointestinal absorption, dietary restrictions (low-protein and low-phosphate diets), and proteinuria. This condition is further worsened by the compromised response of CKD patients to high-dose cholecalciferol supplementation due to the defective activation of renal hydroxylation of vitamin D. Currently, the literature lacks large and interventional studies on the so-called non-calcemic activities of vitamin D and, above all, the modulation of renal and cardiovascular functions and immune response. Here, we review the current state of the art of the benefits of supplementation with native vitamin D in various clinical settings of nephrological interest: CKD, dialysis, and renal transplant, with a special focus on the effects on bone homeostasis and cardiovascular outcomes.

Association Between Vitamin D and Hyperuricemia Among Adults in the United States

Background: Serum uric acid can act as a risk factor for cardiovascular disease (CVD) and as antioxidant defense. Vitamin D deficiency can activate the parathyroid to induce the release of parathyroid hormone, which was thought to increase serum uric acid level, and low vitamin D status may also be associated with risk of CVD. No known studies have explored the association between serum 25(OH) D, vitamin D intake, and HU for the American population.

Methods: We extracted 15,723 US adults aged 20–85 years from the National Health and Nutrition Examination Survey (NHANES) in 2007–2014. All dietary intakes were evaluated through 24-h dietary recalls. Multivariable logistic regression analysis was performed to examine the associations after adjustment for confounders.

Results: Compared to the lowest quintile (Q1), for males, adjusted odds ratios (ORs) of HU in Q2 to Q4 of serum 25(OH) D levels were 0.78 (95% CI, 0.65–0.93), 0.97 (0.81–1.16), and 0.72 (0.60–0.88); ORs in Q2–Q5 of total vitamin D intake were 0.83 (0.69–0.98), 0.69 (0.58–0.83), 0.66 (0.55–0.79), and 0.59 (0.48–0.71), respectively. In females, OR was 0.80 (0.66–0.97) of serum 25(OH) D for Q3, and ORs in Q5 of total vitamin D intake were 0.80 (0.65–0.98).

Conclusions: Our findings indicated that the serum 25(OH) D intakes of dietary vitamin D, supplemental vitamin D, and total vitamin D were inversely associated with HU in males. In females, a lower risk of HU with higher serum 25(OH) D, dietary vitamin D, and total vitamin D intake was found, but with no association between supplemental vitamin D intake and the risk of HU.

Efficacy of single-dose cholecalciferol in the blood pressure of patients with type 2 diabetes, hypertension and hypovitaminoses D

Observational and experimental data reinforce the concept that vitamin D is associated with the pathogenesis of arterial hypertension. We investigated the effect of a single dose of 100,000 IU of cholecalciferol, in office blood pressure (BP), and 24-h ambulatory blood pressure monitoring (ABPM) in patients with type 2 diabetes mellitus (DM), hypertension, and hypovitaminosis D. Forty-three patients were randomized to a placebo or cholecalciferol group. BP was assessed by office measurements and 24-h ABPM, before and after intervention. At week 8, a greater decrease in median ABPM values was observed in cholecalciferol supplementation than in the placebo group for systolic 24-h (− 7.5 vs. − 1; P = 0.02), systolic daytime (− 7 vs. − 1; P = 0.007), systolic nighttime (− 7.0 vs. 3; P = 0.009), diastolic 24-h (− 3.5 vs. − 1; P = 0.037), and daytime DBP (− 5 vs. 0; P = 0.01). Office DBP was also reduced after vitamin D supplementation. A single dose of vitamin D₃ improves BP in patients with type 2 diabetes, hypertension, and vitamin D insufficiency, regardless of vitamin D normalization. Vitamin D supplementation could be a valuable tool to treat patients with type 2 DM, hypertension, and hypovitaminosis D.

Trial registration: Clinicaltrials.gov NCT 02204527.

Combating COVID-19 and Building Immune Resilience: A Potential Role for Magnesium Nutrition?

Background: In December 2019, the viral pandemic of respiratory illness caused by COVID-19 began sweeping its way across the globe. Several aspects of this infectious disease mimic metabolic events shown to occur during latent subclinical magnesium deficiency. Hypomagnesemia is a relatively common clinical occurrence that often goes unrecognized since magnesium levels are rarely monitored in the clinical setting. Magnesium is the second most abundant intracellular cation after potassium. It is involved in >600 enzymatic reactions in the body, including those contributing to the exaggerated immune and inflammatory responses exhibited by COVID-19 patients.Methods: A summary of experimental findings and knowledge of the biochemical role magnesium may play in the pathogenesis of COVID-19 is presented in this perspective. The National Academy of Medicine's Standards for Systematic Reviews were independently employed to identify clinical and prospective cohort studies assessing the relationship of magnesium with interleukin-6, a prominent drug target for treating COVID-19.Results: Clinical recommendations are given for prevention and treatment of COVID-19. Constant monitoring of ionized magnesium status with subsequent repletion, when appropriate, may be an effective strategy to influence disease contraction and progression. The peer-reviewed literature supports that several aspects of magnesium nutrition warrant clinical consideration. Mechanisms include its "calcium-channel blocking" effects that lead to downstream suppression of nuclear factor-Kβ, interleukin-6, c-reactive protein, and other related endocrine disrupters; its role in regulating renal potassium loss; and its ability to activate and enhance the functionality of vitamin D, among others.Conclusion: As the world awaits an effective vaccine, nutrition plays an important and safe role in helping mitigate patient morbidity and mortality. Our group is working with the Academy of Nutrition and Dietetics to collect patient-level data from intensive care units across the United States to better understand nutrition care practices that lead to better outcomes.

Association between serum vitamin D and uric acid in the eastern Chinese population: a population-based cross-sectional study

BACKGROUND

Uric acid (UA) is the end product of purine metabolism, which is thought to be related to many human diseases, such as nephrolithiasis, gout, cardiovascular disease (CVD), type 2 diabetes mellitus, metabolic syndrome. However, the relationship between serum UA (SUA) and 25(OH) D is still unclear in the eastern Chinese population.

METHODS

We did a population-based observational investigation, which included 12,770 residents living in eastern China. Ultimately, data from 9220 subjects were analyzed. Serum 25(OH) D, SUA, fasting plasma glucose (FPG), fasting insulin, HbA1c and other metabolic parameters were tested. Waist circumference (WC), weight and height were also measured. Questionnaires were collected from these subjects for information on smoking and drinking status.

RESULTS

We enrolled 9220 Chinese adults, including 3681 males (age 55.57 ± 13.23 years) and 5539 females (age 54.31 ± 12.83 years). The levels of SUA were 352.07 ± 79.25 nmol/L and 269.29 ± 64.68 nmol/L in males and females, respectively. The proportion of adults with hyperuricemia (HUA) was 12.26% in the total population. Levels of SUA were positively associated with 25(OH) D, and the incidence of HUA increased 9.4% for every 10 nmol/L increase in 25(OH) D (P < 0.001).

CONCLUSIONS

SUA was positively associated with 25(OH) D in the eastern Chinese population. Higher levels of serum 25(OH) D may be a potential predictor of HUA.

Nutraceutical support in heart failure: a position paper of the International Lipid Expert Panel (ILEP)

Heart failure (HF) is a complex clinical syndrome that represents a major cause of morbidity and mortality in Western countries. Several nutraceuticals have shown interesting clinical results in HF prevention as well as in the treatment of the early stages of the disease, alone or in combination with pharmacological therapy. The aim of the present expert opinion position paper is to summarise the available clinical evidence on the role of phytochemicals in HF prevention and/or treatment that might be considered in those patients not treated optimally as well as in those with low therapy adherence. The level of evidence and the strength of recommendation of particular HF treatment options were weighed up and graded according to predefined scales. A systematic search strategy was developed to identify trials in PubMed (January 1970 to June 2019). The terms 'nutraceuticals', 'dietary supplements', 'herbal drug' and 'heart failure' or 'left verntricular dysfunction' were used in the literature search. The experts discussed and agreed on the recommendation levels. Available clinical trials reported that the intake of some nutraceuticals (hawthorn, coenzyme Q10, l-carnitine, d-ribose, carnosine, vitamin D, probiotics, n-3 PUFA and beet nitrates) might be associated with improvements in self-perceived quality of life and/or functional parameters such as left ventricular ejection fraction, stroke volume and cardiac output in HF patients, with minimal or no side effects. Those benefits tended to be greater in earlier HF stages. Available clinical evidence supports the usefulness of supplementation with some nutraceuticals to improve HF management in addition to evidence-based pharmacological therapy.

Nutritional vitamin D in CKD: Should we measure? Should we treat?

Vitamin Ddeficiency is frequently present in patients affected by chronic kidney disease (CKD). Experimental studies demonstrated that Vitamin D may play a role in the pathophysiology of diseases beyond mineral bone disorders in CKD (CKD-MBD). Unfortunately, the lack of large and interventional studies focused on the so called "non-classic" effects of 25(OH) Vitamin D supplementation in CKD patients, doesn't permit to conclude definitely about the beneficial effects of this supplementation in clinical practice. In conclusion, treatment of nutritional vitamin D deficiency in CKD may play a central role in both bone homeostasis and cardiovascular outcomes, but there is not clear evidence to support one formulation of nutritional vitamin D over another in CKD.

Evaluation of serum 25-hydroxyvitamin D concentrations in a heterogeneous canine ICU population

OBJECTIVE

To identify the prevalence of low serum 25-hydroxyvitamin D (25-OH-D) concentrations in critically ill dogs and determine whether vitamin D concentration measured at admission correlates with illness severity and patient outcome.

DESIGN

Prospective observational study from December 2013 to July 2014.

SETTING

Private referral teaching hospital ICU.

ANIMALS

One hundred eleven critically ill dogs admitted to the ICU, and 28 apparently healthy control dogs.

INTERVENTIONS

Measurement of 25-OH-D concentration and assessment of physiological parameters required to calculate illness severity scores.

MEASUREMENTS AND MAIN RESULTS

Blood was sampled to measure serum 25-OH-D concentration, point-of-care laboratory data (packed cell volume, total plasma protein, venous blood gas, electrolytes, plasma lactate, and blood glucose concentration), platelet count, and serum albumin within 12 hours of admission. Primary disease etiologies were determined. Mentation score, Acute Patient Physiologic and Laboratory Evaluation (APPLE) fast score, length of ICU hospitalization, and survival to discharge were recorded. Low serum 25-OH-D concentrations were detected in 25% (28/111) of the ICU cohort; 25-OH-D concentrations (median; IQR) (89.2; 26.3 ng/mL [222; 140.0 nmol/L]) were significantly lower in hospitalized dogs compared with the healthy cohort (127.5; 44.5 ng/mL [318; 111.0 nmol/L]) (P < 0.0001). Serum 25-OH-D concentrations had a weak positive correlation with albumin (r = 0.34, P = 0.0003), but not with any other blood analyte evaluated. Serum concentration of 25-OH-D was also weakly correlated with APPLEfast score (r = 0.31, P = 0.001). 25-OH-D concentrations (median; IQR) were significantly higher in ICU dogs that survived to discharge (95.5; 55 ng/mL [238; 137 nmol/L]) compared with nonsurvivors (60.0; 54 ng/mL [149; 135 nmol/L]; P < 0.001).

CONCLUSIONS

Low serum 25-OH-D was recorded in one-quarter of critically ill dogs, and was significantly lower in nonsurvivors in comparison to survivors. There was weak correlation between serum 25-OH-D and illness severity. Further studies are required to clarify relationships between vitamin D status and outcome.

Vitamin D receptor activation protects against lipopolysaccharide-induced acute kidney injury through suppression of tubular cell apoptosis

Acute kidney injury (AKI) is a common complication of sepsis characterized by a rapid degradation of renal function. The effect of vitamin D on AKI remains poorly understood. Here, we showed that vitamin D receptor (VDR) activation protects against lipopolysaccharide (LPS)-induced AKI by blocking renal tubular epithelial cell apoptosis. Mice lacking VDR developed more severe AKI than wild-type (WT) control mice after LPS treatment, which was manifested by marked increases in body weight loss and accumulation of serum blood urea nitrogen and creatinine as well as the magnitude of apoptosis of tubular epithelial cells. In the renal cortex, LPS treatment led to more dramatic downregulation of Bcl-2, more robust induction of p53-upregulated modulator of apoptosis (PUMA) and miR-155, and more severe caspase-3 activation in VDR knockout mice compared with WT control mice. Conversely, paricalcitol pretreatment markedly prevented LPS-induced AKI. Paricalcitol ameliorated body weight loss, attenuated serum blood urea nitrogen and creatinine accumulation, blocked tubular cell apoptosis, prevented the suppression of Bcl-2, and reversed PUMA and miR-155 induction and caspase-3 activation in LPS-treated WT mice. In HK2 cells, LPS induced PUMA and miR-155 by activating NF-κB, whereas 1,25(OH)2D3 blocked PUMA and miR-155 induction by repressing NF-κB activation. Both PUMA and miR-155 target Bcl-2 to promote apoptosis; namely, PUMA inhibits Bcl-2 activity, whereas miR-155 promotes Bcl-2 mRNA degradation and inhibits Bcl-2 protein translation. Collectively, these data provide strong evidence that LPS induces tubular cell apoptosis via upregulating PUMA and miR-155, whereas vitamin D/VDR signaling protects against AKI by blocking NF-κB-mediated PUMA and miR-155 upregulation.

Novel markers of graft outcome in a cohort of kidney transplanted patients: a cohort observational study

Renal biopsy (RBx) informs about kidney transplantation (KTx) prognosis. In our observational study the prevalence of histological anomalies and the prognostic role of CD45, vimentin (VIM) and periostin (POSTN) in KTx-RBx have been evaluated. One hundred forty-six KTx-RBx (2009-2012) were analysed for general histology and in immunohistochemistry for CD45, VIM and POSTN. Clinical data of the 146-KTx patients were collected at the RBx time (T0), 6 and 12 months before and after RBx. Follow-up time was 21 ± 14 months. Glomerulosclerosis was 20% glomeruli/biopsy. Tubular atrophy (TA), Interstitial infiltrate (I-Inf) and interstitial fibrosis (IF) were slight in 21-18% and 25%, moderate in 22-30% and 26% and severe in 30-18% and 28% of patients. Fifty-eight percent of patients had lesions compatible with IF-TA. CD45, VIM and POSTN correlated to each-other and to TA, I-Inf and IF. VIM and POSTN correlated to GS. CD45 and VIM correlated directly to renal function (RF) and 25(OH)VitD, while POSTN inversely to 25(OH)VitD. Thirty patients restarted dialysis (HD+). HD+ had lower T0-eGFR, and higher CD45, VIM and POSTN than HD-. POSTN resulted the strongest in discriminate for HD+ . CD45, VIM and POSTN correlate to each-other and predict graft outcome. POSTN was the strongest in discriminate for HD+. 25(OH)VitD might influence inflammation and fibrosis in KTx.

25-Hydroxyvitamin D Is Associated with Kidney Function: The Dong-gu Study

Although the kidneys play a leading part in the biosynthesis of vitamin D, there is no consensus regarding the relationship of the vitamin D concentration with kidney function. Thus, we aimed to estimate the correlation among 25-hydroxyvitamin D (25(OH)D), estimated glomerular filtration rate (eGFR), and albumin/creatinine ratio (ACR) in participants aged ≥50 y in Korea. This study consisted of 9,166 people who participated in a basic survey of the Dong-gu Study. Following an overnight fast, the blood and urine sample were assessed. The serum 25(OH)D, eGFR, ACR of each subject were measured. When adjusting for covariates and log-transformed ACR (Model III), the lower eGFR value was significantly associated with increasing 25(OH)D levels (<10.0: 71.5[70.5-72.4]; 10.0-14.9: 70.0 [69.5-70.4]; 15.0-19.9: 68.7 [68.3-69.2]; ≥20.0: 67.4 [66.8-67.9] mL/min/1.73 m², p<0.001). When adjusted for the same covariates and log-transformed eGFR (Model III), the lower ACR value was significantly associated with increasing 25(OH)D levels (<10.0: 57.4 [48.0-66.9]; 10.0-14.9: 40.8 [36.5-45.2]; 15.0-19.9: 34.0 [29.5-38.5]; ≥20.0: 34.3 [28.8-39.8] μg/mg creatinine, p<0.001). In conclusion, the mean values of eGFR were significantly decreased with increasing 25(OH)D levels independent of ACR. In additon, the mean values of ACR were significantly decreased with increasing 25(OH)D levels independent of eGFR in participants aged ≥50 y in Korea.

Oral paricalcitol: expanding therapeutic options for pediatric chronic kidney disease patients

The complex pathophysiology of progressive chronic kidney disease (CKD) and the development of mineral and bone disorder, abbreviated as CKD-MBD, is of vital importance to a pediatric patient. Paricalcitol, the 19 nor-1,25(OH)₂D₂ analogue was shown to be effective and safe in the treatment of secondary hyperparathyroidism (SHPT) in adults almost two decades ago. It also significantly improved survival in dialysis patients compared to the standard calcitriol. The successful treatment of CKD-MBD in children is essential if they are to grow and survive into adulthood. It can be argued that it is more important for children with CKD than adults since they have early and prolonged disease risk exposure. In this issue of Pediatric Nephrology, Webb et.al. report a dual trial of the safety, efficacy, and pharmacokinetics of paricalcitol in children aged 10-16 years with moderate but significant efficacy in meeting the endpoint of >30% decrease in parathyroid hormone (PTH) levels from baseline with minimal adverse events. Much more research needs to be done to expand and develop clinical pharmaceutical trials in the use of paricalcitol in children, especially in the younger age categories. This current study has done much to open the doors for future studies, with the caveat that it has been long coming and much more needs to be done to compensate for this delay in the treatment of children with CKD-MBD and cardiovascular and renal disease progression.

The role of mineral and bone disorders in the development and progression of cardiac and renal pathology in patients with type 1 diabetes mellitus of long duration

AIMS

The objective of our study was to evaluate the role of mineral and bone metabolism disorders associated with chronic kidney disease (MBD-CKD) in the development and progression of cardiac and renal pathology in patients with type 1 diabetes mellitus (T1DM) of long duration.

METHODS

We investigated 96 patients with T1DM of long duration, with CKD at different stages (0-5), including patients on hemodialysis (HD) and with kidney transplantation (KT). Along with overall clinical examination, we assessed markers of MBD (calcium, phosphorus, parathormone, vitamin D, fibroblast growth factor (FGF) 23) and levels of cardiac injury marker (atrial natriuretic peptide, NT-proBNP). Multispiral computer tomography with Agatston index calculation was also included.

RESULTS

Decreased kidney function was associated with increased of levels phosphorus, parathormone, FGF 23, and vitamin D deficiency, with the highest deviation from the reference ranges seen in patients on HD with a very high risk of cardiovascular events. In KT patients with satisfactory graft function, these parameters were at the same levels as in patients with CKD stages 0-4. Progression of cardiovascular pathology was accompanied by elevation of NT-proBNP levels as CKD duration increased, decreased glomerular filtration rate, and were correlated with the main parameters of mineral homeostasis. The severity of coronary arteries calcification was associated with patient age and duration of T1DM and arterial hypertension.

CONCLUSIONS

Development and progression of kidney dysfunction is accompanied by MBD, a significant factor in progression of cardiac pathology, which remains a major cause of mortality in this patient population.

SERUM 25-HYDROXYVITAMIN D(3) LEVELS IN TYPE 2 DIABETIC PATIENTS WITH NORMO-, MICRO-, AND MACROALBUMINURIA

Background

The aim of this study was to observe the differences in serum 25-hydroxyvitamin D(3) levels in nondiabetic healthy control subject and type 2 diabetic patients, and to investigate the differences in serum 25-hydroxyvitamin D(3) levels in type 2 diabetic patients with normo-, micro- and macroalbuminuria.

Patients and Methods

Total 140 nondiabetic healthy controls and 384 type 2 diabetic patients (156 normoalbuminuric, 152 microalbuminuric and 76 macroalbuminuric) were included in the study. 25-hydroxyvitamin D(3) levels were measured in sera with the method of electrochemiluminescence using modular immunoassay analyzer.

Results

Vitamin D deficiency was detected in 70.85% and 22.9% of type 2 diabetic patients and nondiabetic healthy controls, respectively. Serum 25-hydroxyvitamin D(3) levels were significantly lower in type 2 diabetic patients compared to nondiabetic healthy controls (16.4 ± 9.5 ng/mL vs. 28.2 ± 11.6 ng/mL, p=0.0001). Serum 25-hydroxyvitamin D(3) levels were lower in albuminuric and nonalbuminuric diabetic patients (14.3 ± 7.9 ng/mL vs. 19.6±10.9 ng/mL, respectively, p=0.013). Serum 25-hydroxyvitamin D(3) levels were 19.6 ± 10.9 ng/mL in normoalbuminuric, 14.9 ± 8.8 ng/mL in microalbuminuric and 12.9 ± 5.8 ng/mL in macroalbuminuric diabetic patients. While lower serum 25-hydroxyvitamin D(3) levels were detected both in microalbuminuric (p=0.028) and macroalbuminuric diabetic patients (p=0.014) compared to normoalbuminuric diabetic patients, 25-hydroxyvitamin D(3) levels did not change significantly between microalbuminuric and macroalbuminuric diabetic patients (p=0.67). Serum 25-hydroxyvitamin D(3) levels correlated negatively with urinary albumin excretion (r=-0.24, p=0.016) in patients with diabetes mellitus.

Conclusion

Findings of the present study demonstrated reduced serum 25-hydroxyvitamin D(3) levels which were significantly related with albuminuria in type 2 diabetic patients.

Ageing Renal Patients: We Need More Collaboration between Geriatric Services and Nephrology Departments

There has been a significant increase in the number of frail older patients diagnosed with advanced chronic kidney disease (CKD) over the past thirty years. These elderly patients have high levels of comorbidity, and as a consequence the face of renal medicine is changing—There is an increasing need to focus on traditionally geriatric areas of expertise such as falls prevention and rehabilitation, and to shift our emphasis onto improving patient well-being rather than longevity. Over the past decade, many nephrologists have found that they are already acting as de facto “amateur geriatricians”. This denies patients both the benefits of specialist geriatric assessment, and equally importantly denies them access to the wider geriatric multidisciplinary team. This article describes the prevalence and underlying causes of the so-called “Geriatric Giants” in patients with advanced CKD, and discusses possible improvements in care that closer working with geriatricians could bring.

Histoprotective effect of vitamin D against carbon tetrachloride nephrotoxicity in rats

This study investigated the protective effect of vitamin D against carbon tetrachloride (CCl4)-induced nephrotoxicity in rats. Adult male Wistar albino rats were divided into four groups ((A) control; (B) 10-week exposure to CCl4; (C) 10-week exposure to CCl4 + vitamin D treatment; and (D) 10-week exposure to CCl4 + 12 weeks of vitamin D treatment). The CCl4 dose (1.5 ml kg−1) was injected subcutaneously twice a week, while the 0.5 mg kg−1 dose of vitamin D was administered intraperitoneally every day, as appropriate for each group. Whole animal and kidney weights as well as serum urea, creatinine, and glucose levels were measured. Kidney tissue sections were stained with hematoxylin–eosin, Masson’s trichrome, and periodic acid–Schiff. Tubular and glomerular degeneration were detected in the kidney tissues of CCl4-treated rats, together with dilatation and vacuolization within the tubules and hemorrhage in the intertubular region. In the kidney glomeruli; congestion, atrophy, and adhesion to parietal layer were observed. Tissue disorganization and aggregation of Bowman’s capsules were noted. Mononuclear cell infiltration was observed between the glomeruli and the tubules. In contrast, the kidney sections and functional parameters of vitamin D-treated rats were similar to the controls, suggesting that vitamin D treatment is able to reduce renal damage.

The relationship between the level of serum 25-hydroxyvitamin D and renal function in patients without chronic kidney disease: a cross-sectional study

OBJECTIVES

Low level of vitamin D has been suggested as a risk factor for chronic kidney disease (CKD). However, little is known about the effect of vitamin D on renal function in healthy subjects. Our aim was to investigate the question of whether vitamin D status is associated with renal function in subjects without CKD.

METHODS

In this cross-sectional study, 1,648 subjects aged older than 20 years were recruited as study participants. Subjects diagnosed with either CKD or other conditions that could influence serum vitamin D were excluded. Estimated glomerular filtration rate (eGFR) from serum creatinine (sCr) was used for the determination of renal function. Vitamin D status was determined by the measurement of serum 25-hydroxyvitamin D [25(OH)D] levels.

RESULTS

In men, 25(OH)D showed significant positive correlation with age (r = 0.127, P < .001), skeletal muscle mass (r = 0.077, P = .017), sCr (r = 0.128, P < .001), and negative correlation with body fat (r = -0.065, P = .044), eGFR (r = -0.152, P < .001). In women, 25(OH)D showed negative correlation with eGFR (r = -0.085, P = .026), but not with age and body composition. In multiple linear regression analysis, 25(OH)D (β = 0.114, P < .001), total muscle mass (β = 0.202, P = .026), and age (β = 0.117, P = .003) were an independent determinant of sCr in men; in women, 25(OH)D (β = 0.086, P = .023), total muscle mass (β = 0.152, P < .001) were variables showing significant association with sCr.

CONCLUSIONS

Higher level of 25(OH)D is independently associated with sCr elevation. We suggest that a positive correlation between 25(OH)D and muscle mass could be attributed to sCr. It is thought to be another mechanism of serum 25(OH)D level in renal function in populations without CKD.

Vitamin D depletion aggravates hypertension and target-organ damage

Background

We tested the controversial hypothesis that vitamin D depletion aggravates hypertension and target‐organ damage by influencing renin.

Methods and Results

Four‐week‐old double‐transgenic rats (dTGR) with excess angiotensin (Ang) II production due to overexpression of the human renin (hREN) and angiotensinogen (hAGT) genes received vitamin D‐depleted (n=18) or standard chow (n=15) for 3 weeks. The depleted group had very low serum 25‐hydroxyvitamin D levels (mean±SEM; 3.8±0.29 versus 40.6±1.19 nmol/L) and had higher mean systolic BP at week 5 (158±3.5 versus 134.6±3.7 mm Hg, P<0.001), week 6 (176.6±3.3 versus 162.3±3.8 mm Hg, P<0.01), and week 7 (171.6±5.1 versus 155.9±4.3 mm Hg, P<0.05). Vitamin D depletion led to increased relative heart weights and increased serum creatinine concentrations. Furthermore, the mRNAs of natriuretic peptides, neutrophil gelatinase‐associated lipocalin, hREN, and rRen were increased by vitamin D depletion. Regulatory T cells in the spleen and in the circulation were not affected. Ang metabolites, including Ang II and the counter‐regulatory breakdown product Ang 1 to 7, were significantly up‐regulated in the vitamin D‐depleted groups, while ACE‐1 and ACE‐2 activities were not affected.

Conclusions

Short‐term severe vitamin D depletion aggravated hypertension and target‐organ damage in dTGR. Our data suggest that even short‐term severe vitamin D deficiency may directly promote hypertension and impacts on renin‐angiotensin system components that could contribute to target‐organ damage. The findings add to the evidence that vitamin D deficiency could also affect human hypertension.

Oral active vitamin d treatment and mortality in maintenance hemodialysis patients

AIMS

To analyze the relationship between oral active vitamin D treatment and mortality in maintenance hemodialysis (MHD) patients.

METHODS

We examined the association of oral calcitriol treatment with mortality in 156 MHD patients (80 men and 76 women; mean age: 59 ± 15 years). The survival analysis of all-cause and cardiovascular mortality was performed using the Kaplan-Meier survival and Cox proportional-hazards analyses.

RESULTS

In all, 108 of the 156 patients received active vitamin D treatment. The intact parathyroid hormone level was obviously lower in the patients who received active vitamin D treatment than in those who did not. Throughout the whole follow-up, overall mortality was 16.7% (26 deaths, 13 in each group). The cardiovascular mortality rates were 14.6% (8/48) in the control group and 4.6% (5/108) in the calcitriol group. The crude analysis of all-cause and cardiovascular mortality using the Kaplan-Meier curve showed a significant reduction in mortality risk for patients who received oral active vitamin D compared with those who did not receive it (p = 0.015 and 0.026, respectively). Cox's regression analysis showed that active vitamin D treatment was associated with a significantly lower risk of all-cause mortality (RR = 0.399, 95% CI 0.185-0.862, p = 0.019) and cardiovascular mortality (RR = 0.295, 95% CI 0.094-0.93, p = 0.037). However, after adjusting for potential confounding variables, oral active vitamin D therapy was no longer clearly associated with a lower risk of either all-cause or cardiovascular mortality.

CONCLUSION

Oral active vitamin D treatment was associated with improved survival in MHD patients. However, this survival benefit was smaller than previously reported, and a large cohort study should be performed.

Survival Analysis with Electronic Health Record Data: Experiments with Chronic Kidney Disease

This paper presents a detailed survival analysis for chronic kidney disease (CKD). The analysis is based on the EHR data comprising almost two decades of clinical observations collected at New York-Presbyterian, a large hospital in New York City with one of the oldest electronic health records in the United States. Our survival analysis approach centers around Bayesian multiresolution hazard modeling, with an objective to capture the changing hazard of CKD over time, adjusted for patient clinical covariates and kidney-related laboratory tests. Special attention is paid to statistical issues common to all EHR data, such as cohort definition, missing data and censoring, variable selection, and potential for joint survival and longitudinal modeling, all of which are discussed alone and within the EHR CKD context.

Preserving residual renal function in dialysis: what we know

Residual renal function confers a survival benefit among dialysis patients thought to be related to greater volume removal and solute clearance. Whether the presence of residual renal function is protective or merely a marker for better health is not clear. The basic mechanisms governing the decline or persistence of residual renal function are poorly understood and few studies have examined the role of medical therapy in its preservation. Dialysis modality, inflammatory processes often associated with comorbid diseases (including diabetes mellitus and obesity), volume dysregulation, and vitamin D deficiency are predictive of residual renal function decline. We review potential mechanisms for preservation of remaining glomerular filtration rate among chronic dialysis patients.

Vitamin D receptor signaling in renal and cardiovascular protection

The high prevalence of vitamin D deficiency in patients with chronic kidney disease is believed to be an important risk factor for the cardiorenal syndrome commonly seen in this patient population. African Americans suffer a disproportionally high incidence of renal and cardiovascular disease with poor disease outcome, which may be partly attributed to their low vitamin D status in part owing to low subcutaneous photoproduction of vitamin D. Mounting evidence from animal and clinical studies has shown beneficial effects of vitamin D therapy on the renal and cardiovascular systems, and the underlying renoprotective and cardioprotective mechanisms of vitamin D receptor (VDR)-mediated signaling are under intense investigation. In this article, our most recent understanding of the renal protective mechanism of the podocyte VDR signaling against diabetic nephropathy and the anti-atherosclerotic role of macrophage VDR signaling in the regulation of atherosclerosis is reviewed.

Clinical therapeutic strategies for early stage of diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of chronic kidney disease, leading to end-stage renal disease and cardiovascular disease. The overall number of patients with DKD will continue to increase in parallel with the increasing global pandemic of type 2 diabetes. Based on landmark clinical trials, DKD has become preventable by controlling conventional factors, including hyperglycemia and hypertension, with multifactorial therapy; however, the remaining risk of DKD progression is still high. In this review, we show the importance of targeting remission/regression of microalbuminuria in type 2 diabetic patients, which may protect against the progression of DKD and cardiovascular events. To achieve remission/regression of microalbuminuria, several steps are important, including the early detection of microalbuminuria with continuous screening, targeting HbA1c < 7.0% for glucose control, the use of renin angiotensin system inhibitors to control blood pressure, the use of statins or fibrates to control dyslipidemia, and multifactorial treatment. Reducing microalbuminuria is therefore an important therapeutic goal, and the absence of microalbuminuria could be a pivotal biomarker of therapeutic success in diabetic patients. Other therapies, including vitamin D receptor activation, uric acid-lowering drugs, and incretin-related drugs, may also be promising for the prevention of DKD progression.

Paricalcitol downregulates myocardial renin-angiotensin and fibroblast growth factor expression and attenuates cardiac hypertrophy in uremic rats

BACKGROUND

Vitamin D attenuates uremic cardiac hypertrophy, possibly by suppressing the myocardial renin-angiotensin system (RAS) and fibroblast growth factors (FGFs). We compared the suppression of cardiac hypertrophy and myocardial expression of RAS and FGF receptor genes offered by the vitamin D analog paricalcitol (Pc) or the angiotensin-converting enzyme inhibitor enalapril (E) in experimental uremia.

METHODS

Rats with 5/6 nephrectomy received Pc or E for 8 weeks. Renal function, systolic blood pressure, and cardiac hypertrophy were evaluated. Myocardial expression of RAS genes, brain natriuretic peptide (BNP), and FGF receptor-1 (FGFR-1) were determined using quantitative reverse-transcription (pRT)-PCR.

RESULTS

Blood pressure, proteinuria, and serum creatinine were significantly higher in untreated uremic animals. Hypertension was significantly reduced by E but only modestly by Pc; however, cardiac hypertrophy in the untreated group was similarly attenuated by Pc or E. Upregulation of myocardial expressions of renin, angiotensinogen, FGFR-1, and BNP in untreated uremic animals was reduced similarly by Pc and E, while the angiotensin II type 1 receptor was downregulated only by E.

CONCLUSIONS

Uremic cardiac hypertrophy is associated with activation of the myocardial RAS and the FGFR-1. Downregulation of these genes induced by Pc and E results in similar amelioration of left ventricular hypertrophy despite the different antihypertensive effects of these drugs.

Pediatric cardiomyopathies: causes, epidemiology, clinical course, preventive strategies and therapies

Pediatric cardiomyopathies, which are rare but serious disorders of the muscles of the heart, affect at least one in every 100,000 children in the USA. Approximately 40% of children with symptomatic cardiomyopathy undergo heart transplantation or die from cardiac complications within 2 years. However, a significant number of children suffering from cardiomyopathy are surviving into adulthood, making it an important chronic illness for both pediatric and adult clinicians to understand. The natural history, risk factors, prevalence and incidence of this pediatric condition were not fully understood before the 1990s. Questions regarding optimal diagnostic, prognostic and treatment methods remain. Children require long-term follow-up into adulthood in order to identify the factors associated with best clinical practice including diagnostic approaches, as well as optimal treatment approaches. In this article, we comprehensively review current research on various presentations of this disease, along with current knowledge about their causes, treatments and clinical outcomes.

The role of vitamin D in blood pressure, endothelial and renal function in postmenopausal women

BACKGROUND

Vitamin D is a pro-hormone that plays an essential role in the vasculature and in kidney function.

AIMS

To review the extra-skeletal effects of vitamin D on blood pressure, endothelial and renal function with emphasis on recent findings in postmenopausal women.

METHODS

Included in this review was a PubMed database search for English language articles through March 2013. This review discussed the physiology and definition of vitamin D deficiency, the recent evidence for the role vitamin D in blood pressure, vascular and renal function.

RESULTS

Experimental and epidemiological data suggest that vitamin D plays an important role in the vasculature and in kidney function. Low vitamin D concentrations appear to significantly associate with hypertension, endothelial and renal dysfunction. However, the results of clinical trials have generally been mixed. Studies specifically conducted among postmenopausal women are limited and findings are still inconsistent.

CONCLUSIONS

Definitive studies are warranted to elucidate the effects of vitamin D supplementation on vascular and renal function and a more detailed work is needed to outline the route, duration and optimal dose of supplementation. It is premature to recommend vitamin D as a therapeutic option in the improvement of vascular and renal function at the current stage.

Association between vitamin D insufficiency and elevated serum uric acid among middle-aged and elderly Chinese Han women

BACKGROUND

Association between vitamin D insufficiency and hyperuricemia has not been reported so far. We aimed to study the association of vitamin D insufficiency with elevated serum uric acid among middle-aged and elderly Chinese Han women.

METHODS

We collected data from participants residing in Jinchang district of Suzhou from January to May, 2010. Serum uric acid, 25-hydroxy vitamin D and other traditional biomarkers including fasting plasma glucose and blood lipids were determined in 1726 women aged above 30 years. Association between vitamin D insufficiency and elevated uric acid was analyzed in premenopausal and postmenopausal women, respectively.

RESULTS

Among postmenopausal women, 25-hydroxy vitamin D level of participants with elevated uric acid was lower than that of those with normal uric acid (median [interquartile range]: 35[28-57] vs 40[32-58], µg/L; P = 0.006). Elevated uric acid was more prevalent in participants with vitamin D insufficiency compared to those without vitamin D insufficiency (16.50% vs 8.08%; P<0.001). Association between vitamin D insufficiency and elevated uric acid was not significant among premenopausal women. However, participants with vitamin D insufficiency were more likely to have elevated uric acid compared with those without vitamin D insufficiency among postmenopausal women (OR, 95% CI: 2.38, 1.47-3.87). Moreover, after excluding individuals with diabetes and/or hypertension, the association of vitamin D insufficiency with elevated uric acid was still significant (OR, 95% CI: 2.48, 1.17-5.44).

CONCLUSIONS

Vitamin D insufficiency was significantly associated with elevated uric acid among postmenopausal Chinese Han women. This study suggested that a clinical trial should be conducted to confirm the association of vitamin D insufficiency with hyperuricemia.

The association of 25(OH)D with blood pressure, pulse pressure and carotid-radial pulse wave velocity in African women

High susceptibility of the African population to develop cardiovascular disease obliges us to investigate possible contributing risk factors. Our aim was to determine whether low 25(OH)D status is associated with increased blood pressure and carotid-radial pulse wave velocity in black South African women. We studied 291 urban women (mean age: 57.56±9.00 yrs.). 25(OH)D status was determined by serum 25(OH)D levels. Women were stratified into sufficient (>30 ng/ml), and insufficient/deficient (<30 ng/ml) groups. Cardiovascular variables were compared between groups. Women with low 25(OH)D levels had significantly higher SBP (150.8±27.1 vs. 137.6±21.0), DBP (94.7±14.5 vs. 89.3±12.3) and PP (53.15(50.7;55.7) vs. 46.3(29.4;84.6)) compared to women with sufficient levels. No significant difference was observed with regards to c-rPWV. ANCOVA analyses still revealed significant differences between the two groups with regards to SBP, DBP as well as PP. Partial correlations revealed significant inverse association between SBP and 25(OH)D (p = .04;r = −.12). Women with low 25(OH)D levels were ∼2 times more likely to have high SBP (95% CI: 3.23;1.05). To conclude, women with deficient/insufficient 25(OH)D had significantly higher SBP compared to women with a sufficient 25(OH) status.

Vitamin D receptor signaling in podocytes protects against diabetic nephropathy

Vitamin D and its analogs have antiproteinuric activity and podocytes express the vitamin D receptor, but whether vitamin D signaling in podocytes accounts for this renoprotection is unknown. To investigate this question, we used the 2.5 kb podocin promoter to target Flag-tagged human vitamin D receptor (hVDR) to podocytes in DBA/2J mice. After the induction of diabetes with streptozotocin, transgenic mice had less albuminuria than wild-type controls. In transgenic mice, a low dose of the vitamin D analog doxercalciferol prevented albuminuria, markedly attenuated podocyte loss and apoptosis, and reduced glomerular fibrosis, but it had little effect on the progression of diabetic nephropathy in wild-type mice. Moreover, reconstitution of VDR-null mice with the hVDR transgene in podocytes rescued VDR-null mice from severe diabetes-related renal damage. In culture, 1,25-dihydroxyvitamin D suppressed high-glucose-induced apoptosis of podocytes by blocking p38- and ERK-mediated proapoptotic pathways. Taken together, these data provide strong evidence that vitamin D/VDR signaling in podocytes plays a critical role in the protection of the kidney from diabetic injury.

Vitamin D supplementation in pre-dialysis chronic kidney disease: A systematic review

Vitamin D deficiency is associated with a variety of skeletal, cardiometabolic, and immunologic co-morbidities that are present in chronic kidney disease (CKD). We performed a systematic review to investigate the effects of vitamin D supplementation, in the form of ergocalciferol or cholecalciferol, on various health outcomes in early CKD. Seventeen clinical trials were identified, only two of which were randomized, placebo controlled trials. The majority of studies supplementing with > 2,000 IU/day of cholecalciferol achieved optimal vitamin D status, whereas studies supplementing with ergocalciferol were less consistent. Studies varied widely in their effects on lowering serum parathyroid hormone concentrations. Few studies investigated effects of vitamin D treatment on other clinical health indicators in early CKD. Rigorous studies are necessary to investigate optimal vitamin D dosing strategies in early CKD for the maintenance of adequate vitamin D status, management of secondary hyperparathyroidism and improvement of non-skeletal related clinical outcomes.

High-dose cholecalciferol reduces parathyroid hormone in patients with early chronic kidney disease: a pilot, randomized, double-blind, placebo-controlled trial

BACKGROUND

Vitamin D deficiency contributes to secondary hyperparathyroidism, which occurs early in chronic kidney disease (CKD).

OBJECTIVES

We aimed to determine whether high-dose cholecalciferol supplementation for 1 y in early CKD is sufficient to maintain optimal vitamin D status (serum 25-hydroxyvitamin D [25(OH)D] concentration ≥30 ng/mL) and decrease serum parathyroid hormone (PTH). A secondary aim was to determine the effect of cholecalciferol on blood pressure and serum fibroblast growth factor-23 (FGF23).

DESIGN

This was a double-blind, randomized, placebo-controlled trial. Forty-six subjects with early CKD (stages 2-3) were supplemented with oral cholecalciferol (vitamin D group; 50,000 IU/wk for 12 wk followed by 50,000 IU every other week for 40 wk) or a matching placebo for 1 y.

RESULTS

By 12 wk, serum 25(OH)D increased in the vitamin D group only [baseline (mean ± SD): 26.7 ± 6.8 to 42.8 ± 16.9 ng/mL; P < 0.05] and remained elevated at 1 y (group-by-time interaction: P < 0.001). PTH decreased from baseline only in the vitamin D group (baseline: 89.1 ± 49.3 to 70.1 ± 24.8 pg/mL; P = 0.01) at 12 wk, but values were not significantly different from baseline at 1 y (75.4 ± 29.5 pg/mL; P = 0.16; group-by-time interaction: P = 0.09). Group differences were more pronounced in participants with secondary hyperparathyroidism (group-by-time interaction: P = 0.004). Blood pressure and FGF23 did not change in either group.

CONCLUSIONS

After 1 y, this oral cholecalciferol regimen was safe and sufficient to maintain serum 25(OH)D concentrations and prevent vitamin D insufficiency in early CKD. Furthermore, serum PTH improved after cholecalciferol treatment, particularly in patients who had secondary hyperparathyroidism.

25-Hydroxyvitamin D levels and chronic kidney disease in the AusDiab (Australian Diabetes, Obesity and Lifestyle) study

Background

Low 25-hydroxy vitamin D (25(OH)D) levels have been associated with an increased risk of albuminuria, however an association with glomerular filtration rate (GFR) is not clear. We explored the relationship between 25(OH)D levels and prevalent chronic kidney disease (CKD), albuminuria and impaired GFR, in a national, population-based cohort of Australian adults (AusDiab Study).

Methods

10,732 adults ≥25 years of age participating in the baseline survey of the AusDiab study (1999–2000) were included. The GFR was estimated using an enzymatic creatinine assay and the CKD-EPI equation, with CKD defined as eGFR <60 ml/min/1.73 m². Albuminuria was defined as a spot urine albumin to creatinine ratio (ACR) of ≥2.5 mg/mmol for men and ≥3.5 for women. Serum 25(OH)D levels of <50 nmol/L were considered vitamin D deficient. The associations between 25(OH)D level, albuminuria and impaired eGFR were estimated using multivariate regression models.

Results

30.7% of the study population had a 25(OH)D level <50 nmol/L (95% CI 25.6-35.8). 25(OH)D deficiency was significantly associated with an impaired eGFR in the univariate model (OR 1.52, 95% CI 1.07-2.17), but not in the multivariate model (OR 0.95, 95% CI 0.67-1.35). 25(OH)D deficiency was significantly associated with albuminuria in the univariate (OR 2.05, 95% CI 1.58-2.67) and multivariate models (OR 1.54, 95% CI 1.14-2.07).

Conclusions

Vitamin D deficiency is common in this population, and 25(OH)D levels of <50 nmol/L were independently associated with albuminuria, but not with impaired eGFR. These associations warrant further exploration in prospective and interventional studies.