MANAGEMENT OF ENDOCRINE DISEASE: The effect of vitamin D supplementation on glycaemic control in patients with type 2 diabetes mellitus: a systematic review and meta-analysis

New Insights on Low Vitamin D Plasma Concentration as a Potential Cardiovascular Risk Factor

The role of Vitamin D hormone in human health and disease is still debated. Recently, growing attention has been paid to its putative role in cardiovascular system homeostasis with several studies that suggested a correlation between low vitamin D levels and increased cardiovascular risk. Several mechanisms are involved in the development of cardiovascular diseases: systemic inflammation, endothelial dysfunction, arterial hypertension and insulin resistance. In the present paper, we have revised the current literature supporting a role for vitamin D in the development of these pathogenetic processes. Finally, we have evaluated the current evidence linking vitamin D to atherosclerosis and its natural consequence, cardiovascular diseases.

Vitamin D insufficiency: Definition, diagnosis and management

Severe vitamin D deficiency can be defined as the dose of vitamin D or serum 25OHD concentrations needed to prevent nutritional rickets or osteomalacia. There is large international consensus that these diseases can be prevented by 400 IU of vitamin D/d and 25OHD above 30 nmol/l (12 ng/ml). Vitamin D deficiency can also accelerate the risk of fractures and probably also of falls in elderly subjects but there is no consensus on the required daily doses or minimal 25OHD threshold for these endpoints. The majority of experts consider 800 IU/d and serum 25OHD above 50 nmol/l (20 ng/ml) as sufficient, with a minority opinion aiming for 75 nmol/l or even higher. For other extra-skeletal endpoints, no hard evidence is available to define whether or not this is causally related to vitamin D status. Therefore, for these endpoints no minimal dosage or 25OHD threshold can be defined.

The Effect of Vitamin D Supplementation on Glycemic Control in Type 2 Diabetes Patients: A Systematic Review and Meta-Analysis

Observational studies have indicated an inverse association between vitamin D levels and the risk of diabetes, yet evidence from population interventions remains inconsistent. PubMed, EMBASE, Cochrane Library and ClinicalTrials.gov were searched up to September 2017. Data from studies regarding serum 25(OH)D, fasting blood glucose (FBG), hemoglobin A1c (HbA1c), fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) were pooled. Twenty studies (n = 2703) were included in the meta-analysis. Vitamin D supplementation resulted in a significant improvement in serum 25(OH)D levels (weighted mean difference (WMD) = 33.98; 95%CI: 24.60-43.37) and HOMA-IR (standardized mean difference (SMD) = -0.57; 95%CI: -1.09~-0.04), but not in other outcomes. However, preferred changes were observed in subgroups as follows: short-term (WMD_FBG = -8.44; 95%CI: -12.72~-4.15), high dose (WMD_FBG = -8.70; 95%CI: -12.96~-4.44), non-obese (SMD_{Fasting insulin} = -1.80; 95%CI: -2.66~-0.95), Middle Easterners (WMD_FBG = -10.43; 95%CI: -14.80~-6.06), baseline vitamin D deficient individuals (WMD_FBG = -5.77; 95%CI: -10.48~-1.05) and well-controlled HbA1c individuals (WMD_FBG = -4.09; 95%CI: -15.44~7.27). Vitamin D supplementation was shown to increase serum 25(OH)D and reduce insulin resistance effectively. This effect was especially prominent when vitamin D was given in large doses and for a short period of time, and to patients who were non-obese, Middle Eastern, vitamin D deficient, or with optimal glycemic control at baseline.

Antioxidant effects of vitamins in type 2 diabetes: a meta-analysis of randomized controlled trials

BACKGROUND

Vitamins are essential micronutrients with antioxidant potential that may provide a complementary treatment for patients with chronic diseases. Our aim was to assess the effect of vitamin supplementation on the antioxidant status and glycemic index of type 2 diabetes mellitus patients.

METHODS

We performed a systematic review with meta-analyses. Electronic searches were conducted in PubMed, Scopus, and Web of Science (December 2017). Randomized controlled trials evaluating the effect of any vitamin or vitamin complex supplementation on antioxidant status as primary outcome were included. The outcomes considered were: reduction of malondialdehyde (MDA); augmentation of glutathione peroxidase (GPx); changes in total antioxidant capacity (TAC), enhance in superoxide dismutase enzyme-SOD, and thiobarbituric acid reactive substances (TBARS). Outcomes of glycemic control were also evaluated. Pairwise meta-analyses were performed using software Review Manager 5.3.

RESULTS

Thirty trials fulfilled the inclusion criteria, but only 12 could be included in the meta-analyses of antioxidant outcomes. The most commonly studied vitamins were B, C, D and E. Vitamin E was related to significant reduction of blood glucose as well as glycated hemoglobin compared to placebo, while both vitamins C and E were mainly associated with reducing MDA and TBARS and elevating GPx, SOD and TAC, compared to placebo. However, outcome reports in this field are still inconsistent (e.g. because of a lack of standard measures).

CONCLUSIONS

Supplementation of vitamin E may be a valuable strategy for controlling diabetes complications and enhancing antioxidant capacity. The effects of other micronutrients should be further investigated in larger and well-designed trials to properly place these complementary therapies in clinical practice.

The combined effect of vitamin D and parathyroid hormone concentrations on glucose homeostasis in older patients with prediabetes: A cross-sectional study

BACKGROUND

The combined effect of vitamin D and parathyroid hormone on glucose homeostasis has not been adequately investigated. The aim of this study was to examine the role of parathyroid hormone/vitamin D axis on glucose homeostasis in elderly persons with prediabetes.

METHODS

Patients with prediabetes ( n = 144) and healthy age-matched controls ( n = 81) were included in this cross-sectional study. Study parameters included anthropometric characteristics, morning fasting glucose (fasting plasma glucose), insulin (fasting plasma insulin), parathyroid hormone, 25-hydroxyvitamin D, homeostasis model assessment of insulin resistance and homeostasis model assessment of β-cell function. Both groups were stratified into subgroups according to vitamin D status and tertiles of parathyroid hormone.

RESULTS

Both groups were comparable in terms of body mass index, 25-hydroxyvitamin D and parathyroid hormone status. In the prediabetes group, fasting plasma glucose differed significantly across parathyroid hormone tertiles, increasing from the first to the third tertile ( p = 0.011). There were higher fasting plasma glucose values in participants with vitamin D deficiency/parathyroid hormone third tertile compared to all other groups ( p = 0.031, 0.027 and 0.039, respectively).

CONCLUSION

Parathyroid hormone status is associated with impaired glucose homeostasis; hypovitaminosis D combined with high parathyroid hormone concentrations are associated with glycaemic dysregulation in elderly patients with prediabetes.

Association between serum 25-hydroxyvitamin D and glycated hemoglobin levels in type 2 diabetes patients with chronic kidney disease

AIMS/INTRODUCTION

Vitamin D is suggested to influence glucose homeostasis. An inverse relationship between serum 25-hydroxyvitamin D (25[OH]D) and glycemic control in non-chronic kidney disease (CKD) patients with type 2 diabetes was reported. We aimed to examine this association among type 2 diabetes patients with CKD.

MATERIALS AND METHODS

A total of 100 type 2 diabetes participants with stage 3-4 CKD were recruited. Blood for glycated hemoglobin (HbA1c ), serum 25(OH)D, renal and lipid profiles were drawn at enrollment. Correlation and regression analyses were carried out to assess the relationship of serum 25(OH)D, HbA1c and other metabolic traits.

RESULTS

A total of 30, 42, and 28% of participants were in CKD stage 3a, 3b and 4, respectively. The proportions of participants based on ethnicity were 51% Malay, 24% Chinese and 25% Indian. The mean (±SD) age and body mass index were 60.5 ± 9.0 years and 28.3 ± 5.9 kg/m2 , whereas mean HbA1c and serum 25(OH)D were 7.9 ± 1.6% and 37.1 ± 22.2 nmol/L. HbA1c was negatively correlated with serum 25(OH)D (rs = -0.314, P = 0.002), but positively correlated with body mass index (rs = 0.272, P = 0.006) and serum low-density lipoprotein cholesterol (P = 0.006). There was a significant negative correlation between serum 25(OH)D and total daily dose of insulin prescribed (rs = -0.257, P = 0.042). Regression analyses showed that every 10-nmol/L decline in serum 25(OH)D was associated with a 0.2% increase in HbA1c .

CONCLUSIONS

Lower serum 25(OH)D was associated with poorer glycemic control and higher insulin use among multi-ethnic Asians with type 2 diabetes and stage 3-4 CKD.

Vitamin D Supplementation in Patients With Type 2 Diabetes: The Vitamin D for Established Type 2 Diabetes (DDM2) Study

Context

Observational data support a role for vitamin D in type 2 diabetes, but evidence from trials is inconclusive.

Objective

To evaluate the effect of vitamin D supplementation on β-cell function and hemoglobin A1c (HbA1c) in patients with well-controlled type 2 diabetes.

Design

Double-blind, randomized, placebo-controlled clinical trial.

Setting

Tufts Medical Center, Boston, MA; VA Medical Center, Cincinnati, OH.

Participants

A total of 127 patients (mean age, 60 years) with stable (HbA1c ≤7.5%) diabetes managed with lifestyle only or lifestyle plus metformin.

Intervention

Subjects were given 4000 units of vitamin D₃ (cholecalciferol) daily or placebo for 48 weeks.

Main Outcome Measure

Insulin secretion rate (ISR) was estimated from peripheral plasma C-peptide levels after a 3-hour 75-g oral glucose tolerance test done at baseline and week 24. Changes in HbA1c were assessed at 16, 24, 36, and 48 weeks.

Results

Baseline mean plasma 25-hydroxyvitamin D [25(OH)D] concentration was 26.6 ng/mL, mean HbA1c was 6.6%, and 78% of patients were on metformin. At week 24, mean 25(OH)D changed by 20.5 and −1.6 ng/mL in the vitamin D and placebo groups, respectively (P < 0.001). The vitamin D and placebo groups did not differ in change in ISR or HbA1c. Among patients treated with lifestyle only (n = 28), vitamin D supplementation reduced HbA1c compared with placebo (−0.1% vs 0.3%, respectively; P = 0.034) at week 24. This result was not observed at the other time points and could be due to chance.

Conclusion

Vitamin D₃ at 4000 IU/d did not change ISR or HbA1c in patients with well-controlled type 2 diabetes on metformin not selected for vitamin D deficiency.

Effect of Treating Vitamin D Deficiency in Uncontrolled Type 2 Diabetes: A Randomized, Placebo-Controlled Study

BACKGROUND

Literature increasingly supports the inverse relationship of vitamin D (VitD) level and type 2 diabetes (T2DM). Proposed protective mechanisms of VitD include its anti-inflammatory effects, increased insulin secretion via pancreatic β-cell stimulation, and downregulation of parathyroid hormone levels. Interventional studies show mixed results of VitD therapy in prediabetic patients with VitD deficiency or diabetic patients with normal VitD levels.

STUDY QUESTION

Does high-dose VitD replacement improve glycemic control and microalbuminuria (MAU) in uncontrolled T2DM and concurrent VitD deficiency?

STUDY DESIGN

This placebo-controlled, double-blinded study randomized 30 subjects aged 30-65 years with an elevated HbA1c level of 7.5%-10% and a low total 25-hydroxyvitamin-D value of <20 ng/mL to either placebo (n = 16) or ergocalciferol 50,000 IU (n = 14) once weekly for 8 weeks then once monthly for 4 months.

MEASURES AND OUTCOMES

Primary outcome was difference in HbA1c from baseline to month 6 between the VitD-intervention group and the placebo-controlled group. Secondary end points were differences in total 25-hydroxyvitamin-D and MAU. Paired t tests and linear mixed-effects models were used for statistical analysis.

RESULTS

No significant differences were seen in HbA1c or MAU between baseline versus postintervention visits within the placebo group (HbA1c: 8.4% ± 0.2 vs. 8.1% ± 0.3, P = 0.088; MAU: 94.1 mg/g ± 43.9 vs. 45.9 mg/g ± 20.2, P = 0.152) and the intervention group (HbA1c: 8.8% ± 0.3 vs. 8.7% ± 0.4, P = 0.692; MAU: 167.8 mg/g ± 70.1 vs. 108.5 mg/g ± 39.9, P = 0.356). The difference between placebo-slope and intervention-slope was nonsignificant for MAU (β = -0.1 mg/g ± 0.4, P = 0.835) but was significant for total 25-hydroxyvitamin-D (β = 11.7 ng/mL ± 2.5, P ≤ 0.001). Greater HbA1c reduction occurred unexpectedly in the placebo group ((Equation is included in full-text article.)= -0.4% ± 0.2) than in the intervention group ((Equation is included in full-text article.)= -0.2% ± 0.4), although the difference in slopes was not significant (β = 0.2% ± 0.4, P = 0.640).

CONCLUSIONS

Our proof-of-concept study found no benefit of high-dose VitD therapy in glycemic control and MAU in uncontrolled T2DM and VitD deficiency. Post hoc analyses raise concerns for high-dose VitD therapy to delay glycemic improvement. Large-scale interventional trials are much needed in this patient population to substantiate our findings and elucidate VitD's mechanisms on glucose metabolism.

Type 2 diabetes mellitus and bone

Type 2 diabetes (T2DM) is a rapidly growing public health problem. It is associated with an increased risk of fracture, particularly of the hip, despite normal or high bone mineral density. Longer duration of disease and poor glycaemic control are both associated with higher fracture risk. The factors underlying increased fracture risk have not been clearly established, but increased falls risk, obesity, sarcopenia and co-morbidities are likely to contribute. The basis for reduced bone strength despite higher bone mineral density remains to be fully elucidated. Bone turnover is reduced in individuals with T2DM, with evidence of impaired bone formation. Most studies indicate normal or superior trabecular bone structure although reduced lumbar spine trabecular bone score (TBS) has been reported. Deficits in cortical bone structure have been demonstrated in some, but not all, studies whilst reduced bone material strength index (BMSi), as assessed by microindentation, has been a consistent finding. Accumulation of advanced glycation end products in bone may also contribute to reduced bone strength. The use of FRAX in individuals with T2DM underestimates fracture probability. Clinical management should focus on falls prevention strategies, avoidance of known risk factors, maintenance of good glycaemic control and bone protective intervention in individuals at high risk of fracture. Dietary and surgical strategies to reduce weight have beneficial effects on diabetes but may have adverse effects on skeletal health. Future research priorities include better definition of the mechanisms underlying increased fracture risk in T2DM and optimal strategies for identifying and treating those at high risk.

Vitamin D and Heart Failure

PURPOSE

Vitamin D is principally known for its role in calcium homeostasis, but preclinical studies implicate multiple pathways through which vitamin D may affect cardiovascular function and influence risk for heart failure. Many adults with cardiovascular disease have low vitamin D status, making it a potential therapeutic target. We review the rationale and potential role of vitamin D supplementation in the prevention and treatment of chronic heart failure.

RECENT FINDINGS

Substantial observational evidence has associated low vitamin D status with the risk of heart failure, ventricular remodeling, and clinical outcomes in heart failure, including mortality. However, trials assessing the influence of vitamin D supplementation on surrogate markers and clinical outcomes in heart failure have generally been small and inconclusive. There are insufficient data to recommend routine assessment or supplementation of vitamin D for the prevention or treatment of chronic heart failure. Prospective trials powered for clinical outcomes are warranted.

Vitamin D diminishes the high platelet aggregation of type 2 diabetes mellitus patients

Platelet activation is found in inflammatory conditions and implicated in the pathogenesis of chronic medical conditions, such as atherosclerosis, coronary vascular disease, cerebrovascular disease, and diabetes mellitus (DM). HbA1c is inversely related to vitamin D25 levels in individuals with and without DM. This study aimed to determine the relation between platelet aggregation, vitamin D and HbA1c among healthy individuals and those with Type 2 DM (T2DM). The direct effect of vitamin D1, 25 (calcitriol) on platelet aggregation was also investigated. The study included four groups: A. normoglycemic Control group: HbA1c<5.7%; B. Pre-diabetes (DM): 5.7% ≥ HbA1c ≤ 6.4%; C. DM on aspirin therapy: HbA1c>6.4%(+)Asp.; and D. DM not on aspirin therapy: HbA1c > 6.4%(-)Asp. Platelet aggregation was tested with and without calcitriol or saline pre-treatment, using collagen or adenosine diphosphate (ADP) as agonists. Platelet aggregation was higher in DM(-)Asp group compared to normoglycemic and DM(+)Asp, and higher, but not significant compared to pre-DM. The entire study population exhibited negative correlation between HbA1c and serum concentration of vitamin D25. Excluding DM(+)Asp, aggregation induced by collagen was significantly higher in patients with insufficient (<76 nmol/L) vitamin D25 compared to sufficient (≥76 nmol/L) vitamin D25. In this cohort, a negative correlation was found between serum concentrations of vitamin D25 and collagen-induced percent maximum (%max) aggregation and area under curve (AUC) aggregation. In the DM(-)Asp group, collagen-induced aggregation was reduced by approximately 25% after calcitriol treatment. Calcitriol decreased ADP-induced aggregation of control and DM(+)Asp groups to approximately 85% of saline treatment. We conclude that glycemic control is inversely associated with high platelet aggregation and low vitamin D25 levels. This elevated aggregation could be regulated by a novel, direct effect of calcitriol, indicating a beneficial effect of vitamin D on vascular complications related to diabetes. We offer a possible non-genomic mechanism for the vitamin D/Vitamin D receptor (VDR) pathway.

Effects of Vitamin D Supplementation on Glucose and Insulin Homeostasis and Incident Diabetes among Nondiabetic Adults: A Meta-Analysis of Randomized Controlled Trials

AIMS

Emerging evidence has suggested a mechanistic link from vitamin D metabolism to glucose and insulin homeostasis. This study is aimed at specifically quantifying the direct effects of vitamin D supplementation on indexes of glucose and insulin homeostasis as well as incidence of type 2 diabetes (T2D) among nondiabetic adults.

METHODS

We systematically searched randomized controlled trials (RCTs) of vitamin D supplementation in nondiabetic adults in PubMed, EMBASE, and CENTRAL. Random-effects meta-analysis was conducted to pool the estimates.

RESULTS

Our meta-analysis included 47 RCTs involving 44,161 nondiabetic individuals with a median trial duration of 4 months and a median dose of 4000 IU/d. Vitamin D supplementation significantly reduced fasting glucose by 0.11 mmol/L, fasting insulin by 1.47 mIU/L, and HOMA-IR by 0.32 while increasing total 25 (OH) D levels by 40.14 nmol/L. We found no significant effects of vitamin D supplementation on insulin secretion or beta cell function indexes. Based on the data from six trials involving 39,633 participants and 2533 incident T2D cases, vitamin D supplementation was not associated with the risk of incident diabetes compared to placebo (pooled relative risk: 1.01, 95% confidence interval: 0.93 to 1.08).

CONCLUSIONS

Our meta-analysis found that vitamin D supplementation might improve glucose and insulin metabolism without affecting the risk of T2D among nondiabetic adults.

Lower vitamin D levels are associated with higher blood glucose levels in Asian Indian women with pre-diabetes: a population-based cross-sectional study in North India

BACKGROUND

Asian Indian women are predisposed to develop obesity, metabolic syndrome and vitamin D deficiency. Relationship of vitamin D deficiency with blood glucose levels has not been explored in Asian Indian women with pre-diabetes.

OBJECTIVE

We evaluated the associations of serum 25-hydroxy vitamin D (25(OH)D) concentrations among adult women with the pre-diabetes residing in North India (Delhi).

METHODS

This cross-sectional population-based study involved 797 women with pre-diabetes aged 20-60 years. Blood pressure, body mass index (BMI), fasting blood glucose (FBG), extent of sun exposure and serum 25(OH)D levels were assessed. For purpose of analysis, serum 25(OH)D levels (nmol/L) were categorized in quintiles as follows: 0-21.5 (first quintile), 21.51-35.60 (second quintile), 35.61-46.50 (third quintile), 46.51-62.30 (fourth quintile) and >62.31 (fifth quintile).

RESULT

The prevalence (%) of vitamin D deficiency, insufficiency and sufficiency was 68.6, 25.9 and 5.5, respectively. Mean age (p=0.004), systolic (p=0.05) and diastolic (p=0.04) blood pressure, weight (p=0.03), BMI (p=0.04) and FBG (p=0.02) were significantly higher in subjects with vitamin D deficiency as compared with those with vitamin D insufficiency and sufficiency. Unadjusted mean values of FBG were significantly decreased in fourth (p=0.02) and fifth quintiles (p=0.030) of 25(OH)D levels as compared with second quintile. Furthermore, after adjusting for age and family income FBG levels were significantly increased in first quintile (compared with fourth (p=0.012) and fifth (p=0.018) quintiles) and second quintile (compared with fourth (p=0.003) and fifth (p=0.004) quintiles) of 25(OH)D levels, respectively.

CONCLUSION

Lower vitamin D levels are associated with higher blood glucose values in Asian Indian women with pre-diabetes. These findings need confirmation in case-control and prospective studies.

Vitamin supplements in type 2 diabetes mellitus management: A review

Type 2 diabetes mellitus (T2DM) is a major public health challenge that affects countries across the world. The use of pharmacological therapy is often limited in some patients due to a loss of effect over time or development of adverse effects such as weight gain or hypoglycaemia. This has prompted searches into the role of non-pharmacological therapies in T2DM. The availability and use of vitamin supplements in developed countries have increased significantly and there is evidence that certain vitamins may have roles in the management of T2DM. This review examines the literature assessing the use of vitamins A, C, E, D, K and the B group vitamins (B1, B3, B7, B6, B9, B12) in the management of T2DM. No clear evidence supporting the beneficial role of any specific vitamin in the treatment of T2DM was found. Thus, it is recommended that until further studies are conducted to clarify the role of such vitamins in T2DM management, they should not be routinely recommended in clinical practice.

The Relationship between Vitamin D and Type 2 Diabetes Is Intriguing: Glimpses from the Spect-China Study

OBJECTIVE

Vitamin D is a multifunctional vitamin for our body. Type 2 diabetes mellitus (T2DM) is a common metabolic disease. Whether T2DM affects the serum 25(OH)D level has not been reported. The objective of this study was to reveal the extent to which vitamin D is present in the population in East China and to explore the relationship between serum 25(OH)D and T2DM.

METHODS

The cohort was selected based on a large investigation named Survey on Prevalence in East China including 12,702 participants aged 21-92 years old. All the participants completed the questionnaire and went through a physical examination. Fasting blood samples were collected to test serum 25(OH)D and other metabolism-related indicators. AVONA was used to test the significance of differences among groups. Multinomial logistic regression was used to assess the association of T2DM with serum 25(OH)D level.

RESULTS

The overall percentage of vitamin D deficiency was 80.55% (male 74.1%, female 85.0%). Men with lower serum 25(OH)D level had high value in homeostasis model assessment of insulin resistance and HbA1c. The serum 25(OH)D level of those who were diagnosed with T2DM was higher than that in non-diabetics. The serum 25(OH)D level of pre-diabetes was the highest. T2DM patients trended to have higher serum 25(OH)D levels.

CONCLUSION

Vitamin D deficiency is common among the people in East-China. T2DM patients had higher levels of serum 25(OH)D. The relationship between vitamin D and T2DM is intriguing. It seemed that vitamin D was either irrelevant directly to T2DM or resisted in T2DM patients.

Vitamin D and type 2 diabetes

Vitamin D deficiency is associated with a decreased insulin release, insulin resistance and type 2 diabetes in experimental and epidemiological studies. Animal studies show that 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) stimulates the pancreatic β-cell to secrete insulin. The relationship between vitamin D deficiency and insulin resistance could develop through inflammation, as vitamin D deficiency is associated with increased inflammatory markers. In addition, genetic polymorphisms of vitamin D -related genes may predispose to impaired glycemic control and type 2 diabetes. Epidemiologic studies showed an association between low serum 25-hydroxyvitamin D₃ (25(OH)D₃) concentration and an increased risk for the metabolic syndrome and type 2 diabetes. This may be partly explained by an increased fat mass. A possible causal relationship between vitamin D deficiency and type 2 diabetes should be proven by randomized clinical trials showing that either type 2 diabetes can be prevented or insulin release and insulin sensitivity can be improved by vitamin D supplements. The results of randomized clinical trials on the effect of vitamin D versus placebo, sometimes combined with calcium, in patients with impaired glucose tolerance ("prediabetes") or type 2 diabetes are inconsistent. Some studies showed a slight decrease of fasting plasma glucose or improvement of insulin resistance, but often only in posthoc analyses. These effects are mainly visible in patients with vitamin D deficiency and impaired glucose tolerance at baseline. Meta-analyses of randomized clinical trials in general did not show significant effects of vitamin D supplementation on glycemic control. Currently, several large scale randomized clinical trials with vitamin D supplementation in doses of 1600-4000IU/d are ongoing with glycemic control or incidence of diabetes mellitus as outcome. Vitamin D deficiency needs to be prevented or cured, but until the results of these trials are published, high-dose vitamin D supplementation cannot be recommended for prevention or amelioration of type 2 diabetes.

Vitamin D supplementation and glycemic control in type 2 diabetes patients: A systematic review and meta-analysis

INTRODUCTION

Low vitamin D status has been found to be associated with impaired glycemic control in patients who suffer from type 2 diabetes; however, whether vitamin D supplementation is associated with improved glycemic status remains controversial. The aim of this study was to summarize evidence from randomized controlled trials (RCTs) to assess the efficacy of vitamin D supplementation in reducing glycosylated haemoglobinA1c (HbA1c) and fasting blood glucose (FBG) levels.

MATERIALS/METHODS

We searched PubMed, Web of Science and the Cochrane Library for reports published up to March 2017. We selected parallel RCTs investigating the effect of vitamin D or vitamin D analogues on HbA1c or FBG levels in type 2 diabetes patients. Cohen's d was calculated to represent the standardized mean difference (SMD) for each study, and the SMDs with 95%confidence intervals (CIs) were pooled using a random effects model.

RESULTS

Twenty-four studies were included that evaluated HbA1c levels and 18 studies were included that evaluated FBG levels. Meta-analyses showed that vitamin D supplementation was associated with reduced HbA1c levels (standardized mean difference (SMD) -0.25 [-0.45 to -0.05]) but had no influence on FBG levels (SMD -0.14 [-0.31 to 0.03]). However, the subgroup analyses suggested that vitamin D supplementation was associated with reduced HbA1c levels (SMD -0.39 [-0.67 to -0.10]) and FBG (SMD -0.27 [-0.46 to -0.07]) among patients with 25-hydroxyvitamin D (25(OH) D) deficiency at baseline. Significantly reduced HbA1c levels were also observed in association with vitamin D supplementation in the subgroup including type 2 diabetes patients with a body mass index (BMI) <30kg m^-2 (SMD -0.30 [-0.54 to -0.07]).

CONCLUSIONS

Vitamin D supplementation could be effective at improving glycemic control in vitamin D deficient or non-obese type 2 diabetes patients.

Effects of Vitamin D Supplementation on Insulin Sensitivity and Insulin Secretion in Subjects With Type 2 Diabetes and Vitamin D Deficiency: A Randomized Controlled Trial

OBJECTIVE

In observational studies, low vitamin D levels are associated with type 2 diabetes (T2D), impaired glucose metabolism, insulin sensitivity, and insulin secretion. We evaluated the efficacy of vitamin D supplementation on insulin sensitivity and insulin secretion in subjects with T2D and low vitamin D (25-hydroxyvitamin D [25(OH)D] <50 nmol/L).

RESEARCH DESIGN AND METHODS

Sixty-two men and women with T2D and vitamin D deficiency participated in a 6-month randomized, double-blind, placebo-controlled trial. Participants received a single dose of 400,000 IU oral vitamin D₃ or placebo, and the vitamin D group received an additional 200,000 IU D₃ if serum 25(OH)D was <100 nmol/L after 4 weeks. Primary end points were total R_d by euglycemic clamp with assessment of endogenous glucose production and first-phase insulin secretion by intravenous glucose tolerance test.

RESULTS

In the vitamin D group, the mean ± SD baseline serum 25(OH)D of 38.0 ± 12.6 nmol/L increased to 96.9 ± 18.3 nmol/L after 4 weeks, 73.2 ± 13.7 nmol/L after 3 months, and 53.7 ± 9.2 nmol/L after 6 months. The total exposure to 25(OH)D during 6 months (area under the curve) was 1,870 ± 192 and 1,090 ± 377 nmol/L per week in the vitamin D and placebo groups, respectively (P < 0.001). Insulin sensitivity, endogenous glucose production, and glycemic control did not differ between or within groups after treatment (P = 0.52). First-phase insulin secretion did not change significantly after treatment (P = 0.10).

CONCLUSIONS

Replenishment with a large dose of vitamin D₃ to patients with T2D and vitamin D deficiency did not change insulin sensitivity or insulin secretion. These findings do not support such use of therapeutic vitamin D₃ supplementation to improve glucose homeostasis in patients with T2D.

The effect of vitamin D supplementation on glucose metabolism in type 2 diabetes mellitus: A systematic review and meta-analysis of intervention studies

AIMS

We aimed to assess whether vitamin D supplementation improves glucose metabolism in adults with type 2 diabetes.

METHODS

PubMed and Cochrane database were searched up to July 1st 2016 for randomized controlled trials that assessed the relationship between vitamin D supplementation and glucose metabolism (change in hemoglobin A1C (HbA1C) and fasting blood glucose (FBG)) among adults with type 2 diabetes.

RESULTS

Twenty nine trials (3324 participants) were included in the systematic review. Among 22 studies included in the meta-analysis, 19 reported HbA1C, 16 reported FBG outcomes and 15 were deemed poor quality. There was a modest reduction in HbA1C (-0.32% [-0.53 to -0.10], I2=91.9%) compared to placebo after vitamin D supplementation but no effect on FBG (-2.33mg/dl [-6.62 to 1.95], I2=59.2%). In studies achieving repletion of vitamin D deficiency (n=7), there were greater mean reductions in HbA1C (-0.45%, [-1.09 to 0.20]) and FBG (-7.64mg/dl [-16.25 to 0.97]) although not significant.

CONCLUSIONS

We found a modest reduction of HbA1C after vitamin D treatment in adults with type 2 diabetes albeit with substantial heterogeneity between studies and no difference in FBG. Larger studies are needed to further evaluate the glycemic effects of vitamin D treatment especially in patients with vitamin D deficiency.

Vitamin D status is inversely associated with markers of risk for type 2 diabetes: A population based study in Victoria, Australia

A growing body of evidence suggests a protective role of vitamin D on the risk of type 2 diabetes mellitus (T2DM). We investigated this relationship in a population sample from one Australian state. The data of 3,393 Australian adults aged 18-75 years who participated in the 2009-2010 Victorian Health Monitor survey was analyzed. Socio-demographic information, biomedical variables, and dietary intakes were collected and fasting blood samples were analyzed for 25, hydroxycholecalciferol (25OHD), HbA1c, fasting plasma glucose (FPG), and lipid profiles. Logistic regression analyses were used to evaluate the association between tertiles of serum 25OHD and categories of FPG (<5.6 mmol/L vs. 5.6-6.9 mmol/L), and HbA1c (<5.7% vs. 5.7-6.4%). After adjusting for social, dietary, biomedical and metabolic syndrome (MetS) components (waist circumference, HDL cholesterol, triglycerides, and blood pressure), every 10 nmol/L increment in serum 25OHD significantly reduced the adjusted odds ratio (AOR) of a higher FPG [AOR 0.91, (0.86, 0.97); p = 0.002] and a higher HbA1c [AOR 0.94, (0.90, 0.98); p = 0.009]. Analysis by tertiles of 25OHD indicated that after adjustment for socio-demographic and dietary variables, those with high 25OHD (65-204 nmol/L) had reduced odds of a higher FPG [AOR 0.60, (0.43, 0.83); p = 0.008] as well as higher HbA1c [AOR 0.67, (0.53, 0.85); p = 0.005] compared to the lowest 25OHD (10-44 nmol/L) tertile. On final adjustment for other components of MetS, those in the highest tertile of 25OHD had significantly reduced odds of higher FPG [AOR 0.61, (0.44, 0.84); p = 0.011] and of higher HbA1c [AOR 0.74, (0.58, 0.93); p = 0.041] vs. low 25OHD tertile. Overall, the data support a direct, protective effect of higher 25OHD on FPG and HbA1c; two criteria for assessment of risk of T2DM.

Vitamin D and diabetes mellitus: Causal or casual association?

The incidence of both type 2 and type 1 diabetes mellitus has been increasing worldwide. Vitamin D deficiency, or the awareness of its prevalence, has also been increasing. Vitamin D may have a role in the pathogenic mechanisms predisposing to type 2 diabetes by modulating insulin resistance and/or pancreatic β-cell function. Vitamin D status or elements involved in its activation or transport may also be involved in the development of type 1 diabetes mellitus through immunomodulatory role . Based on these observations a potential association between vitamin D and diabetes has been hypothesized. In this review we discuss up to date evidence linking vitamin D with the development of diabetes. Moreover, the role of vitamin D supplementation in the prevention of both types of diabetes is analysed together with its role in improving glycemic control in diabetic patients. We also address the potential role of vitamin D deficiency in the development of macro- and microvascular complications in diabetes. Finally, we provide recommendation for Vitamin D therapy in diabetes in view of current evidence and highlight areas for potential future research in this area.

Acute Vitamin D₃ Supplementation in Severe Obesity: Evaluation of Multimeric Adiponectin

Obesity predisposes to vitamin D deficiency (VDD) and glucose abnormalities. It is currently debated if vitamin D administration may improve glucose homeostasis by interacting with modulators of insulin sensitivity, such as adiponectin and its oligomers. In a 4-week inpatient study on a metabolic rehabilitation program, consisting of individualized caloric restriction and aerobic physical exercise in obese subjects with VDD, we assessed the acute effects of 600,000 IU cholecalciferol given per os VD group, 12 subjects; body mass index (BMI) 42.7 ± 1.3 kg/m²) or placebo per os (PL group, 12 subjects, BMI 39.8 ± 0.9 kg/m²) on high (HWM-A), medium (MMW-A), and low molecular weight adiponectin (LMW-A), as quantified by western immunoblot (WIB) and ELISA. During the 4-week study, dieting promoted a similar magnitude of weight loss in VD and PL groups. Compared to the PL group, cholecalciferol administration increased 25(OH)Vit D levels (p < 0.001) and promoted a significant increase of HMW-A expression analyzed by WIB (p = 0.02). In parallel, a significant decrease of leptin/HMW-A ratio (p < 0.05), a biomarker of metabolic homeostasis, was observed. During the study, changes of MMW-A and LMW-A occurred independently of cholecalciferol administration, and were likely explained by weight loss. At odds with these findings, the ELISA assessment of adiponectin oligomers showed no modifications in the VD group or PL group. Current findings suggest that acute cholecalciferol administration selectively modifies HMW-A and the leptin/HMW-A ratio.

Vitamin D status correction in Saudi Arabia: an experts' consensus under the auspices of the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis, and Musculoskeletal Diseases (ESCEO)

BACKGROUND

Vitamin D deficiency is common in the Middle East and in Saudi Arabia, in particular. While several international recommendations on the management of vitamin D deficiency have been documented and practiced globally, these recommendations should be adapted to the conditions of the Middle Eastern region. To address this challenge, the Prince Mutaib Chair for Biomarkers of Osteoporosis (PMCO) in King Saud University (KSU), Riyadh, KSA, together with local experts and in cooperation with the European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis (ESCEO), organized a panel that formulated unified recommendations in the diagnosis and treatment of vitamin D deficiency in the region.

METHODS

The selection of local and international experts commenced during the 2nd International Vitamin D Symposium conducted in Riyadh, Saudi Arabia, last January 20--21, 2016. Reviews of the most recent literature were done, and face-to-face meetings were conducted for revisions and final recommendations.

RESULTS

Vitamin D sufficiency is defined as circulating serum 25(OH)D ≥50 nmol (≥20 ng/ml) for the general population and vitamin D adequacy as serum 25(OH)D >75 nmol/L l (>30 ng/ml) for the frail and osteoporotic elderly. Despite overwhelming prevalence of vitamin D deficiency, universal screening is not recommended. Recommendations for the general population, children, pregnant/lactating women, post-menopausal women, the elderly, and those with subsequent metabolic diseases were provided.

RESULTS

Vitamin D sufficiency is defined as circulating serum 25(OH)D ≥50 nmol (≥20 ng/ml) for the general population and vitamin D adequacy as serum 25(OH)D >75 nmol/L l (>30 ng/ml) for the frail and osteoporotic elderly. Despite overwhelming prevalence of vitamin D deficiency, universal screening is not recommended. Recommendations for the general population, children, pregnant/lactating women, post-menopausal women, the elderly, and those with subsequent metabolic diseases were provided.

CONCLUSION

Vitamin D supplementation/correction is advised in all persons whose serum 25(OH)D falls below 50 nmol/l (20 ng/ml), and achieving a target of 75 nmol/l (30 ng/ml) is particularly suited for frail, osteoporotic, and older patients. Conducting well-designed clinical trials in the region that will address economic implications and investigations on the treatment persistence and compliance to vitamin D treatment in the region are encouraged.