Serum 25-Hydroxyvitamin D Deficiency and the 5-Year Incidence of CKD

Sex differences in the association between vitamin D and early-stage chronic kidney disease: A population-based study

Vitamin D deficiency (VDD) is commonly observed in people with late-stage chronic kidney disease (CKD) and end-stage renal disease; it has also been associated with the progression of kidney disease. We hypothesized that VDD played a role in early-stage chronic kidney disease as well. Thus, this cross-sectional study aimed to evaluate the association between serum 25-hydroxyvitamin D concentration and CKD stages 1 through 3 (early-stage CKD) in a relatively healthy population in China. A total of 3142 Chinese individuals were included in this cross-sectional study. VDD was observed in 108 (5.6%) males and 307 (25.33%) females. We found a significant inverse association between serum 25(OH)D concentration with CKD stages in both sexes. Furthermore, VDD was associated with CKD stages 1 through 3 in males (adjusted odds ratio, 15.84; 95% confidence interval, 7.85-31.98; P < .001), but not in females. Vitamin D status should be evaluated in people who are newly diagnosed with CKD stages 1 through 3 or decreased estimated glomerular filtration rate, especially in males.

Effects of 25-Hydroxyvitamin D Levels on Renal Function: A Bidirectional Mendelian Randomization Study

CONTEXT

Observational studies investigating the role of vitamin D in renal function have yielded inconsistent results.

OBJECTIVE

We tested whether 25-hydroxyvitamin D (25[OH]D) serum levels are associated with renal function, and inversely, whether altered renal function causes changes in 25(OH)D, using Mendelian randomization (MR).

METHODS

In this two-sample MR study, we used single nucleotide polymorphisms (SNP) associated with 25(OH)D in 443 734 Europeans and evaluated their effects on estimated glomerular filtration rate (eGFR), blood urea nitrogen (BUN), chronic kidney disease (CKD) risk and progression in genome-wide association studies totaling over 1 million Europeans. To control for pleiotropy, we also used SNPs solely in DHCR7, CYP2R1, and GC, all genes with known roles in vitamin D metabolism. We performed a reverse MR, using SNPs for the above indices of renal function to study causal effects on 25(OH)D levels.

RESULTS

We did not find robust evidence supporting effects of 25(OH)D on eGFR, BUN, and CKD or its progression. Our inverse variance weighted MR demonstrated a 0.56 decrease in standardized log-transformed 25(OH)D (95% CI -0.73, -0.41; P = 2.89 × 10-12) per unit increase in log-transformed eGFR. Increased BUN was associated with increased 25(OH)D (β = 0.25, 95% CI 0.15, 0.36; P = 4.12 × 10-6 per unit increase in log-transformed BUN). Finally, genetically predicted CKD conferred a 0.05 increase in standardized log-transformed 25(OH)D level (95% CI 0.04, 0.06; P = 1.06 × 10-13). Other MR methods confirmed the findings of the main analyses.

CONCLUSION

Genetically predicted CKD, increased BUN, and decreased eGFR are associated with increased 25(OH)D levels, but we found no causal effect of 25(OH)D on renal function in Europeans.

Vitamin D status and biomarkers of renal graft function after kidney transplantation: a longitudinal study

Introduction

Introduction: Low 25-hydroxyvitamin D [25(OH)D] levels occur after kidney transplantation (KTx), and can be associated with increase the risk of graft loss. This longitudinal study aimed to evaluate the vitamin D status and association with biomarkers of the renal graft function after KTx. Methods: this longitudinal study included 42 patients evaluated at baseline, 3 and 6 months after KTx. Biodemographic, clinical, and biochemical parameters such as 25(OH)D and parathyroid hormone (PTH), and biomarkers of renal graft function, such as creatinine, estimated glomerular filtration rate (eGFR), and albumin/creatinine ratio (ACR), were assessed. Sun exposure was also evaluated. Patients were categorized according to their 25(OH)D levels. Results: at baseline, 25(OH)D levels < 30 ng/mL were found in 43 % patients, and 38 % of these patients failed to improve their 25(OH)D levels by 6 months after KTx. Low 25(OH)D levels occurred regardless of sun exposure. Further, 44 % patients developed albuminuria at 6 months. An increased ACR was observed in patients with 25(OH)D levels < 30 ng/mL (p = 0.002) compared to that in patients with 25(OH)D > 30 ng/mL. Additionally, 25(OH)D levels were negatively correlated with ACR at 6 months post-KTx (r = -0.444; p = 0.003). Twelve (28.6 %) patients with 25(OH)D levels < 30 ng/mL showed no eGFR recovery until 6 months after KTx. Conclusion: low vitamin D levels and increased albuminuria were observed at 6 months after KTx, even in a region with high sun exposure. The association between vitamin D status and biomarkers of renal graft function after KTx should be explored in further studies.

Correlates of Calcidiol Deficiency in Adults-Cross-Sectional, Observational, Population-Based Study

The prevalence, determinants, and clinical significance of vitamin D deficiency in the population are debated. The population-based study investigated the cross-sectional associations of several variables with serum 25-hydroxyvitamin D (calcidiol) measured using standardized calibrators. The study cohort consisted of 979 persons of the Moli-sani study, both sexes, ages ≥35 years. The correlates in the analyses were sex, age, education, local solar irradiance in the month preceding the visit, physical activity, anthropometry, diabetes, kidney function, albuminuria, blood pressure, serum cholesterol, smoking, alcohol intake, calorie intake, dietary vitamin D intake, and vitamin D supplement. The serum calcidiol was log transformed for linear regression because it was positively skewed (skewness = 1.16). The prevalence of calcidiol deficiency defined as serum calcidiol ≤12 ng/mL was 24.5%. In multi-variable regression, older age, lower solar irradiance, lower leisure physical activity, higher waist/hip ratio, higher systolic pressure, higher serum cholesterol, smoking, lower alcohol intake, and no vitamin D supplement were independent correlates of lower serum calcidiol (95% confidence interval of standardized regression coefficient ≠ 0) and of calcidiol deficiency (95% confidence interval of odds ratio > 1). The data indicate that low serum calcidiol in the population could reflect not only sun exposure, age, and vitamin D supplementation but also leisure physical activity, abdominal obesity, systolic hypertension, hypercholesterolemia, smoking, and alcohol intake.

Prevalence of vitamin D deficiency and impact on clinical outcomes after kidney transplantation: a systematic review and meta-analysis

CONTEXT

The prevalence of vitamin D deficiency (VDD) and its impact on clinical outcomes after kidney transplant (KT) remain poorly defined.

OBJECTIVES

We conducted a meta-analysis to evaluate the impact of early VDD on clinical outcomes after KT.

DATA SOURCES

Electronic databases (PubMed, Embase, Web of Science, and The Cochrane Library) were systematically searched for eligible publications up to April 30, 2020.

DATA EXTRACTION

Relative risk was presented as hazard ratios (HRs) or odds ratios (ORs) and 95%CIs for dichotomous outcomes. Mean difference (MD) and 95%CIs were presented for continuous outcomes.

RESULTS

A total of 28 studies (13 prospective and 15 retrospective) were included. VDD was common early after KT, with a prevalence of 52% (95%CI: 41%-64%) at transplant, 34% (95%CI: 17%-51%) at 3 months, and 23% (95%CI: 10%-35%) at 6 months. Early VDD was associated with higher mortality rate after KT (HR, 1.56; 95%CI: 1.32-1.84; P < 0.001). In addition, early VDD led to higher risk of bacterial infection (OR, 1.82; 95%CI: 1.40-2.36; P < 0.001), BK polyomavirus infection (OR, 2.11, 95%CI: 1.23-3.61; P = 0.006), and cytomegalovirus infection (OR, 1.69; 95%CI: 1.24-2.31; P = 0.001). Early VDD increased the risk of acute rejection as well (HR, 2.28; 95%CI: 1.57-3.30; P < 0.001). Recipients with early VDD had lower estimated glomerular filtration rates (mean difference: -5.06; 95%CI: -7.28 to 2.83 mL/min; P < 0.001). Sensitivity analyses showed good stability of the pooled results.

CONCLUSION

VDD was common early after KT and associated with higher risk of death and adverse outcomes.

Effect of Vitamin D Supplementation on Kidney Function in Adults with Prediabetes: A Secondary Analysis of a Randomized Trial

BACKGROUND AND OBJECTIVES

Low serum 25-hydroxyvitamin D (25[OH]D) concentration has been associated with higher levels of proteinuria and lower levels of eGFR in observational studies. In the Vitamin D and Type 2 Diabetes (D2d) study, we investigated the effect of vitamin D supplementation on kidney outcomes in a population with prediabetes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Overweight/obese adults with high risk for type 2 diabetes (defined by meeting two of three glycemic criteria for prediabetes) were randomized to vitamin D₃ 4000 IU per day versus placebo. Median duration of treatment was 2.9 years (interquartile range 2.0-3.5 years). Kidney outcomes included (1) worsening in Kidney Disease: Improving Global Outcomes (KDIGO ) risk score (low, moderate, high, very high) on two consecutive follow-up visits after the baseline visit and (2) mean changes in eGFR and urine albumin-to-creatinine ratio (UACR).

RESULTS

Among 2166 participants (mean age 60 years, body mass index 32 kg/m², serum 25(OH)D 28 ng/ml, eGFR 87 ml/min per 1.73 m², UACR 11 mg/g, 79% with hypertension), 10% had moderate, high, or very high KDIGO risk score. Over a median follow-up of 2.9 years, there were 28 cases of KDIGO worsening in the vitamin D group and 30 in the placebo group (hazard ratio, 0.89; 95% confidence interval [95% CI], 0.52 to 1.52]). Mean difference in eGFR from baseline was -1.0 ml/min per 1.73 m² (95% CI, -1.3 to -0.7) in the vitamin D group and -0.1 ml/min per 1.73 m² (95% CI, -0.4 to 0.2) in the placebo group; between-group difference was -1.0 ml/min per 1.73 m² (95% CI, -1.4 to -0.6). Mean difference in UACR was 2.7 mg/g (95% CI, 1.2 to 4.3) in the vitamin D group and 2.0 (95% CI, 0.5 to 3.6) in the placebo group; between-group difference was 0.7 mg/g (95% CI, -1.5 to 2.9).

CONCLUSIONS

Among persons with prediabetes, who were not preselected on the basis of serum 25(OH)D concentration, vitamin D supplementation did not affect progression of KDIGO risk scores and did not have a meaningful effect on change in UACR or eGFR.

Plasma 25-Hydroxyvitamin D3 Concentrations and Risk of New-Onset Proteinuria in Patients With Hypertension

OBJECTIVE

We aimed to evaluate the relationship of plasma 25-hydroxyvitamin D3 (25[OH]D3) with the risk of new-onset proteinuria and examine the possible effect modifiers in patients with hypertension and without chronic kidney disease at baseline.

METHODS

This is a post hoc analysis of the renal substudy of the China Stroke Primary Prevention Trial. A total of 1655 patients with hypertension, who had plasma 25(OH)D3 measurements, as well as without proteinuria and with an estimated glomerular filtration rate of ≥60 mL/min/1.73 m² at baseline, were included in the present study. The main outcome was new-onset proteinuria, defined as a urine dipstick reading of ≥1+ at the exit visit.

RESULTS

The mean (standard deviation) 25(OH)D3 level at baseline was 18.6 (7.5) ng/mL. The median follow-up duration was 4.4 years. Overall, there was a significant inverse association between plasma 25(OH)D3 and the risk of new-onset proteinuria (per standard deviation increment; [odds ratio] OR: 0.70; 95% confidence interval [CI]: 0.50, 0.97). Accordingly, when 25(OH)D3 was assessed as quartiles, a significantly lower risk of new-onset proteinuria was found in participants in quartiles 3-4 (≥17.8 ng/mL; OR: 0.45; 95% CI: 0.23, 0.87), compared with those in quartile 1 (<13.1 ng/mL). Furthermore, a stronger inverse relationship of plasma 25(OH)D3 and new-onset proteinuria was observed in nondiabetic participants (per standard deviation increment; OR: 0.57; 95% CI: 0.39, 0.83; vs. diabetics: OR: 1.48; 95% CI: 0.67, 3.28; P for interaction = 0.028).

CONCLUSION

There was a significant inverse association between plasma 25(OH)D3 and the risk of proteinuria in patients with hypertension, especially in those without diabetes.

KDOQI Clinical Practice Guideline for Nutrition in CKD: 2020 Update

The National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (KDOQI) has provided evidence-based guidelines for nutrition in kidney diseases since 1999. Since the publication of the first KDOQI nutrition guideline, there has been a great accumulation of new evidence regarding the management of nutritional aspects of kidney disease and sophistication in the guidelines process. The 2020 update to the KDOQI Clinical Practice Guideline for Nutrition in CKD was developed as a joint effort with the Academy of Nutrition and Dietetics (Academy). It provides comprehensive up-to-date information on the understanding and care of patients with chronic kidney disease (CKD), especially in terms of their metabolic and nutritional milieu for the practicing clinician and allied health care workers. The guideline was expanded to include not only patients with end-stage kidney disease or advanced CKD, but also patients with stages 1-5 CKD who are not receiving dialysis and patients with a functional kidney transplant. The updated guideline statements focus on 6 primary areas: nutritional assessment, medical nutrition therapy (MNT), dietary protein and energy intake, nutritional supplementation, micronutrients, and electrolytes. The guidelines primarily cover dietary management rather than all possible nutritional interventions. The evidence data and guideline statements were evaluated using Grading of Recommendations, Assessment, Development and Evaluation (GRADE) criteria. As applicable, each guideline statement is accompanied by rationale/background information, a detailed justification, monitoring and evaluation guidance, implementation considerations, special discussions, and recommendations for future research.

Vitamin D3 reduces risk of cardiovascular and liver diseases by lowering homocysteine levels: double-blinded, randomised, placebo-controlled trial

The objective of this study was to evaluate the effect of vitamin D3 on total homocysteine (tHcy) and C-reactive protein (CRP) levels and liver and kidney function tests in overweight women with vitamin D deficiency. Therefore, a randomised, double-blind placebo, controlled clinical trial was conducted on 100 eligible women. Subjects were randomly divided into two groups: the placebo (n 50) and the vitamin D (n 50) which received 1250 µg vitamin D3 per week for 2 months. The participants' 25-hydroxyvitamin D (25(OH)D), tHcy, CRP, alanine aminotransferase (ALT), aspartate aminotransferase (AST), urea, creatinine and estimated glomerular filtration rate (eGFR) were measured and compared before and after treatment. Results showed that the tHcy, CRP, AST, ALT and eGFR levels after the 2nd month of vitamin D3 intervention were significantly (P < 0·001) decreased and the 25(OH)D, urea and creatinine levels were significantly (P < 0·001) increased in the treatment group. In the placebo group, no significant changes were identified throughout the follow-up period. In conclusion, vitamin D3 intervention with a treatment dose of 1250 µg/week for at least 2 months may help in lowering Hcy and CRP levels and may improve liver function tests, which in turn might help in minimising the risk of CVD and liver diseases among overweight women but negatively affect kidney function.

Vitamin D Status and Indices of Mineral Homeostasis in the Population: Differences Between 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D

Opinions are conflicting about the epidemiology of vitamin D deficiency. This population-based study investigated cross-sectionally the associations of 25-hydroxyvitamin D (calcidiol) and 1,25-dihydroxyvitamin D (calcitriol) with indices of mineral homeostasis. Study cohort consisted of 979 persons of the Moli-Sani study, both sexes, ages ≥35 years. Data collection included serum calcidiol by different assays, serum calcitriol, serum parathyroid hormone, serum and urine calcium, and phosphorus. Prevalence of mild-to-moderate calcidiol deficiency (10–19 ng/mL) was 36.4% and did not associate with hypocalcemia or hyperparathyroidism. Prevalence of severe calcidiol deficiency (<10 ng/mL) was 16.8% and associated with hyperparathyroidism only (odds ratio = 8.81, 95% confidence interval = 2.4/32.9). Prevalence of calcitriol deficiency (<18 pg/mL) was 3.1% and associated with hypocalcemia (29.1, 7.4/114.5) but not hyperparathyroidism. In ANOVA along concentration strata, lower calcidiol associated with higher parathyroid hormone only (p < 0.001). Lower calcitriol associated with lower serum and urine calcium (p < 0.001) but not with parathyroid hormone. Calcidiol findings were consistent with different calcidiol assays. In the population, mild-to-moderate calcidiol deficiency did not associate with abnormal mineral homeostasis. Severe calcidiol deficiency and calcitriol deficiency associated with different disorders: lower calcidiol associated with hyperparathyroidism whereas lower calcitriol associated with hypocalcemia and low urine calcium.

ASSOCIATIONS BETWEEN VITAMIN D AND MICROVASCULAR COMPLICATIONS IN MIDDLE-AGED AND ELDERLY DIABETIC PATIENTS

Objective: The objective of this cross-sectional study was to investigate the association of serum 25-hydroxyvitamin D (25[OH]D) levels with estimated glomerular filtration rate (eGFR), albumin/creatinine ratio (ACR), and the prevalence of diabetic retinopathy (DR) in Chinese diabetic adults. Methods: A total of 4,767 diabetic participants were enrolled from seven communities in Shanghai, China, in 2018. Participants underwent several examinations, which included the measurement of anthropometric parameters, blood pressure, glucose, lipid profiles, 25(OH)D, and ACR. DR was detected based on high-quality fundus photographs and remotely read by ophthalmologists. Results: Compared with the first 25(OH)D quartile, participants in the fourth quartile had a lower prevalence of high ACR (odds ratio [OR], 0.77; 95% confidence interval [CI], 0.61 to 0.96) (P for trend <.01). No association was found between 25(OH)D levels and eGFR. For DR, the OR (95% CI) for DR ranging from 0 to 4 in ordinal logistic regression associated with 25(OH)D was 0.62 (0.47 to 0.82) for the fourth 25(OH)D quartile (P for trend <.01) compared with the first quartile. These associations were all fully adjusted for confounding factors. Conclusion: Lower serum 25(OH)D concentration is significantly associated with increased ACR and higher prevalence of DR in middle-aged and elderly diabetic adults. However, the possibility of a causal relationship between 25(OH)D deficiency and diabetic microvascular complications remains to be demonstrated. Abbreviations: 25(OH)D = 25-hydroxyvitamin D; ACR = albumin/creatinine ratio; BMI = body mass index; CI = confidence interval; DKD = diabetic kidney disease; DR = diabetic retinopathy; eGFR = estimated glomerular filtration rate; HbA1c = glycated hemoglobin; HDL = high-density lipoprotein; LDL = low-density lipoprotein; OR = odds ratio; T2DM = type 2 diabetes mellitus.

Negative effect of vitamin D on kidney function: a Mendelian randomization study

Background

The kidney plays a central role in the regulation of vitamin D metabolism. It is not clear, however, whether vitamin D influences kidney function. Previous studies have reported conflicting results, which may have been influenced by reverse causation and residual confounding. We conducted a Mendelian randomization (MR) study to obtain unconfounded estimates of the association between genetically instrumented vitamin D metabolites and estimated glomerular filtration rate (eGFR) as well as the urinary albumin:creatinine ratio (UACR).

Methods

We performed a two-sample MR study based on three single nucleotide variants associated with 25(OH)D levels: rs2282679, rs10741657 and rs12785878, related to the genes GC, CYP2R1 and DHCR7, respectively. Estimates of the allele-dependent effects on serum 25(OH)D and eGFR/UACR were obtained from summary statistics of published genome-wide association meta-analyses. Additionally, we performed a one-sample MR analysis for both 25(OH)D and 1,25(OH)2 D using individual-level data from six cohorts.

Results

The combined MR estimate supported a negative causal effect of log transformed 25(OH)D on log transformed eGFR (β = -0.013, P = 0.003). The analysis of individual-level data confirmed the main findings and also revealed a significant association of 1,25(OH)2 D on eGFR (β = -0.094, P = 0.008). These results show that a 10% increase in serum 25(OH)D levels causes a 0.3% decrease in eGFR. There was no effect of 25(OH)D on UACR (β = 0.032, P = 0.265).

Conclusion

Our study suggests that circulating vitamin D metabolite levels are negatively associated with eGFR. Further studies are needed to elucidate the underlying mechanisms.

Vitamin D Deficiency in Chronic Kidney Disease: Recent Evidence and Controversies

Vitamin D (VD) is a pro-hormone essential for life in higher animals. It is present in few types of foods and is produced endogenously in the skin by a photochemical reaction. The final step of VD activation occurs in the kidneys involving a second hydroxylation reaction to generate the biologically active metabolite 1,25(OH)₂-VD. Extrarenal 1α-hydroxylation has also been described to have an important role in autocrine and paracrine signaling. Vitamin D deficiency (VDD) has been in the spotlight as a major public healthcare issue with an estimated prevalence of more than a billion people worldwide. Among individuals with chronic kidney disease (CKD), VDD prevalence has been reported to be as high as 80%. Classically, VD plays a pivotal role in calcium and phosphorus homeostasis. Nevertheless, there is a growing body of evidence supporting the importance of VD in many vital non-skeletal biological processes such as endothelial function, renin-angiotensin-aldosterone system modulation, redox balance and innate and adaptive immunity. In individuals with CKD, VDD has been associated with albuminuria, faster progression of kidney disease and increased all-cause mortality. Recent guidelines support VD supplementation in CKD based on extrapolation from cohorts conducted in the general population. In this review, we discuss new insights on the multifactorial pathophysiology of VDD in CKD as well as how it may negatively modulate different organs and systems. We also critically review the latest evidence and controversies of VD monitoring and supplementation in CKD patients.

Serum 25-hydroxyvitamin D level is negatively associated with serum phosphorus level among stage 3a-5 chronic kidney disease patients

BACKGROUND

Serum 25-hydroxyvitamin D (25(OH)D) negatively correlates with serum phosphorus level of stage 3a-5 chronic kidney disease (CKD) patients. So far, no explanation has been provided for this negative association.

OBJECTIVE

To confirm this negative association and determine if this relationship is mediated through other known co-morbid factors.

CASES AND METHODS

One hundred (57 male and 43 female) pre-dialysis stage 3a-5 CKD patients were selected. Estimated glomerular filtration rate (eGFR), serum calcium (Ca), phosphorus (P), 25(OH)D, parathyroid hormone (PTH), and intact fibroblast growth factor-23 (FGF23) were assessed. A correlation analysis between serum 25(OH)D and the different parameters studied was performed. Multivariate linear regression analysis was carried out to determine predictors of 25(OH)D.

RESULTS

The negative association between serum 25(OH)D and serum P was confirmed in univariate and multivariate correlation analysis. On the other hand, we failed to detect a significant association between 25(OH)D and serum FGF23. Serum P is the most important independent predictor of 25(OH)D in these patients (partial R²=0.15, p<0.0001).

CONCLUSION

Serum P is likely to have a direct negative impact on serum 25(OH)D. Further studies are needed to determine the underlying mechanism.

Vitamin D and Incidence of Prediabetes or Type 2 Diabetes: A Four-Year Follow-Up Community-Based Study

Aim

To examine whether the baseline 25-hydroxyvitamin D [25(OH)D] level was predictive of the onset of prediabetes or type 2 diabetes (T2DM) in the Chinese population.

Methods

This was a 4-year follow-up study that was conducted in the Chengdu region of China as part of the China National Diabetes and Metabolic Disorders Study. The study included 490 participants that were free of prediabetes and type 2 diabetes mellitus (T2DM) at baseline and had complete data by follow-up examinations. Glucose, insulin, and 25(OH)D levels were measured at baseline and at 4 years later. Prediabetes and T2DM were defined by results obtained from an oral glucose tolerance test.

Results

Over a 4-year follow-up, 95 (48.5‰) developed prediabetes and 31 (15.8‰) individuals developed diabetes. Low 25(OH)D status was significantly associated with the risk of developing prediabetes [OR 3.01 (95% CI: 1.50–6.06), P = 0.002] and T2DM [OR 5.61 (95% CI: 1.73–18.27), P = 0.004] after adjustment for multiple potential confounders. In a multiple linear regression analysis, low baseline levels of 25(OH)D were an independent predictor of increased insulin resistance over a 4-year period (P < 0.05).

Conclusions

The current prospective study suggests that low 25(OH)D levels might have contributed to the incidence of prediabetes or T2DM in Chinese individuals. This trial is registered with TR-CCH-ChiCTR-OCS-09000361.

Vitamin D Status and Kidney Function Decline in HIV-Infected Men: A Longitudinal Study in the Multicenter AIDS Cohort Study

Vitamin D may play an important role in a range of disease processes. In the general population, lower vitamin D levels have been associated with kidney dysfunction. HIV-infected populations have a higher risk of chronic kidney disease. Few studies have examined the link between lower vitamin D levels and kidney function decline among HIV-infected persons. We investigated the associations of serum 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)₂D] with kidney function decline in a cohort of HIV-infected white and black men under highly active antiretroviral therapy treatment in the vitamin D ancillary study of the Multicenter AIDS Cohort Study. The associations of 25(OH)D and 1,25(OH)₂D with annual change in estimated glomerular filtration rate (eGFR) were evaluated using linear mixed effects models. This study included 187 whites and 86 blacks with vitamin D measures and eGFR ≥60 ml/min/1.73 m² at baseline. Over a median follow-up of 8.0 years, lower 25(OH)D levels were significantly associated with faster eGFR decline in whites (adjusted annual change in eGFR, tertile 1: -2.06 ml/min/1.73 m² vs. tertile 3: -1.23 ml/min/1.73 m², p trend .03), while no significant association was detected in blacks. Lower 1,25(OH)₂D was associated with faster kidney function decline in both whites and blacks, although the estimates were not statistically significant. In conclusion, lower 25(OH)D levels were significantly associated with faster eGFR decline in a cohort of HIV-infected white men, but not in those with black ancestry. Further research is warranted to investigate the association of 25(OH)D and 1,25(OH)₂D with kidney function decline in larger and ethnically diverse populations.

Serum 25-hydroxyvitamin D concentration is not associated with glomerular filtration rate in a predominantly obese otherwise healthy population

Evidence from observational studies indicates a role for vitamin D in kidney function and progression to chronic kidney disease. Findings from animal studies have proposed underlying mechanisms including increased activation of the renin-angiotensin system, increased blood pressure, insulin resistance and chronic low-grade inflammation. However, human studies are limited by confounders arising from heterogeneous samples of participants. We examined the relationship between 25(OH)D and estimated glomerular filtration rate (eGFR) in a predominantly obese otherwise healthy and drug-naive population with no history of chronic kidney disease (CKD). One hundred and twenty one non-diabetic (75g oral glucose tolerance test; OGTT) volunteers (70 males and 51 females), aged 18-57 years participated in the study. Median 25(OH)D level was 37nmol/L with no difference by sex. Twenty six participants (21.5%) had 25(OH)D <25 nmol/L, 75 participants (62%) had 25(OH)D of 25-49.99nmol/L, and 20 participants (16.5%) had 25(OH)D ≥50nmol/L. In univariate analysis, 25(OH)D was related negatively to percent body fat and 2-h glucose level post OGTT. Mean (SD) eGFR was 113.1 (14.9)mL/min/1.73m², and in the multivariable analysis, it was related to age, sex, percent body fat and 2-h glucose level post OGTT, but not to 25(OH)D. Furthermore, there was no relationship between eGFR and 25(OH)D across BMI categories. Our data suggest that measuring 25(OH)D in predominantly obese otherwise healthy individuals with no history of CKD may not be beneficial in early recognition of kidney disease.

Vitamin D status in renal transplant recipients living in a low-latitude city: association with body fat, cardiovascular risk factors, estimated glomerular filtration rate and proteinuria

Recent evidence suggests that vitamin D deficiency is associated with CVD, impaired kidney function and proteinuria. To date, no study has evaluated these associations in renal transplant recipients (RTR) adjusting for body adiposity assessed by a ‘gold standard’ method. This study aimed to evaluate the vitamin D status and its association with body adiposity, CVD risk factors, estimated glomerular filtration rate (eGFR) and proteinuria in RTR, living in Rio de Janeiro, Brazil (a low-latitude city (22°54'10"S)), taking into account body adiposity evaluated by dual-energy X-ray absorptiometry (DXA). This cross-sectional study included 195 RTR (114 men) aged 47·6 (sd11·2) years. Nutritional evaluation included anthropometry and DXA. Risk factors for CVD were hypertension, diabetes mellitus, dyslipidaemia and the metabolic syndrome. eGFR was evaluated using the Chronic Kidney Disease Epidemiology Collaboration equation. Serum 25-hydroxyvitamin D (25(OH)D) concentration was used to define vitamin D status as follows: 10 % (n19) had vitamin D deficiency (<16 ng/ml), 43 % (n85) had insufficiency (16–30 ng/ml) and 47 % (n91) had sufficiency (>30 ng/ml). Percentage of body fat (DXA) was significantly associated with vitamin D deficiency independently of age, sex and eGFR. Lower 25(OH)D was associated with higher odds of the metabolic syndrome and dyslipidaemia after adjustment for age, sex and eGFR, but not after additional adjustment for body fat. Hypertension and diabetes were not related to 25(OH)D. Lower serum 25(OH)D was associated with increasing proteinuria and decreasing eGFR even after adjustments for age, sex and percentage of body fat. This study suggests that in RTR of a low-latitude city hypovitaminosis D is common, and is associated with excessive body fat, decreased eGFR and increased proteinuria.

Vitamin D and Albuminuria in Youth with and without Type 1 Diabetes

BACKGROUND/AIMS

In adults, lower vitamin D has been associated with increased albuminuria. This association has not been extensively studied in youth with or without type 1 diabetes.

METHODS

We examined the cross-sectional association between vitamin D and albuminuria (urine albumin to creatinine ratio ≥30 mg/g) in 8,789 participants of the National Health and Nutrition Survey 2001-2006 (NHANES), who were 6-19 years old. Further, we examined the association between vitamin D and albuminuria in 938 participants from the SEARCH Nutritional Ancillary Study (SNAS), a longitudinal cohort of youth with type 1 diabetes.

RESULTS

Of the NHANES participants, 5.3, 19.5, and 53.7% had vitamin D levels <30, 50 and 80 nmol/L, respectively. Albuminuria was present in 12.8% and was more common in younger children, females, non-Hispanic whites, non-obese children, and children with hypertension. After adjustments, there was no association between vitamin D and albuminuria. Among the SNAS participants with type 1 diabetes, we also found no association between baseline vitamin D and subsequent albuminuria in unadjusted or adjusted analyses.

CONCLUSION

We did not find an association between serum vitamin D and albuminuria in either non-diabetic youth or those with type 1 diabetes. Further research is needed to more fully understand this relationship.

Association between Obesity and Serum 25(OH)D Concentrations in Older Mexican Adults

Background: Vitamin D is essential for maintaining bone mineralization and calcium homeostasis, and prevents falls and fractures in older adults. Mexico is undergoing an epidemiologic and demographic transition with increasing obesity rates. The study’s aim was to determine the association of obesity with serum 25-hydroxyvitamin D [25(OH)D] concentrations in older Mexican adults. Methods: Data from 1772 Mexicans, aged ≥50 years, enrolled in a sub-sample of the 3rd wave of the Mexican Health and Aging Study, were included. Serum 25(OH)D concentrations were used to define vitamin D status, and were categorized into tertiles. Body mass index measures were used to categorize older adults into under/normal weight, overweight, and obese groups. Multinomial logistic regression models were used to assess the relationship, adjusting for potential confounders. Results: Approximately 40% and 37% of older Mexican adults were either overweight or obese, respectively. Compared to under/normal weight older Mexicans, obese adults were 1.78 times (95% Confidence Interval (CI) 1.27–2.48) and 1.94 times (95% CI 1.40–2.68) more associated with the first and second tertile concentrations of serum 25(OH)D, respectively. Overweight adults were 1.52 times (95% CI 1.12–2.06) more associated with the second tertile of serum 25(OH)D concentration than under/normal weight adults. Conclusion: Overweight/Obesity was found to be significantly associated with low concentrations of serum 25(OH) in older Mexican adults.

A double-blind, randomized, placebo-controlled trial of combined calcitriol and ergocalciferol versus ergocalciferol alone in chronic kidney disease with proteinuria

Background

KDOQI guideline suggests that nutritional vitamin D should be supplemented in chronic kidney disease (CKD) patients who have vitamin D insufficiency/deficiency. However, there are scarce data regarding the additional benefit of active vitamin D supplement in CKD patients who were receiving nutritional vitamin D supplement. This study was conducted to explore the effect of adding active vitamin D to nutritional vitamin D supplement on proteinuria and kidney function in CKD with vitamin D insufficiency/deficiency.

Methods

This double-blind, randomized placebo-controlled trial was performed to answer the above question. Sixty-eight patients with CKD stage 3–4, urine protein to creatinine ratio (UPCR) > 1 g/g, and serum 25OH-D level < 30 ng/mL were enrolled. Patients were randomly assigned to receive 12-week treatment with oral ergocalciferol plus placebo (n = 36) or oral ergocalciferol plus calcitriol (n = 32).

Results

The mean baseline values of UPCR of both groups were comparable (3.6 ± 3.8 g/g in combined group and 3.5 ± 3.0 g/g in ergocalciferol group). Following 12-week treatment, there were significant reductions in UPCR from baseline in both groups (2.3 ± 2.1 g/g in combined group and 2.4 ± 2.0 g/g in ergocalciferol group). The percentage reductions in UPCR of both groups were not significantly different. The mean eGFR and blood pressure did not differ between baseline and 12-week follow-up and between both groups. No severe hypercalcemia or serious side effects were noted in both groups.

Conclusions

The proteinuria lowering effect of ergocalciferol in CKD patients with vitamin D deficiency was demonstrated. Additional calcitriol supplement did not have more effects on proteinuria.

Trial registration

(Thai Clinical Trials Registry (TCTR) 20140929002). Date of registration: September 27, 2014.

Serum 25-hydroxyvitamin D deficiency; a risk factor for chronic kidney disease in ambulatory indigent patients

OBJECTIVE

To assess whether 25-hydroxyvitamin D (25[OH]D) deficiency is a risk factor for chronic kidney disease (CKD) in ambulatory indigent patients.

METHODS

Data for all serum 25(OH)D concentrations measured during 2010 in our ambulatory nondialysis-dependent patients were analyzed along with CKD-related parameters. Patients were stratified into groups based on 25(OH)D levels of <10, 10 to 19, 20 to 29, and ≥30 ng/mL. CKD was defined by estimated glomerular filtration rate (eGFR; Chronic Kidney Disease-Epidemiology Collaboration [CKD-EPI] equation) and abnormal urine protein to creatinine ratios. CKD-associated parameters included serum parathyroid hormone (PTH), 1,25-dihydroxyvitamin D (1,25[OH]2D), alkaline phosphatase, albumin, corrected calcium, and total CO2 levels.

RESULTS

A total of 2,811 patients had 25(OH)D levels measured. Patients with 25(OH)D levels <10 ng/mL had significantly increased relative risk (RR) of an eGFR <15 mL/min/1.73 m2 (RR, 4.0), an eGFR of 15 to 29 mL/min/1.73 m2 (RR, 2.6), urine protein to creatinine ratio >3.5 g/g (RR, 5.6), and serum PTH >100 pg/mL (RR, 2.8) compared to patients with a 25(OH)D level ≥30 ng/mL. Patients with 25(OH)D levels of 10 to19 ng/mL had significantly increased RR of a urine protein to creatinine ratio >3.5 g/g (RR, 4.8) and serum PTH >100 pg/mL (RR, 1.5) compared to patients with 25(OH)D levels ≥30 ng/mL.

CONCLUSION

25(OH)D deficiency (<10 ng/mL) was associated with reduced eGFR, nephrotic-range proteinuria, and increased PTH levels in our population of ambulatory urban indigent patients.

Relative importance of the determinants of serum levels of 25-hydroxy vitamin D in patients with chronic kidney disease

INTRODUCTION

The cause of vitamin D deficiency in chronic kidney disease (CKD) is probably multi-factorial; however, the relative importance of each potential determinant is uncertain.

AIMS

To determine factors associated with serum levels of 25-hydroxy vitamin D (25OHD) and their relative importance in a cohort of pre-dialysis CKD patients.

MATERIAL AND METHODS

Incident patients admitted to a CKD outpatient clinic were included. Those who were receiving vitamin D supplements or anticonvulsants were excluded. In addition to demographic and clinical data, information about outdoor physical activity, season of blood collection, prescription of statins, anti-angiotensin drugs and xanthine-oxidase inhibitors were included as potential determinants. Johnson's relative weights analysis was used to estimate the relative importance of each potential determinant and the results were expressed as percentage contribution to multiple R.

RESULTS

The study group consisted of 397 patients, 30 of whom were excluded. The mean serum level of 25OHD was 13.7±7.4ng/ml, and 81% of patients had serum levels lower than 20ng/ml. By multiple linear regression and relative weights analyses, the best determinants of low serum 25OHD levels and their relative importance were: higher proteinuria (28.5%), old age (21.4%), low physical activity (19.4%), female gender (19.3%) and low serum bicarbonate levels (11.4%).

CONCLUSIONS

Proteinuria and age are the determinants with the highest relative importance for predicting 25OHD levels in CKD patients.

Exposure to lithium through drinking water and calcium homeostasis during pregnancy: A longitudinal study

There is increasing evidence of adverse health effects due to elevated lithium exposure through drinking water but the impact on calcium homeostasis is unknown. This study aimed at elucidating if lithium exposure through drinking water during pregnancy may impair the maternal calcium homeostasis. In a population-based mother-child cohort in the Argentinean Andes (n=178), with elevated lithium concentrations in the drinking water (5-1660μg/L), blood lithium concentrations (correlating significantly with lithium in water, urine and plasma) were measured repeatedly during pregnancy by inductively coupled plasma mass spectrometry and used as exposure biomarker. Markers of calcium homeostasis included: plasma 25-hydroxyvitamin D3, serum parathyroid hormone (PTH), and calcium, phosphorus and magnesium concentrations in serum and urine. The median maternal blood lithium concentration was 25μg/L (range 1.9-145). In multivariable-adjusted mixed-effects linear regression models, blood lithium was inversely associated with 25-hydroxyvitamin D3 (-6.1nmol/L [95%CI -9.5; -2.6] for a 25μg/L increment in blood lithium). The estimate increased markedly with increasing percentiles of 25-hydroxyvitamin D3. In multivariable-adjusted mixed-effects logistic regression models, the odds ratio of having 25-hydroxyvitamin D3<30nmol/L (19% of the women) was 4.6 (95%CI 1.1; 19.3) for a 25μg/L increment in blood lithium. Blood lithium was also positively associated with serum magnesium, but not with serum calcium and PTH, and inversely associated with urinary calcium and magnesium. In conclusion, our study suggests that lithium exposure through drinking water during pregnancy may impair the calcium homeostasis, particularly vitamin D. The results reinforce the need for better control of lithium in drinking water, including bottled water.

Deficient serum 25-hydroxyvitamin D is associated with an atherogenic lipid profile: The Very Large Database of Lipids (VLDL-3) study

BACKGROUND

Cross-sectional studies have found an association between deficiencies in serum vitamin D, as measured by 25-hydroxyvitamin D (25[OH]D), and an atherogenic lipid profile. These studies have focused on a limited panel of lipid values including low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG).

OBJECTIVE

Our study examines the relationship between serum 25(OH)D and an extended lipid panel (Vertical Auto Profile) while controlling for age, gender, glycemic status, and kidney function.

METHODS

We used the Very Large Database of Lipids, which includes US adults clinically referred for analysis of their lipid profile from 2009 to 2011. Our study focused on 20,360 subjects who had data for lipids, 25(OH)D, age, gender, hemoglobin A1c, insulin, creatinine, and blood urea nitrogen. Subjects were split into groups based on serum 25(OH)D: deficient (<20 ng/mL), intermediate (≥ 20-30 ng/mL), and optimal (≥ 30 ng/mL). The deficient group was compared to the optimal group using multivariable linear regression.

RESULTS

In multivariable-adjusted linear regression, deficient serum 25(OH)D was associated with significantly lower serum HDL-C (-5.1%) and higher total cholesterol (+9.4%), non-HDL-C (+15.4%), directly measured LDL-C (+13.5%), intermediate-density lipoprotein cholesterol (+23.7%), very low-density lipoprotein cholesterol (+19.0%), remnant lipoprotein cholesterol (+18.4%), and TG (+26.4%) when compared with the optimal group.

CONCLUSION

Deficient serum 25(OH)D is associated with significantly lower HDL-C and higher directly measured LDL-C, intermediate-density lipoprotein cholesterol, very low-density lipoproteins cholesterol, remnant lipoprotein cholesterol, and TG. Future trials examining vitamin D supplementation and cardiovascular disease risk should consider using changes in an extended lipid panel as an additional outcome measurement.

The Prevalence of 25-hydroxyvitamin D Deficiency in Japanese Patients with Diabetic Nephropathy

Objective The purpose of this study was to measure serum 25-hydroxyvitamin D [25(OH)D] levels in Japanese patients with diabetic nephropathy and determine the relationship between 25(OH)D concentrations and various factors. Methods The study subjects included 442 patients with type 2 diabetes. Their serum levels of creatinine, HbA1c, intact-parathyroid hormone, urinary albumin, 25(OH)D, and 1,25-dihydroxyvitamin D [1,25(OH)2D] were measured and their estimated glomerular filtration rate (eGFR) was determined. The patients were divided into four groups based on the risk for progression to chronic kidney disease (CKD): low, moderate, high, very high, based on their eGFR and their level of albuminuria. Results The median 25(OH)D level was 14.6 ng/mL; 11% of the patients had 25(OH)D deficiency (<10 ng/mL), and 2% of patients had active vitamin D deficiency, as defined by a 1,25(OH)2D level of <22 pg/mL. The serum 25(OH)D level was correlated with the serum 1,25(OH)2D level in patients with a very high risk for CKD, but not in those with a moderate or high risk for CKD. Conclusion Although the vitamin D levels of the Japanese patients with diabetic nephropathy and CKD were low, the prevalence of vitamin D deficiency, as defined by the 1,25(OH)2D level, was low. Albuminuria, younger age, and female gender were associated with a low 25(OH)D level. The serum level of 25(OH)D should be monitored to assess the vitamin D status of patients with nephropathy and CKD.

Plasma Vitamin D Level and Change in Albuminuria and eGFR According to Sodium Intake

BACKGROUND AND OBJECTIVES

Low circulating 25-hydroxyvitamin D [25(OH)D] and high sodium intake are both associated with progressive albuminuria and renal function loss in CKD. Both vitamin D and sodium intake interact with the renin-angiotensin-aldosterone system. We investigated whether plasma 25(OH)D or 1,25-dihydroxyvitamin D [1,25(OH)2D] is associated with developing increased albuminuria or reduced renal function and whether these associations depend on sodium intake.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline plasma 25(OH)D and 1,25(OH)2D were measured by liquid chromatography tandem mass spectrometry, and sodium intake was assessed by 24-hour urine collections in the general population-based Prevention of Renal and Vascular End-Stage Disease cohort (n=5051). Two primary outcomes were development of urinary albumin excretion >30 mg/24 h and eGFR (creatinine/cystatin C-based CKD Epidemiology Collaboration) <60 ml/min per 1.73 m(2). Participants with CKD at baseline were excluded. In Cox regression analyses, we assessed associations of vitamin D with developing increased albuminuria or reduced eGFR and potential interaction with sodium intake.

RESULTS

During a median follow-up of 10.4 (6.2-11.4) years, 641 (13%) participants developed increased albuminuria, and 268 (5%) participants developed reduced eGFR. Plasma 25(OH)D was inversely associated with increased albuminuria (fully adjusted hazard ratio [HR] per SD higher, 0.86; 95% confidence interval [95% CI], 0.78 to 0.95; P=0.003) but not reduced eGFR (HR, 0.99; 95% CI, 0.87 to 1.12; P=0.85). There was interaction between 25(OH)D and sodium intake for risk of developing increased albuminuria (P interaction =0.03). In participants with high sodium intake, risk of developing increased albuminuria was inversely associated with 25(OH)D (lowest versus highest quartile: adjusted HR, 1.81; 95% CI, 1.20 to 2.73, P<0.01), whereas this association was nonsignificant in participants with low sodium intake (HR, 1.29; 95% CI, 0.94 to 1.77; P=0.12). Plasma 1,25(OH)2D was not significantly associated with increased albuminuria or reduced eGFR.

CONCLUSIONS

Low plasma 25(OH)D is associated with higher risk of developing increased albuminuria, particularly in individuals with high sodium intake, but not of developing reduced eGFR. Plasma 1,25(OH)2D is not associated with risk of developing increased albuminuria or reduced eGFR.

Serum 25-hydroxyvitamin D level and kidney function decline in a Swiss general adult population

BACKGROUND AND OBJECTIVES

Molecular evidence suggests that levels of vitamin D are associated with kidney function loss. Still, population-based studies are limited and few have considered the potential confounding effect of baseline kidney function. This study evaluated the association of serum 25-hydroxyvitamin D with change in eGFR, rapid eGFR decline, and incidence of CKD and albuminuria.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline (2003-2006) and 5.5-year follow-up data from a Swiss adult general population were used to evaluate the association of serum 25-hydroxyvitamin D with change in eGFR, rapid eGFR decline (annual loss >3 ml/min per 1.73 m(2)), and incidence of CKD and albuminuria. Serum 25-hydroxyvitamin D was measured at baseline using liquid chromatography-tandem mass spectrometry. eGFR and albuminuria were collected at baseline and follow-up. Multivariate linear and logistic regression models were used considering potential confounding factors.

RESULTS

Among the 4280 people included in the analysis, the mean±SD annual eGFR change was -0.57±1.78 ml/min per 1.73 m(2), and 287 (6.7%) participants presented rapid eGFR decline. Before adjustment for baseline eGFR, baseline 25-hydroxyvitamin D level was associated with both mean annual eGFR change and risk of rapid eGFR decline, independently of baseline albuminuria. Once adjusted for baseline eGFR, associations were no longer significant. For every 10 ng/ml higher baseline 25-hydroxyvitamin D, the adjusted mean annual eGFR change was -0.005 ml/min per 1.73 m(2) (95% confidence interval, -0.063 to 0.053; P=0.87) and the risk of rapid eGFR decline was null (odds ratio, 0.93; 95% confidence interval, 0.79 to 1.08; P=0.33). Baseline 25-hydroxyvitamin D level was not associated with incidence of CKD or albuminuria.

CONCLUSIONS

The association of 25-hydroxyvitamin D with eGFR decline is confounded by baseline eGFR. Sufficient 25-hydroxyvitamin D levels do not seem to protect from eGFR decline independently from baseline eGFR.

Obesity and vitamin D deficiency: a systematic review and meta-analysis

Over the past decade, there have been an increasing number of studies on the association between vitamin D deficiency and anthropometric state. However, we did not identify any meta-analyses of the relationship between obesity and vitamin D deficiency in different age groups. Thus, we evaluated the association between obesity and vitamin D deficiency. We searched for observational studies published up to April 2014 in PubMed/Medline, Web of Science and Scopus databases. We performed a meta-analysis in accordance with the random-effects model to obtain the summary measurement (prevalence ratio, PR). Among the 29,882 articles identified, 23 met the inclusion criteria. The prevalence of vitamin D deficiency was 35% higher in obese subjects compared to the eutrophic group (PR: 1.35; 95% CI: 1.21-1.50) and 24% higher than in the overweight group (PR: 1.24; 95% CI: 1.14-1.34). These results indicate that the prevalence of vitamin D deficiency was more elevated in obese subjects. The vitamin D deficiency was associated with obesity irrespective of age, latitude, cut-offs to define vitamin D deficiency and the Human Development Index of the study location.

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.

Non-linear association of serum 25-hydroxyvitamin D with urinary albumin excretion rate in normoalbuminuric subjects

Background

Vitamin D deficiencies and increases in urinary albumin excretion (UAE) are both important and potentially related health problems; however, the nature of their relationship has not been established in normoalbuminuric subjects.

Methods

We obtained data from 14,594 normoalbuminuric Korean adults who underwent voluntary health screenings. We used a generalized additive model to examine the threshold level for relationship between serum 25-hydroxyvitamin D [25(OH)D] and urinary-albumin creatinine ratio (UACR) levels. We conducted multivariate logistic regression for high-normal UAE (UACR, 10–29 mg/g), according to various categories of vitamin D status.

Results

The generalized additive model confirmed a non-linear relationship between serum 25(OH)D and UACR levels, and the threshold concentration of 25(OH)D was 8.0 ng/mL after multivariate adjustment. Comparing subjects who fell into the lowest category of serum 25(OH)D levels with subjects who were in the reference range (the highest category), we observed that the multivariate adjusted odds ratio (OR) for high-normal UAE was significantly increased, regardless of the criteria used to categorize vitamin D levels: OR of the 1^st quartile over the 4^th quartile, 1.20 (95% CI, 1.04-1.39); OR of the 1.0-4.9^th percentile over the 50-100^th percentile, 1.56 (95% CI, 1.25-1.93); and OR of vitamin D deficiency group over vitamin D sufficiency group, 1.28 (95% CI, 1.08-1.52).

Conclusions

We demonstrated that there was an inverse relationship between serum 25(OH)D less than 8.0 ng/mL and UACR in normoalbuminuric subjects, suggesting that severe vitamin D deficiency could cause an increase in UAE in subjects with normoalbuminuria.

The role of vitamin D deficiency in cardiovascular disease: where do we stand in 2013?

The high worldwide prevalence of vitamin D deficiency is largely the result of low sunlight exposure with subsequently limited cutaneous vitamin D production. Classic manifestations of vitamin D deficiency are linked to disturbances in bone and mineral metabolism, but the identification of the vitamin D receptor in almost every human cell suggests a broader role of vitamin D for overall and cardiovascular health. The various cardiovascular protective actions of vitamin D such as anti-diabetic and anti-hypertensive effects including renin suppression as well as protection against atherosclerosis and heart diseases are well defined in previous experimental studies. In line with this, large epidemiological studies have highlighted vitamin D deficiency as a marker of cardiovascular risk. However, randomized controlled trials (RCTs) on vitamin D have largely failed to show its beneficial effects on cardiovascular diseases and its conventional risk factors. While most prior vitamin D RCTs were not designed to assess cardiovascular outcomes, some large RCTs have been initiated to evaluate the efficacy of vitamin D supplementation on cardiovascular events in the general population. When considering the history of previous disappointing vitamin RCTs in general populations, more emphasis should be placed on RCTs among severely vitamin D-deficient populations who would most likely benefit from vitamin D treatment. At present, vitamin D deficiency can only be considered a cardiovascular risk marker, as vitamin D supplementation with doses recommended for osteoporosis treatment is neither proven to be beneficial nor harmful in cardiovascular diseases.

Evaluating hormonal mechanisms of vitamin D receptor agonist therapy in diabetic kidney disease: the VALIDATE-D study

BACKGROUND

Insufficient vitamin D status and increased renin-angiotensin system (RAS) activity have been associated with renal-vascular disease and nephropathy in diabetes. Accumulating evidence indicates that vitamin D receptor (VDR) activation lowers unfavorable RAS activity; however, more human intervention studies evaluating whether this mechanism could influence diabetic kidney disease are needed. We previously reported that both vitamin D levels and genetic variation at the VDR predict human RAS activity, and that vitamin D therapy can lower RAS activity in non-diabetics. The VALIDATE-D study is a randomized, placebo-controlled, intervention study designed to extend these findings by evaluating whether direct VDR activation in diabetes lowers circulating and local renal-vascular tissue RAS activity (Aims 1 and 2) in a manner similar to the action of ACE inhibitors (Aim 3).

METHODS/DESIGN

Forty subjects with type 2 diabetes, microalbuminuria, and without chronic kidney disease will be recruited to undergo detailed assessment of the RAS before and after randomization to calcitriol 0.75 mcg/day or placebo. Primary analyses will evaluate whether calcitriol therapy reduces circulating and renal-vascular tissue-RAS activity in comparison to placebo. All subjects will thereafter be treated with lisinopril and followed for 3.5 months to evaluate whether combination therapy (calcitriol + lisinopril vs. placebo + lisinopril) additively or synergistically improves renal-vascular function, and lowers proteinuria.

DISCUSSION

The VALIDATE-D study is the first human intervention study to evaluate whether direct VDR activation can lower the human RAS in diabetes, compared to the effect of an ACE inhibitor, and whether this mechanism can translate to clinically relevant endpoints for diabetic kidney disease. The outcomes of VALIDATE-D will have major implications for the recommendation of vitamin D supplementation for the primary prevention of kidney complications in diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01635062.