Effects of vitamin D deficiency and repletion on insulin and glucagon secretion in man

Obstructive sleep apnea and vitamin D: an updated systematic review and meta-analysis

PURPOSE  : Obstructive sleep apnea (OSA) is a chronic, sleep-related breathing disorder which leads to increased cardiovascular risks. Vitamin D deficiency is associated with various cardiometabolic complications, including increased cardiovascular morbidity and mortality. We aimed to analyze the difference in serum 25-hydroxyvitamin D (25-OHD) level, prevalence of vitamin D insufficiency and deficiency, and the effect of CPAP treatment on serum 25-OHD levels among adult patients with OSA.

METHODS

We pooled data from 18 observational studies involving 5592 individuals. Baseline parameters that might have contributed to the significant differences observed were also analyzed.

RESULTS

Patients with OSA had significantly lower serum 25-OHD levels (pooled d +  - 0.74 [95% CI: - 1.19 to - 0.28], p < 0.01) and higher prevalence of vitamin D deficiency (pooled log (odds ratio) 0.98 [95% CI: 0.30 to 1.67], p < 0.01) compared to those without OSA. Subgroup analysis demonstrated that these differences were significant only in moderate OSA and severe OSA. Neither age nor BMI nor geographical latitude contributed significantly to the differences observed in serum 25-OHD levels. The use of CPAP did not lead to significant changes in serum 25-OHD levels.

CONCLUSION

Patients with OSA have lower serum 25-OHD levels with a higher prevalence of vitamin D deficiency, regardless of age or BMI, pointing to an independent association between vitamin D and OSA.

Vitamin D in Diabetes: Uncovering the Sunshine Hormone's Role in Glucose Metabolism and Beyond

Over the last decades, epidemiology and functional studies have started to reveal a pivotal role of vitamin D in both type 1 and type 2 diabetes pathogenesis. Acting through the vitamin D receptor (VDR), vitamin D regulates insulin secretion in pancreatic islets and insulin sensitivity in multiple peripheral metabolic organs. In vitro studies and both T1D and T2D animal models showed that vitamin D can improve glucose homeostasis by enhancing insulin secretion, reducing inflammation, reducing autoimmunity, preserving beta cell mass, and sensitizing insulin action. Conversely, vitamin D deficiency has been shown relevant in increasing T1D and T2D incidence. While clinical trials testing the hypothesis that vitamin D improves glycemia in T2D have shown conflicting results, subgroup and meta-analyses support the idea that raising serum vitamin D levels may reduce the progression from prediabetes to T2D. In this review, we summarize current knowledge on the molecular mechanisms of vitamin D in insulin secretion, insulin sensitivity, and immunity, as well as the observational and interventional human studies investigating the use of vitamin D as a treatment for diabetes.

Relationship Between Vitamin D Levels and β Cell Function and Insulin Resistance

Background This study aimed to determine the relationship between vitamin D levels and β cell function and insulin resistance in patients with diabetes, glucose tolerance disorder, or impaired fasting glucose. Methodology A total of 75 outpatients (55 females and 20 males) between the ages of 30 and 65 years were included in the study. There were 25 healthy individuals, 25 individuals with prediabetes, and 25 individuals with diabetes. The Homeostasis Model Assessment (HOMA) score was used to evaluate insulin resistance. Results The mean levels of vitamin 25(OH)D among the groups included in the study were 35 ± 16.9 nmol/L in the control group, 44.5 ± 34.5 nmol/L in the prediabetes group, and 35.7 ± 13.1 nmol/L in the diabetes group. There were no significant differences. The mean level of vitamin 1.25(OH)₂D₃ was 15.95 ± 8 pg/mL in the control group, 18.4 ± 7.5 pg/mL in the prediabetes group, and 21.5 ± 7.9 pg/mL in the diabetes group. While the levels of vitamin 25(OH)D were similar between the groups, the levels of vitamin 1,25(OH)₂D₃  were significantly higher in the diabetes group. Considering all individuals, no significant difference was found between the vitamin 25(OH)D and glucose levels at minutes 0, 30, 60, 90, and 120. While there was a significant positive relationship between the 1,25(OH)₂D₃ vitamin and glucose levels at minutes 0, 30, 60, and 90, there was no significant relationship between the levels at minute 120. When the 1,25(OH)₂D₃ vitamin and HOMA insulin resistance and HOMA β scores were compared, a significant positive relationship was found between the 1,25(OH)₂D₃ vitamin and HOMA β levels. Conclusions In our study, there was no significant difference between the groups (control, prediabetes, and diabetes) in 25(OH)D levels. Similarly, there was no significant relationship between the 25(OH)D levels and insulin sensitivity and resistance between the groups. The positive relationship identified between the 1,25(OH)₂D₃ vitamin levels and the glucose concentration at minutes 0, 30, 60, and 90 and the higher 1,25(OH)₂D₃ vitamin levels in the diabetes group compared to the control group in our study can be interpreted as the effort of the organism to prevent glucose-induced β-cell apoptosis.

A High Dose, Not Low Dose, of Vitamin D Ameliorates Insulin Resistance in Saudi Women

Vitamin D has been traditionally seen to be mainly involved in the regulation of bone homeostasis. However, vitamin D has also been clinically linked to various diseases, including metabolic syndrome. The aim of this study was to examine the effect of low and high doses of a vitamin D supplement on the serum levels of 25(OH)D3 and insulin resistance. A total of 120 females were recruited in this study and supplemented weekly with 25,000 IU vitamin D or 50,000 IU vitamin D for three months. Anthropometric measurements were taken at the beginning of the study. Blood samples were collected at the beginning of the study to determine the baseline of the clinical variables and collected again after three months. Insulin resistance was measured using Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). After vitamin D supplementation, a non-significant increase was observed in the serum levels of 25(OH)D3 in the group treated with a low dose of vitamin D (LDVD) and a highly significant increase was seen in the group treated with a high dose of vitamin D (HDVD). In the group treated with a higher dose (HDVD), a significant improvement in insulin sensitivity was observed. The high dose of vitamin D (50,000 IU) supplementation was more effective in both correcting the blood levels of vitamin D and improving the sensitivity of insulin.

The Weak Relationship between Vitamin D Compounds and Glucose Homeostasis Measures in Pregnant Women with Obesity: An Exploratory Sub-Analysis of the DALI Study

Studies on the relationship between vitamin D (VitD) and glucose homeostasis usually consider either total VitD or 25OHD3 but not 25OHD2 and epimers. We aimed to evaluate the cross-sectional association of VitD compounds with glucose homeostasis measurements in pregnant women with overweight/obesity participating in the Vitamin D And Lifestyle Intervention for Gestational Diabetes Mellitus Prevention study. Methods: The analysis included 912 women. Inclusion criteria: <20 weeks gestation, body mass index ≥29 kg/m2 and information on exposure and outcome variables at baseline. Measurements: A 75 g OGTT at <20, 24−28 and 35−37 weeks gestation (except if previous diabetes diagnosis). Exposure variables: 25OHD2, 25OHD3 and C3-epimer. Outcome variables: fasting and post-challenge insulin sensitivity and secretion indices, corresponding disposition indices (DI), plasma glucose at fasting and 1 and 2 h, hyperglycemia in pregnancy (HiP). Statistics: Multivariate regression analyses with adjustment. Results: Baseline VitD sufficiency was 66.3%. Overall, VitD compounds did not show strong associations with any glucose homeostasis measures. 25OHD3 showed direct significant associations with: FPG at <20 and 24−28 weeks (standardized β coefficient (β) 0.124, p = 0.030 and 0.111, p = 0.026 respectively), 2 h plasma glucose at 24−28 weeks (β 0.120, p = 0.018), and insulin sensitivity (1/HOMA-IR, β 0.127, p = 0.027) at 35−37 weeks; it showed an inverse association with fasting DI (QUCKI*HOMA-β) at <20 and 24−28 weeks (β −0.124, p = 0.045 and β −0.148, p = 0.004 respectively). 25OHD2 showed direct associations with post-challenge insulin sensitivity (Matsuda, β 0.149, p = 0.048) at 24−28 weeks) and post-challenge DI (Matsuda*Stumvoll phase 1) at 24−28 and 35−37 weeks (β 0.168, p = 0.030, β 0.239, p = 0.006). No significant association with C3-epimer was observed at any time period. Conclusions: In these women with average baseline VitD in sufficiency range, VitD compounds did not show clear beneficial associations with glucose homeostasis measures.

Associations of Vitamin D Level and Glucoregulatory Parameters in Type 2 Diabetes Mellitus

Vitamin D is known to affect the functions of pancreatic beta cells, but the effects of vitamin D deficiency on glucoregulatory mechanisms are still inconclusive. The aim of this study was to link vitamin D levels with parameters of insulin resistance and insulin secretion. The study included 70 male and female participants, 40 newly diagnosed patients with type 2 diabetes mellitus (T2DM) and 30 healthy controls. All participants were tested for fasting glucose, hemoglobin A1c, fasting insulin, vitamin D levels, and the HOMA indexes were calculated using HOMA2 calculator. Fasting glucose levels, insulinemia, hemoglobin A1c levels and HOMA IR were all significantly higher in the diabetic group (p<0.001), while vitamin D levels and HOMA S index were significantly lower (p<0.001). HOMA-B values did not differ between the two groups (p=0.31). Vitamin D levels moderately correlated with HOMA S and HOMA B indexes (r=0.466, p<0.001; r=0.394, p<0.001, respectively), whereas a negative correlation was found between vitamin D levels and HOMA IR (r=−0.285; p<0.001). Multiple regression analysis showed that vitamin D levels significantly predicted the values of HOMA B index (p=0.001), but they had no predictive value on HOMA IR (p=0.26). In conclusion, the group of newly diagnosed patients with T2DM showed significantly lower vitamin D values compared to the healthy control group. The connection between vitamin D, glucose levels, hemoglobin A1c and insulin secretion index underlines the role of this vitamin in glucoregulation.

Vitamin D Deficiency Is Inversely Associated with Homeostatic Model Assessment of Insulin Resistance

The study was conducted to comprehensively assess the association of the concentration of vitamin D in the blood and insulin resistance in non-diabetic subjects. The objective was to pool the results from all observational studies from the beginning of 1980 to August 2021. PubMed, Medline and Embase were systematically searched for the observational studies. Filters were used for more focused results. A total of 2248 articles were found after raw search which were narrowed down to 32 articles by the systematic selection of related articles. Homeostatic Model Assessment of Insulin Resistance (HOMAIR) was used as the measure of insulin resistance and correlation coefficient was used as a measure of the relationship between vitamin D levels and the insulin resistance. Risk of bias tables and summary plots were built using Revman software version 5.3 while Comprehensive meta-analysis version 3 was used for the construction of forest plot. The results showed an inverse association between the status of vitamin D and insulin resistance (r = -0.217; 95% CI = -0.161 to -0.272; p = 0.000). A supplement of vitamin D can help reduce the risk of insulin resistance; however further studies, like randomized controlled trials are needed to confirm the results.

Insulin Resistance Is Inversely Associated with the Status of Vitamin D in Both Diabetic and Non-Diabetic Populations

Vitamin D has been implicated in the regulation of glucose metabolism and insulin resistance. We designed this study to provide evidence that insulin resistance is dependent on the concentration of vitamin D in the body. Forty observational studies of both type 2 diabetes mellitus patients and healthy subjects were included in this meta-analysis. Related articles were searched from Embase, PubMed, and Medline through January 2021. Filters for search were used to obtain more focused results. We used Comprehensive Meta-Analysis Version 3 for the construction of forest plots. RevMan software version 5.3 was used to build the risk of bias tables and summary plots. The observational studies included in this systematic review and meta-analysis showed an inverse relationship of insulin resistance with the status of vitamin D both in non-diabetic (r = -0.188; 95% CI = -0.141 to -0.234; p = 0.000) and diabetic (r = -0.255; 95% CI = -0.392 to -0.107, p = 0.001) populations. From the meta-analysis we concluded that hypovitaminosis D is related to increased levels of insulin resistance in both type 2 diabetes patients and the healthy population all over the world.

The correlation between vitamin D, glucose homeostasis and androgen level among polycystic ovary syndrome patients: a cross-sectional study

MATERIAL AND METHODS

A total of 290 women with PCOS participated in this cross-sectional study. Glucose homeostasis was assessed by a 75-g oral glucose tolerance test and the concentration of serum 25-hydroxy vitamin D was determined among all subjects. The homeostasis model assessment of insulin resistance (HOMA-IR) was taken as the indicator of insulin resistance. Beta cell function was estimated using the insulinogenic index and the disposition index. Free androgen index (FAI) was used to represent the androgen level.

RESULTS

In our study, 7.2% of the patients had Vit D severe deficiency, 75.2% had Vit D deficiency and 15.5% had vit D insufficiency. The level of serum 25(OH)D showed a significant positive association with insulinogenic index (r = 0.147, p < .05), disposition index (r = 0.280, p < .05), and SHBG (r = 0.178, p < .05) but exhibited a negative association with HOMA-IR (r = -0.198, p < .05), FAI (r = -0.178, p < .05). Adjusted age and BMI, 25(OH)D would be the dependent variable on disposition index [B = 0.259, 95%CI(0.041,0.477)] and FAI [B = -0.125, 95%CI(-0.232, -0.017)].

CONCLUSIONS

According to our results, the low levels of serum 25(OH)D were common in women with PCOS, which was speculated to be associated with glucose homeostasis and the androgen level.

Milk consumption and multiple health outcomes: umbrella review of systematic reviews and meta-analyses in humans

In order to recapitulate the best available evidence of milk consumption and multiple health-related outcomes, we performed an umbrella review of meta-analyses and systematic reviews in humans. Totally, 41 meta-analyses with 45 unique health outcomes were included. Milk consumption was more often related to benefits than harm to a sequence of health-related outcomes. Dose–response analyses indicated that an increment of 200 ml (approximately 1 cup) milk intake per day was associated with a lower risk of cardiovascular disease, stroke, hypertension, colorectal cancer, metabolic syndrome, obesity and osteoporosis. Beneficial associations were also found for type 2 diabetes mellitus and Alzheimer's disease. Conversely, milk intake might be associated with higher risk of prostate cancer, Parkinson’s disease, acne and Fe-deficiency anaemia in infancy. Potential allergy or lactose intolerance need for caution. Milk consumption does more good than harm for human health in this umbrella review. Our results support milk consumption as part of a healthy diet. More well-designed randomized controlled trials are warranted.

Correlating Circulating Vitamin D3 with Aspects of the Metabolic Syndrome and Nonalcoholic Fatty Liver Disease in Healthy Female Volunteers

Background: Significant inverse correlations between circulating vitamin D3 and the presence and strength of common clinical entities influenced by insulin resistance (IR) have been reported. Among these entities are common maladies such as the metabolic syndrome (MS) and nonalcoholic fatty liver disease (NAFLD). Since hypovitaminosis D3 is considered a common worldwide health disturbance, the consequences emanating from such relationships once soundly established might reasonably be ameliorated by vitamin replacement. Accordingly, a need exists for definitive confirmatory support for the existence of these linkages particularly in ordinary, relatively healthy individuals.Methodology: Many aspects of MS and NAFLD were examined in healthy females via linear regression analyses to determine significant correlations mainly using vitamin D3 and fasting blood glucose (FBG), the latter a surrogate for IR, as independent variables.Results: A descending linear regression between vitamin D3 and FBG did not reach full statistical significance, but a negative correlation of vitamin D3 with HbA1C was statistically significant and that with circulating insulin concentrations showed a downward statistical trend. These findings are consistent with previous ones by others suggesting an ameliorating effect of vitamin D3 on IR. Body weight, body mass index (BMI), and body fat correlated statistically significantly with vitamin D3 levels, as did systolic blood pressure. Again, these correlations were negative instead of positive unlike the case when FBG was the independent variable. The significant negative correlation of ALT with vitamin D3 was also consistent with previous reports that higher circulating vitamin D3 favorably influences the extent and intensity of NAFLD.Conclusions: Employing FBG as a surrogate for IR and ALT for status of NAFLD, linear correlations reasonably suggest that increasing circulating vitamin D3 can favorably influence the initial development of and/or strength of risk factors for MS including NAFLD in relatively fit females.

Vitamin-D-Binding Protein Contributes to the Maintenance of α Cell Function and Glucagon Secretion

Vitamin-D-binding protein (DBP) or group-specific component of serum (GC-globulin) carries vitamin D metabolites from the circulation to target tissues. DBP is highly localized to the liver and pancreatic α cells. Although DBP serum levels, gene polymorphisms, and autoantigens have all been associated with diabetes risk, the underlying mechanisms remain unknown. Here, we show that DBP regulates α cell morphology, α cell function, and glucagon secretion. Deletion of DBP leads to smaller and hyperplastic α cells, altered Na+ channel conductance, impaired α cell activation by low glucose, and reduced rates of glucagon secretion both in vivo and in vitro. Mechanistically, this involves reversible changes in islet microfilament abundance and density, as well as changes in glucagon granule distribution. Defects are also seen in β cell and δ cell function. Immunostaining of human pancreata reveals generalized loss of DBP expression as a feature of late-onset and long-standing, but not early-onset, type 1 diabetes. Thus, DBP regulates α cell phenotype, with implications for diabetes pathogenesis.

Vitamin D Receptor Overexpression in β-Cells Ameliorates Diabetes in Mice

Vitamin D deficiency has been associated with increased incidence of diabetes, both in humans and in animal models. In addition, an association between vitamin D receptor (VDR) gene polymorphisms and diabetes has also been described. However, the involvement of VDR in the development of diabetes, specifically in pancreatic β-cells, has not been elucidated yet. Here, we aimed to study the role of VDR in β-cells in the pathophysiology of diabetes. Our results indicate that Vdr expression was modulated by glucose in healthy islets and decreased in islets from both type 1 diabetes and type 2 diabetes mouse models. In addition, transgenic mice overexpressing VDR in β-cells were protected against streptozotocin-induced diabetes and presented a preserved β-cell mass and a reduction in islet inflammation. Altogether, these results suggest that sustained VDR levels in β-cells may preserve β-cell mass and β-cell function and protect against diabetes.

Effect of High-dose Vitamin D Supplementation on Beta Cell Function in Obese Asian-Indian Children and Adolescents: A Randomized, Double Blind, Active Controlled Study

OBJECTIVE

Vitamin D deficiency has been found to be associated with insulin resistance. In an attempt to explore this association, we planned a study to investigate the effects of high-dose vitamin D supplementation on beta cell function in obese children and adolescents.

METHODS

A randomized, double blind, active-controlled study was carried out to investigate the effects of high dose (120,000 IU once a month) vitamin D supplementation in comparison to recommended daily allowance (12,000 IU/month) for 12 months. Beta cell function was assessed by disposition index. Inflammatory cytokines and cardiovascular risk factors were also assessed before and after supplementation.

RESULTS

A total of 189 obese children and adolescents were recruited. The mean serum 25OHD level of the study population was 8.36 ± 5.45 ng/ml. At baseline, 94.7% subjects were vitamin D deficient (<20 ng/mL). After 12 months of supplementation, serum 25OHD level in intervention group was 26.89 ± 12.23 ng/mL, while in control group, it was 13.14 ± 4.67 ng/mL (P < 0.001). No significant difference in disposition index as well as other parameters of insulin resistance, sensitivity, inflammatory cytokines, and pulse wave velocity was seen after supplementation.

CONCLUSION

Vitamin D supplementation in doses of 120,000 IU per month for 12 months in obese Asian-Indian children and adolescents did not affect beta cell function as well as cardiovascular risk factors.

Vitamin D and cardiometabolic disorders: a review of current evidence, genetic determinants and pathomechanisms

Vitamin D deficiency has been implicated in the pathophysiology of cardiometabolic disorders including obesity, type 2 diabetes mellitus, cardiovascular diseases and polycystic ovary syndrome. Despite a large number of experimental and observational studies supporting a role for vitamin D in these pathologies, randomized controlled trials have reported little to no effect of vitamin D supplementation in the prevention or treatment of these disorders, although some results remain ambiguous. Polymorphisms in genes related to vitamin D metabolism, particularly in the vitamin D receptor and binding protein and the metabolizing enzyme 1-α-hydroxylase, have emerged as potential contributors to these divergent results. It is now becoming increasingly recognized that the effects and potential benefits of vitamin D supplementation may vary by several factors including vitamin D deficiency status, ethnicity and/or the presence of genetic variants, which affect individual responses to supplementation. However, these factors have seldom been explored in the available literature. Future trials should consider inter-individual differences and, in particular, should aim to clarify whether certain subgroups of individuals may benefit from vitamin D supplementation in the context of cardiometabolic health.

Longitudinal association of 25-hydroxyvitamin D with adipokines and markers of glucose metabolism among Brazilian pregnant women

This study aimed to evaluate the longitudinal association of vitamin D status with glycaemia, insulin, homoeostatic model assessment of insulin resistance, adiponectin and leptin. A prospective cohort with 181 healthy, pregnant Brazilian women was followed at the 5th–13th, 20th–26th and 30th–36th gestational weeks. In this cohort, 25-hydroxyvitamin D (25(OH)D) plasma concentrations were analysed using liquid chromatography–tandem MS. Vitamin D status was categorised as sufficient or insufficient using the Endocrine Society Practice Guidelines (≥75/<75 nmol/l) and the Institute of Medicine (≥50/<50 nmol/l) thresholds. Linear mixed-effect regression models were employed to evaluate the association between vitamin D status and each outcome, considering interaction terms between vitamin D status and gestational age (P<0·1). At baseline, 70·7 % of pregnant women had 25(OH)D levels <75 nmol/l and 16 % had levels <50 nmol/l. Women with sufficient vitamin D status at baseline, using both thresholds, presented lower glycaemia than those with insufficient 25(OH)D. Pregnant women with 25(OH)D concentrations <75 nmol/l showed lower insulin (β=−0·12; 95 % CI −0·251, 0·009;P=0·069) and adiponectin (β=−0·070; 95 % CI −0·150, 0·010;P=0·085) concentrations throughout pregnancy than those with 25(OH)D levels ≥75 nmol/l. Pregnant women with 25(OH)D <50 nmol/l at baseline presented significantly higher leptin concentrations than those with 25(OH)D levels ≥50 nmol/l (β=−0·253; 95 % CI −0·044, 0·550;P=0·095). The baseline status of vitamin D influences the biomarkers involved in glucose metabolism. Vitamin D-sufficient women at baseline had higher increases in insulin and adiponectin changes throughout gestation than those who were insufficient.

Effect of oral vitamin D supplementation on glycemic control in patients with type 2 diabetes mellitus with coexisting hypovitaminosis D: A parellel group placebo controlled randomized controlled pilot study

CONTEXT

Vitamin D supplementation in type 2 diabetes mellitus patients may lead to improved glycemic control by improving insulin secretion and decreasing insulin resistance.

AIMS

To investigate effect of oral vitamin D supplementation on glycemic control, in patients with type 2 diabetes mellitus and coexisting hypovitaminosis D.

SETTINGS AND DESIGN

Randomized, Parallel Group, Placebo Controlled Trial carried out in a tertiary care hospital of Indian Armed Forces.

METHODS AND MATERIAL

Sixty patients with coexisting type 2 diabetes mellitus and hypovitaminosis D were randomized into cases and controls and were supplemented with oral Vitamin D and microcrystalline cellulose respectively for six months. Subjects' HbA1c and vitamin D levels were monitored at the beginning and end of the study, fasting plasma glucose (FPG) & post prandial plasma glucose (PPPG) during monthly OPD visits.

STATISTICAL ANALYSIS USED

Intra-group comparison was made by paired t test & unpaired t test was used for inter-group (A v/s B) comparisons. Repeated measures ANOVA was undertaken to compare values over time.

RESULTS

The two groups were comparable for all parameters at baseline. Case group showed significant decrease in mean HbA1c levels (7.29% to 7.02%; P = 0.01), mean FPG levels (131.4 to 102.6 mg/dl; P = 0.04) and mean PPPG levels (196.2 to 135.0 mg/dl; P < 0.001). Incidentally, significant improvement in systolic as well as diastolic blood pressure and total cholesterol was also noted in the cases, while for LDL cholesterol improvement tended towards significance (p = 0.05).

CONCLUSIONS

We found that oral vitamin D supplementation was associated with improved glycemic control and other metabolic parameters in patients with type 2 diabetes mellitus. Supplementation to achieve normal levels of vitamin D can be a promising adjuvant therapy for T2DM patients & coexisting hypovitaminosis D.

Impact of vitamin D treatment on 25 hydroxy vitamin D levels and insulin homeostasis in obese African American adolescents in a randomized trial

BACKGROUND

Obesity is affecting children in epidemic proportions in the United States with nearly 25% of children being obese. Consequences of obesity including dyslipidemia, type 2 diabetes and cardiovascular disease are leading to morbidity at younger ages. Parallel to the obesity and diabetes epidemics, the prevalence of vitamin D deficiency has reached very high levels and has been associated with insulin resistance and dyslipidemia. Studies exploring the impact of vitamin D repletion on insulin sensitivity and dyslipidemia in children are sparse.The aim of this study was to determine the impact of treatment with vitamin D (ergocalciferol) in obese African American (AA) children on vitamin D levels and insulin secretion and sensitivity.

METHODS

This pilot study was conducted in a tertiary care Pediatric Emergency Department (ED). African American obese children (n = 29; 22 female) 13-17 y, with 25-hydroxy vitamin D level [25(OH)D] <20 ng/ml, were randomized to receive either 50,000 IU vitamin D2/week or a placebo for 12 weeks. Pre- and post- oral glucose tolerance testing with glucose and insulin levels drawn at 0, 30, 60, 90 and 120 min were performed. Pre/post intervention lipid profiles and calcium levels were also evaluated.

RESULTS

There was no difference in serum 25(OH)D between groups at baseline. Follow-up 25(OH)D level was greater in the treatment vs. placebo group, and significantly increased from baseline in the treatment group only. However, there was no difference between groups in baseline vs. follow-up insulin- or lipid-related parameters. Follow-up serum 25(OH)D was positively correlated with fasting insulin and high-density lipoprotein (HDL) level in the vitamin D treated group only.

CONCLUSION

While serum 25(OH)D levels in obese AA teens increased adequately with vitamin treatment for 12 weeks and correlated with fasting insulin, it did not significantly impact insulin secretion or sensitivity. Larger studies are required over a longer period of time to confirm and explore the reasons for this finding.

Is Hypovitaminosis D Related to Incidence of Type 2 Diabetes and High Fasting Glucose Level in Healthy Subjects: A Systematic Review and Meta-Analysis of Observational Studies

There is evidence that vitamin D status is associated with type 2 diabetes. Many observational studies have been performed investigating the relationship of vitamin D status and circulating biomarkers of glycemic regulation. To find out whether this association holds, we conducted a systematic review and meta-analysis of cross sectional and longitudinal studies. We searched Pubmed, Medline and Embase, all through June 2017. The studies were selected to determine the effect of vitamin D on the parameters of glucose metabolism in diabetic and non-diabetic subjects. Correlation coefficients from all studies were pooled in a random effects meta-analysis. The risk of bias was assessed using Grading of Recommendations Assessment, Development and Evaluation (GRADE) system. We found significant inverse relationship of vitamin D status with glycemic level in both diabetic (r = -0.223, 95% CI = -0.184 to -0.261, p = 0.000) and non-diabetic (r = -0.073, 95% CI = -0.052 to -0.093, p = 0.000) subjects. This meta-analysis concludes that hypovitaminosis D is associated with increased risk of hyperglycemia both in diabetic and non-diabetic subjects. A future strategy for the prevention of impaired glycemic regulation could be individualized supplementation of vitamin D.

Bone Disease and Serum Fibroblast Growth Factor-23 Levels in Renal Transplant Recipients

BACKGROUND

Posttransplantation bone disease develops commonly and results in important complications. In this study, we aimed to investigate the relationship between bone diseases and serum fibroblast growth factor-23 (FGF-23) in renal transplant recipients.

METHODS

This study was conducted in 106 kidney transplant recipients (KTrs; group G1) and 30 patients with chronic kidney disease (group G2). Patients with fever, heart failure, angina pectoris, acute renal failure, malignant disease, or any gastrointestinal disease were excluded. KTrs were treated with triple immunosuppressive drugs including glucocorticoids. Complete blood count (CBC), blood urea nitrogen (BUN), creatinine, glomerular filtration rate (GFR, Modification of Diet in Renal Disease [MDRD] formula), lipid profile, calcium (Ca), phosphorous (P), parathormone (PTH), 25OHD3, serum levels of tacrolimus/cyclosporine, and intact FGF-23 were measured. Bone mineral density (BMD) was measured with dual energy X-ray absorptiometry.

RESULTS

The mean patient age was 40.1 ± 11.1 years and 39.2 ± 11.3 years in G1 and G2, respectively (P > .05). In G1 and G2, 76 and 15 patients were male, respectively. Compared with the G2 patients, G1 patients had lower body mass index (BMI), serum glucose levels, P, Mg, and Ca·P (P < .05 for all). T scores of the lumbar vertebrae/femur were -1.82 ± 0.99/-1.34 ± 0.89 and -1.13 ± 1.34/-0.51 ± 1.18 in G1 and G2 patients, respectively (P < .05 for all). The incidences of osteopenia/osteoporosis in the lumbar spine and femur were 50.9%/27.4% and 57.5%/10.4% in G1 and 16.6%/23.3%, and 40%/3.3% in G2. There were positive correlations between BMD and BMI, the time elapsed after renal transplantation, and GFR. In our study, a statistically significant relationship was found between lipid parameters and BMD, PTH, and 250HD3 levels, as well as use of corticosteroid and calcineurin inhibitors (P < .05 for all). In G1 and G2, BMD of the lumbar spine in patients with serum creatinine >1.5 mg/dL was lower than that in patients with serum creatinine <1.5 mg/dL.

CONCLUSION

The association between age and BMD was found only in the femur of KTrs. No relationship was observed between serum FGF-23 levels and BMD values. In both groups, the BMD T score of the lumbar spine was lower compared to the BMD T score of the femur and in patients with serum creatinine >1.5 mg/dL. In long-term follow-up of renal transplantation by as much as 58 months, the incidence of bone disease such as osteoporosis/osteopenia was as high as 67% and was also higher than that of nontransplant patients with similar GFR. In addition to decreased renal function, dyslipidemia, inflammation, and continuing hypophosphatemia were also accompanied by decreased BMD as in cardiovascular disease in KTrs.

T-lymphocyte and glycemic status after vitamin D treatment in type 1 diabetes: A randomized controlled trial with sequential crossover

BACKGROUND

Type 1 diabetes mellitus (T1D) is mediated by autoaggressive T effector cells with an underlying regulatory T-cell (Treg) defect. Vitamin D deficiency is highly prevalent in T1D, which can aggravate immune dysfunction. High-dose vitamin D treatment may enhance Tregs and improve metabolism in T1D patients.

METHODS

In a randomized double-blind placebo-controlled trial with crossover design, patients received either for 3 months cholecalciferol 4000 IU/d followed by 3 months placebo or the sequential alternative. Thirty-nine T1D patients (19 women and 20 men) completed the trial.

RESULTS

Primary outcome was a change of Tregs, secondary HbA1C, and insulin demand. Effects were evaluated based on intra-individual changes between treatment and placebo periods for outcome measures. Exploratory analyses included vitamin D system variant genotyping and C-peptide measurements. Median 25(OH)D₃ increased to 38.8 ng/ml with males showing a significantly stronger increase (p = .003). T-lymphocyte profiles did not change significantly (p > 2); however, the intra-individual change of Tregs between males and females was different with a significantly stronger increase in men (p = .017), as well as between genotypes of the vitamin D receptor (Apa, Taq, and Bsm: genotypes aa, TT, and bb; p = .004-0.015). Insulin demands declined significantly (p = .003-.039) and HbA1C improved (p < .001). Random C-peptide levels were low but rising (median, 0.125 ng/ml; range, 0.02-0.3) in 6 patients. No toxicity was observed.

CONCLUSION

A daily vitamin D dose of 4000 IU for 3 months was well tolerated and enhanced Tregs in males. Glucometabolic control improved in all. Subsequent larger trials need to address ß-cell function and genotyping for individualized vitamin D doses.

Pharmacokinetics and effects of demographic factors on blood 25(OH)D3 levels after a single orally administered high dose of vitamin D3

AIM

To examine the biological consequences and demographic factors that might affect the pharmacokinetics of vitamin D3 after a single high dose intervention in a young Chinese population with vitamin D insufficiency status.

METHODS

A total of 28 young subjects (25 to 35 years old) with vitamin D insufficiency status [serum 25(OH)D <30 ng/mL] was recruited in Shanghai, China. The subjects were orally administered a single high dose of vitamin D3 (300 000 IU). Baseline characteristics and blood samples were collected at d 0, 1, 2, 3, 7, 28, 56, 84 and 112 after the intervention. The blood biomarker levels were determined with standardized methods.

RESULTS

The intervention markedly increased the blood 25(OH)D3 levels within the first five days (mean T_max=5.1±2.1 d) and sustained an optimal circulating level of 25(OH)D3 (≥30 ng/mL) for 56 d. After the intervention, body weight and baseline 25(OH)D3 levels were significantly correlated with circulating 25(OH)D3 levels. No adverse events and no consistently significant changes in serum calcium, creatinine, glucose, parathyroid hormone, vitamin D binding protein, or the urinary calcium/reatinine ratio were observed. However, there was a significant increase in phosphorus after the vitamin D3 intervention. Total cholesterol and triglyceride levels were decreased at the end of the trial.

CONCLUSION

The pharmacokinetics of vitamin D after intervention were influenced by baseline 25(OH)D3 levels and the body weight of the subjects. The results suggest that a single high oral vitamin D3 intervention is safe and efficient for improving the vitamin D status of young Chinese people with vitamin D insufficiency.

Metabolic effects of vitamin D supplementation in vitamin D deficient patients (a double-blind clinical trial)

BACKGROUND

Vitamin D has recently been given a lot of attention for its role in controlling insulin secretion. Many studies have spoken of its role in weight management, blood sugar control and many other metabolic variables.

PATIENT AND METHODS

In a randomized double-blind clinical trial, 210 people with vitamin D deficiency were randomly allocated into two groups receiving vitamin D (50,000 units per week) or placebo for 8 weeks.

RESULTS

Vitamin D levels were significantly increased in the group receiving vitamin D supplementation (13.7±5.2 unit increase versus 0.8±2.8). The increased levels of vitamin D lead to significant changes in fasting insulin levels (6.8±8.1 unit reduction versus 2.3±3.7), a 2-h insulin (31.1±34.9 unit reduction versus 4.5±24.6) and Homeostasis Model Assessment (HOMA) indices.

CONCLUSION

Correction of vitamin D deficiency leads to increased insulin sensitivity that was significantly able to maintain glucose in the normal range with lower levels of insulin.

No Effect of High-Dose Vitamin D Treatment on β-Cell Function, Insulin Sensitivity, or Glucose Homeostasis in Subjects With Abnormal Glucose Tolerance: A Randomized Clinical Trial

OBJECTIVE

There has been conflicting evidence regarding the potential role of vitamin D in glucose homeostasis. This study was designed to investigate the effect of high-dose vitamin D3 treatment on β-cell function, insulin sensitivity, and glucose tolerance in subjects with prediabetes or diet-treated type 2 diabetes.

RESEARCH DESIGN AND METHODS

Subjects (n = 44) were randomized to 30,000 IU vitamin D3 once weekly or placebo for 8 weeks. Hyperglycemic clamp assessed first-phase (0-12 min) and second-phase (12-120 min) insulin response, insulin sensitivity, and disposition index (DI). An oral glucose tolerance test assessed glucose tolerance and glycosylated hemoglobin assessed glycemic control.

RESULTS

A total of 21 (vitamin D) and 22 (placebo) subjects completed the study, respectively. Season-adjusted 25-OH-vitamin D [25(OH)D] levels were doubled in the active treated group (43-82 nmol/L). No effect of vitamin D treatment, compared with placebo, was seen on first-phase or second-phase insulin secretion. There were no group differences in insulin sensitivity, DI, or any measures of glycemic control. No hypercalcemia or other adverse effects of vitamin D treatment were seen compared with placebo. Subgroup analyses of those with the lowest basal and greatest increase in 25(OH)D levels did not change these results.

CONCLUSIONS

This study gives no support for any substantial effect of high-dose vitamin D treatment for 8 weeks in prediabetes or diet-treated type 2 diabetes on β-cell function, insulin sensitivity, or glycemic control.

Effects of vitamin D repletion on glycemic control and inflammatory cytokines in adolescents with type 1 diabetes

OBJECTIVE

Little is known about the relationship between vitamin D deficiency and adolescents with type 1 diabetes. On the basis of adult studies showing that vitamin D improves insulin sensitivity and decreases inflammatory cytokines linked to microvascular complications, we hypothesized that treating vitamin D deficiency in adolescents with type 1 diabetes would improve glycemia and reduce inflammatory markers.

RESEARCH DESIGN AND METHODS

This was a randomized, prospective, crossover study of 25 adolescents with type 1 diabetes for at least a year (aged: 13-21 yr; 62% female; 62% Hispanic) and vitamin D deficiency (25-OH vitamin D ≤30 ng/mL). Subjects received vitamin D3 (20 000 IU/week) for 6 months, either immediately or after 6 months of observation.

RESULTS

At baseline, 63% of subjects screened were vitamin D deficient and randomized. Interleukin-6 (IL-6) was significantly higher in the vitamin D deficient group compared with the sufficient group (medians: 0.36 vs. 0.18) (p = 0.026), whereas neither C-reactive protein (CRP) nor tumor necrosis factor-α (TNF-α) differed. Vitamin D treatment increased serum levels of 25-OH vitamin D from 22 ± 5.3 to 34.3 ± 12.1 ng/mL (p < 0.01). However, treatment did not affect glycated hemoglobin (HbA1c), insulin dosage, CRP, interleukin-6 (IL-6), or TNF-α.

CONCLUSIONS

Vitamin D deficiency is prevalent in the adolescent type 1 diabetes population, and could be associated with changes in inflammatory markers. However, vitamin D repletion over 6 months did not affect glycemia or markers of inflammation in our study, highlighting the need for additional research to validate these findings.

The effect of vitamin D supplementation on gestational diabetes in high-risk women: Results from a randomized placebo-controlled trial

Background:

Vitamin D deficiency is common in pregnancy, leading to increase in the frequency of preeclampsia, cesarean delivery, neonatal bacterial vaginosis, and gestational diabetes. The current study was designed and implemented to investigate the effect of vitamin D during the first and second trimesters of pregnancy in reducing the risk of gestational diabetes mellitus (GDM) in women who are at high risk [history of GDM, birth macrosomia, family history, and high body mass index (BMI)].

Materials and Methods:

In a randomized, double-blind, and placebo-controlled trial, 90 pregnant women who had at least one risk factor for GDM were randomized into intervention (46 participants) and control (44 participants) groups. Participants in the intervention group took 5000 units of vitamin D daily and the control group took placebo until the 26th week of pregnancy. Then the glucose challenge test (GCT) and the glucose tolerance test (GTT) were performed to evaluate GDM.

Results:

Mean ± standard deviation (SD) age was 31.28 ± 6.38 years and 29 ± 6.24 years for the intervention group and the placebo group, respectively, (P > 0.05). In addition, there were no significant differences between two groups in terms of vitamin D levels and GCT (P > 0.05), and the difference was not significant. The incidence of diabetes in the intervention groups was statistically lower than in control group (11.4% vs 34.8; P < 0.01). The results showed that abnormal GCT in the placebo group was statistically higher than in intervention group (35.9% vs 10.9 P < 0.005).

Conclusion:

The results of the current study showed that the prescription of vitamin D supplementation in the first and second trimesters of pregnancy was effective in reducing GDM and controlling GTT and GTC.

Causes of Vitamin D Deficiency and Effect of Vitamin D Supplementation on Metabolic Complications in Obesity: a Review

Obese subjects are often characterized by low plasma 25-hydroxy-vitamin D (25OHD) levels. Many explanations for this association have been proposed. Low plasma 25OHD is associated with obesity-related comorbidities such as insulin resistance, type 2 diabetes mellitus, and low-grade inflammation. In this review, we discuss the proposed mechanisms for low 25OHD in obesity and explore the results of recent RCTs on vitamin D (VD) supplementation on obesity and its metabolic complications such as insulin resistance and type 2 diabetes. Although the results from these clinical randomized controlled trials vary, the general picture is that VD treatment of obese individuals does not seem to be an effective treatment of obesity-related metabolic complications.

The Apparent Relation between Plasma 25-Hydroxyvitamin D and Insulin Resistance is Largely Attributable to Central Adiposity in Overweight and Obese Adults

BACKGROUND

Research indicates that plasma 25-hydroxyvitamin D [25(OH)D] is associated with insulin resistance, but whether regional adiposity confounds this association is unclear.

OBJECTIVE

This study assessed the potential influence of adiposity and its anatomical distribution on the relation between plasma 25(OH)D and insulin resistance.

METHODS

A secondary analysis of data from middle-aged overweight and obese healthy adults [n = 336: 213 women and 123 men; mean ± SD (range); age: 48 ± 8 y (35-65 y); body mass index (BMI; in kg/m2): 30.3 ± 2.7 (26-35)] from West Lafayette, Indiana (40.4 °N), were used for this cross-sectional analysis. Multiple linear regression analyses that controlled for multiple covariates were used as the primary statistical model.

RESULTS

Of all participants, 8.6% and 20.5% displayed moderate [20.1-37.5 nmol/L plasma 25(OH)D] to mild (37.6-49.9 nmol/L) vitamin D insufficiency, respectively. A regression analysis controlling for age, sex, race, plasma parathyroid hormone concentration, season of year, and supplement use showed that 25(OH)D was negatively associated with fasting insulin (P = 0.021). Additional regression analyses showed that total and central adiposity but not peripheral adiposity predicted low plasma 25(OH)D [total fat mass index (FMI): P = 0.018; android FMI: P = 0.052; gynoid FMI: P = 0.15; appendicular FMI: P = 0.07) and insulin resistance (homeostasis model assessment of insulin resistance: total and android FMI, P <0.0001; gynoid FMI, P = 0.94; appendicular FMI, P = 0.86). The associations of total and central adiposity with insulin resistance remained significant after adjusting for plasma 25(OH)D. However, adjusting for central adiposity but not other anatomical measures of fat distribution eliminated the association between plasma 25(OH)D and insulin resistance.

CONCLUSION

Central adiposity drives the association between plasma 25(OH)D and insulin resistance in overweight and obese adults. The trial was registered at clinicaltrials.gov as NCT00812409.

Effect of vitamin D supplementation on insulin kinetics and cardiovascular risk factors in polycystic ovarian syndrome: a pilot study

To assess the effect of vitamin D supplementation on parameters of insulin sensitivity/resistance (IS/IR) and insulin secretion in subjects with polycystic ovarian syndrome (PCOS). A prospective double-blind randomized control trial was conducted to assess the effect of vitamin D on insulin kinetics in women with PCOS. The trial was conducted in a tertiary care research hospital. A total of 36 subjects with PCOS, aged 18-35 years, were included in this study. Vitamin D3 4000 IU/day versus placebo was given once a month for 6 months and both groups received metformin. IS (by whole-body IS index or Matsuda index), IR (by homeostasis model assessment IR (HOMA-IR)), and insulin secretion (by insulinogenic index; II30) were the main outcome measures. Secondary outcome included blood pressure (BP), lipid profile, disposition index (DI), and vascular stiffness. Out of 36 subjects who consented, 32 completed the study. Subjects were randomized into two groups: group A (n=15; metformin and vitamin D 4000 IU/day) or group B (n=17; metformin and placebo). Oral glucose tolerance tests with 75 g glucose were carried out at baseline and 6 months after supplementation. Hypovitaminosis D was observed in 93.8% of all subjects with mean serum 25 hydroxy vitamin D level of 7.30±4.45 ng/ml. After 6 months of vitamin D supplementation, there was no significant difference in any of the parameters of IS/IR (area under curve (AUC)-glucose, AUC-insulin, insulin:glucose ratio, HOMA-IR, Matsuda index, insulinogenic index, and DI), II30, and cardiovascular risk factors between the two groups. Supplementation of vitamin D, at a dose of 4000 IU/day for 6 months, did not have any significant effect on parameters of IS/IR and insulin secretion in subjects with PCOS.

Vitamin D Status in Women with Gestational Diabetes Mellitus during Pregnancy and Postpartum

Of many vitamin D extraskeletal functions, its modulatory role in insulin secretion and action is especially relevant for gestational diabetes mellitus (GDM). The aims of the present study were to determine midgestational and early postpartum vitamin D status in pregnant women with and without GDM and to describe the relationship between midgestational and postpartum vitamin D status and parallel changes of glucose tolerance. A total of 76 pregnant women (47 GDM and 29 healthy controls) were included in the study. Plasma levels of 25(OH)D were measured using an enzyme immunoassay. Vitamin D was not significantly decreased in GDM compared to controls during pregnancy; however, both groups of pregnant women exhibited high prevalence of vitamin D deficiency. Prevalence of postpartum 25(OH)D deficiency in post-GDM women remained significantly higher and their postpartum 25(OH)D levels were significantly lower compared to non-GDM counterparts. Finally, based on the oGTT repeated early postpartum persistent glucose abnormality was ascertained in 15% of post-GDM women; however, neither midgestational nor postpartum 25(OH)D levels significantly differed between subjects with GDM history and persistent postpartum glucose intolerance and those with normal glucose tolerance after delivery.

Vitamin D Actions on CD4(+) T Cells in Autoimmune Disease

This review summarizes and integrates research on vitamin D and CD4⁺ T-lymphocyte biology to develop new mechanistic insights into the molecular etiology of autoimmune disease. A deep understanding of molecular mechanisms relevant to gene–environment interactions is needed to deliver etiology-based autoimmune disease prevention and treatment strategies. Evidence linking sunlight, vitamin D, and the risk of multiple sclerosis and type 1 diabetes is summarized to develop the thesis that vitamin D is the environmental factor that most strongly influences autoimmune disease development. Evidence for CD4⁺ T-cell involvement in autoimmune disease pathogenesis and for paracrine calcitriol signaling to CD4⁺ T lymphocytes is summarized to support the thesis that calcitriol is sunlight’s main protective signal transducer in autoimmune disease risk. Animal modeling and human mechanistic data are summarized to support the view that vitamin D probably influences thymic negative selection, effector Th1 and Th17 pathogenesis and responsiveness to extrinsic cell death signals, FoxP3⁺CD4⁺ T-regulatory cell and CD4⁺ T-regulatory cell type 1 (Tr1) cell functions, and a Th1–Tr1 switch. The proposed Th1–Tr1 switch appears to bridge two stable, self-reinforcing immune states, pro- and anti-inflammatory, each with a characteristic gene regulatory network. The bi-stable switch would enable T cells to integrate signals from pathogens, hormones, cell–cell interactions, and soluble mediators and respond in a biologically appropriate manner. Finally, unanswered questions and potentially informative future research directions are highlighted to speed delivery of etiology-based strategies to reduce autoimmune disease.

Vitamin D and its effects on glucose homeostasis, cardiovascular function and immune function

In recent years there has been increasing interest in the non-skeletal effects of vitamin D. It has been suggested that vitamin D deficiency may influence the development of diabetes, cardiovascular dysfunction and autoimmune diseases. This review focuses on the current knowledge of the effects of vitamin D and its deficiency on cardiovascular function, glucose homeostasis and immune function, with a particular focus on children. Although, there is good evidence to show that there is an association between vitamin D deficiency and an abnormality of the above systems, there is little evidence to show that vitamin D supplementation leads to an improvement in function, especially in childhood.

Effects of 12 weeks high dose vitamin D3 treatment on insulin sensitivity, beta cell function, and metabolic markers in patients with type 2 diabetes and vitamin D insufficiency - a double-blind, randomized, placebo-controlled trial

OBJECTIVES

Vitamin D insufficiency is common in subjects with type 2 diabetes. Observational studies suggest that vitamin D plays a role in the pathogenesis of type 2 diabetes. However, results of intervention studies have been inconsistent. We investigated the effects of improving vitamin D status on insulin sensitivity, insulin secretion, and inflammatory markers in patients with type 2 diabetes.

MATERIALS/METHODS

A double blind, randomized, placebo controlled trial was conducted. Sixteen patients with type 2 diabetes and hypovitaminosis D were recruited. Eight patients received colecalciferol and (280 μg daily for 2 weeks, 140 μg daily for 10 weeks) and 8 patients received identical placebo tablets for 12 weeks. Before and after intervention, patients underwent IVGTT, hyperinsulinemic euglycemic clamp, assessment of baseline high-frequency insulin pulsatility, glucose-entrained insulin pulsatility, DXA scans, 24-hour-ambulatory blood pressure monitorings, and fasting blood samples.

RESULTS

Serum-25(OH) vitamin D and serum-1,25(OH)₂ vitamin D increased significantly after 12 weeks in the intervention group (p=0.01, p=0.004). Serum-25(OH) vitamin D was also significantly higher in the vitamin D group compared to the placebo group (p=0.02) after intervention. Although no significant changes in insulin sensitivity, inflammation, blood pressure, lipid profile, or HbA1c were found, we observed borderline (p between 0.05 and 0.10) improvements of insulin secretion, in terms of c-peptide levels, first phase incremental AUC insulin and insulin secretory burst mass.

CONCLUSIONS

Improvement in vitamin D status does not improve insulin resistance, blood pressure, inflammation or HbA1c, but might increase insulin secretion in patients with established type 2 diabetes.

Low 25-hydroxyvitamin D level is associated with insulin sensitivity in obese adolescents with non-alcoholic fatty liver disease

AIM

The aim of this study was to investigate the relationships between 25-hydroxy-vitamin D (25(OH)D) and insulin resistance in obese adolescents with non-alcoholic fatty liver disease (NAFLD).

PATIENTS AND METHODS

Eighty-seven obese adolescents (45 girls and 42 boys, mean age: 12.7 ± 1.3 years, mean body mass index standard deviation score (BMI-SDS): 2.1 ± 0.3) and 30 lean subjects (15 girls and 15 boys, mean age: 12.3 ± 1.45 years, mean BMI-SDS: 0.5 ± 0.7) were enrolled for the study. The obese subjects were divided into two subgroups based on the presence or absence of fatty liver with high transaminases (NAFLD group and non-NAFLD group). Fasting blood samples were assayed for 25(OH)D, transaminases, glucose, and insulin levels. Insulin resistance was calculated by the homeostasis model assessment (HOMA-IR).

RESULTS

25(OH)D measurements were decreased in both obese groups (NAFLD and non-NAFLD) in comparison with the lean group (29.5 ± 18.4 vs. 41.0 ± 17.9 vs. 48.1 ± 22.2 ng/mL). However; the NAFLD group had significantly lower measurements of 25(OH)D than the non-NAFLD group (p < 0.001) and lean group (p < 0.001). 25(OH)D was negatively correlated with HOMA-IR (r = 0.158, p = 0.01) and with alanine aminotransferase (r = 0.794, p = 0.03) in the NAFLD obese group. There was no significant associations between fasting insulin, BMI-SDS and 25(OH)D in obese groups.

CONCLUSION

We suggest that low 25(OH)D occurs commonly in obese adolescents with NAFLD and we demonstrated an association between insufficient vitamin D status and low insulin sensitivity in obese adolescents with NAFLD.

Analysis of the associations between vitamin D and albuminuria or β-cell function in Chinese type 2 diabetes

Objective. To investigate the associations of 25-(OH)D and β-cell function or insulin resistance or albuminuria in Chinese type 2 diabetic patients. Methods. In total, 1408 type 2 diabetic patients without vitamin D supplement were included in this retrospective study. Results. Comparison between patients with and without 25-(OH)D deficiency indicated that, compared with patients with 25-(OH)D ≥ 50 nmol/L, patients with 25-(OH)D < 50 nmol/L showed a higher level of urine albumin-creatinine ratio (ACR) (90.15 ± 10.30 mg/g versus 52.79 ± 14.97 mg/g). Multiple regression analysis indicated that 25-(OH)D was independently and negatively correlated with urine ACR (OR = 0.985, 95%CI 0.972–0.999, P = 0.03), adjusted by age, diabetic duration, HBP duration, SBP, HbA1c, creatinine, LDL-C, triglyceride, total cholesterol, and HDL-C. Compared with patients with normal level of urine ACR, patients with higher level of urine ACR showed a significant lower level of 25-(OH)D (34.49 ± 13.52 nmol/L versus 37.46 ± 13.6 nmol/L, P = 0.00). Analysis of the associations of 25-(OH)D and β-cell function or insulin resistance showed that 25-(OH)D may not correlate with β-cell function or insulin resistance. Conclusion. 25-(OH)D was independently associated with albuminuria in Chinese type 2 diabetic patients but was not associated with β-cell function or insulin resistance.

Vitamin D and diabetes mellitus

The vitamin D endocrine system in now recognized as subserving a wide range of fundamental biological functions in cell differentiation, inhibition of cell growth as well as immunomodulation. Both forms of immunity, namely adaptive and innate, are regulated by 1,25(OH)2D3. The immune-modulatory properties of vitamin D suggest that it could play a potential therapeutic role in prevention of type 1 diabetes mellitus (T1DM). It is postulated that large doses of vitamin D supplementation may influence the pattern of immune regulation and subsequent progression to T1DM in a genetically susceptible individual. More studies are required to substantiate the relation between T1DM and vitamin D/vitamin D analogues in the pattern of immune regulations in susceptible individuals. In type 2 diabetes mellitus (T2DM), vitamin D may influence both insulin secretion and sensitivity. An inverse relationship between T2DM and vitamin D is postulated from cross-sectional and prospective studies, though conclusive proof is as yet lacking. Available studies differ in their design and in the recommended daily allowances (RDA) of vitamin D in non-skeletal diseases and β-cell function. Large, well designed, controlled, randomized interventional studies on the potential role of vitamin D and calcium in prevention and management of T2DM are required to clarify the relationship between vitamin D and glucose homeostasis in T2DM.

Vitamin D concentration, obesity, and risk of diabetes: a mendelian randomisation study

BACKGROUND

Low plasma 25-hydroxyvitamin D (25[OH]D) concentration and high BMI have been associated with increased risk of diabetes. We tested the hypotheses that genetic variants associated with low concentrations of 25(OH)D are associated with diabetes, and that the effect on diabetes of genetic variants associated with high BMI is partly mediated through reduced plasma 25(OH)D concentration.

METHODS

In this mendelian randomisation study, we genotyped 96 423 white Danes aged 20-100 years from three studies. 5037 of these participants had type 2 diabetes. All individuals were surveyed for diabetes from 1977 to 2011. 31 040 participants had their plasma 25(OH)D concentration measured and 90 169 had their BMI measured. We assessed the effects of genetic variation in DHCR7 (related to endogenous production) and CYP2R1 (related to liver conversion) on plasma 25(OH)D concentration, and the effects of variation in FTO, MCR4, and TMEM18 on BMI. We then assessed the effect of genetic variation in these genes on risk of type 2 diabetes, and the association of measured plasma 25(OH)D concentration and BMI with risk of type 2 diabetes. We did a mediation analysis to assess how much of the effect of BMI genotype on risk of diabetes was mediated through plasma 25(OH)D concentration.

FINDINGS

The odds ratios for type 2 diabetes for participants who had a 20 nmol/L reduction in plasma 25(OH)D concentration as determined by genetics were 1·51 (95% CI 0·98-2·33) for DHCR7 and 1·02 (0·75-1·37) for CYP2R1. The DHCR7 allele score was significantly associated with increased risk of type 2 diabetes (p for trend=0·04), whereas the allele score for CYP2R1 was not. For participants who had a measured 20 nmol/L reduction in plasma 25(OH)D concentration, the adjusted odds ratio for type 2 diabetes was 1·16 (1·08-1·25). For participants who had a 10 kg/m(2) increase in BMI as determined by genetics, the odds ratio for type 2 diabetes was 19·4 (6·4-59·1); this was associated with an 11·1 nmol/L (2·6-19·6) lower plasma 25(OH)D concentration. For a 10 kg/m(2) increase in measured BMI, the adjusted odds ratio for type 2 diabetes was 4·33 (3·70-5·07); this was associated with a 9·1 nmol/L (8·4-9·7) lower plasma 25(OH)D concentration. Mediation analysis showed that 3% (1-5) of the effect of BMI on risk of type 2 diabetes was mediated through lowered plasma 25(OH)D concentrations.

INTERPRETATION

Genetic variants associated with low plasma 25(OH)D concentrations are associated with type 2 diabetes and low plasma 25(OH)D concentrations might be a modest mediator between obesity and increased risk of diabetes. Genetic variants associated with endogenous production of 25(OH)D might partially explain this increased risk; however, as findings for DHCR7 were not statistically significant, our results require independent confirmation.

FUNDING

Danish Heart Foundation, Copenhagen University Hospital.

Efficacy of supplementary vitamin D on improvement of glycemic parameters in patients with type 2 diabetes mellitus; a randomized double blind clinical trial

Introduction: Studies have revealed the association between vitamin D deficiency and changes in blood glucose and insulin levels as well as sensitivity of the target tissues to insulin.

Objective: In this study, we examined the effect of adding vitamin D (cholecalciferol ; 50,000 units) to therapeutic regimen of T2DM patients compared to placebo on regulating the blood glucose and glycemic parameters.

Patients and Methods: This study was a double blind clinical trial conducted on 60 type 2 diabetes mellitus (T2DM) patients. Exclusion criteria were taking calcium, vitamin D supplements or any drugs effecting calcium and vitamin D metabolism in the past 6 months. Serum 25-Hydroxy vitamin D [25(OH)D] level was measured with ELISA method. Patients were administered weekly vitamin D supplementation (50000 units) for 12 weeks.

Results: There was no significant relation between HbA1c and 25(OH)D level prior the study (p> 0.05). After intervention, 25(OH)D level in interventional group was significantly higher compared to that of control group. HbA1c in male interventional group was significantly less than that of control group (p= 0.0068).

Conclusion: Weekly vitamin D supplementation had beneficial effect on glycemic parameters in male type 2 diabetic patients.

Vitamin D and cardiovascular disease: an appraisal of the evidence

BACKGROUND

Supplementation with vitamin D has received attention as a potential cardioprotective strategy. Biologically plausible mechanisms have been proposed to link vitamin D to coronary heart disease (CHD) prevention, and observational studies suggest an inverse association between serum 25-hydroxyvitamin D (25OHD) concentrations and CHD. Few randomized clinical trials of vitamin D supplementation and CHD have been conducted, however, and no trial with CHD as the primary prespecified outcome has been completed.

CONTENT

A search was conducted in PubMed to find prospective studies of the use of vitamin D supplementation and its relationship to cardiovascular risk factors (RFs) and/or cardiovascular disease (CVD). The exact search query was: ((vitamin D supplement*[Title/Abstract]) AND cardiovascular [Title/Abstract]) AND prospective [Title/Abstract]. This query yielded 42 results. "Randomized Controlled Trial" (article type) was used as a filter in a subsequent query with the same search terms. We review the evidence that vitamin D supplementation modifies coronary RFs, such as blood pressure, lipids, glucose tolerance, and/or affects the development of clinical CHD events. We address potential sources of confounding in observational epidemiologic studies of the relationship between serum 25OHD and CHD. We also address laboratory assay issues relevant to the reliable measurement of 25OHD.

SUMMARY

Most vitamin D supplementation trials have not demonstrated improvement in CVD, but they have tested relatively low vitamin D doses. Thus, the evidence remains inconclusive, highlighting the need for rigorous randomized trials of higher vitamin D doses with cardiovascular events as prespecified outcomes. While we await the results of ongoing trials, the recommended dietary allowances from the Institute of Medicine remain the best guidepost for nutritional requirements.

Nuclear receptors in bone physiology and diseases

During the last decade, our view on the skeleton as a mere solid physical support structure has been transformed, as bone emerged as a dynamic, constantly remodeling tissue with systemic regulatory functions including those of an endocrine organ. Reflecting this remarkable functional complexity, distinct classes of humoral and intracellular regulatory factors have been shown to control vital processes in the bone. Among these regulators, nuclear receptors (NRs) play fundamental roles in bone development, growth, and maintenance. NRs are DNA-binding transcription factors that act as intracellular transducers of the respective ligand signaling pathways through modulation of expression of specific sets of cognate target genes. Aberrant NR signaling caused by receptor or ligand deficiency may profoundly affect bone health and compromise skeletal functions. Ligand dependency of NR action underlies a major strategy of therapeutic intervention to correct aberrant NR signaling, and significant efforts have been made to design novel synthetic NR ligands with enhanced beneficial properties and reduced potential negative side effects. As an example, estrogen deficiency causes bone loss and leads to development of osteoporosis, the most prevalent skeletal disorder in postmenopausal women. Since administration of natural estrogens for the treatment of osteoporosis often associates with undesirable side effects, several synthetic estrogen receptor ligands have been developed with higher therapeutic efficacy and specificity. This review presents current progress in our understanding of the roles of various nuclear receptor-mediated signaling pathways in bone physiology and disease, and in development of advanced NR ligands for treatment of common skeletal disorders.

The effect of different doses of vitamin D supplementation on insulin resistance during pregnancy

Low serum vitamin D levels are correlated with insulin resistance during pregnancy. We have assessed the effects of different doses of vitamin D on insulin resistance during pregnancy. A randomized clinical trial was done on 120 women with a gestational age of less than 12 weeks. The women were divided into three groups randomly. Group A received 200 IU vitamin D daily, group B 50,000 IU vitamin D monthly and group C 50,000 IU vitamin D every 2 weeks from 12 weeks of pregnancy until delivery. The serum levels of fasting blood sugar (FBS), insulin, calcium and 25-hydroxyvitamin D were measured before and after intervention. We used the homeostatic model assessment of insulin resistance (HOMA-IR) as a surrogate measure of insulin resistance. The mean ± standard deviation of serum 25-hydroxyvitamin D increased in group C from 7.3 ± 5.9 to 34.1 ± 11.5 ng/ml and in group B it increased from 7.3 ± 5.3 to 27.23 ± 10.7 ng/ml, but the level of vitamin D in group A increased from 8.3 ± 7.8 to 17.7 ± 9.3 ng/ml (p < 0.001). The mean differences of insulin and HOMA-IR before and after intervention in groups A and C were significant (p = 0.01, p = 0.02). This study has shown that supplementation of pregnant women with 50 000 IU vitamin D every 2 weeks improved insulin resistance significantly.

The effect of vitamin D on insulin resistance in patients with type 2 diabetes

INTRODUCTION

Over the past decade, numerous non-skeletal diseases have been reported to be associated with vitamin D deficiency including type2 diabetes mellitus (T2DM). Different studies provide evidence that vitamin D may play a functional role in glucose tolerance through its effects on insulin secretion and insulin sensitivity. This study evaluates the effects of vitamin D supplementation on insulin resistance in T2DM.

METHOD

Through a before-after study, 100 patients with T2DM, 30-70 years old, were recruited from an Arak diabetes clinic as consecutive attenders. Participants were assessed for clinical and biochemistry. Serum insulin and, 25(OH)D concentration, and HOMA-IR was calculated. All measurements were performed at the beginning and the end of the study. Patients received 50,000 unit of vitamin D3 orally per week for eight weeks, Statistical analysis was made using SPSS17. The results were analyzed by descriptive tests, and a comparison between variables were made using paired T-tests or Wilcoxon tests, as appropriate.

RESULTS

100 participants including 70 women (70%) and 30 men (30%) took part in the study. All results were presented as Mean±SD, or medians of non-normally distributed.24% of the participants were Vitamin D deficient {serum 25(OH)D ≤ 20 ng/ml(50 nmol/l)}.Mean serum 25 (OH) D concentration was 43.03± 19.28 ng/ml (107.5±48.2 nmol/l).The results at baseline and at the end, for FPG were 138.48±36.74 and 131.02±39 mg/dl (P=0.05), for insulin, 10.76±9.46 and 8.6±8.25 μIu/ml (P=0.028) and for HOMA-IR, 3.57±3.18 and 2.89±3.28 (P=0.008) respectively.

CONCLUSION

Our data showed significant improvements in serum FPG, insulin and in HOMA-IR after treatment with vitamin D, suggested that vitamin D supplementation could reduce insulin resistance in T2DM.

Low 25-hydroxyvitamin D and risk of type 2 diabetes: a prospective cohort study and metaanalysis

BACKGROUND

Vitamin D deficiency has been implicated in decreased insulin secretion and increased insulin resistance, hallmarks of type 2 diabetes mellitus. We tested the hypothesis that low plasma 25-hydroxyvitamin D [25(OH)D] is associated with increased risk of type 2 diabetes in the general population.

METHODS

We measured 25(OH)D in 9841 participants from the general population, of whom 810 developed type 2 diabetes during 29 years of follow-up. Analyses were adjusted for sex, age, smoking status, body mass index, income, physical activity, HDL cholesterol, and calendar month of blood draw.

RESULTS

Lower 25(OH)D concentrations, by clinical categories or seasonally adjusted quartiles, were associated with higher cumulative incidence of type 2 diabetes (trend, P = 2×10(-7) and P = 4×10(-10)). Multivariable adjusted hazard ratios of type 2 diabetes were 1.22 (95% CI 0.85-1.74) for 25(OH)D <5 vs ≥20 μg/L and 1.35 (1.09-1.66) for lowest vs highest quartile. Also, the multivariable adjusted hazard ratio of type 2 diabetes for a 50% lower concentration of 25(OH)D was 1.12 (1.03-1.21); the corresponding hazard ratio for those ≤58 years old was 1.26 (1.15-1.41). Finally, in a metaanalysis of 16 studies, the odds ratio for type 2 diabetes was 1.50 (1.33-1.70) for the bottom vs top quartile of 25(OH)D.

CONCLUSIONS

We observed an association of low plasma 25(OH)D with increased risk of type 2 diabetes. This finding was substantiated in a metaanalysis.

Vitamin D deficiency: a new risk factor for type 2 diabetes?

Recent compelling evidence suggests a role of vitamin D deficiency in the pathogenesis of insulin resistance and insulin secretion derangements, with a consequent possible interference with type 2 diabetes mellitus. The mechanism of this link is incompletely understood. In fact, vitamin D deficiency is usually detected in obesity in which insulin resistance is also a common finding. The coexistence of insulin resistance and vitamin D deficiency has generated several hypotheses. Some cross-sectional and prospective studies have suggested that vitamin D deficiency may play a role in worsening insulin resistance; others have identified obesity as a risk factor predisposing individuals to exhibit both vitamin D deficiency and insulin resistance. The available data from intervention studies are largely confounded, and inadequate considerations of seasonal effects on 25(OH)D concentrations are also a common design flaw in many studies. On the contrary, there is strong evidence that obesity might cause both vitamin D deficiency and insulin resistance, leaving open the possibility that vitamin D and diabetes are not related at all. Although it might seem premature to draw firm conclusions on the role of vitamin D supplementation in reducing insulin resistance and preventing type 2 diabetes, this manuscript will review the circumstances leading to vitamin D deficiency and how such a deficiency can eventually independently affect insulin sensitivity.

Vitamin D, type 2 diabetes and other metabolic outcomes: a systematic review and meta-analysis of prospective studies

Vitamin D status may influence the risk of developing metabolic diseases such as Type 2 diabetes (T2D), metabolic syndrome (MetS) and insulin resistance (IR). Several studies have assessed vitamin D in relationship with metabolic outcomes; however, results remain inconsistent. A systematic review and meta-analysis using multiple databases (MEDLINE, Web of Science and EMBASE), was performed up to 10 August 2012. Prospective studies reporting association of circulating or dietary vitamin D with incident T2D, MetS and IR outcomes were included. Relative risks (RR) were pooled using random effects and subgroup analysis by pertinent study-level characteristics was performed. A total of seventeen articles based on eighteen unique prospective studies, and comprising 210 107 participants with 15 899 metabolic events, collected during a median follow up of 10 years (range 3-22 years), were included. RR for individuals in top v. bottom thirds of baseline vitamin D were 0·81 (95% CI 0·71, 0·92); 0·86 (95% CI 0·80, 0·92); and 0·84 (95% CI 0·64, 1·12) for T2D, MetS and IR outcomes, respectively. Moderate heterogeneity was found between fourteen studies (I 2 = 67%, P < 0·001) reporting on T2D. Findings were generally consistent across various study-level characteristics. In conclusion, vitamin D status at baseline in apparently healthy adults is inversely associated with future risks of T2D and MetS. Interventions aimed at maintaining adequate levels of vitamin D in addition to preventing deficiency may be a useful preventive measure for metabolic diseases. However, reliable evidence from carefully designed intervention studies, particularly those based on healthy populations, is needed to confirm observational findings.

Role of vitamin D in insulin resistance

Vitamin D is characterized as a regulator of homeostasis of bone and mineral metabolism, but it can also provide nonskeletal actions because vitamin D receptors have been found in various tissues including the brain, prostate, breast, colon, pancreas, and immune cells. Bone metabolism, modulation of the immune response, and regulation of cell proliferation and differentiation are all biological functions of vitamin D. Vitamin D may play an important role in modifying the risk of cardiometabolic outcomes, including diabetes mellitus (DM), hypertension, and cardiovascular disease. The incidence of type 2 DM is increasing worldwide and results from a lack of insulin or inadequate insulin secretion following increases in insulin resistance. Therefore, it has been proposed that vitamin D deficiency plays an important role in insulin resistance resulting in diabetes. The potential role of vitamin D deficiency in insulin resistance has been proposed to be associated with inherited gene polymorphisms including vitamin D-binding protein, vitamin D receptor, and vitamin D 1alpha-hydroxylase gene. Other roles have been proposed to involve immunoregulatory function by activating innate and adaptive immunity and cytokine release, activating inflammation by upregulation of nuclear factor κB and inducing tumor necrosis factor α, and other molecular actions to maintain glucose homeostasis and mediate insulin sensitivity by a low calcium status, obesity, or by elevating serum levels of parathyroid hormone. These effects of vitamin D deficiency, either acting in concert or alone, all serve to increase insulin resistance. Although there is evidence to support a relationship between vitamin D status and insulin resistance, the underlying mechanism requires further exploration. The purpose of this paper was to review the current information available concerning the role of vitamin D in insulin resistance.