Serum 25-hydroxyvitamin D levels are inversely associated with glycated haemoglobin (HbA1c). The Tromsø Study

The Association Between Glycated Hemoglobin (HbA1c) Level and Vitamin D Level in Diabetes Mellitus Patients: A Cross-Sectional Study

BACKGROUND

Prior research has established noteworthy correlations between inadequate glycemic management and a multitude of problems in individuals diagnosed with diabetes mellitus (DM).

METHODS

This is a cross-sectional retrospective study that was conducted at the Jeddah Center for the Care of Diabetes and Blood Pressure Patients, Jeddah, Kingdom of Saudi Arabia. The medical records of patients diagnosed with DM between 2015 and 2022 were identified and reviewed for the purpose of this study. Pearson correlation coefficient was used to examine the correlation between glycated haemoglobin (HbA1c) and vitamin D levels. Multiple linear regression analysis was applied to identify the association between HbA1c and vitamin D levels.

RESULTS

A total of 152 patients were included in this study. The mean HbA1c level for the patients in this study was 8.2% (SD: 1.7). The median vitamin D level for the patients was 20.9 ng/ml (interquartile range (IQR): 13-30.4). More than half of the patients (n= 92; 60.5%) were found to have vitamin D insufficiency. Pearson correlation coefficient identified that there is an inverse correlation between the level of HbA1c and vitamin D level (r= -0.21 (95%CI -0.36 to -0.06; p-value= 0.007). Multiple linear regression analysis (adjusting for age and type of DM) identified that poor glycaemic control has a negative association with vitamin D level (regression coefficient (B) = -0.027; 95%CI -0.053 to - 0.001; p-value= 0.039).

CONCLUSION

Poor glycaemic control is associated with vitamin D deficiency in DM patients. It is recommended that patients with DM adhere to their medications and maintain a healthy lifestyle in order to manage their condition. This will improve their overall health, specifically their vitamin D status.

Effects of vitamin D supplementation on the regulation of blood lipid levels in prediabetic subjects: A meta-analysis

This meta-analysis aimed to systematically investigate whether vitamin D supplementation reduces blood lipid—total cholesterol (TC), LDL cholesterol (LDL-C), HDL cholesterol (HDL-C), and triglyceride (TG)—levels in prediabetic individuals. Pubmed, Web of Science, Cochrane Library, Embase, CNKI, and WANFANG databases were searched for studies published before 13 February 2022 (including 13 February 2022). Five articles were included. The results showed that vitamin D intervention led to a significant reduction in TG compared with control or placebo treatment (−0.42 [−0.59, −0.25], P < 0.001). Subgroup analyses showed that this effect was particularly significant among the studies that included obese subjects (−0.46 [−0.65, −0.28], P < 0.001), the studies that also included men (not only women) (−0.56 [−0.78, −0.34], P < 0.001), and the studies with intervention durations longer than 1 year (−0.46 [−0.65, −0.28], P < 0.001). Both relatively low doses of 2,857 IU/day (−0.65 [−0.92, −0.38], P < 0.001) and relatively high doses of 8,571 IU/day (−0.28 [−0.54, −0.02] P = 0.04) of vitamin D supplementation reduced TG levels, and the effect was observed both in Northern Europe (−0.65 [−0.92, −0.38], P < 0.001) and Asian (−0.25 [−0.48, −0.03], P = 0.03) country subgroups. No significant effects on TC, HDL-C, and LDL-C were shown. In conclusion, vitamin D supplementation might beneficially affect TG levels in individuals with prediabetes. Particularly longer durations of treatment, more than 1 year, with doses that correct vitamin deficiency/insufficiency, can have a beneficial effect. This meta-analysis was registered at www.crd.york.ac.uk/prospero (CRD42020160780).

The correlation of vitamin D with HOMA-IR and glycated hemoglobin in type 2 diabetes mellitus patients

Background and objective: Diabetes mellitus, the most common endocrine condition, is characterised by an elevated level of plasma glucose. Vitamin D's primary functions are homeostasis of calcium and metabolism of bone, but it also has a significant role in homeostasis of plasma glucose. This study sought to examine the relationship between vitamin D and glycated haemoglobin and insulin resistance in type 2 diabetes mellitus (T2DM) subjects by analysing vitamin D, homeostasis model assessment of insulin resistance (HOMA-IR), and haemoglobin A1c (HbA1c) levels. Methods: 150 patients with newly diagnosed T2DM participated in this case-control research. Additionally, 150 controls of the same age and gender were also recruited. Serum vitamin D and fasting insulin levels were estimated by the electrochemiluminescence immunoassay (ECLIA) method. High-performance liquid chromatography (HPLC) was used to analyse HbA1c. Pearson's correlation coefficient was used to determine the relationship of vitamin D with HbA1c and HOMA-IR. Results: Around 70.7% of diabetes subjects had low vitamin D levels, compared to 31.3% in the control group. Vitamin D-deficient T2DM subjects had significantly higher HOMA-IR and HbA1c levels. Both vitamin D and HOMA-IR (r = -0.75) and vitamin D and HbA1c (r = -0.73) showed a strong inverse connection in T2DM patients. Conclusions: Vitamin D deficiency is correlated with ineffective glycemic control, and the reason might be its potential role in the secretion and sensitivity of insulin. Therefore, vitamin D screening must be incorporated as a routine check-up for T2DM patients.

Vitamin D Levels as an Important Predictor for Type 2 Diabetes Mellitus and Weight Regain Post-Sleeve Gastrectomy

Weight Loss Surgery (WLS), including sleeve-gastrectomy (SG), results in significant weight loss and improved metabolic health in severe obesity (BMI ≥ 35 kg/m2). Previous studies suggest post-operative health benefits are impacted by nutrient deficiencies, such as Vitamin D (25(OH)D) deficiency, while it is currently unknown whether nutrient levels may actually predict post-surgery outcomes. As such, this study investigated whether 25(OH)D levels could predict metabolic improvements in patients who underwent SG. Patients with severe obesity (n = 309; 75% female) undergoing SG participated in this ethics-approved, non-randomized retrospective cohort study. Anthropometry, clinical data, 25(OH)D levels and serum markers were collected at baseline, 6-, 12- and 18-months post-surgery. SG surgery resulted in significant improvements in metabolic health at 6- and 12-months post-surgery compared with baseline, as expected. Patients with higher baseline 25(OH)D had significantly lower HbA1c levels post-surgery (p < 0.01) and better post-surgical T2DM outcomes, including reduced weight regain (p < 0.05). Further analysis revealed that baseline 25(OH)D could predict HbA1c levels, weight regain and T2DM remission one-year post-surgery, accounting for 7.5% of HbA1c divergence (p < 0.01). These data highlight that higher circulating 25(OH)D levels are associated with significant metabolic health improvements post-surgery, notably, that such baseline levels are able to predict those who attain T2DM remission. This highlights the importance of 25(OH)D as a predictive biomarker of post-surgery benefits.

Vitamin D binding protein is related to cardiac autonomic function and metabolic status in prediabetes

A putative causal relationship between vitamin D status and glucose metabolism and a direct effect of vitamin D on cardiac autonomic function (CAF) have been suggested. We hypothesized that vitamin D binding protein (DBP), as a transporter of vitamin D, might also influence CAF and the overall metabolic risk. The present study aims to assess the relationship between DBP and CAF and metabolic status in a high-risk population with prediabetes. A total of 174 subjects (mean age 49.1±12.9 years, mean body mass index 30.2±6.2 kg/m²) were divided into 2 groups according to glucose tolerance: 48 with normal glucose tolerance and 126 with prediabetes. Glucose tolerance was assessed during oral glucose tolerance test, applying 2006 World Health Organization criteria. Fasting and postload glucose and immunoreactive insulin were measured (homeostatic model assessment of insulin resistance and homeostatic model assessment of β-cell function were calculated). Anthropometric indexes, blood pressure, hemoglobin A1c, creatinine, lipids, high-sensitivity C-reactive protein, total 25-hydroxyvitamin D, DBP (free 25-hydroxyvitamin D was calculated), and intact parathormone were measured. Body composition was estimated by impedance analysis (InBody 720), whereas tissue advanced glycation end products were assessed by skin autofluorescence (AGE Reader, DiagnOptics, the Netherlands). CAF was evaluated by АNX-3.0 system, applying standard autonomic tests. DBP was found to be elevated in women, as well as in the presence of cardiac autonomic dysfunction and metabolic syndrome. DBP was related to parasympathetic activity in both sexes and in prediabetes; to body fat in women and in prediabetes; and to age and high-density lipoprotein cholesterol in men. Vitamin D deficiency was established in 40.8% of the studied cohort. These results support the hypothesis that DBP is associated with CAF and some metabolic parameters in prediabetes.

Vitamin D receptor rs7975232, rs731236 and rs1544410 single nucleotide polymorphisms, and 25-hydroxyvitamin D levels in Egyptian children with type 1 diabetes mellitus: effect of vitamin D co-therapy

Purpose: We aimed to examine the possible association role of vitamin D and vitamin D receptor (VDR) single nucleotide polymorphisms (SNPs) in type 1 diabetes mellitus (T1DM) development, glycemic control and complications among a cohort of Egyptian children. Subjects and methods: A prospective case-control study has been conducted on 50 Egyptian children with T1DM who were comparable with 50 controls. Vitamin D and HbA1c were measured. VDR-SNPs [ApaI (rs7975232), TaqI (rs731236) and BsmI (rs1544410)] detection was done by polymerase chain reaction through restriction fragment length polymorphism (PCR-RFLP) technique. Vitamin D supplements were given to the included T1DM children with low vitamin D and reassessments of both HbA1c% and 25(OH)D serum levels were performed in those children three months later. Results: Eighty percent of the included diabetic patients have poor glycemic control. Vitamin D was deficient in 68% and insufficient in 16% of diabetic patients. Significant improvements in both vitamin D and glycemic status among T1DM children, who have low vitamin D and received vitamin D supplementations. There were significantly negative correlations between serum levels of vitamin D with both HbA1c % (r= -0.358, P˂0.05) and daily insulin dose (r=-0.473, P˂0.05). Compared with controls, T1DM children presented more commonly with ApaI a allele (OR: 2.87; 95%CI: 1.39-5.91, P˂0.05) and BsmI b allele (OR: 4.38; 95%CI: 2.30-8.33, P˂0.05). TaqI t allele wasn't significantly differing among patients and controls (P˃0.05). Aa+aa and Bb+bb genotypes were significantly higher among T1DM vs the controls (OR: 3.08;, 95%CI: 1.33-7.15, P˂0.05 and OR: 9.33; 95%CI: 3.61-24.17, P˂0.05respectively). Conclusion: ApaI and BsmI were associated with risk of T1DM development among Egyptian children. Low vitamin D status was frequently occurring among T1DM with significant improvement in the glycemic control of such children when adding vitamin D supplements to the standard insulin therapy.

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.

Association of Glycosylated Hemoglobin Levels With Vitamin D Status

Background

The discovery of vitamin D is one of medicine’s great achievements. Despite all the positive evidence emerging about the beneficial effect of vitamin D, we still find many are vitamin D deficient. The purposes of this study were to examine the association between serum 25-hydroxyvitamin D (25(OH)D) and glycosylated hemoglobin (HbA1c) levels, to test the hypothesis that lower 25(OH)D levels are associated with poorer glucose control in diabetes mellitus (DM) patients and to investigate the effect of vitamin D supplementation on HbA1c levels.

Methods

This was a prospective observational cohort study of all patients with type 1 and type 2 diabetes (above 12 years) who attended the outpatient clinics of a tertiary center in Riyadh. HbA1c and vitamin D levels were recorded prior to supplementation and after 9 months of supplementation with vitamin D. All patients were divided into four groups according to their vitamin D level and an association between 25(OH)D and HbA1c was tested.

Results

Results showed that 73.1% of the patients had 25(OH)D levels < 50 nmol/L. We observed lowering of HbA1c after vitamin D supplementation (from mean HbA1c of 10.55 to 7.70). We found HbA1c to be inversely related to serum vitamin D levels (r = -0.14 (P < 0.0000002) before supplementation and -0.16 (P < 0.000001) after supplementation with vitamin D).

Conclusions

Advising patients with higher HbA1c to test their vitamin D level and correct any deficiency will result in better blood glucose control and benefit the patient’s overall health.

Vitamin D in the Spectrum of Prediabetes and Cardiovascular Autonomic Dysfunction

Vitamin D is a fat-soluble secosteroid hormone with pleiotropic effects. 1,25-Dihydroxyvitamin D coordinates the biosynthesis of neurotransmitters in the central nervous system, which regulate cardiovascular autonomic function and may explain its putative role in the development of cardiovascular autonomic neuropathy (CAN). CAN is an independent risk factor for mortality in patients with diabetes and prediabetes and is associated with an increased risk of developing type 2 diabetes and cardiovascular disease. Accumulating data indicate the presence of peripheral nerve injury at these early stages of dysglycemia and its multifactorial pathogenesis. Prediabetes is associated with vitamin D insufficiency. Vitamin D is proposed to prevent the progression of glucose intolerance. The putative underlying mechanisms include maintenance of the intracellular calcium concentration, direct stimulation of insulin receptor expression, and enhancement of the insulin response to glucose transporters. Vitamin D exerts a protective effect on peripheral nerve fibers by decreasing the demyelination process and inducing axonal regeneration. The effects of vitamin D supplementation on glucose tolerance and related autonomic nerve dysfunction have been a recent focus of scientific interest. Although well-designed observational studies are available, the causative relation between vitamin D deficiency, glucose intolerance, and CAN is still debatable. One reason might be that interventional studies are unpersuasive with regard to the beneficial clinical effects of vitamin D supplementation. Because of its favorable side effect profile, vitamin D supplementation might represent an attractive therapeutic option for treating the pandemic prevalence of prediabetes and vitamin D deficiency. Vitamin D supplementation can improve glucose tolerance and cardiovascular autonomic function and can thus reduce cardiovascular mortality among subjects with different stages of glucose intolerance and autonomic dysfunction. However, more patient-centered trials on the use of vitamin D supplementation in different conditions are needed.

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.

High and low vitamin D level is associated with cardiovascular autonomic neuropathy in people with Type 1 and Type 2 diabetes

AIM

To investigate the possible association between vitamin D deficiency and cardiovascular autonomic neuropathy in people with diabetes.

METHODS

A total of 113 people with Type 1 or Type 2 diabetes [mean (interquartile range) diabetes duration 22.0 (12-31) years, mean (sd) age 56.2 (13.0) years, 58% men] underwent vitamin D (D2 and D3) assessment, and were screened for cardiovascular autonomic neuropathy using three cardiovascular reflex tests [heart rate response to deep breathing (E/I ratio), to standing (30/15 ratio) and to the Valsalva manoeuvre] and assessment of 5-min resting heart rate and heart rate variability indices.

RESULTS

We found an inverse U-shaped association between serum vitamin D level and E/I ratio, 30/15 ratio and three heart rate variability indices (P < 0.05). Vitamin D level was non-linearly associated with cardiovascular autonomic neuropathy diagnosis (P < 0.05 adjusted for age and sex). Linear regression models showed that an increase in vitamin D level from 25 to 50 nmol/l was associated with an increase of 3.9% (95% CI 0.1;7.9) in E/I ratio and 4.8% (95% CI 4.7;9.3) in 30/15 ratio. Conversely, an increase from 125 to 150 nmol/l in vitamin D level was associated with a decrease of 2.6% (95% CI -5.8;0.1) and 4.1% (95% CI -5.8;-0.5) in the respective outcome measures.

CONCLUSIONS

High and low vitamin D levels were associated with cardiovascular autonomic neuropathy in people with diabetes. Future studies should explore this association and the efficacy of treating dysvitaminosis D to prevent cardiovascular autonomic neuropathy.

Vitamin D deficiency increases the risk of peripheral neuropathy in Chinese patients with type 2 diabetes

BACKGROUND

Vitamin D deficiency was reported to be associated with diabetic peripheral neuropathy. But the association in Chinese population and the screening value of vitamin D deficiency for diabetic peripheral neuropathy were unknown.

METHODS

A total of 861 patients with type 2 diabetes were recruited in this cross-sectional study. Vitamin D deficiency was defined as serum circulating 25-hydroxyvitamin D(25(OH)D) level < 20 ng/mL. Peripheral neuropathy was evaluated by neurological symptoms, neurological signs, neurothesiometer and electromyogram.

RESULTS

The patients with diabetic peripheral neuropathy had significantly lower serum 25(OH)D concentration (15.59 ± 7.68 ng/mL) and higher prevalence of vitamin D deficiency (80%) than patients with signs of diabetic peripheral neuropathy (17.66 ± 7.50 ng/mL; 64.5%) and non-DPN patients (18.35 ± 6.60; 61.7%) (all p < 0.01). Spearman's correlation analysis showed that serum circulating 25(OH)D level was closely associated with DPN (r = 0.121) and signs of DPN (r = 0.111) (both p < 0.01). After adjusting for all potential confounders, VDD was still linked with increased risk of DPN [odds ratio 2.59 (1.48-4.53)] (p < 0.01). Logistical regression analysis further revealed that VDD was an independent risk factor for DPN (β = 0.88) (p < 0.01). Receiver operating characteristic analysis indicated that serum 25(OH)D < 17.22 ng/mL hinted the signs of DPN and serum 25(OH)D < 16.01 ng/mL predicted the occurrence of DPN (both p < 0.01).

CONCLUSIONS

Vitamin D deficiency is an independent risk factor for diabetic peripheral neuropathy and may be a potential biomarker for peripheral neuropathy in Chinese patients with type 2 diabetes. Copyright © 2016 John Wiley & Sons, Ltd.

Vitamin D 20,000 IU per Week for Five Years Does Not Prevent Progression From Prediabetes to Diabetes

CONTEXT

Vitamin D deficiency is associated with insulin resistance and risk of future diabetes.

OBJECTIVE

The objective of the study was to test whether supplementation with vitamin D to subjects with prediabetes will prevent progression to type 2 diabetes mellitus (T2DM).

DESIGN

This was a randomized controlled trial performed in 2008 through 2015.

SETTING

The study was conducted at the clinical research unit at a teaching hospital.

PATIENTS

Five hundred eleven subjects (mean age 62 y, 314 males) with prediabetes diagnosed with an oral glucose tolerance test as part of the Tromsø Study 2007–2008 were included. A total of 256 were randomized to vitamin D and 255 to placebo. Twenty-nine subjects in the vitamin D and 24 in the placebo group withdrew because of adverse events.

INTERVENTIONS

Interventions included vitamin D (cholecalciferol) 20 000 IU/wk vs placebo for 5 years. Annual oral glucose tolerance tests were performed.

MAIN OUTCOME MEASURE

Progression to T2DM was the main outcome measure. Secondary outcomes were change in glucose levels, insulin resistance, serum lipids, and blood pressure.

RESULTS

The mean baseline serum 25-hydroxyvitamin D level was 60 nmol/L (24 ng/mL). One hundred three in the vitamin D and 112 in the placebo group developed T2DM (hazard risk 0.90; 95% confidence interval 0.69–1.18, Cox regression, P = .45, intention to treat analysis). No consistent significant effects on the other outcomes were seen. Subgroup analyses in subjects with low baseline 25-hydroxyvitamin D yielded similar results. No serious side effects related to the intervention were recorded.

CONCLUSIONS

In subjects without vitamin D deficiency, vitamin D supplementation is unlikely to prevent progression from prediabetes to diabetes. Very large studies with inclusion of vitamin D-deficient subjects will probably be needed to show such a putative effect. This study tested if supplementation with vitamin D to subjects with prediabetes will prevent progression to type 2 diabetes (T2DM).

Vitamin D and Diabetic Complications: True or False Prophet?

Vitamin D deficiency is now recognized as a condition of increasing prevalence worldwide. Vitamin D has an established role in calcium and bone metabolism; however, more recently associations with vitamin D deficiency and risk of developing diabetes, diabetes complications, and cardiovascular disease have all been acknowledged. The vitamin D receptor is ubiquitously expressed, and experimental, in vitro, and in vivo studies strongly suggest a role in regulating the transcription of multiple genes beyond calcium homeostasis. These include antiproliferative, immunomodulatory, angiogenic, inhibition of the renin-angiotensin-aldosterone system, and neurotrophic factor expression. Observational studies report a strong association between vitamin D deficiency and cardiovascular and metabolic disorders; however, there remains a paucity of large long-term randomized clinical trials showing a benefit with treatment. An increasing body of literature suggests a possible pathogenetic role of vitamin D in the long-term complications of diabetes and vitamin D deficiency may also exacerbate symptoms of painful diabetic peripheral neuropathy. It remains unknown if supplementation of vitamin D to normal or non-deficient levels alters pathogenetic processes related to diabetic microvascular complications. With the high prevalence of vitamin D deficiency in patients with diabetes and putative mechanisms linking vitamin D deficiency to diabetic complications, there is a compelling argument for undertaking large well-designed randomized controlled trials of vitamin D supplementation.

Genetic Variations in the Vitamin D Receptor Predict Type 2 Diabetes and Myocardial Infarction in a Community-Based Population: The Tromsø Study

BACKGROUND

Though the associations between low serum 25-hydroxyvitamin D (25(OH)D) levels and health outcomes such as type 2 diabetes (T2D), myocardial infarction (MI), cancer, and mortality are well-studied, the effect of supplementation with vitamin D is uncertain. This may be related to genetic differences. Thus, rs7968585, a single nucleotide polymorphism (SNP) of the vitamin D receptor (VDR), has recently been reported as a predictor of composite health outcome. We therefore aimed to evaluate whether rs7968585 predicts separate clinical outcomes such as T2D, MI, cancer, and mortality in a community-based Norwegian population.

METHODS AND FINDINGS

Measurements and DNA were obtained from the participants in the Tromsø Study in 1994-1995, registered with the outcomes of interest and a randomly selected control group. The impact of the rs7968585 genotypes was evaluated with Cox proportional hazards. A total of 8,461 subjects were included among whom 1,054 subjects were registered with T2D, 2,287 with MI, 3,166 with cancer, and 4,336 with death. Mean follow-up time from birth was 60.8 years for T2D and MI, 61.2 years for cancer, while mean follow-up time from examination date was 16.5 years for survival. Mean serum 25(OH)D levels did not differ across the rs7968585 genotypes. With the major homozygote genotype as reference, the minor homozygote subjects had hazard ratios of 1.25 (95% CI 1.05-1.49) for T2D and 1.14 (1.02-1.28) for MI (P = 0.011 and 0.023, respectively, without the Bonferroni correction). No significant interaction between serum 25(OH)D status and the rs7968585 genotype was found for any of the endpoints.

CONCLUSIONS

The VDR-related SNP rs7968585 minor allele is a significant and positive predictor for T2D and possibly for MI. Since the functional mechanism of this SNP is not yet understood, and the association with T2D is reported for the first time, confirmatory studies are needed.

Is vitamin D deficiency related to accumulation of advanced glycation end products, markers of inflammation, and oxidative stress in diabetic subjects?

OBJECTIVES

In diabetes accumulated advanced glycation end products (AGEs) are involved in the striking cardiovascular morbidity/mortality. We asked whether a hypovitaminosis D associates with an increased formation and toxicity of AGEs in diabetes.

METHODS

In 276 diabetics (160 M/116 F, age: 65.0 ± 13.4; 43 type 1,T1DM, and 233 type 2 patients, T2DM) and 121 nondiabetic controls (60 M/61 F; age: 58.6 ± 15.5 years) routine biochemistry, levels of 25-hydroxyvitamin D3 (25-(OH)D), skin autofluorescence (SAF), plasma AGE-associated fluorescence (AGE-FL), N (ε) -(carboxymethyl)lysine (CML), soluble receptor for AGEs (sRAGE), soluble vascular adhesion protein-1 (sVAP-1), high sensitive C-reactive protein (hs-CRP), and renal function (eGFR) were determined.

RESULTS

In the diabetics SAF and AGE-Fl were higher than those of the controls and correlated with age, duration of diabetes, and degree of renal impairment. In T2DM patients but not in T1DM the age-dependent rise of SAF directly correlated with hs-CRP and sVAP-1. 25-(OH)D levels in diabetics and nondiabetics were lowered to a similar degree averaging 22.5 ng/mL. No relationship between 25-(OH)D and studied markers except for sVAP-1 was observed in the diabetics.

CONCLUSION

In diabetics hypovitaminosis D does not augment accumulation of AGEs and studied markers of microinflammation and oxidative stress except for sVAP-1.

Does vitamin D play a significant role in type 2 diabetes?

BACKGROUND

Vitamin D deficiency reportedly is associated with type 2 diabetes (T2DM). We aim to examine whether 25-hydroxyvitamin D (25OHD) has clinically significant influence on hemoglobin glycation (HbA1c) and insulin resistance (HOMA-IR) in T2DM subjects.

METHODS

Present study was carried out in 912 subjects (429 T2DM cases and 483 non-diabetic controls) from Western India. The enrolled study subjects were investigated for biochemical parameters like FBS, PPBS, HbA1c, FI, HOMA-IR and 25OHD levels in blood.

RESULTS

Vitamin D deficiency was seen in 91.4% and 93.0% of T2DM cases and control subjects respectively. There was no association of serum 25OHD deficiency on HbA1c or HOMA-IR in T2DM cases (p = 0.057 & p = 0.257 respectively) and in control subjects (p = 0.675 & p = 0.647 respectively).

CONCLUSION

Our findings suggests that though vitamin D deficiency is prevalent in T2DM and non-diabetic subjects, its role in hemoglobin glycation and insulin resistance could not be established.

Shining the light on Sunshine: a systematic review of the influence of sun exposure on type 2 diabetes mellitus-related outcomes

Prospective observational studies uniformly link vitamin D deficiency with the incidence of type 2 diabetes mellitus (T2DM), yet trials supplementing participants at risk of T2DM with vitamin D to reduce progression to T2DM have yielded inconsistent results. Inconsistencies between supplementation trials may be due to insufficient dosing or small sample sizes. Observational studies may also have reported spurious associations due to uncontrolled confounding by lifestyle or genetic factors. Alternatively, observational and intervention studies may not be entirely comparable. Observational studies show an association between higher vitamin D status, which is predominantly derived from sun exposure, and decreased incidence of T2DM. Trials intervene with vitamin D supplementation, and therefore may be missing alternate causes of the effect of sun exposure, as seen in observational studies. We propose that sun exposure may be the driving force behind the associations seen in observational studies; sun exposure may have additional benefits beyond increasing serum 25-hydroxyvitamin D (25OHD) levels. We performed an electronic literature search to identify articles that examined associations between sun exposure and T2DM and/or glucose metabolism. A best evidence synthesis was then conducted using outcomes from analyses deemed to have high methodological quality. Ten eligible full-text articles were identified, yielding 19 T2DM-related outcomes. The best evidence analysis considered 11 outcomes which were grouped into six outcome types: T2DM, fasting glucose, glucose tolerance, fasting insulin, insulin secretion and insulin sensitivity. There was moderate evidence to support a role of recreational sun exposure in reducing odds of T2DM incidence. High-level evidence was lacking; evidence presented for other outcomes was of low or insufficient level. This review highlights significant gaps in research pertaining to sun exposure and T2DM-related outcomes. Further research is encouraged as we aim to identify novel preventative strategies for T2DM.

Is there an association between diabetic neuropathy and low vitamin D levels?

In the past few years, the effects of vitamin D that go beyond its relationship with bone metabolism have come into the focus of scientific attention. Research concerning diabetes and its complications has become a public health priority. An increasing number of reports link vitamin D deficiency to diabetes; however, so far, there has only been limited and contradictory data available on the correlation between diabetic peripheral neuropathy and vitamin D. Studies of people with type 2 diabetes confirmed the relationship between vitamin D deficiency and neuropathy incidence as well as the severity of the symptoms caused by neuropathy. The latest studies are also suggesting a relationship between the incidence of plantar ulcers and vitamin D deficiency.

Effect of vitamin D3 supplementation on glycated hemoglobin (HbA1c), fructosamine, serum lipids, and body mass index: a randomized, double-blinded, placebo-controlled trial among healthy immigrants living in Norway

OBJECTIVE

Despite the suggested role of vitamin D in the prevention of diabetes and cardiovascular disease or its risk factors, the evidence is not consistent and there is a paucity of randomized controlled trials in this field. We aimed to investigate the effect of 16-week daily vitamin D3 supplementation on glycated hemoglobin (HbA1c), fructosamine, body mass index (BMI), and serum lipids.

DESIGN

Double-blind, randomized, placebo-controlled trial.

SETTING

Immigrant community centers in Oslo, Norway.

PARTICIPANTS

251 healthy adults aged 18-50 years with a non-Western immigrant background. All participants performed the baseline test and 215 (86%) returned to the follow-up test.

INTERVENTION

16 weeks of daily oral supplementation with either 10 μg vitamin D3, 25 μg vitamin D3, or placebo.

MAIN OUTCOME MEASURES

Difference in absolute change during the 16-week intervention between the intervention groups combined (10 or 25 μg of vitamin D3/day) and placebo, in HbA1c, fructosamine, serum lipids (total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides), and BMI.

RESULTS

A total of 215 (86%) participants completed the study. Serum 25-hydroxyvitamin D increased from 29 nmol/L at baseline to 49 nmol/L after intervention, with little change in the placebo group. However, there was no difference in change of HbA1c between those receiving vitamin D3 compared with placebo (mean difference: 0.01% (95% CI -0.04 to 0.06, p=0.7)). Neither did the vitamin D3 supplementation have any effect on the other end points: fructosamine, serum lipids, and BMI.

CONCLUSIONS

16-week vitamin D3 supplementation to healthy immigrants from South Asia, the Middle East, or Africa and now living in Norway with low vitamin D status did not improve HbA1c, fructosamine, lipid profiles, or BMI. An updated meta-analysis of similar published trials showed that our results were generally consistent with those of other studies.

TRIAL REGISTRATION NUMBER

NCT01263288.

Glycated haemoglobin is inversely related to serum vitamin D levels in type 2 diabetic patients

Objective

A correlation between glucose control and 25(OH)D metabolism has been suggested by previous studies. However, this correlation has not yet been evaluated considering the impact of chronic complications of type 2 diabetes, especially the presence of nephropathy. Thus, the aim of this study was to determine the correlation between A1C and 25(OH)D in a well characterized cohort of type 2 diabetic patients.

Research Design and Methods

We cross-sectionally examined the association between A1C and serum 25(OH) D in 715 type 2 diabetic patients attending our clinic during the years 2011–2012. The average age was 68±12 years (range 26–94 years). The relation between A1C and serum 25(OH)D levels was modelled by multiple linear regression analyses.

Results

Serum 25(OH)D levels were inversely associated with A1C levels (r = −0.116, p = .003). This relation maintains its independence in the multivariate analysis after adjusting for age, sex, A1C, BMI, treatment and duration of diabetes and nephropathy.

Conclusions

In type 2 diabetic patients, high A1C levels are associated with low concentrations of serum 25(OH)D independently of duration of diabetes, diabetic treatment and nephropathy. Future studies are needed to clarify the biological relation between glucose control and vitamin D metabolism in type 2 diabetes.

Hypovitaminosis d in patients with type 2 diabetes mellitus: a relation to disease control and complications

Aims. This study aims at assessing the relationship between 25 (OH) vitamin D (25-OHD) levels and microvascular complications in patients with type 2 diabetes mellitus (DM2). Methods. 136 patients (59 ± 11 years) with DM2 (disease duration 8.6 ± 7 years) participated in this cross-sectional study. Anthropometric data, HbA1c, 25-OHD levels, serum creatinine, and urine microalbumin/creatinine ratio were collected. Dilated retinal exam was performed, and diabetic neuropathy was assessed using the United Kingdom Screening Score. Results. Serum 25-OHD correlated negatively with HbA1c (r = -0.20,  P = 0.049). Mean 25-OHD levels were lower in subjects with diabetic retinopathy compared to those without retinopathy (12.3 ± 5.5 versus 21.8 ± 13.7, P < 0.001) and lower in subjects with diabetic neuropathy compared to those without neuropathy (16.4 ± 10.4 versus 23.5 ± 14.5, P = 0.004). After adjustment for BMI, diabetes duration, and smoking, 25-OHD was an independent predictor of HbA1c ( β   -0.14; P = 0.03). After adjustment for HbA1c, age, smoking, BMI and disease duration, 25-OHD were independent predictors for diabetic retinopathy: OR 2.8 [95% CI 2.1-8.0] and neuropathy: OR 4.5 [95% CI 1.6-12] for vitamin D < 20 versus vitamin D ≥ 20 ng/mL. Conclusion. Low serum 25-OHD level was an independent predictor of HbA1c, diabetic neuropathy, and diabetic retinopathy in patients with DM2.

Relationship between glycated hemoglobin and circulating 25-hydroxyvitamin D concentration in African American and Caucasian American men

OBJECTIVES

To examine whether (1) serum 25-hydroxyvitamin D level (25[OH]D) is a risk factor for hyperglycemia, as assessed by glycated hemoglobin (HbA1c), in African American men (AAM) and (2) 25(OH)D is a predictor of HbA1c in AAM and Caucasian American men (CAM).

METHODS

We prospectively assessed 25(OH)D and HbA1c in 1,074 men, outpatients with and without diabetes, at an urban Veteran Administration Medical Center (66.8% AAM, 26.4% CAM, 6% Hispanic, 0.4% Asian, and 0.4% Native American men). Multivariate regression analyzed the determinants of HbA1c after accounting for potential confounders.

RESULTS

We found high prevalence of low (< 30 ng/mL) 25(OH)D (81%) and elevated (≥5.7%) HbA1c (53.5%). The 25(OH)D was inversely associated with HbA1c in all men (r = -0.12, P<.001), in AAM (r = -0.11, P = .003), and in CAM (r = -0.15, P = .01). In the entire group the independent determinants of HbA1c included body mass index (BMI), age, 25(OH)D levels, systolic blood pressure (BP), triglycerides, high-density lipoprotein (HDL), and current alcohol use (P<.0001, .013, .009, .01, .008, .034, and .048, respectively) while glomerular filtration rate (GFR) and marital status showed borderline significance (P = .08 and .09, respectively). In AAM these determinants included BMI, 25(OH)D levels, systolic BP, and current alcohol use (P<.0001, .01, .02, and .03, respectively), while age had borderline significance (P = .06). In CAM, these included BMI, age, and triglycerides (P = .01, .03, and .004, respectively) but not 25(OH)D levels (P = .50).

CONCLUSION

Circulating low 25(OH)D is a risk factor for hyperglycemia, as assessed by HbA1c, in AAM. The 25(OH)D level is an independent determinant of HbA1c in AAM, but not in CAM, including men with and without diabetes.

Association of 25-hydroxyvitamin D with type 2 diabetes among patients undergoing coronary angiography: cross-sectional findings from the LUdwigshafen Risk and Cardiovascular Health (LURIC) Study

OBJECTIVE

Evidence suggests that vitamin D may protect against the onset of diabetes. However, the mechanisms underlying the role of vitamin D on glycaemic status are unclear and warrant further investigation. We sought to determine the relationship between serum 25-hydroxyvitamin D (25[OH]D) and glycaemic status among intermediate-to-high-risk patients scheduled for coronary angiography.

METHODS

Participants were 3316 male and female patients (mean ± SD age, 62·7 ± 10·6 years). Four categories were formed according to serum 25[OH]D levels. The association between serum 25[OH]D and diabetes was assessed using multivariable logistic regression.

RESULTS

Fasting and 2 h post-load glucose, HbA1c and the HOMA-IR indices diminished with increasing serum 25[OH]D levels (P < 0·001). However, no associations were observed between insulin, pro-insulin or C-peptide and serum 25[OH]D concentrations. The pro-inflammatory markers IL-6 and hs-CRP also decreased considerably with higher vitamin D levels (P < 0·001). After full adjustment, those with optimal serum 25[OH]D levels had a reduced odds for fasting diabetes (OR = 0·63; 95% CI, 0·46-0·86; Ptrend = 0·01), 2 h post-load diabetes (OR = 0·46; 95% CI, 0·29-0·74; Ptrend = 0·004), both fasting/2 h post-load diabetes (OR = 0·61; 95% CI, 0·42-0·87; Ptrend = 0·001) and all of the combined hyperglycaemic states (OR = 0·68; 95% CI, 0·52-0·80; Ptrend = 0·01).

CONCLUSIONS

Higher serum 25[OH]D levels were associated with better glycaemic status and lower inflammation. Should these observations be confirmed in future studies, vitamin D supplementation may prove a useful adjunct in attenuating the onset of diabetes.

Supplementation with High Doses of Vitamin D to Subjects without Vitamin D Deficiency May Have Negative Effects: Pooled Data from Four Intervention Trials in Tromsø

Data were pooled from four randomized clinical trials with vitamin D performed in Tromsø with weight reduction, insulin sensitivity, bone density, and depression scores as endpoints. Serum lipids, glycated hemoglobin (HbA1c), and high sensitivity C-Reactive Protein, (HS-CRP) were measured at baseline and after 6-12 months of supplementation with vitamin D 20 000 IU-40 000 IU per week versus placebo. A total of 928 subjects who completed the interventions were included. At baseline the mean serum 25-hydroxyvitamin D (25(OH)D) level in those given vitamin D was 55.9 (20.9) nmol/L and the mean increase was 82.4 (40.1) nmol/L. Compared with the placebo group there was in the vitamin D group at the end of the studies a slight, but significant, increase in HbA1c of 0.04%, an increase in HS-CRP of 0.07 mg/L in those with serum 25(OH)D < 50 nmol/L, and in those with low baseline HDL-C and serum 25(OH)D < 50 nmol/L a slight decrease serum HDL-C of 0.08 mmol/L (P < 0.05). No serious side-effects were seen. In conclusion, in subjects without vitamin D deficiency, there is no improvement in serum lipids, HbA1c, or HS-CRP with high dose vitamin D supplementation. If anything, the effect is negative.

Polymorphisms related to the serum 25-hydroxyvitamin D level and risk of myocardial infarction, diabetes, cancer and mortality. The Tromsø Study

OBJECTIVE

Low serum 25(OH)D levels are associated with cardiovascular risk factors, and also predict future myocardial infarction (MI), type 2 diabetes (T2DM), cancer and all-cause mortality. Recently several single nucleotide polymorphisms (SNPs) associated with serum 25-hydroxyvitamin D (25(OH)D) level have been identified. If these relations are causal one would expect a similar association between these SNPs and health.

METHODS

DNA was prepared from subjects who participated in the fourth survey of the Tromsø Study in 1994-1995 and who were registered with the endpoints MI, T2DM, cancer or death as well as a randomly selected control group. The endpoint registers were complete up to 2007-2010. Genotyping was performed for 17 SNPs related to the serum 25(OH)D level.

RESULTS

A total of 9528 subjects were selected for genetic analyses which were successfully performed for at least one SNP in 9471 subjects. Among these, 2025 were registered with MI, 1092 with T2DM, 2924 with cancer and 3828 had died. The mean differences in serum 25(OH)D levels between SNP genotypes with the lowest and highest serum 25(OH)D levels varied from 0.1 to 7.8 nmol/L. A genotype score based on weighted risk alleles regarding low serum 25(OH)D levels was established. There was no consistent association between the genotype score or individuals SNPs and MI, T2DM, cancer, mortality or risk factors for disease. However, for rs6013897 genotypes (located at the 24-hydroxylase gene (CYP24A1)) there was a significant association with breast cancer (P<0.05).

CONCLUSION

Our results do not support nor exclude a causal relationship between serum 25(OH)D levels and MI, T2DM, cancer or mortality, and our observation on breast cancer needs confirmation. Further genetic studies are warranted, particularly in populations with vitamin D deficiency.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01395303.