Association between serum 25-hydroxyvitamin D and diabetic kidney disease in Chinese patients with type 2 diabetes

Role of vitamin D in the development and progression of diabetic kidney disease: an overview of meta-analyses

Background

The effectiveness of vitamin D supplementation in the progression of diabetic kidney disease (DKD) remains controversial. Our review tries to provide a comprehensive summary of all the relevant articles in the area to assess the association of vitamin D deficiency with the development of DKD and the effect of vitamin D supplementation on the progression of DKD.

Methods

PubMed, Embase, Scopus, Cochrane Library and Web of Science were accessed from inception till June 2024 to obtain all the relevant meta-analyses assessing the function of vitamin D in the onset and prognosis of DKD. The summary data were extracted by two independent reviewers. A Measurement Tool to Assess Systematic Reviews (AMSTAR) 2 tool was used for the assessment of the methodological quality of the included meta-analyses.

Results

A total of 4579 articles were obtained from 5 databases in the initial search, of which 8 meta-analyses were included for the evidence synthesis. The methodological quality of the retrieved articles ranged from critically low to high. Serum vitamin D levels were significantly correlated with the prevalence of DKD. The review suggested that vitamin D supplementation could help in reducing proteinuria. However, no such changes were observed in other renal function parameters of DKD patients following vitamin D supplementation.

Conclusion

The current evidence indicates that vitamin D supplementation could be beneficial in reducing proteinuria among DKD patients.PROSPERO registration number: CRD42022375194.

Exploring the interplay between DHCR7, vitamin D deficiency, and type 2 diabetes mellitus (T2DM): a systematic review

Type 2 diabetes mellitus (T2DM) is a growing global health concern. The pathogenesis of T2DM is multifactorial and intricate, involving a complex interplay of genetic predisposition, environmental factors, and molecular interactions. Vitamin D (circulating 25-hydroxyvitamin D concentration) regulates factors crucial for T2DM, including insulin secretion, sensitivity, and inflammation. Thus, vitamin D deficiency has been linked to poor health outcomes in T2DM patients. The cholesterol-synthesizing enzyme 7-dehydrocholesterol reductase (DHCR7) represents a critical regulatory switch between cholesterol and vitamin D3 synthesis. Recent findings suggest that the enzyme DHCR7 may indicate T2DM glycolipid metabolic disorder and is associated with deficient circulating vitamin D (circulating 25-hydroxyvitamin D concentration) status. In this PRISMA-guided systematic review, articles were sourced from two databases, namely, PubMed and Cochrane Library, to evaluate the impact of vitamin D deficiency in patients with T2DM and to explore the emerging role of DHCR7 in T2DM pathogenesis. Our findings strongly indicate a positive correlation between deficient vitamin D status and poor health outcomes in T2DM patients. Finally, this systematic review presents a novel perspective on T2DM development, focusing on the interplay between T2DM-associated hyperglycemia, expression of DHCR7, and abrogation of vitamin D synthesis.

Identification of crucial genes and possible molecular pathways associated with active vitamin D intervention in diabetic kidney disease

Background

A significant cause of advanced renal failure is diabetic nephropathy (DKD), with few treatment options available. Calcitriol shows potential in addressing fibrosis related to DKD, though its molecular mechanisms remain poorly understood. This research seeks to pinpoint the crucial genes and pathways influenced by calcitriol within the scope of DKD-related fibrosis.

Methods

Single-cell gene expression profiling of calcitriol treated DKD rat kidney tissue and screening of fibrosis-associated cell subsets. Mendelian randomization and enrichment analyses (CIBERSORT, GSVA, GSEA, Motif Enrichment) were used to explore gene-immune cell interactions and signaling pathways. Key findings were validated using independent datasets and protein expression data from the Human Protein Atlas.

Results

Calcitriol treatment reduced proliferative cell populations and highlighted the FoxO signaling pathway's role in DKD. SUMO3 and CD74 were identified as key markers linked to immune infiltration and renal function. These genes were significantly associated with creatinine levels and eGFR, indicating their potential role in DKD progression.

Conclusion

Our results suggest that calcitriol modulates DKD fibrosis through the FoxO pathway, with SUMO3 and CD74 serving as potential biomarkers for kidney protection. These results provide fresh insights into strategies for treating DKD.

Relationship between bone turnover markers and renal disease in elderly patients with type 2 diabetes: a cross-sectional study

OBJECTIVE

The prevalence of type 2 diabetes mellitus (T2DM) and bone metabolism disorders increase with age. Diabetic kidney disease (DKD) is one of the most serious microvascular complications of T2DM, and bone metabolism disorders are closely linked to the occurrence of DKD. The relationship between bone turnover markers(BTMs) and the kidney disease in elderly patients with T2DM remains unclear. Therefore, this study aims to investigate the association between common BTMs and DKD in a large sample of elderly patients. The goal is to provide a basis for early identification of high-risk individuals for DKD among elderly T2DM patients from a bone metabolism perspective.

METHODS

In this cross-sectional study, BTMs were collected from a cohort of 2,051 hospitalized Chinese patients. The relationships between 25-hydroxyvitamin D (25-OH-D), β-CrossLaps (β-CTX), osteocalcin (OSTEOC), intact parathyroid hormone (iPTH), and total type I collagen N-terminal propeptide (TP1NP), and DKD, as well as urinary albumin-to-creatinine ratio (UACR) and estimated glomerular filtration rate (eGFR) were analyzed using regression analysis and restrictive cubic spline (RCS) curves.

RESULTS

Higher 25-OH-D levels were independently linked to a lower incidence of DKD and decreased UACR. The RCS curves showed a linear association of 25-OH-D and DKD, approaching the L-shape. β-CTX was independently and positively correlated with UACR. There is an independent positive correlation between OSTEOC and UACR and a negative correlation with eGFR. iPTH is independently and positively correlated with DKD incidence and UACR, and negatively correlated with eGFR. Additionally, the RCS curves showed a non-linear association of OSTEOC and iPTH and DKD, approaching the J-shape, and the point of inflection is 10.875 ng/L and 34.15 pg/mL respectively. There is an independent positive correlation between TP1NP and UACR incidence, and a negative correlation with eGFR. Risk estimates significantly increase with higher TP1NP levels in the RCS model.

CONCLUSION

BTMs are closely associated with kidney disease in elderly patients with T2DM. These discoveries potentially assist clinicians in establishing more preventive measures and targeted treatment strategies for elderly patients with T2DM.

Associations of dietary inflammatory index with low estimated glomerular filtration rate, albuminuria and chronic kidney disease in U.S adults: Results from the NHANES 2011-2018

BACKGROUND AND AIMS

Chronic Kidney Disease (CKD) is characterized by a high inflammation status with ever-increasing prevalence, and defined as low estimated glomerular filtration rate (eGFR) or albuminuria. Both low eGFR and albuminuria can have independent effects on the body. The dietary inflammatory index (DII) is a validated tool used to assess the inflammatory potential of the diet. We aim to explore not only the association between DII and CKD, but also the associations of DII with low eGFR and albuminuria, respectively. In addition, their associations in different subgroups remain to be explored.

METHODS AND RESULTS

18,070 participants from the 2011-2018 NHANES with complete data of dietary intake and laboratory data were involved in our study. The data of 24-hour dietary recall interview was used to calculate DII, CKD could be reflected by laboratory data of creatinine and albumin. Then weighted multivariate logistic regression models and subgroup analyses were performed. The prevalence of low eGFR, albuminuria and CKD were 6.8%, 9.8% and 14.5%, respectively. A positive association between DII and low eGFR was observed (OR=1.12, 95%CI: 1.05-1.21), Q2, Q3 and Q4 are positively associated with a significant 39%, 65% and 71% increased risk of low eGFR compared with Q1 (P for trend<0.05). DII was also associated with CKD (OR=1.06, 95%CI: 1.01-1.11).

CONCLUSION

Significant positive associations of DII with CKD and low eGFR were observed. But we didn't find such association between DII and albuminuria.

Relationship of Vitamin-D Deficiency with Kidney Disease in Patients with Type-2 Diabetes Mellitus (T2DM) in the Makkah Region: A Cross-Sectional Study

Aim

Vitamin D deficiency is linked with type 2 diabetes mellitus (T2DM) and the occurrence of complications in patients with type 2 diabetes mellitus. None of the studies have focused on the association between vitamin D levels in patients with type 2 diabetes mellitus and diabetic nephropathy (DN) in the Makkah region, Saudi Arabia. Hence, the purpose of this study is to investigate the relationship of vitamin D with kidney disease in patients with T2DM in the Makkah region, of Saudi Arabia.

Materials and Methods

This descriptive cross-sectional study was conducted at different hospitals in the Makkah region on T2DM patients from 2021 to 2022. In total, 328 patients with confirmed diabetes were enrolled in this study. T2DM patients over the aged>18 to 92 years were included in the study. General laboratory characteristics of the study population were measured, including fasting blood sugar, HbA1C (Glycated hemoglobin), vitamin D, kidney function (BUN-Blood urea nitrogen and creatinine), and lipid profiles (cholesterol, triglycerides, LDL-Low density lipoprotein, and HDL-High density lipoprotein).

Results

46.6% (n=153) of participants had normal serum vitamin D levels. Insufficient and deficient serum vitamin D level were observed in 43.9% (n=144) and 9.5% (n=31) of participants, respectively. Of the participants, 25.9% (n=85) had good glycemic control (<7.0%). Moderate and poor glycemic control were observed in 39.9% (n=131) and 34.1% (n=112) of the participants, respectively. A significant negative correlation (p<0.5) was found between vitamin D levels and kidney function test results (blood urea nitrogen and serum creatinine levels). An inverse relationship was observed between HbA1c levels and vitamin D deficiency.

Conclusion

Nephropathy is more likely to develop in people with type 2 diabetes mellitus and vitamin D deficiency.

Progression of diabetic nephropathy and vitamin D serum levels: A pooled analysis of 7722 patients

BACKGROUND AND AIM

Low serum Vitamin D levels have been associated with diabetic nephropathy (DN). Our study aimed to analyse the serum levels of vitamin D in patients suffering from DN and the subsequent changes in serum vitamin D levels as the disease progresses.

METHODS

PubMed, Embase, SCOPUS and Web of Science were searched using keywords such as '25 hydroxyvitamin D' and 'diabetic nephropathy'. We included observational studies that reported the association between the serum 25 hydroxy vitamin D levels and diabetic nephropathy without restriction to age, gender, and location. R Version 4.1.2 was used to perform the meta-analysis. The continuous outcomes were represented as mean difference (MD) and standard deviation (SD) and dichotomous outcomes as risk ratios (RR) with their 95% confidence interval (CI).

RESULTS

Twenty-three studies were included in our analysis with 7722 patients. Our analysis revealed that vitamin D was significantly lower in diabetic patients with nephropathy than those without nephropathy (MD: -4.32, 95% CI: 7.91-0.74, p-value = .0228). On comparing diabetic patients suffering from normoalbuminuria, microalbuminuria, or macroalbuminuria, we found a significant difference in serum vitamin D levels across different groups. Normoalbuminuria versus microalbuminuria showed a MD of -1.69 (95% CI: -2.28 to -1.10, p-value = .0002), while microalbuminuria versus macroalbuminuria showed a MD of (3.75, 95% CI: 1.43-6.06, p-value = .0058), proving that serum vitamin D levels keep declining as the disease progresses. Notwithstanding, we detected an insignificant association between Grade 4 and Grade 5 DN (MD: 2.29, 95% CI: -2.69-7.28, p-value = .1862).

CONCLUSION

Serum Vitamin D levels are lower among DN patients and keep declining as the disease progresses, suggesting its potential benefit as a prognostic marker. However, on reaching the macroalbuminuria stage (Grades 4 and 5), vitamin D is no longer a discriminating factor.

Vitamin D deficiency and its associated factors among patients with type 2 diabetes mellitus: a systematic review and meta-analysis

OBJECTIVE

The study intended to assess the pooled prevalence of vitamin D deficiency (VDD) and its associated factors among patients with type 2 diabetes mellitus (T2DM).

DESIGN

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were employed to plan and conduct this systematic review and meta-analysis.

DATA SOURCES

PubMed, Medline, Google Scholar, Web of Science, Science Direct and the Worldwide Science database were searched from their inception to 31 January 2023.

METHODS

Data were extracted using a standardised data extraction format prepared in Microsoft Excel. The inverse variance (I2) test was used to evaluate the presence of heterogeneity across the included studies. To identify the possible source of heterogeneity, subgroup analysis was carried out. Funnel plot symmetry, Begg's and Egger's tests were used to evaluate the existence of publication bias. In addition, factors associated with VDD among patients with T2DM were examined. All statistical analyses were carried out with STATA V.14 software.

RESULTS

A total of 54 studies with 38 016 study participants were included in the study. The pooled prevalence of VDD among patients with T2DM was found to be 64.2% (95% CI 60.6% to 67.8%) with a substantial level of heterogeneity (I2=98.2%; p<0.001). Results of the subgroup analysis indicated that the pooled prevalence of VDD among patients with T2DM was highest (70.9%) in African nations and lowest (57.1%) in Middle East countries. Being female (pooled OR (POR) 1.60, 95% CI 1.29 to 1.97), having poor glycaemic control (POR 2.50; 95% CI 1.74 to 3.59), hypertension (POR 1.21; 95% CI 1.08 to 1.36), obesity (body mass index ≥25) (POR 1.68; 95% CI 1.16 to 2.44), dyslipidaemia (POR 2.54, 95% CI 1.37 to 4.73), albuminuria (POR 2.22, 95% CI 1.71 to 2.95), nephropathy (POR 1.58; 95% CI 1.08 to 2.31) and retinopathy (POR 1.48: 95% CI 1.17 to 1.89) were predictors of VDD among patients with T2DM.

CONCLUSIONS

More than half of patients with T2DM were suffering from VDD. Being female, having poor glycaemic control, hypertension, obesity, dyslipidaemia, albuminuria, nephropathy and retinopathy were the predictors of VDD among patients with T2DM.

[Applying Serum Vitamin D Metabolites in the Assessment of Renal Impairment in Diabetic Kidney Disease of Type 2 Diabetes Mellitus Patients: A Retrospective Study]

OBJECTIVE

Total 25(OH)D (t-25[OH]D), a marker traditionally used in the assessment of vitamin D (VitD) in the human body, includes 25(OH)D 2, 25(OH)D 3, and C 3-epimers-25(OH)D 3(C 3-epi). In this study, we analyzed the relationship between serum VitD metabolites and renal impairment in patients with diabetic kidney disease (DKD).

METHODS

We covered, in the study, 339 subjects, including 114 otherwise healthy controls (HC), 74 type 2 diabetes mellitus (DM) patients with no glomerular filtration dysfunction, and 151 DKD patients. According to the results of combined evaluation of estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (UACR), the DKD patients were further divided into four subgroups, stage 2 subgroup of patients of DM combined with stage-2 chronic kidney disease (CKD2), stage 3 subgroup of patients of DM combined with CKD3, stage 4 subgroup of patients of DM combined with CKD4, and stage 5 subgroup of patients of DM combined with CKD5. The levels of 25(OH)D 2, 25(OH)D 3, and C 3-epi were measured by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the activity level of 25(OH) 3 (AVitD 3), t-25(OH)D concentration, 25(OH)D 2/25(OH)D 3 ratio, C 3-epi/t-25(OH)D ratio, and C 3-epi/AVitD 3 ratio were calculated.

RESULTS

The levels of 25(OH)D 3, t-25(OH)D, and AVitD 3 were lower in the DKD group than those in the DM and HC groups (all P<0.05). C 3-epi/t-25(OH)D ratio and C 3-epi/AVitD 3 ratio were higher in the DKD group than those in the HC group (all P<0.05). The levels of 25(OH)D 3, t-25(OH)D, AVitD 3, and C 3-epi were lower in the stage 5 subgroup than those in the stage 2 and stage 3 subgroups (all P<0.05). The levels of 25(OH)D 3, t-25(OH)D, and C 3-epi were lower in the stage 4 subgroup than those in the stage 3 subgroup (all P<0.05). The 25(OH)D 3, t-25(OH)D, and AVitD 3 levels were lower in the stage 4 subgroup than those in the stage 2 subgroup (all P<0.05).

CONCLUSIONS

UPLC-MS/MS can be used to perform accurate evaluation of VitD nutritional status in DKD patients. DKD patients have decreased levels of serum t-25(OH)D, 25(OH)D 3, and AVitD 3, all of which progressively decrease along with the rise in CKD staging. The trend of C 3-epi and 25(OH)D 3 changes were not consistent.

Vitamin D supplementation alleviates insulin resistance in prediabetic rats by modifying IRS-1 and PPARγ/NF-κB expressions

Background

Prediabetes is a condition of intermediate hyperglycemia that may progress to type 2 diabetes. Vitamin D deficiency has been frequently linked to insulin resistance and diabetes. The study aimed to investigate the role of D supplementation and its possible mechanism of action on insulin resistance in prediabetic rats.

Method

The study was conducted on 24 male Wistar rats that were randomly divided into 6 rats as healthy controls and 18 prediabetic rats. Prediabetic rats were induced with a high-fat and high-glucose diet (HFD-G) combined with a low dose of streptozotocin. Rats with the prediabetic condition were then randomized into three groups of 12-week treatment: one group that received no treatment, one that received vitamin D3 at 100 IU/kg BW, and one group that received vitamin D3 at 1000 IU/kg BW. The high-fat and high-glucose diets were continuously given throughout the twelve weeks of treatment. At the end of the supplementation period, glucose control parameters, inflammatory markers, and the expressions of IRS1, PPARγ, NF-κB, and IRS1 were measured.

Results

Vitamin D3 dose-dependently improves glucose control parameters, as shown by the reduction of fasting blood glucose (FBG), oral glucose tolerance test (OGTT), glycated albumin, insulin levels, and markers of insulin resistance (HOMA-IR). Upon histological analysis, vitamin D supplementation resulted in a reduction of the islet of Langerhans degeneration. Vitamin D also enhanced the ratio of IL-6/IL-10, reduced IRS1 phosphorylation at Ser307, increased expression of PPAR gamma, and reduced phosphorylation of NF-KB p65 at Ser536.

Conclusion

Vitamin D supplementation reduces insulin resistance in prediabetic rats. The reduction might be due to the effects of vitamin D on IRS, PPARγ, and NF-κB expression.

The Impact of Vitamin D Deficiency and Insufficiency on the Outcome of Type 2 Diabetes Mellitus Patients: A Systematic Review

Vitamin D deficiency and insufficiency are public health concerns that have contributed to multiple negative health outcomes. Recent studies have revealed that vitamin D deficiency and insufficiency influence glycaemic control and the development of diabetes complications. The goal of this systematic review is to summarise the latest evidence on the impact of vitamin D deficiency and insufficiency on the outcome of Type 2 Diabetes Mellitus (T2DM) patients. In this PRISMA-guided systematic review, articles were sourced from three databases, namely, PubMed, Scopus, and Web of Science. The review only included literature published from 2012 until 2022, and 33 eligible studies met the inclusion criteria for this review. The included articles were critically appraised using the Mixed Method Appraisal Tool (MMAT). According to our findings, vitamin D deficiency or insufficiency is associated with mental health status, macrovascular and microvascular complications of T2DM, metabolic syndrome, increased risk of obesity, increased blood pressure, dyslipidaemia, glycaemic control, nerve-related disease, musculoskeletal-related complications, and reduced quality of life. Due to the diverse implications of vitamin D deficiency and insufficiency, screening for vitamin D levels in T2DM patients may be beneficial.

Dose-response relationship between dietary inflammatory index and diabetic kidney disease in US adults

OBJECTIVE

The impact of the dietary potential inflammatory effect on diabetic kidney disease (DKD) has not been adequately investigated. The present study aimed to explore the association between dietary inflammatory index (DII) and DKD in US adults.

DESIGN

This is a cross-sectional study.

SETTING

Data from the National Health and Nutrition Examination Survey (2007-2016) were used. DII was calculated from 24-h dietary recall interviews. DKD was defined as diabetes with albuminuria, impaired glomerular filtration rate or both. Logistic regression and restricted cubic spline models were adopted to evaluate the associations.

PARTICIPANTS

Data from the National Health and Nutrition Examination Survey (2007-2016) were used, which can provide the information of participants.

RESULTS

Four thousand two-hundred and sixty-four participants were included in this study. The adjusted OR of DKD was 1·04 (95 % CI 0·81, 1·36) for quartile 2, 1·24 (95 % CI 0·97, 1·59) for quartile 3 and 1·64 (95 % CI 1·24, 2·17) for quartile 4, respectively, compared with the quartile 1 of DII. A linear dose-response pattern was observed between DII and DKD (Pnonlinearity = 0·73). In the stratified analyses, the OR for quartile 4 of DII were significant among adults with higher educational level (OR 1·83, 95 % CI 1·26, 2·66) and overweight or obese participants (OR 1·67, 95 % CI 1·23, 2·28), but not among the corresponding another subgroup. The interaction effects between DII and stratified factors on DKD were not statistically significant (all P values for interactions were >0·05).

CONCLUSIONS

Our findings suggest that a pro-inflammatory diet, shown by a higher DII score, is associated with increased odd of DKD.

Assessment of the relationship between 25-hydroxyvitamin D and albuminuria in type 2 diabetes mellitus

BACKGROUND

Diabetic nephropathy occurs in about one-third of diabetic patients. This health problem is characterized by increased urinary albumin excretion, leading to decreased glomerular filtration rate and renal failure. In this regard, previous investigations have revealed the possibility of a relationship between vitamin D deficiency and diabetic nephropathy. The present study assessed the relationship between vitamin D deficiency and albuminuria in patients with type 2 diabetes.

METHODS

This study was conducted with 200 participants with type 2 diabetes mellitus from December 2019 to January 2021. The patients' 25-hydroxyvitamin D (25OHD) serum level and urinary albumin-to-creatinine ratio (UACR) were measured concurrently. Afterward, the subjects were divided into three groups based on their albuminuria level. Finally, 25OHD serum level and other clinical characteristics were compared among these albuminuria groups, and the relation between albuminuria level and 25OHD was analyzed.

RESULTS

The prevalence of vitamin D deficiency in macroalbuminuric patients (UACR≥300 mg/g) was 61.8%, and in microalbuminuric (30 ≤ UACR< 300 mg/g) and normoalbuminuric groups (UACR< 30 mg/g) was 33.3% and 24%, respectively. Further analysis revealed a significant negative relationship between 25OHD and albuminuria(r = - 0.257, p-value< 0.001). According to ROC curve analysis, a 25OHD level ≤ 21 ng/ml was considered an optimal cut-off point value for having macroalbuminuria in diabetic patients.

CONCLUSIONS

The current study evaluates the relation between vitamin D deficiency and the prevalence of albuminuria in the setting of diabetes. Overall, the prevalence of macroalbuminuria increased when the 25OHD serum level was less than 20 ng/ml.

Correlation between Serum 25-Hydroxyvitamin D Level and Peripheral Arterial Stiffness in Chronic Kidney Disease Stage 3-5 Patients

Vitamin D deficiency and high brachial-ankle pulse wave velocity (baPWV) are each independently associated with higher incidence of mortality and cardiovascular (CV) disease or CV events, respectively. This study aimed to evaluate the relationship between serum 25-hydroxyvitamin D levels and baPWV in non-dialysis patients with stage 3−5 chronic kidney disease (CKD). We enrolled 180 CKD patients. A commercial enzyme-linked immunosorbent assay was used to measure 25-hydroxyvitamin D levels. BaPWV values were measured using an automatic pulse wave analyzer. Either left or right baPWV > 18.0 m/s was considered indicative of peripheral arterial stiffness (PAS). In this study, 73 (40.6%) patients were found to have PAS. Compared to those without PAS (control group), patients with PAS were older and had higher incidence of diabetes mellitus, higher systolic and diastolic blood pressure, higher levels of intact parathyroid hormone, and C-reactive protein, and lower levels of 25-hydroxyvitamin D. Multivariate logistic regression analysis found 25-hydroxyvitamin D levels (odds ratio [OR]: 0.895, 95% confidence interval [CI] 0.828−0.968, p = 0.005) and old age (OR: 1.140, 95% CI 1.088−1.194, p < 0.001) to be independently associated with PAS in patients with stage 3−5 CKD. Lower serum 25-hydroxyvitamin D levels and older age were associated with PAS in these patients.

Association between Vitamin D Status and Mortality among Adults with Diabetic Kidney Disease

OBJECTIVE

Emerging evidence demonstrates that vitamin D status contributes to the incidence of diabetic kidney disease (DKD). However, the causal relationships between vitamin D and mortality among individuals with DKD are inconclusive. Our study is aimed at exploring the relationship between serum 25-hydroxyvitamin D (25(OH)D) concentrations and mortality among adults with DKD. Research Design and Methods. Our study included 1,202 adult participants with DKD from the National Health and Nutrition Examination Survey (NHANES) 2001-2014. Cox and competing-risks regression were used to estimate hazard ratios (HRs) and 95% CIs for associations between 25(OH)D concentrations and survival.

RESULTS

The overall mean serum 25(OH)D concentration was 55.9 ± 26.3. Vitamin D deficiency (25(OH)D < 50 nmol/l), insufficiency group (50 ≤ 25(OH)D < 75 nmol/l), and sufficiency group (25(OH)D ≥ 75 nmol/l) were observed in 552 (45.9%), 409 (34.0%), and 241 (20.0%) participants, respectively. Higher levels of vitamin D were significantly associated with improved all-cause and nonaccident- and malignant neoplasm-cause mortality among individuals with DKD after adjusting for the potential confounding factors.

CONCLUSIONS

We observed widespread vitamin D deficiency or insufficiency in DKD patients. Higher 25(OH)D values were significantly correlated with lower risk of mortality after adjusting for confounding variables.

Metformin attenuates high glucose-induced injury in islet microvascular endothelial cells

As one of the most frequently prescribed antidiabetic drugs, metformin can lower glucose levels, improve insulin resistance manage body weight. However, the effect of metformin on islet microcirculation remains unclear. In the present study, to explore the effect of metformin on islet endothelial cells and investigated the underlying mechanism, we assessed the effects of metformin on islet endothelial cell survival, proliferation, oxidative stress and apoptosis. Our results suggest that metformin stimulates the proliferation of pancreatic islet endothelial cells and inhibits the apoptosis and oxidative stress caused by high glucose levels. By activating farnesoid X receptor (FXR), metformin increases the expression of vascular endothelial growth factor-A (VEGF-A) and endothelial nitric oxide synthase (eNOS), improves the production of nitric oxide (NO) and decreases the production of ROS. After the inhibition of FXR or VEGF-A, all of the effects disappeared. Thus, metformin appears to regulate islet microvascular endothelial cell (IMEC) proliferation, apoptosis and oxidative stress by activating the FXR/VEGF-A/eNOS pathway. These findings provide a new mechanism underlying the islet-protective effect of metformin.

Associations of serum amyloid A and 25-hydroxyvitamin D with diabetic nephropathy: A cross-sectional study

BACKGROUND

The present study investigated the relationships between serum amyloid A (SAA), 25-hydroxyvitamin D (25(OH)VD) and diabetic nephropathy (DN) to provide evidence for the prevention and management of DN.

METHODS

A total of 182 patients with type 2 diabetes mellitus (T2DM) were enrolled in this study. The levels of SAA, 25(OH)VD, and other conventional indicators were measured and analyzed. Receiver operating characteristic curve analysis was applied for the combined measurement of SAA and 25(OH)VD, and risk factors for DN were evaluated using binary logistic regression analysis.

RESULTS

The levels of SAA in T2DM patients were significantly higher than those in healthy subjects, and the level significantly increased with the progression of DN (p < 0.05). In contrast, the level of 25(OH)VD in T2DM patients was significantly lower than that in healthy subjects, and the level significantly decreased with the progression of DN (p < 0.05). The combined measurement of SAA and 25(OH)VD distinguished DN patients from T2DM patients better than the measurement of SAA or 25(OH)VD alone. SAA was an independent risk factor for DN, and 25(OH)VD was an independent protective factor for DN.

CONCLUSION

SAA and 25(OH)VD might be used as potential markers to identify patients at increased risk of developing DN.

The Role of Vitamin D in Diabetic Nephropathy: A Translational Approach

According to several animal and human studies, vitamin D appears to play a significant role in the development of diabetic nephropathy. However, the possible renoprotective effect of vitamin D and its influence on the reversal of already existing renal damage remains doubtful. At this moment, there are a few hypotheses concerning the underlying molecular and genetic mechanisms including the link between vitamin D and inflammation, oxidative stress, and extracellular matrix accumulation. The present review aims to investigate the potential role of vitamin D in the development of diabetic kidney disease from a translational approach.

Association of Serum 25 (OH) Vitamin D With Chronic Kidney Disease Progression in Type 2 Diabetes

OBJECTIVES

Growing evidence demonstrated that vitamin D levels had been linked to type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD) in light of various extraskeletal effects. Therefore, the present study aimed to evaluate the association of 25-hydroxyvitamin D [25(OH)D] level with the clinicopathological features and CKD progression in T2DM.

METHODS

A total of 182 patients with T2DM with CKD stages 1 through 4 (G1-G4) were retrospectively included. Identification of the serum 25(OH)D level associated with CKD progression was executed by Kaplan-Meier survival analysis and Cox proportional hazards models. We further performed sensitivity analyses with a time-weighted average (TWA) of the serum 25(OH)D level in 75 participants to reinforce the findings.

RESULTS

The median serum 25(OH)D level was 26 (IQR, 14; 39) nmol/L in the study participants. Median follow-up time was 42 months, during which 70 (38%) patients confronted CKD progression. Cumulative kidney outcomes were significantly higher in the lowest tertile of the serum 25(OH)D level in Kaplan-Meier analyses (P < 0.001). Consistently, the analyses of Cox proportional hazards regression models indicated a significantly greater risk for CKD progression in the lowest tertile of the serum 25(OH)D level compared with the highest tertile of the serum 25(OH)D level (P = 0.03). These relationships remained robust with further sensitivity analysis of data with TWA of the serum 25(OH)D level, showing an independent association between lower TWA of the serum 25(OH)D level and an unfavorable renal outcome in patients with T2DM with CKD.

CONCLUSIONS

Our findings demonstrated that patients with T2DM with a decreased 25(OH)D level had deteriorated renal function. Both lower levels of baseline and TWA of serum 25(OH)D were associated with an increased risk of CKD progression in patients with T2DM, which suggested that the long-term maintenance of optimal vitamin D levels from early in life might be associated with reduced future risk of CKD development in T2DM.

Vitamin D Analogs Can Retard the Onset or Progression of Diabetic Kidney Disease: A Systematic Review

INTRODUCTION

Previous studies have shown that vitamin D analogs (such as paricalcitol) can reduce albuminuria in patients with diabetes mellitus and retard the progression of diabetic kidney disease (DKD). A recent systematic review reported significant improvement of renal function in patients with DKD who received vitamin D or its analogs. Study-driven data about their use in improving DKD outcomes have continued to accumulate over the years.

AIM

This paper aims to systematically review the contemporary evidence about the effectiveness of vitamin D analogs in retarding the onset or progression of DKD.

METHODS

With appropriate descriptors, two electronic databases (PubMed and Google Scholar) were searched for articles published between 2015 and 2021 in the English language. Primary studies that fulfilled the inclusion criteria were selected; their titles and abstracts were screened, and duplicates were removed. Relevant data were retrieved from the final selected studies using a preconceived data-extraction form.

RESULTS

A total of eight studies (three randomized-controlled trials, one prospective study, and four cross-sectional studies) were reviewed. A total of 6,243 participants were investigated in the eight studies and comprised young adults, middle-aged adults, and the elderly with a male-gender predominance. One randomized controlled trial reported that paricalcitol significantly improved renal function in type 1 diabetes patients with renal impairment when combined with renin-angiotensin-aldosterone system (RAAS) blockers. A strong correlation between vitamin D deficiency and DKD risk was noted in the majority of the cross-sectional studies. High doses of cholecalciferol (4,000 or 10,000 IU/day), given early in DKD, significantly reduced disease prevalence.

CONCLUSION

Paricalcitol may retard the onset or progression of DKD, especially if administered in combination with RAAS blockers. The association of vitamin D deficiency with DKD risk also supports this therapeutic effect. Future systematic reviews are still needed to strengthen the current evidence on therapeutic benefit of vitamin D or its analogs in DKD.

NADH/NAD+ Redox Imbalance and Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a common and severe complication of diabetes mellitus. If left untreated, DKD can advance to end stage renal disease that requires either dialysis or kidney replacement. While numerous mechanisms underlie the pathogenesis of DKD, oxidative stress driven by NADH/NAD⁺ redox imbalance and mitochondrial dysfunction have been thought to be the major pathophysiological mechanism of DKD. In this review, the pathways that increase NADH generation and those that decrease NAD⁺ levels are overviewed. This is followed by discussion of the consequences of NADH/NAD⁺ redox imbalance including disruption of mitochondrial homeostasis and function. Approaches that can be applied to counteract DKD are then discussed, which include mitochondria-targeted antioxidants and mimetics of superoxide dismutase, caloric restriction, plant/herbal extracts or their isolated compounds. Finally, the review ends by pointing out that future studies are needed to dissect the role of each pathway involved in NADH-NAD⁺ metabolism so that novel strategies to restore NADH/NAD⁺ redox balance in the diabetic kidney could be designed to combat DKD.

Association Between 25(OH)Vitamin D, HbA1c and Albuminuria in Diabetes Mellitus: Data From a Population-Based Study (VIDAMAZON)

BACKGROUND

The effect of glycemic control on diabetic kidney disease (DKD) is well known. Recent evidence has suggested that Vitamin D (VD) may have a nephroprotective effect in diabetes, but the relationship between VD, glycemic control, and albuminuria has yet to be clarified.

OBJECTIVE

Evaluate the relationship between 25-hydroxy-vitamin D [25(OH)D], HbA1c, and albuminuria in Diabetes Mellitus (DM).

PATIENTS AND METHODS

Cross-sectional study with 1576 individuals with DM who had 25(OH)D, HbA1c, and albuminuria levels measured. Patients with abnormal creatinine levels were excluded, in order to avoid interference on VD levels by impaired kidney function.

RESULTS

Patients with HbA1c ≥7% had lower 25(OH)D when compared to patients with HbA1c <7% (29.7 ± 10.2 vs 28.1 ± 9.9 ng/ml, p = 0.003) and 25(OH)D levels seems to predict 1.5% of HbA1c behavior. The 25(OH)D concentrations in patients with normoalbuminuria were higher than the levels observed in those with micro or macroalbuminuria (29.8 ± 9.0 vs 26.8 ± 8.6 and 25.1 ± 7.6, respectively, p = 0.001), patients who had 25(OH)D <20 ng/ml and 25(OH)D <30 ng/ml were at a higher risk of presenting albuminuria [OR = 2.8 (95% CI = 1.6 - 4.9), p<0.001, and OR = 2.1 (95% CI = 1.3 - 4.6), p<0.001, respectively]. In our regression model, albuminuria was influenced by HbA1c (r² = 0.076, p<0.00001) and 25(OH)D (r² = 0.018, p = 0.002) independently.

CONCLUSION

Our study found an association between vitamin D levels, HbA1c and DKD. Additionally, our data suggest that the association between urinary albumin excretion and vitamin D levels is independent of glycemic control in patients with diabetes. Even though our patients presented normal creatinine levels, it is necessary further prospective studies to confirm if this association precedes or not the loss of renal function.

A Nonlinear Relationship Between Serum 25-Hydroxyvitamin D and Urine Albumin to Creatinine Ratio in Type 2 Diabetes: A Cross-Sectional Study in China

BACKGROUND

Diabetic kidney disease often presents as increased urine albumin to creatinine ratio (UACR). 25-hydroxyvitamin D (25(OH)D) is considered as the best indicator of vitamin D status. Previous studies have shown that 25(OH)D is related to the UACR. However, evidence concerning the connection between 25(OH)D and UACR is still limited in the Chinese population.

MATERIALS AND METHODS

A total of 549 participants with type 2 diabetes were enrolled in the study from Shenzhen People's Hospital, China. The participants were grouped by the tertiles of 25(OH)D level. The association between 25(OH)D and UACR was examined by multiple linear regression. A generalized additive model (GAM) was used to verify a non-linear relationship. We conducted a subgroup analysis to evaluate the robustness of the results.

RESULTS

After adjusting for relevant variables, 25(OH)D was negatively correlated with UACR (β = -8.7, 95% CI (-12.0, -5.4)). A non-linear relationship was discovered between 25(OH)D and UACR, and the 25(OH)D threshold was 67. The effect sizes and confidence intervals on the left and right sides of the inflection point were -13.9 (-18.2, -9.6) and 8.9 (-1.1, 18.9), respectively. Subgroup analysis showed a stronger correlation could be detected in males. The same trend also could be found in patients older than 70 years old, those with using ACEI/ARB, with history of hypertension, with SBP ≥140 mmHg and eGFR <60 mL/min/1.73m².

CONCLUSION

The relationship between 25(OH)D and UACR is non-linear. 25(OH)D was negatively related to UACR when 25(OH)D is less than 67 nmol/L.

Association Between Vitamin D Status and Diabetic Complications in Patients With Type 2 Diabetes Mellitus: A Cross-Sectional Study in Hunan China

Background: Vitamin D status has been linked to diabetes-related complications due to multiple extraskeletal effects. We aimed to investigate the association between vitamin D deficiency (VDD) and diabetic vascular complications, including diabetic retinopathy (DR), diabetic kidney disease (DKD), and diabetic foot ulcers (DFU). Methods: A total of 4,284 Chinese patients with type 2 diabetic mellitus (T2DM) were enrolled into the cross-sectional study. VDD was defined as serum 25-hydroxyvitamin D <50 nmol/L. Demographic data, physical measurements, laboratory measurements, comorbidities, and related medications were collected and analyzed by VDD status. Poisson regression with robust variance estimation and binary logistic regression were performed to explore the relationship between VDD and diabetic complications. Results: The prevalence of VDD, DR, DKD, DFU accounted to 71.7% (95% confidence intervals [CI]: 70.3-73.0%), 28.5% (95% CI: 27.2-29.9%), 28.2% (95% CI: 26.8-29.5%), and 5.7% (95% CI: 5.1-6.5%), respectively. The prevalence ratios (95% CI) for DR and DKD by VDD status, adjusted for demographics, physical measurements, laboratory measurements, related complications, and comorbidities, and medications, were 1.093 (0.983-1.215) and 1.041 (0.937-1.156), respectively. The odds ratio (95% CI) for DFU by VDD status was 1.656 (1.159-2.367) in the final adjusted model. Meanwhile, the prevalence of VDD was significantly higher in patients with DFU compared with patients without DFU. Conclusions: The present study firstly indicated that VDD was significantly associated with a higher prevalence of DFU among Chinese T2DM patients. The association between VDD status and DR or DKD was not significant when adjusting for all potential covariates. Vitamin D screening or supplementation may be beneficial to prevent DFU and improve the prognosis of T2DM patients.