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

Evaluating Vitamin D Status in Pre- and Postmenopausal Type 2 Diabetics and Its Association with Glucose Homeostasis

Background

Type 2 Diabetes Mellitus (T2DM) and menopause are associated with vitamin D status. Oestrogen decline during menopausal stages promotes hypovitaminosis D. However, the interplay between vitamin D, menopause, lifestyle, and T2DM cannot be overlooked. This study assessed vitamin D status among pre- and postmenopausal T2DM women and determined its association with glycemic control and influence of lifestyle habits on hypovitaminosis D.

Methods

This cross-sectional study was conducted at the Komfo Anokye Teaching Hospital, Kumasi, Ghana. Structured questionnaires were administered to 192 T2DM women; blood samples were collected for estimation of 25(OH) D and insulin using ELISA. Fasting blood glucose (FBG), lipid profile, glycated haemoglobin (HbA1c), and calcium were measured. Statistical analyses were performed using Graphpad Prism 6.

Results

The prevalence of vitamin D inadequacy was 92.2%. Hypovitaminosis D was more prevalent among the postmenopausal T2DM women (63.8% versus 58.2%). Hypovitaminosis D significantly associated with insulin [R² = 0.01760, p = 0.0008], HbA1c [R² = 0.3709, p = <0.0001], and FBG [R² = 0.3465, p = 0.0001] in only the postmenopausal women.

Conclusion

Vitamin D deficiency is prevalent in pre- and postmenopausal T2DM but higher among postmenopausal women. Adequate vitamin D levels in both groups were associated with improved glucose control while hypovitaminosis D in the postmenopausal women was related to poorer glucose control. Vitamin D screening should be incorporated into management plan for T2DM to serve as an early tool for prevention of vitamin D deficiency.

Nonalcoholic Fatty Liver Disease and Abdominal Fat Accumulation According to Vitamin D Status in Patients with Type 2 Diabetes

Background

Vitamin D deficiency is known to increase the incidence of metabolic syndrome. Nonalcoholic fatty liver disease is a common metabolic disease in patients with type 2 diabetes. This study evaluated nonalcoholic fatty liver disease and abdominal fat accumulation according to 25-hydroxyvitamin D status in patients with type 2 diabetes.

Methods

The study comprised 302 patients with type 2 diabetes. Patients were divided into three groups based upon their 25-hydroxyvitamin D status: vitamin D deficient group (<10 ng/mL), vitamin D insufficient group (≥10 to <20 ng/mL) and vitamin D sufficient group (≥20 ng/mL). Patient clinical and laboratory markers were evaluated retrospectively.

Results

Visceral fat thickness was significantly higher in the vitamin D deficient group. There were no differences in glycemic control, body mass index, and subcutaneous fat thickness correlated with 25-hydroxyvitamin D status. The prevalence of nonalcoholic fatty liver disease was significantly higher in the vitamin D deficient group compared to the vitamin D sufficient and vitamin D insufficient groups. In multivariate logistic analysis, after adjustment for age, sex, body mass index, glycated hemoglobin and homeostasis model assessment of insulin resistance, patients with type 2 diabetes in the vitamin D sufficient group showed significantly lower odds ratio for nonalcoholic fatty liver disease than those within the vitamin D deficient group.

Conclusion

In type 2 diabetes, the vitamin D deficient group showed thicker visceral fat thickness and higher nonalcoholic fatty liver disease prevalence.

Vitamin D, Calcium, and Cardiovascular Disease: A"D"vantageous or "D"etrimental? An Era of Uncertainty

While the function of vitamin D in regulating calcium homeostasis is well established, there has been growing interest in its role in the prevention of numerous chronic diseases, including cardiovascular disease (CVD). There is mounting epidemiological evidence suggesting that vitamin D deficiency is linked to increased CVD risk. However, the results of previous vitamin D supplementation trials have yielded mixed results in regards to cardiovascular health, and the results of ongoing large-scale randomized controlled trials are not yet available. Further complicating the issue, calcium supplementation, which is often prescribed concurrently with vitamin D, has been associated with increased CVD risk in some (but not all) studies. Thus, it is currently unclear whether vitamin D supplements, particularly for those that are deficient, can help prevent the development of CVD. In addition, there has not been uniform consensus regarding the threshold of 25-hydroxyvitamin D levels that constitutes "sufficiency" across organizational guidelines. This review will provide an update on the most recent evidence regarding the effects of vitamin D and calcium supplements on CVD clinical outcomes, summarize ongoing vitamin D trials, and discuss the current but remarkably disparate recommendations regarding vitamin D deficiency screening and supplementation.

Prevalence of vitamin D deficiency and its associated factors among the urban elderly population in Hyderabad metropolitan city, South India

BACKGROUND

Deficiency of vitamin D has been associated with various health conditions. However, vitamin D deficiency (VDD) and factors associated with VDD are not well studied, especially among the urban elderly population of India.

AIM

To assess the prevalence of VDD and its associated factors among the urban free-living elderly population in Hyderabad.

SUBJECTS AND METHODS

A community-based cross-sectional study was conducted among 298 urban elderly (≥60 years) by adapting a random sampling procedure. Demographic particulars were collected. Blood pressure and anthropometric measurements were recorded using standard equipment. Fasting glucose, lipid profile and 25-hydroxy vitamin D [25(OH) D] were estimated in plasma samples.

RESULTS

The mean ± SE plasma vitamin D and the prevalence of VDD among the urban elderly population were 19.3 ± 0.54 (ng/ml) and 56.3%, respectively. The prevalence of VDD was significantly associated with education, high body mass index (BMI), hypertension (HT) and metabolic syndrome (MS). Multiple logistic regression analysis revealed HT as a significant predictor of vitamin D deficiency and the risk of VDD was double among the elderly with hypertension.

CONCLUSIONS

The prevalence of VDD was high among the urban elderly population in the south Indian city of Hyderabad. High BMI, MS, HT and education are significant associated factors of VDD.

Vitamin D and pancreas: The role of sunshine vitamin in the pathogenesis of diabetes mellitus and pancreatic cancer

Increasing evidence suggests that vitamin D exerts multiple effects beyond bone and calcium metabolism. Vitamin D seems to play a role in pancreatic disease, including type 1 and type 2 diabetes mellitus as well as pancreatic cancer. Vitamin D's immune-modulatory action suggests that it could help prevent type 1 diabetes. In type 2 diabetes, vitamin D may influence β-cell function, insulin sensitivity, and systematic inflammation-all characteristic pathways of that disease. Data from observational studies correlated vitamin D deficiency with risk of type 1 and type 2 diabetes. Prospective and ecological studies of pancreatic cancer incidence generally support a beneficial effect of higher 25-hydroxyvitamin D concentration as well as inverse correlations between UVB dose or exposure and incidence and/or mortality rate of pancreatic cancer. This review discusses the literature regarding vitamin D's role in risk of diabetes and pancreatic cancer. The results to date generally satisfy Hill's criteria for causality regarding vitamin D and incidence of these pancreatic diseases. However, large randomized, blinded, prospective studies are required to more fully evaluate the potential therapeutic role of vitamin D in preventing pancreatic diseases.

Associations of vitamin D with insulin resistance, obesity, type 2 diabetes, and metabolic syndrome

The aim of this study is to determine the relationships of vitamin D with diabetes, insulin resistance obesity, and metabolic syndrome. Intra cellular vitamin D receptors and the 1-α hydroxylase enzyme are distributed ubiquitously in all tissues suggesting a multitude of functions of vitamin D. It plays an indirect but an important role in carbohydrate and lipid metabolism as reflected by its association with type 2 diabetes (T2D), metabolic syndrome, insulin secretion, insulin resistance, polycystic ovarian syndrome, and obesity. Peer-reviewed papers, related to the topic were extracted using key words, from PubMed, Medline, and other research databases. Correlations of vitamin D with diabetes, insulin resistance and metabolic syndrome were examined for this evidence-based review. In addition to the well-studied musculoskeletal effects, vitamin D decreases the insulin resistance, severity of T2D, prediabetes, metabolic syndrome, inflammation, and autoimmunity. Vitamin D exerts autocrine and paracrine effects such as direct intra-cellular effects via its receptors and the local production of 1,25(OH)₂D₃, especially in muscle and pancreatic β-cells. It also regulates calcium homeostasis and calcium flux through cell membranes, and activation of a cascade of key enzymes and cofactors associated with metabolic pathways. Cross-sectional, observational, and ecological studies reported inverse correlations between vitamin D status with hyperglycemia and glycemic control in patients with T2D, decrease the rate of conversion of prediabetes to diabetes, and obesity. However, no firm conclusions can be drawn from current studies, because (A) studies were underpowered; (B) few were designed for glycemic outcomes, (C) the minimum (or median) serum 25(OH) D levels achieved are not measured or reported; (D) most did not report the use of diabetes medications; (E) some trials used too little (F) others used too large, unphysiological and infrequent doses of vitamin D; and (G) relative paucity of rigorous clinical data on the effects of vitamin D sufficiency on non-calcium endpoints. Although a large number of observational studies support improving T2D, insulin resistance, obesity, and metabolic syndrome with vitamin D adequacy, there is a lack of conclusive evidence from randomized control clinical trials that, these disorders are prevented following optimization of serum levels of 25(OH)D. However, none of the currently conducted clinical studies would resolve these issues. Thus, specifically designed, new clinical studies are needed to be conducted in well-defined populations, following normalizing the serum vitamin D levels in vitamin D deficient prediabetes subjects, to test the hypothesis that hypovitaminosis D worsens these disorders and correction would alleviate it.

Non-musculoskeletal benefits of vitamin D

The aim of this study is to determine and critically evaluate the plausible relationships of vitamin D with extra-skeletal tissues in humans. Severe vitamin D deficiency results in rickets in children and osteomalacia in adults; these beneficial effects in the musculoskeletal system and certain physiological functions are well understood. Nevertheless, mounting reports support additional beneficial effects of vitamin D, outside the musculoskeletal system. This review explores the recent advances in knowledge about the non-skeletal effects of vitamin D. Peer-reviewed papers were extracted from research databases using key words, to assess correlations between vitamin D and extra-skeletal diseases and conditions. As per the guidelines of the Preferred Reporting Items for Systematic Reviews (PRISMA); general interpretations of results are included; taking into consideration the broader evidence and implications. This review summarizes current knowledge of the effects of vitamin D status on extra-skeletal tissues with special attention given to relationships between vitamin D status and various diseases commonly affecting adults; the effects of intervention with vitamin D and exposure to sunlight. Evidence suggests that vitamin D facilitates the regulation of blood pressure; and cardiac; endothelial; and smooth muscle cell functions; playing an important role in cardiovascular protection. In addition; 1,25(OH)₂D improves immunity; subdues inflammation; and reduces the incidence and severity of common cancers; autoimmune diseases and infectious diseases. Almost all adequately powered; epidemiological and biological studies that use; adequate doses of vitamin D supplementation in D-deficient populations have reported favorable outcomes. These studies have concluded that optimizing 25(OH)D status improves the functionality of bodily systems; reduces comorbidities; improves the quality of life; and increases survival. Although accumulating evidence supports biological associations of vitamin D sufficiency with improved physical and mental functions; no definitive evidence exists from well-designed; statistically powered; randomized controlled clinical trials. Nevertheless, most studies point to significant protective effects of vitamin D in humans when the minimum 25(OH)D serum level exceeds 30ng/mL and is maintained throughout the year.

1α,25-Dihydroxyvitamin D3 promotes bone formation by promoting nuclear exclusion of the FoxO1 transcription factor in diabetic mice

1α,25-Dihydroxyvitamin D3 (1,25(OH)2D3) is the active form of vitamin D, which is responsible for reducing the risk for diabetes mellitus (DM), decreasing insulin resistance, and improving insulin secretion. Previous studies have shown that 1,25(OH)2D3 inhibited the activity of FoxO1, which has been implicated in the regulation of glucose metabolism. However, its function and mechanism of action in DM-induced energy disorders and also in bone development remains unclear. Here, using in vitro and in vivo approaches including osteoblast-specific, conditional FoxO1-knock-out mice, we demonstrate that 1,25(OH)2D3 ameliorates abnormal osteoblast proliferation in DM-induced oxidative stress conditions and rescues the impaired glucose and bone metabolism through FoxO1 nuclear exclusion resulting from the activation of PI3K/Akt signaling. Using alizarin red staining, alkaline phosphatase assay, Western blot, and real-time qPCR techniques, we found that 1,25(OH)2D3 promotes osteoblast differentiation and expression of osteogenic phenotypic markers (i.e. alkaline phosphatase (1), collagen 1 (COL-1), osteocalcin (OCN), and osteopontin (OPN)) in a high-glucose environment. Moreover, 1,25(OH)2D3 increased both total OCN secretion and levels of uncarboxylated OCN (GluOC) by phosphorylating FoxO1 and promoting its nuclear exclusion, indicated by Western blot and cell immunofluorescence analyses. Taken together, our findings confirm that FoxO1 is a key mediator involved in glucose homeostasis and indicate that 1,25(OH)2D3 improves glucose metabolism and bone development via regulation of PI3K/Akt/FoxO1/OCN pathway.

Impact of Three Doses of Vitamin D3 on Serum 25(OH)D Deficiency and Insufficiency in At-Risk Schoolchildren

OBJECTIVE

We investigated the daily dose of vitamin D needed to achieve serum 25-hydroxyvitamin D [25(OH)D] sufficiency among schoolchildren at risk for deficiency.

STUDY DESIGN

The Daily D Health Study was a randomized double-blind vitamin D supplementation trial among racially/ethnically diverse schoolchildren (n = 685) in the northeastern United States. Children were supplemented with vitamin D3 at 600, 1000, or 2000 IU/d for 6 months. Measurements included serum 25(OH)D at baseline (October to December), 3 months (January to March), 6 months (April to June), and 12 months (6 months after supplementation).

RESULTS

At baseline, mean ± standard deviation serum 25(OH)D level was 22.0 ± 6.8 ng/mL, with 5.5% severely vitamin D deficient (<12 ng/mL), 34.1% deficient (12 to 19 ng/mL), 49.0% insufficient (20 to 29 ng/mL), and 11.4% sufficient (≥30 ng/mL). The lowest levels of serum 25(OH)D were found among black (17.9 ± 6.7 ng/mL) and Asian children (18.9 ± 4.8 ng/mL), with no baseline differences by weight status. Serum 25(OH)D increased over 6 months in all three dose groups. The 2000 IU/d group achieved a higher mean serum 25(OH)D level than the other two dose groups (33.1 vs 26.3 and 27.5 ng/mL; P < 0.001), with 59.9% of this group attaining sufficiency at 3 months and only 5.3% remaining severely deficient/deficient at 6 months. All dose groups demonstrated a fall in 25(OH)D at 12 months.

CONCLUSIONS

Children at risk for vitamin D deficiency benefited from daily sustained supplementation of 2000 IU/d compared with lower doses closer to the current recommended daily allowance for vitamin D intake. This benefit occurred over the winter months, when serum 25(OH)D level tend to fall.

Vitamin D, parathyroid hormone and metabolic syndrome - the PORMETS study

BACKGROUND

Vitamin D (VitD) and parathyroid hormone (PTH) play important roles in calcium metabolism and skeletal homeostasis. Estimates of the VitD status in several European countries show large variations between them. In addition, no national population-based estimate has been published. VitD and PTH may also play important roles in cardiovascular risk, which has been suggested to be associated with metabolic syndrome (MetS) and is very prevalent in Portugal. The goal of our study was to evaluate the prevalence of hypovitaminosis D and its determinants as well as PTH serum level determinants and associations of the 25-hydroxyvitamin D and PTH serum levels with MetS and its individual components in a sample of the Portuguese mainland population.

METHODS

PORMETS is a national cross-sectional study that includes a total sample of 4095 adults. A subsample, including 500 participants, was randomly selected for the present study. A structured questionnaire was administered to collect information on personal medical histories and socio-demographic and behavioral characteristics. Blood pressure and anthropometrics measurements were performed. Fasting venous samples were collected and PTH and 25-hydroxyvitamin D were measured. VitD adequacy was classified according to the Institute of Medicine, and MetS was classified according to the Joint Interim Statement recommendations. Multiple linear regression and unconditional logistic regression models were used to estimate the associations between the levels of PTH and 25-hydroxyvitamin D and with MetS and its individual components.

RESULTS

The prevalence of VitD deficiency was 37.7%, and MetS was present in 191 participants (38.4%). The serum PTH levels showed a positive association (OR: 1.014; 95%CI: 1.002, 1.026) with the waist circumference component of MetS. The serum 25-hydroxyvitamin D levels were negatively associated with MetS (OR: 0.957; 95%CI: 0.922, 0.993) as well as with its blood pressure (OR: 0.949; 95%CI: 0.912, 0.987) and triglycerides (OR: 0.930; 95%CI: 0.892, 0.969) components.

CONCLUSION

This study showed a high national prevalence of hypovitaminosis D. The PTH levels showed a significant positive association with the WC component of MetS, and the VitD levels were negatively associated with the BP and triglycerides components as well as with the MetS.

Prognostic value of the Glasgow prognostic score in lung cancer: evidence from 10 studies

Objective:

To conduct a meta-analysis of prospective and retrospective studies to reveal the relationship between the Glasgow prognostic score (GPS) and overall survival (OS) or progression-free survival (PFS) in patients with lung cancer.

Methods:

Correlative studies were included by searching the databases of PubMed, Web of Science, Embase, and PubMed Cochrane Library until April 16, 2017. We combined the hazard ratios (HRs) and 95% confidence intervals (CIs) to assess the correlation between GPS and OS or PFS in patients with lung cancer.

Results:

Ten studies involving 5,369 participants from several regions were identified through searching databases. In a pooled analysis of all studies, elevated GPS was associated with poorer OS (HR = 2.058; 95% CI, 1.51-2.80; p<0.05). However, the combined data showed no significant relationship between the GPS of 1 or 2, and PFS, respectively. Subgroup analysis showed that the patients with GPS ≥1 had poorer OS compared with those with GPS = 0 (HR = 2.01; 95% CI, 1.75-2.32; p<0.001). A similar trend was observed in patients receiving chemotherapy (HR = 1.66; 95% CI, 1.17-2.36; p<0.05) and surgery (HR = 2.88; 95% CI, 1.59-5.22; p<0.001) when stratified by treatment.

Conclusions:

Increased level of GPS may have a prognostic value in lung cancer. We detected a statistical difference in the association of elevated GPS and poorer OS, though the association was not significant in PFS settings. However, further studies are warranted to draw firm conclusions.

No effect of vitamin D supplementation on cardiovascular risk factors in subjects with metabolic syndrome: a pilot randomised study

Introduction

Patients with metabolic syndrome (MetS) may have lower 25-hydroxyvitamin D (25(OH)VitD) serum levels compared with non-MetS individuals. Vitamin D (VitD) deficiency is associated with various cardiovascular disease (CVD) risk factors. Yet, the effect of VitD supplementation on MetS remains uncertain. Our aim was to examine the effect of VitD supplementation on CVD risk factors in MetS subjects.

Material and methods

This pilot study had a PROBE (prospective, randomised, open-label, blinded end-point) design. Fifty patients with MetS were included and randomised either to dietary instructions (n = 25) (control group) or dietary instructions plus VitD 2000 IU/day (n = 25) (VitD group) for 3 months. This study is registered in ClinicalTrials.gov (NCT01237769).

Results

In both groups a similar small weight reduction was achieved. In the VitD group serum 25(OH)VitD levels significantly increased by 91% (from 16.0 (3.0–35.0) to 30.6 (8.4–67.0) ng/ml, p < 0.001), while in the control group no significant change was observed (from 10.0 (4.0–39.6) to 13.0 (3.5–37.0) ng/ml). In both groups triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, fasting glucose, haemoglobin A_1c, homeostasis model assessment index and diastolic blood pressure did not significantly change. Systolic blood pressure decreased by 3.7% (from 134 ±14 to 129 ±13 mm Hg, p = 0.05) in the VitD group, while it decreased by 1.5% (from 132 ±13 to 130 ±16 mm Hg, p = NS) in the control group (p = NS between groups). In the VitD group serum 25(OH)VitD increase was negatively correlated with SBP decrease (r = –0.398, p = 0.049).

Conclusions

VitD supplementation (2000 IU/day) did not affect various CVD risk factors in patients with MetS.

The association of vitamin D deficiency and glucose control among diabetic patients

Objective

To evaluate the association between the level of vitamin D and glycemic control among patients with diabetes.

Research design and method

We analyzed data collected from NHANES 2003–2006. We included only non-pregnant adult diabetic persons 18 years or older. Participants who had vitamin D level less than 20 ng/ml were considered as having vitamin D deficiency. Participants were considered to have a glucose control if the HbA_1c level was less than 7% [53 mmol/L]. We used student’s t test to compare the difference in HbA_1c means between people with Diabetes with and without a vitamin D deficiency. We used a multivariate logistic regression model to predict the relationship between glucose control and vitamin D deficiency. We used race/ethnicity, BMI, age, gender, type of diabetic medication used, having health insurance or not, and comorbid conditions (hypertension, anemia, cholesterol, liver disease, and kidney disease) as control variables.

Results

The study population included a total of 929 non-institutionalized, non-pregnant, diabetic adult persons. About 57% of patients with diabetes had a vitamin D deficiency. Blacks (non-Hispanic patients) with diabetes had the highest rate of vitamin D deficiency (79%). The unadjusted means of HbA_1c were significantly different between diabetic patients with no vitamin D deficiency and those with a vitamin D deficiency (7.06% [54 mmol/L], 7.56 % [59 mmol/L], respectively, P < 0.0001). Multivariate adjustment showed a small but not significant, increase in odds (11%) of having uncontrolled diabetes in patients with a vitamin D deficiency after adjustment for other factors.

Conclusion

Vitamin D deficiency is very common in patients with diabetes. We found no significant association between vitamin D level and glycemic control in patients with diabetes after adjustment for control variables.

Circulating levels of miR-7, miR-152 and miR-192 respond to vitamin D supplementation in adults with prediabetes and correlate with improvements in glycemic control

Vitamin D may play an important role in modifying the risk of type 2 diabetes. Supplementation with cholecalciferol has been shown to improve β cell function and to attenuate the rise in glycated hemoglobin in people at high risk of diabetes. We examined whether circulating microRNAs (miRNAs) reflect disease progression and/or respond to vitamin D supplementation. We measured plasma levels of select miRNAs implicated in diabetes in people with prediabetes treated either with placebo (n=21) or 2000 U of cholecalciferol daily (n=21) for 4 months in the Calcium and Vitamin D for Diabetes Mellitus trial and compared the baseline-adjusted changes after correcting for age, body mass index, race, time of study entry (season) and baseline disposition index. Circulating levels of miR-7 (sixfold reduction, P=.01), miR-152 (1.5-fold increase, P=.03), and miR-192 (1.7-fold reduction, P=.026) displayed significant treatment-by-time interactions between the placebo- and the vitamin-D-treated groups. Plasma levels of miR-7 were reduced in the vitamin D and increased in the placebo group. The change in miR-152 positively correlated with the change in levels of the circulating metabolite 25-hydroxyvitamin D (r=0.33, P=.046) and negatively correlated with the change in glycated hemoglobin (r=-0.37, P=.024). The change in miR-192 positively correlated with the change in fasting glucose (r=0.41, P<.011). In conclusion, reduction of circulating miR-7 and miR-192, accompanied by elevation of miR-152, reflects a beneficial metabolic response to vitamin D treatment in people with prediabetes. These miRNAs may be useful biomarkers in diabetes prevention trials and other studies of vitamin D.

Evaluation of two fully automated immunoassay based tests for the measurement of 1α,25-dihydroxyvitamin D in human serum and comparison with LC-MS/MS

BACKGROUND

1α,25-Dihydroxyvitamin D [1,25(OH)2 vitD] is the bioactive form of vitamin D. Due to the very low concentrations of 1,25(OH)2 vitD in the blood and its lipophilic character, measurement of this parameter is analytically challenging. Requiring preceding manual extraction steps before analysis, previous assays have been laborious.

METHODS

In the presented study, we evaluated the performance of two immunoassays from DiaSorin and from Immunodiagnostic Systems (IDS) which combine fully automated extraction and measurement of 1,25(OH)2 vitD. Imprecision and linearity were verified according to Clinical and Laboratory Standards Institute EP15-A3 and EP6-A guidelines, respectively. Ninety-three patient serum samples sent to our institute for determination of 1,25(OH)2 vitD, as well as 20 Vitamin D External Quality Assessment Scheme (DEQAS) samples, were used to evaluate correlation and agreement of 1,25(OH)2 vitD measurements between the two immunoassays and with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS).

RESULTS

Total imprecision was 5.2% or less for the DiaSorin test but reached 20.1% for the IDS iSYS test. 1,25(OH)2 vitD concentrations measured with the DiaSorin assay showed a strong correlation with 1,25(OH)2 vitD levels measured by LC-MS/MS and a good agreement with method specific means of DEQAS samples. By contrast, the IDS iSYS test overestimated 1,25(OH)2 vitD concentrations in human serum, particularly at higher concentrations.

CONCLUSIONS

Due to its high sensitivity, low imprecision, broad measurement range, and good agreement with 1,25(OH)2 vitD concentrations measured by LC-MS/MS, the DiaSorin test is a valuable analytical option for the determination of 1,25(OH)2 vitD.

High glucose induces O-GlcNAc glycosylation of the vitamin D receptor (VDR) in THP1 cells and in human macrophages derived from monocytes

Chronic hyperglycemia increases the carbon flux through the hexosamine pathway, allowing the accumulation of UDP-GlcNAc. UDP-GlcNAc is the sugar donor for the enzyme-mediated protein glycosylation event known as OGlcNAcylation. This posttranslational modification targets several transcription factors implicated in glucose toxicity, insulin resistance, and diabetes. Vitamin D plays an important role in glucose homeostasis and insulin secretion through transcriptional mechanisms mediated by its receptor (VDR). Vitamin D deficiency has been associated with higher susceptibility to bacterial diseases in diabetic patients. However, it has not been explored whether VDR is subject to OGlcNAcylation or whether high glucose affects its transcriptional or biological activities. The aim of this study was to evaluate the effect of hyperglycemia on VDR OGlcNAcylation and its effects on vitamin D-mediated transcription. We predicted potential OGlcNAcylation sites using free software. Our results showed that hyperglycemia (30 mM) induces the OGlcNAcylation of VDR in THP1 cells and in human macrophages derived from monocytes (MDM). This condition did not hamper the vitamin D-dependent activation of LL-37 gene expression, and even did not impair the macrophage bactericidal activity. Our study provides new insight into vitamin D receptor posttranslational modification that may have relevance on the physiological responses of long-term hyperglycemia.

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

INTRODUCTION

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

MATERIALS/METHODS

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

RESULTS

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

CONCLUSIONS

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

Association of Directly Measured Plasma Free 25(OH)D With Insulin Sensitivity and Secretion: The IRAS Family Study

Objectives

We aimed to compare the associations of directly measured plasma free 25-hydroxyvitamin D [25(OH)D] and total 25(OH)D concentrations with insulin sensitivity (SI) and β-cell function in nondiabetic Hispanics and African Americans. We hypothesized that directly measured free 25(OH)D would be more strongly associated with these measures of glucose homeostasis and that associations would differ by race.

Design

We studied 1189 nondiabetic participants in the Insulin Resistance Atherosclerosis Study Family Study using data from baseline examinations from 2000 to 2002. SI, acute insulin response, and disposition index (DI) were determined from frequently sampled intravenous glucose tolerance tests. Plasma free and total 25(OH)D concentrations were measured by enzyme-linked immunosorbent assay and radioimmunoassay, respectively.

Results

The median concentrations of plasma free 25(OH)D were 3.46 pg/mL for Hispanics and 2.17 pg/mL for African Americans (P < 0.0001), whereas the median concentrations of plasma total 25(OH)D were 16 ng/mL for Hispanics and 10 ng/mL for African Americans (P < 0.0001). Plasma free and total 25(OH)D were both positively associated with SI and DI in generalized estimating equations adjusted for demographic and lifestyle factors. After further adjustment with body mass index, the associations were no longer statistically significant, except for a significant association between plasma free 25(OH)D and SI. There was no effect modification by ethnicity on any of the exposure-outcome associations.

Conclusions

Our data showed that plasma free 25(OH)D had a slightly stronger association with SI compared with plasma total 25(OH)D, although the difference was modest and there were no marked differences in the associations between Hispanics and African Americans.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Gene-Diet Interactions in Type 2 Diabetes: The Chicken and Egg Debate

Consistent evidence from both experimental and human studies indicates that Type 2 diabetes mellitus (T2DM) is a complex disease resulting from the interaction of genetic, epigenetic, environmental, and lifestyle factors. Nutrients and dietary patterns are important environmental factors to consider in the prevention, development and treatment of this disease. Nutritional genomics focuses on the interaction between bioactive food components and the genome and includes studies of nutrigenetics, nutrigenomics and epigenetic modifications caused by nutrients. There is evidence supporting the existence of nutrient-gene and T2DM interactions coming from animal studies and family-based intervention studies. Moreover, many case-control, cohort, cross-sectional cohort studies and clinical trials have identified relationships between individual genetic load, diet and T2DM. Some of these studies were on a large scale. In addition, studies with animal models and human observational studies, in different countries over periods of time, support a causative relationship between adverse nutritional conditions during in utero development, persistent epigenetic changes and T2DM. This review provides comprehensive information on the current state of nutrient-gene interactions and their role in T2DM pathogenesis, the relationship between individual genetic load and diet, and the importance of epigenetic factors in influencing gene expression and defining the individual risk of T2DM.

Vitamin D and diabetes mellitus: Causal or casual association?

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

Vitamin D, sub-inflammation and insulin resistance. A window on a potential role for the interaction between bone and glucose metabolism

Vitamin D is a key hormone involved in the regulation of calcium/phosphorous balance and recently it has been implicated in the pathogenesis of sub-inflammation, insulin resistance and obesity. The two main forms of vitamin D are cholecalciferol (Vitamin D3) and ergocalciferol (Vitamin D2): the active form (1,25-dihydroxyvitamin D) is the result of two hydroxylations that take place in liver, kidney, pancreas and immune cells. Vitamin D increases the production of some anti-inflammatory cytokines and reduces the release of some pro-inflammatory cytokines. Low levels of Vitamin D are also associated with an up-regulation of TLRs expression and a pro-inflammatory state. Regardless of the effect on inflammation, Vitamin D seems to directly increase insulin sensitivity and secretion, through different mechanisms. Considering the importance of low grade chronic inflammation in metabolic syndrome, obesity and diabetes, many authors hypothesized the involvement of this nutrient/hormone in the pathogenesis of these diseases. Vitamin D status could alter the balance between pro and anti-inflammatory cytokines and thus affect insulin action, lipid metabolism and adipose tissue function and structure. Numerous studies have shown that Vitamin D concentrations are inversely associated with pro-inflammatory markers, insulin resistance, glucose intolerance and obesity. Interestingly, some longitudinal trials suggested also an inverse association between vitamin D status and incident type 2 diabetes mellitus. However, vitamin D supplementation in humans showed controversial effects: with some studies demonstrating improvements in insulin sensitivity, glucose and lipid metabolism while others showing no beneficial effect on glycemic control and on inflammation. In conclusion, although the evidences of a significant role of Vitamin D on inflammation, insulin resistance and insulin secretion in the pathogenesis of obesity, metabolic syndrome and type 2 diabetes, its potential function in treatment and prevention of type 2 diabetes mellitus is unclear. Encouraging results have emerged from Vitamin D supplementation trials on patients at risk of developing diabetes and further studies are needed to fully explore and understand its clinical applications.

Vitamin D status and its association with insulin resistance among type 2 diabetics: A case -control study in Ghana

Background

Vitamin D plays a major role in physiological processes that modulate mineral metabolism and immune function with probable link to several chronic and infectious conditions. Emerging data suggests a possible influence of vitamin D on glucose homeostasis. This study sought to provide preliminary information on vitamin D status among Ghanaian type 2 diabetics and assessed its association with glucose homeostasis.

Methods

In a case control study, 118 clinically diagnosed Type 2 Diabetes Mellitus (T2DM) patients attending Diabetic Clinic at the Nkawie Government Hospital were enrolled between October and December 2015. Hundred healthy non-diabetics living in Nkawie district were selected as controls. Structured questionnaires were administered to obtain socio-demographic data. Venous blood samples were taken from both cases and controls to estimate their FBG, Lipid profile spectrophotometrically and IPTH, 25OHD by ELISA. Statistical analyses were performed using SPSS v20.0 Statistics.

Results

The average age of the study participants was 58.81years for cases and 57.79year for controls. There was vitamin D deficiency of 92.4% among T2DM cases and 60.2% among the non diabetic controls. Vitamin D deficiency did not significantly associate with HOMA-β [T2DM: r² = 0.0209, p = 0.1338 and Control: r² = 0.0213, p = 0.2703] and HOMA-IR [T2DM: r² = 0.0233, p = 0.1132 and Control: r² = 0.0214, p = 0.2690] in both the controls and the cases.

Conclusion

Vitamin D deficiency is prevalent in both T2DM and non-diabetics. There is no association between vitamin D deficiency and insulin resistance or beta cell function in our study population. Vitamin D supplementation among type 2 diabetics is recommended.

Low vitamin D levels increase the risk of type 2 diabetes in older adults: A systematic review and meta-analysis

Low serum levels of 25 hydroxyvitamin D (25OHD) (hypovitaminosis D) is common in older adults and associated with several negative outcomes. The association between hypovitaminosis D and diabetes in older adults is equivocal, however. We conducted a meta-analysis investigating if hypovitaminosis D is associated with diabetes in prospective studies among older participants. Two investigators systematically searched major electronic databases, from inception until 10/07/2016. The cumulative incidence of diabetes among groups was estimated according to baseline serum 25OHD levels. Random effect models were used to assess the association between hypovitaminosis D and diabetes at follow-up. From 4268 non-duplicate hits, 9 studies were included; these followed 28,258 participants with a mean age of 67.7 years for a median of 7.7 years. Compared with higher levels of 25OHD, lower levels of 25OHD were associated with a higher risk of developing diabetes (6 studies; n=13,563; RR=1.31; 95% CI: 1.11-1.54; I²=37%). The findings remained significant after adjusting for a median of 11 potential confounders in all the studies available (9 studies; n=28,258; RR=1.17; 95% CI: 1.03-1.33; p=0.02; I²=0%). In conclusion, our data suggest that hypovitaminosis D is associated with an elevated risk of future diabetes in older people. Future longitudinal studies are required and should seek to confirm these findings and explore potential pathophysiological underpinnings.

Association of serum 25-hydroxyvitamin D3 with adipokines and inflammatory marker in persons with prediabetes mellitus

BACKGROUND

The association of vitamin D status and inflammation prediabetes mellitus (PreDM) individuals has not been investigated. We investigated the association of serum 25-hydroxyvitamin D₃ (25(OH) D₃) with adipokines and inflammatory markers in persons with PreDM.

METHODS

In this cross-sectional study, we stratified 418 nondiabetic subjects as having PreDM or normal fasting glucose (NFG), and divided PreDM or NFG subjects into vitamin D sufficient, vitamin D insufficient and vitamin D deficient subgroups. 25(OH) D₃ concentrations were determined by HPLC. Serum tumor necrosis factor-α (TNF-α), interleiukin-6 (IL-6) and high-sensitivity C-reactive protein (hs-CRP), adiponectin, leptin and resistin were measured by ELISA.

RESULTS

In the PreDM group, compared with those in the vitamin D sufficient subgroup, vitamin D insufficient subgroup and vitamin D deficient subgroup had higher concentrations of hs-CRP and leptin (P<0.05). In the PreDM-deficient or PreDM-insufficient subgroup, mean hs-CRP and leptin concentration was higher than in the PreDM-sufficient, NFG-deficient, NFG-insufficient and NFG-sufficient subgroups (P<0.05). Serum 25(OH) D₃ concentrations were inversely associated with hs-CRP and leptin concentrations after adjusted the BMI only in the PreDM group (P<0.05). At the multivariate analysis, hs-CRP and leptin were the major determinant of 25(OH) D₃ concentration (β=-0.174 and β=-0.171, respectively).

CONCLUSIONS

25(OH) D₃ status in PreDM individuals was inversely correlated with concentrations of hs-CRP and leptin, suggesting their involvement in the inflammation response between vitamin D status and PreDM.

Association between serum 25(OH)D3 and cardiovascular morbidity and mortality in people with Type 2 diabetes: a community-based cohort study

AIM

We aimed to explore the association between vitamin D and cardiovascular morbidity and mortality in people with Type 2 diabetes recruited from a community-based study because there is limited and inconsistent research of this group.

METHODS

A prospective community-based cohort study among people aged 55-66 years with Type 2 diabetes as part of The Cardiovascular Risk in Type 2 Diabetes - A Prospective Study in Primary Care (CARDIPP). We analysed serum 25-hydroxyvitamin D₃ [25(OH)D₃ ] at baseline. Cox regression analyses were used to calculate hazard ratios (HR) for the first myocardial infarction, stroke or cardiovascular mortality according to 25(OH)D₃ .

RESULTS

We examined 698 people with a mean follow-up of 7.3 years. Serum 25(OH)D₃ was inversely associated with the risk of cardiovascular morbidity and mortality: HR 0.98 [95% confidence interval (CI) 0.96 to 0.99, P = 0.001]. Compared with the fourth quartile (Q4) [25(OH)D₃ > 61.8 nmol/l], HR (with 95% CI) was 3.46 (1.60 to 7.47) in Q1 [25(OH)D₃ < 35.5 nmol/l] (P = 0.002); 2.26 (1.01 to 5.06) in Q2 [25(OH)D₃ 35.5-47.5 nmol/l] (P = 0.047); and 1.62 (0.70 to 3.76) in Q3 [25(OH)D₃ 47.5-61.8 nmol/l] (P = 0.26) when adjusting for age, sex and season. The results remained significant after adjusting also for cardiovascular risk factors, physiological variables including parathyroid hormone and previous cardiovascular disease (P = 0.027).

CONCLUSIONS

Low 25(OH)D₃ is associated with an increased risk of cardiovascular morbidity and mortality in people with Type 2 diabetes independent of parathyroid hormone. Vitamin D could be considered as a prognostic factor. Future studies are needed to explore whether vitamin D deficiency is a modifiable risk factor in Type 2 diabetes.

25-Hydroxyvitamin D Status and Risk for Colorectal Cancer and Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis of Epidemiological Studies

Epidemiological evidence suggests an association between low vitamin D status and risk for various outcomes including cardiovascular diseases, cancer, and type 2 diabetes mellitus (T2DM). Analyzing serum 25-hydroxyvitamin D [25(OH)D] is the most established means to evaluate an individual's vitamin D status. However, cutoff values for 25(OH)D insufficiency as well as for optimal 25(OH)D levels are controversial. This systematic review critically summarizes the epidemiological evidence regarding 25(OH)D levels and the risk for colorectal cancer and T2DM. The meta-analytical calculation revealed a pooled relative risk (RR) of 0.62 (CI 0.56-0.70; I² = 14.7%) for colorectal cancer and an RR of 0.66 (CI 0.61-0.73; I² = 38.6%) for T2DM when comparing individuals with the highest category of 25(OH)D with those in the lowest. A dose-response analysis showed an inverse association between 25(OH)D levels and RR for both outcomes up to concentrations of about 55 ng/mL for colorectal cancer and about 65 ng/mL for T2DM. At still higher 25(OH)D levels the RR increases slightly, consistent with a U-shaped association. In conclusion, a higher 25(OH)D status is associated with a lower risk for colorectal cancer and T2DM; however, this advantage is gradually lost as levels increase beyond 50-60 ng/mL.

SNP rs11185644 of RXRA gene is identified for dose-response variability to vitamin D3 supplementation: a randomized clinical trial

The level of serum 25-Hydroxyvitamin D [25(OH)D] has high heritability, suggesting that genes may contribute to variations in serum 25(OH)D level and vitamin D dose-response. As vitamin D deficiency has been linked to numerous diseases, understanding how genetic variation contributes to vitamin D dose-response is important for personalized vitamin D treatment and cost-effective disease prevention. To identify genetic variants responsible for vitamin D status and dose-response, we performed two vitamin D3 and calcium clinical supplementation trials in 2,207 postmenopausal Caucasian women. We examined the association of 291 SNPs with baseline serum 25(OH)D levels and 25(OH)D dose-response. Five SNPs, rs10500804 (P = 4.93 × 10⁻⁷), rs2060793 (P = 6.63 × 10⁻⁷), rs10741657 (P = 1.49 × 10⁻⁶), rs10766197 (P = 1.05 × 10⁻⁵) and rs11023380 (P = 7.67 × 10⁻⁵) in the CYP2R1 gene, as well as 6 SNPs, rs4588 (P = 7.86 × 10⁻⁷), rs2298850 (P = 1.94 × 10⁻⁶), rs1155563 (P = 6.39 × 10⁻⁶), rs705119 (P = 2.80 × 10⁻⁵), rs705120 (P = 1.08 × 10⁻⁴) and rs222040 (P = 1.59 × 10⁻⁴) in the GC gene were associated with baseline serum 25(OH)D levels. SNP rs11185644 near the RXRA was significantly associated with 25(OH)D dose-response (P = 1.01 × 10⁻⁴). Our data suggest that polymorphisms in the CYP2R1 and GC gene may contribute to variation in baseline serum 25(OH)D concentration, and that polymorphism rs11185644 may contribute to variation in 25(OH)D dose-response in healthy postmenopausal Caucasian women.

Vitamin D and Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) has become a significant global health care problem and its reported incidence is increasing at an alarming rate. Despite the improvement in therapy and development of new drugs, treatment still remains insufficient especially due to the associated side effects of most available drugs. Efforts are continuing toward disease prevention and search for safer drugs. Conflicting evidence is associating low levels of vitamin D in the body to T2DM and as such studies have been conducted to test the effect of vitamin D levels on incidence of diabetes, diabetic control as well as diabetic complications.Despite the conflicting evidence, vitamin D replacement seems to have some beneficial effect on the many aspects of diabetes: incidence, control and complications. Further long term and more convincing controlled trials are required in order to draw firmer conclusions on this beneficial role of vitamin D treatment on T2DM.

Pancreatic Elastase Levels in Feces As A Marker of Exocrine Pancreatic Function in Patients With Diabetes Mellitus

OBJECTIVE

The measurement of pancreatic elastase (PE) in feces is used widely to screen for pancreatic exocrine insufficiency. The aim of our study was to evaluate the relationship of PE with residual beta cell secretion and metabolic control in patients with diabetes mellitus.

METHOD

We determined the presence of PE in specimens via enzyme-linked immunosorbent assay (ELISA), whereas serum fasting glucose, C-peptide, amylase, lipase, triglycerides, total 25(OH)-vitamin D, C-reactive protein (CRP), and hemoglobin A1c (HbA1c) concentrations were assayed using routine laboratory tests.

RESULTS

PE values in 48 patients with diabetes were significantly lower than in 24 healthy volunteers (P = 001). In one-third of participants with diabetes mellitus, PE were less than 200 µg per g, indicating pancreatic functional insufficiency. Among the patients in the cohort, PE correlated positively with C-peptide levels (P = 04), lipase (P = 009), CRP (P = 04), sex (P = 03), and BMI (P = 02) but not significantly with duration of diabetes (P = 81) or levels of HbA1c(P = 87), amylase (P = 06), total 25(OH)-vitamin D (P = 16), or triglycerides (P = 52).

CONCLUSION

Our results demonstrated a strong association of diabetes with low PE levels.

Associations between Vitamin D and Cardiovascular Disease Risk Factors in African Americans Are Partly Explained by Circulating Adipokines and C-Reactive Protein: The Jackson Heart Study

BACKGROUND

Although it is recognized that vitamin D deficiency is associated with cardiovascular disease (CVD) risk factors, and is more common in African Americans (AAs), the pathologic mechanisms by which vitamin D may influence these risk factors are poorly understood.

OBJECTIVES

We explored the association between vitamin D status, as reflected by serum 25-hydroxyvitamin D [25(OH)D] concentrations, and CVD risk factors including mean arterial pressure (MAP), fasting plasma glucose (FPG), plasma HDL cholesterol, and waist circumference (WC) in adult AAs. We also tested whether plasma C-reactive protein (CRP), adipokines (adiponectin and leptin), and aldosterone mediated the associations between 25(OH)D and these risk factors.

METHODS

Data on 4010 (63.8% women; mean age: 54.0 y) individuals from the Jackson Heart Study were analyzed. Multivariable linear regression models were used to examine the associations of 25(OH)D with CVD risk factors. We used path analysis and bootstrapping methods to quantify and test the share of these associations that was statistically explained by each of the mediators by decomposing the associations into direct and indirect effects.

RESULTS

Serum 25(OH)D concentrations were inversely associated with WC, FPG, and MAP and were positively associated with HDL cholesterol in multivariable analysis. A nearly 20% effect of 25(OH)D on MAP was masked by aldosterone (total indirect effect: β = 0.01, P < 0.05). Approximately 23% of the effect of 25(OH)D on WC (β = -0.03, P < 0.05) and ∼9% of the effect of 25(OH)D on FPG (β = -0.02, P < 0.05) were mediated through CRP, adiponectin, and leptin together. A 23% share of the association between 25(OH)D and HDL cholesterol was mediated by adiponectin alone (β = 0.03, P < 0.05).

CONCLUSIONS

Our findings suggest that the associations between vitamin D status and CVD risk factors in AAs are partially mediated through circulating adipokines and CRP. More evidence, however, is required from longitudinal and randomized controlled studies to validate our findings.

Vitamin D and spinal cord injury: should we care?

STUDY DESIGN

Narrative review.

OBJECTIVES

This review provides an overview of the etiological factors and consequences of vitamin D insufficiency in relation to spinal cord injury (SCI) as well as important considerations for vitamin D supplementation.

SETTING

Montreal, Canada.

METHODS

Literature search.

RESULTS

Vitamin D insufficiency is common in SCI individuals owing to the presence of many contributing factors including limited sun exposure and intake, use of medication and endocrine perturbations. Although there are several biological plausible mechanisms by which vitamin D may act upon musculoskeletal and cardiometabolic health, the impact of vitamin D insufficiency on such systems remains ill defined in SCI. In the absence of guidelines for the management of vitamin D insufficiency in this high-risk population and in an attempt to provide clinical guidance, considerations for vitamin D supplementation such as the type of vitamin D, dosing regimens and toxicity are discussed and tentative recommendations suggested with particular reference to issues faced by SCI patients.

CONCLUSION

Although high rates of vitamin D insufficiency are encountered in SCI individuals, its consequences and the amount of vitamin D required to prevent insufficiency are still unknown, indicating a need for more intervention studies with well-defined outcome measures. Routine screening and monitoring of vitamin D as well as treatment of suboptimal status should be instituted in both acute and chronic setting. The close interactions between vitamin D and related bone minerals should be kept in mind when supplementing SCI individuals, and practices should be individualized with clinical conditions.

Vitamin D receptor gene associations with pulmonary tuberculosis in a Tibetan Chinese population

BACKGROUND

The vitamin D receptor (VDR) mediates the immunological function of vitamin D3, which activates macrophages, and vitamin D deficiency has been linked to tuberculosis risk. Single nucleotide polymorphisms (SNPs) in VDR may influence the function of vitamin D and susceptibility to tuberculosis.

METHODS

This study included 217 patients with pulmonary tuberculosis (PTB) and 383 healthy subjects in a Tibetan Chinese population living in and near Xi'an. Association analyses of SNPs in VDR were performed with the SPSS 17.0 statistical packages, SNP stats software, Haploview software package (version 4.2), and the SHEsis software platform.

RESULTS

Our results revealed a correlation between three SNPs (rs11574143, odds ratio [OR]: 1.47, 95 % confidence interval [CI]: 1.11 - 1.94, p = 0.006, p-adjust = 0.030; rs11574079, OR: 0.48, 95 % CI: 0.25 - 0.92, p = 0.023, p-adjust = 0.115; rs11168287, OR: 2.55, 95 % CI: 2.00 - 3.25, p = 1.730E-14, p-adjust = 0.865E-13) and PTB based on Chi-square tests. We observed the allele "A" of rs11574143 and rs11168287 increased the PTB risk and the allele "A" of rs11574079 provided a protective effect against PTB.

CONCLUSIONS

The goal of this study was the identification of putative associations between five SNPs (rs11574143, rs7975232, rs11574079, rs3819545 and rs11168287) in VDR and susceptibility to PTB. Our findings demonstrated associations between VDR polymorphisms and PTB development.

Vitamin D Receptor Gene Polymorphisms Are Associated with Abdominal Visceral Adipose Tissue Volume and Serum Adipokine Concentrations but Not with Body Mass Index or Waist Circumference in African Americans: The Jackson Heart Study

BACKGROUND

The biological actions of vitamin D are mediated through the vitamin D receptor (VDR). Single-nucleotide polymorphisms (SNPs) in the VDR gene have been previously associated with adiposity traits. However, to our knowledge, few studies have included direct measures of adiposity and adipokine concentrations.

OBJECTIVE

We examined the association of tagging SNPs in the VDR gene with multiple adiposity measures, including waist circumference (WC), body mass index (BMI), body fat percentage, subcutaneous and visceral adipose tissue (VAT) volume, and serum adipokine (adiponectin and leptin) concentrations in adult African Americans (AAs).

METHODS

Data from 3020 participants (61.9% women; mean age, 54.6 y) from the Jackson Heart Study were used for this analysis. Forty-five tag SNPs were chosen with the use of genotype data from the International HapMap project. We used linear regression to test the associations of imputed VDR SNPs with each of the traits, adjusted for age, sex, educational status, physical activity, smoking, alcohol intake, serum vitamin D concentration, European ancestry, and multiple testing.

RESULTS

The G allele of the SNP rs4328262 remained associated with increased VAT volume after multiple testing correction (β = 45.7; P < 0.001). The A allele of another SNP (rs11574070) was nominally associated with body fat percentage (β = 0.96; P = 0.002). None of the VDR SNPs analyzed showed any link with WC or BMI. The A allele of rs2228570 (β = 0.08; P = 0.001) for men and the T allele of rs2853563 (β = 0.04; P < 0.001) for women remained positively associated with serum adiponectin concentrations after multiple testing correction.

CONCLUSION

Although we did not find any association for anthropometric measures, we did observe associations of VDR variants with serum adipokines and with the more metabolically active fat, VAT. Therefore, our findings demonstrate a possible role of VDR variants in regulating adipose tissue activity and adiposity among AAs.

Low Vitamin D Levels Do Not Predict Hyperglycemia in Elderly Endurance Athletes (but in Controls)

BACKGROUND AND AIM

Recent studies revealed a link between hypovitaminosis D3 and the risk for hyperglycemia. Further mechanistic and interventional investigations suggested a common reason for both conditions rather than a causal relationship. Exposure to sunlight is the most relevant source of vitamin D3 (25(OH)D), whereas adipose tissue is able to store relevant amounts of the lipophilic vitamin. Since running/bicycling leads to increased out-door time and alters physiological response mechanisms, it can be hypothesized that the correlation between hypovitaminosis D3 and hyperglycemia might be disturbed in outdoor athletes.

METHODS

47 elderly marathoners/bicyclists and 47 age/sex matched controls were studied in a longitudinal setting at baseline and after three years. HbA1c as a surrogate for (pre-)diabetic states was quantified via HPLC, 25(OH)D levels were measured by means of chemiluminescent assays. Physical performance was assessed by ergometry.

RESULTS

When adjusted for seasonal variations, 25(OH)D was significantly higher in athletes than in controls. 25(OH)D levels inversely correlated with triglycerides in both groups, whereas only in controls an association between high BMI or low physical performance with hypovitaminosis D3 had been found. Likewise, the presence of hypovitaminosis D3 at baseline successfully predicted hyperglycemia at the follow up examinations within the control group (AUC = 0.85, 95% CI [0.74, 0.96], p < .001, statistically independent from BMI), but not in athletes.

CONCLUSION

Our data suggest that mechanisms of HbA1c elevation might differ between athletes and controls. Thus, intense physical activity must be taken into account as a potential pre-analytic confounder when it is aimed to predict metabolic risk by vitamin D3 levels.

Associations between Vitamin D Status and Type 2 Diabetes Measures among Inuit in Greenland May Be Affected by Other Factors

OBJECTIVE

Epidemiological studies have provided evidence of an association between vitamin D insufficiency and type 2 diabetes. Vitamin D levels have decreased among Inuit in Greenland, and type 2 diabetes is increasing. We hypothesized that the decline in vitamin D could have contributed to the increase in type 2 diabetes, and therefore investigated associations between serum 25(OH)D3 as a measure of vitamin D status and glucose homeostasis and glucose intolerance in an adult Inuit population.

METHODS

2877 Inuit (≥18 years) randomly selected for participation in the Inuit Health in Transition study were included. Fasting- and 2hour plasma glucose and insulin, C-peptide and HbA1c were measured, and associations with serum 25(OH)D3 were analysed using linear and logistic regression. A subsample of 330 individuals who also donated a blood sample in 1987, were furthermore included.

RESULTS

After adjustment, increasing serum 25(OH)D3 (per 10 nmol/L) was associated with higher fasting plasma glucose (0.02 mmol/L, p = 0.004), 2hour plasma glucose (0.05 nmol/L, p = 0.002) and HbA1c (0.39%, p<0.001), and with lower beta-cell function (-1.00 mmol/L, p<0.001). Serum 25(OH)D3 was positively associated with impaired fasting glycaemia (OR: 1.08, p = 0.001), but not with IGT or type 2 diabetes.

CONCLUSIONS

Our results did not support an association between low vitamin D levels and risk of type 2 diabetes. Instead, we found weak positive associations between vitamin D levels and fasting- and 2hour plasma glucose levels, HbA1c and impaired fasting glycaemia, and a negative association with beta-cell function, underlining the need for determination of the causal relationship.

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).

Role of vitamin D in diabetes mellitus and chronic kidney disease

Approximately 30%-50% of people are recognized to have low levels of vitamin D, and insufficiency and deficiency of vitamin D are recognized as global health problems worldwide. Although the presence of hypovitamin D increases the risk of rickets and fractures, low vitamin D levels are also associated with hypertension, cancer, and cardiovascular disease. In addition, diabetes mellitus (DM) and chronic kidney disease (CKD) are also related to vitamin D levels. Vitamin D deficiency has been linked to onset and progression of DM. Although in patients with DM the relationship between vitamin D and insulin secretion, insulin resistance, and β-cell dysfunction are pointed out, evidence regarding vitamin D levels and DM is contradictory, and well controlled studies are needed. In addition, vitamin D influences the renin-angiotensin system, inflammation, and mineral bone disease, which may be associated with the cause and progression CKD. There is increasing evidence that vitamin D deficiency may be a risk factor for DM and CKD; however, it remains uncertain whether vitamin D deficiency also predisposes to death from DM and CKD. Although at this time, supplementation with vitamin D has not been shown to improve glycemic control or prevent incident DM, clinical trials with sufficient sample size, study periods, and optimal doses of vitamin D supplementation are still needed. This review focuses on the mechanism of vitamin D insufficiency and deficiency in DM or CKD, and discusses the current evidence regarding supplementation with vitamin D in patients with these diseases.

Post-Transplant Diabetes Mellitus: Causes, Treatment, and Impact on Outcomes

Post-transplant diabetes mellitus (PTDM) is a frequent consequence of solid organ transplantation. PTDM has been associated with greater mortality and increased infections in different transplant groups using different diagnostic criteria. An international consensus panel recommended a consistent set of guidelines in 2003 based on American Diabetes Association glucose criteria but did not exclude the immediate post-transplant hospitalization when many patients receive large doses of corticosteroids. Greater glucose monitoring during all hospitalizations has revealed significant glucose intolerance in the majority of recipients immediately after transplant. As a result, the international consensus panel reviewed its earlier guidelines and recommended delaying screening and diagnosis of PTDM until the recipient is on stable doses of immunosuppression after discharge from initial transplant hospitalization. The group cautioned that whereas hemoglobin A1C has been adopted as a diagnostic criterion by many, it is not reliable as the sole diabetes screening method during the first year after transplant. Risk factors for PTDM include many of the immunosuppressant medications themselves as well as those for type 2 diabetes. The provider managing diabetes and associated dyslipidemia and hypertension after transplant must be careful of the greater risk for drug-drug interactions and infections with immunosuppressant medications. Treatment goals and therapies must consider the greater risk for fluctuating and reduced kidney function, which can cause hypoglycemia. Research is actively focused on strategies to prevent PTDM, but until strategies are found, it is imperative that immunosuppression regimens are chosen based on their evidence to prolong graft survival, not to avoid PTDM.

The NRAMP1, VDR, TNF-α, ICAM1, TLR2 and TLR4 gene polymorphisms in Iranian patients with pulmonary tuberculosis: A case-control study

The innate immune response drives early events in Mycobacterium tuberculosis infection. Since human genetic variation is an important determinant in the outcome of infection with M. tuberculosis, we typed polymorphisms in the innate immune molecules, such as natural-resistance-associated macrophage protein 1 (NRAMP1), Vitamin D receptor (VDR), Tumor necrosis factor alpha (TNF-α), intercellular adhesion molecule1 (ICAM-1), Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4) in a case-control study of pulmonary tuberculosis in Iranian population. We conducted an association study and included 96 patients and 122 matched healthy individuals. We used single ARMS-PCR technique to simultaneously genotype fourteen polymorphisms in this survey. Among all fourteen polymorphisms that were examined, three polymorphisms were significantly different between case and control groups. The TNF -308A polymorphism showed significant increase in allele and genotype frequencies among patients compared to control individuals [-308A allele: 19.3 vs. 9.4%, GA genotype: 28.1 vs. 17.2%, AA genotype: 5.2 vs. 0.8%; Corrected P (Pc)<0.05], and the TLR4 variant allele and genotypes prevalence (D299G and T399I) were significantly higher among patients compared to controls [DG genotype: 14.6 vs. 5.7%, Pc<0.05 and I399 allele: 4.2 vs. 0.8%, TI genotype: 8.3 vs. 1.6%; Pc<0.05], respectively. In conclusion, our data suggest that TLR4 (D299G and T399I) and TNF (-308G/A) genetic polymorphisms may influence the risk of developing tuberculosis after exposure to Mycobacterium.

The risks and benefits of sun exposure 2016

Public health authorities in the United States are recommending that men, women and children reduce their exposure to sunlight, based on concerns that this exposure will promote skin cancer. On the other hand, data show that increasing numbers of Americans suffer from vitamin D deficiencies and serious health problems caused by insufficient sun exposure. The body of science concerning the benefits of moderate sun exposure is growing rapidly, and is causing a different perception of sun/UV as it relates to human health. Melanoma and its relationship to sun exposure and sunburn is not adequately addressed in most of the scientific literature. Reports of favorable health outcomes related to adequate serum 25(OH)D concentration or vitamin D supplementation have been inappropriately merged, so that benefits of sun exposure other than production of vitamin D are not adequately described. This review of recent studies and their analyses consider the risks and benefits of sun exposure which indicate that insufficient sun exposure is an emerging public health problem. This review considers the studies that have shown a wide range health benefits from sun/UV exposure. These benefits include among others various types of cancer, cardiovascular disease, Alzheimer disease/dementia, myopia and macular degeneration, diabetes and multiple sclerosis. The message of sun avoidance must be changed to acceptance of non-burning sun exposure sufficient to achieve serum 25(OH)D concentration of 30 ng/mL or higher in the sunny season and the general benefits of UV exposure beyond those of vitamin D.

Incidence rate of type 2 diabetes is >50% lower in GrassrootsHealth cohort with median serum 25-hydroxyvitamin D of 41 ng/ml than in NHANES cohort with median of 22 ng/ml

Higher serum 25-hydroxyvitamin D [25(OH)D] concentrations have been associated with lower risk of type 2 diabetes. This study compared incidence rates of type 2 diabetes among participants aged ≥20 years in two U.S. cohorts with markedly different median 25(OH)D concentrations. The median 25(OH)D concentration in the GrassrootsHealth (GRH) cohort was 41 ng/ml (N=4933) while in the 2005-6 National Health and Nutrition Examination Survey (NHANES) it was 22 ng/ml (N=4078) (P<0.0001). The adjusted annual incidence rate of type 2 diabetes was 3.7 per 1000 population (95% confidence interval=1.9, 6.6) in the GRH cohort, compared to 9.3 per 1000 population (95% confidence interval=6.7, 12.6) in NHANES. In the NHANES cohort, the lowest 25(OH)D tertiles (<17, 17-24 ng/ml) had higher odds of developing diabetes than the highest tertile (OR: 4.9, P=0.02 and 4.8, P=0.01 respectively), adjusting for covariates. Differences in demographics and methods may have limited comparability. Raising serum 25(OH)D may be a useful tool for reducing risk of diabetes in the population.

Fish consumption and frying of fish in relation to type 2 diabetes incidence: a prospective cohort study of Swedish men

Purpose

Epidemiological evidence on the association between fish consumption and risk of type 2 diabetes is heterogeneous across geographical regions. Differences related to fish consumption pattern could possibly help explain the discrepancy between the findings. We therefore aimed to investigate the association between fish consumption (total, fried, specific fish items) and type 2 diabetes incidence, taking exposure to contaminants present in fish (polychlorinated biphenyls and methyl mercury) into consideration.

Methods

The population-based Cohort of Swedish Men, including 35,583 men aged 45–79 years, was followed from 1998 to 2012. We estimated hazard ratios (HRs) with 95 % confidence intervals (CIs) using Cox proportional hazards models.

Results

During 15 years of follow-up, 3624 incident cases were identified. Total fish consumption (≥4 servings/week vs. <1 serving/week) was not associated with type 2 diabetes in multivariable-adjusted analysis (HR 1.00; 95 % CI 0.85–1.18); however, a statistically non-significant inverse association was observed after adjustment for dietary contaminant exposures (HR 0.79; 95 % CI 0.60–1.04). Fried fish (≥6 servings/month vs. ≤1 servings/month) and shellfish consumption (≥1 serving/week vs. never/seldom) were associated with HRs of 1.14 (95 % CI 1.03–1.31) and 1.21 (95 % CI 1.07–1.36), respectively.

Conclusions

We observed no overall association between total fish consumption and type 2 diabetes. The results indicated that dietary contaminants in fish may influence the relationship. Fried fish and shellfish consumption were associated with higher type 2 diabetes incidence. These findings suggest that more specific advice on fish species sub-types (varying in contamination) and preparation methods may be warranted.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-015-1132-6) contains supplementary material, which is available to authorized users.

Significant differences in fecal microbiota are associated with various stages of glucose tolerance in African American male veterans

The importance of gut microbiota in pathogenesis of diabetes remains unknown. This study investigated the relationship between microbiota and metabolic markers in African American men (AAM) with prediabetes and hypovitaminosis D. The study was ancillary to a randomized trial of vitamin D supplementation with weekly ergocalciferol (50,000 IU) conducted in AAM veterans over 12 months (D Intervention in Veterans Affairs). Glycemic groups (Gr) were characterized based on changes in oral glucose tolerance between baseline and exit. Subjects with stable normal glucose tolerance were assigned to Gr-1 and those with stable prediabetes (impaired glucose tolerance and impaired fasting glucose) to Gr-2. Microbiota composition was analyzed in stool collected at the exit (n = 115) and compared between Gr-1 and Gr-2, as well as between the lowest and highest quartiles of dietary intake of energy and fat, hemoglobin A1c, and serum 25-hydroxyvitamin D (25[OH]D) level. Differences between Gr-1 and Gr-2 included the Bacteroidetes/Firmicutes and Bacteroidales/Clostridia ratios and differences in genera such as Ruminococcus and Dialister. Changes in specific taxa associated with the lowest and highest quartiles of 25(OH)D (eg, Ruminococcus, Roseburia, Blautia, Dorea) were clearly distinct from those of dietary intake (eg, Bacteroides, Bacteroides/Prevotella ratio) or A1c (eg, Faecalibacterium, Catenibacterium, Streptococcus). These findings suggest a novel interaction between microbiota and vitamin D and a role for microbiota in early stages of diabetes development. Although results suggest that specific taxa are associated with glycemic stability over time, a causative relationship between microbiota makeup and dysglycemia is still to be demonstrated.

Oral Vitamin D Supplements Increase Serum 25-Hydroxyvitamin D in Postmenopausal Women and Reduce Bone Calcium Flux Measured by 41Ca Skeletal Labeling

BACKGROUND

Ensuring adequate vitamin D status in older adults may reduce the risk of osteoporosis. The serum 25-hydroxyvitamin D [25(OH)D] concentration is the recommended biomarker of vitamin D status, but the optimal serum 25(OH)D concentration for bone health in postmenopausal women remains unclear.

OBJECTIVE

The aim of this study was to apply the highly sensitive (41)Ca skeletal labeling technique and the measurement of urinary (41)Ca:(40)Ca ratios to determine the serum 25(OH)D concentration that has greatest benefit on bone calcium flux in postmenopausal women.

METHODS

We administered a mean intravenous (41)Ca dose of 870 pmol to healthy postmenopausal women [n = 24, age (mean ± SD): 64 ± 6.0 y] without osteoporosis. After 6 mo, at the nadir of their wintertime serum 25(OH)D status, each of the women sequentially consumed daily oral cholecalciferol supplements of 10, 25, and 50 μg/d (in this order), each for 3 mo. We assessed serum 25(OH)D concentrations monthly and urinary (41)Ca:(40)Ca ratios biweekly. (41)Ca:(40)Ca ratios were measured with low-energy accelerator mass spectrometry. With the use of pharmacokinetic analysis, we determined the effect of varying serum 25(OH)D concentrations on (41)Ca transfer rates.

RESULTS

At baseline, the mean (95% CI) serum 25(OH)D concentration was 16.2 (13.5, 18.8) μg/L. After the first, second, and third intervention periods, mean (95% CI) serum 25(OH)D increased to 29.8 (27.2, 32.4), 36.9 (34.2, 39.7), and 46.6 (41.2, 52.0) μg/L, respectively. Supplementation was associated with a downward shift in the urinary (41)Ca:(40)Ca ratio compared with the predicted (41)Ca:(40)Ca ratio without vitamin D supplementation. In the model, the most likely site of action of the increase in serum 25(OH)D was transfer from the central compartment to a fast exchanging compartment. At this transfer rate, predicted values were a concentration with half-maximal effect of 2.33 μg/L and an estimate of the maximal effect of 31.7%. After the first, second, and third intervention periods, the mean changes in this transfer rate were +18.0%, +25.7%, and +28.5%, respectively.

CONCLUSION

In healthy postmenopausal women, increasing serum 25(OH)D primarily affects calcium transfer from the central compartment to a fast exchanging compartment; it is possible that this represents transfer from the extracellular space to the surface of bone. A serum 25(OH)D concentration of ~40 μg/L achieves ~90% of the expected maximal effect on this transfer rate. This trial was registered at clinicaltrials.gov as NCT01053481.

Maternal-fetal impact of vitamin D deficiency: a critical review

Research into the extra-skeletal functions of vitamin D has been expanding in recent years. During pregnancy, maternal vitamin D status may be of concern because of the key role of this vitamin in fetal skeletal development and due to the association between hypovitaminosis D and adverse maternal-fetal outcomes. Therefore, the objective of this manuscript was to review the maternal-fetal impact of gestational vitamin D deficiency and the benefits of vitamin D supplementation during pregnancy. A literature search was performed in PubMed and Embase employing the following keywords: vitamin D deficiency, pregnancy, 25-hydroxyvitamin D, and hypovitaminosis D. All relevant articles in English language published since 1980 were analysed by the two authors. Neonatal complications derived from vitamin D deficiency include low birth weight, growth restriction, and respiratory tract infection. In the mother, vitamin D deficiency has been associated with altered glucose homeostasis and increased incidence of gestational diabetes mellitus, pre-eclampsia, and bacterial vaginosis. However, the current state of the evidence is controversial for some other endpoints and the actual benefit of vitamin D supplementation in pregnancy remains unclear. Additional longitudinal studies may clarify the actual impact of vitamin D deficiency during pregnancy, and randomised trials are required to define the benefits of vitamin D supplementation in reducing the incidence of adverse outcomes in the mother and infant.

Circulating 25-hydroxyvitamin D and risk of lung cancer: a dose-response meta-analysis

BACKGROUND

Mounting experimental evidence supports a protective effect of high 25-hydroxyvitamin D (25[OH]D), a good indicator of vitamin D status, on risk of various cancers including lung cancer. However, prospective observational studies examining the 25(OH)D-lung cancer association reported inconsistent findings. A dose-response meta-analysis was carried out to elucidate the subject.

METHODS

Potentially eligible studies were identified by searching PubMed and EMBASE databases, and by carefully reviewing the bibliographies of retrieved publications. The summary relative risks (RRs) with 95% confidence intervals (CIs) were calculated using the random-effects model.

RESULTS

Thirteen reports from ten prospective studies were included, totaling 2,227 lung cancer events. Results of the meta-analysis showed a significant 5% (RR 0.95, 95% CI 0.91-0.99) reduction in the risk of lung cancer for each 10 nmol/L increment in 25(OH)D concentrations. This inverse association was not significantly modified by area, study duration, sex, methods for 25(OH)D measurement, baseline 25(OH)D levels, or quality score of included studies. There was evidence of a nonlinear relationship between 25(OH)D and risk of lung cancer (p-nonlinearity = 0.02), with the greatest reductions in risk observed at 25(OH)D of nearly 53 nmol/L, and remained protective until approximately 90 nmol/L. Further increases showed no significant association with cancer risk, but scanty data were included in the analyses of high-level 25(OH)D. There was no evidence of publication bias.

CONCLUSION

This dose-response meta-analysis of prospective studies suggests that 25(OH)D may be associated with reduced risk of lung cancer, in particular among subjects with vitamin D deficiencies.

Seasonal variations in serum 25-hydroxy vitamin D levels in a Swedish cohort

To study seasonal inter-individual and intra-individual variations in serum 25-hydroxy vitamin D (25(OH)D) and to explore parameters associated with 25(OH)D in a healthy Swedish adult population. 540 blood donors (60 % men; mean age 41 ± 13 years) and 75 thrombocyte donors (92 % men, aged 46 ± 11 years) were included. Serum was collected during 12 months and analyzed for 25(OH)D and parathyroid hormone (S-iPTH). The blood donors answered questionnaires concerning vitamin D supplements, smoking, physical activity, sunbed use and sun holidays. Repeated serum samples were collected from the thrombocyte donors to study the intra-individual variations in S-25(OH)D. S-25(OH)D varied greatly over the year correlating with the intensity of the UV-B irradiation (r S = 0.326; p < 0.001). During January-March, a S-25(OH)D level below the thresholds of 50 and 75 nmol/L was observed in 58 and 88 %, respectively, and during July-September in 11 and 50 % (p < 0.001). S-25(OH)D was negatively correlated with body mass index and S-iPTH, but was significantly higher in holiday makers in sunny destinations, sunbed users, non-smokers, and in the physically active. The intra-individual analyses showed a mean increase in S-25(OH)D by 8 nmol/L/month between April and August. Approximately 75 % had serum 25(OH)D values <75 nmol/L during 75 % of the year and 50 % had serum 25(OH)D <50 nmol/L during 50 % of the year. Serum 25(OH)D was strongly associated with parameters related to sun exposure, but only weakly with intake of vitamin D supplements.

Is there a relationship between vitamin D with insulin resistance and diabetes mellitus?

Available data suggest a possible link between abnormal vitamin D level and abnormal glucose homeostasis, two of the most common chronic medical conditions. Both conditions are associated with inflammation, and the exact mechanism for role of either on the other is not well clear. Literature investigating the link between vitamin D and either pre-diabetic states or diabetes is reviewed. Vitamin D deficiency is detrimental to insulin synthesis and secretion in animal and human studies. In humans, it has been shown by majority of observational studies, that vitamin D is positively correlated with insulin sensitivity and its role is mediated both by direct mechanism through the availability of vitamin D receptors in several tissues and indirectly through the changes in calcium levels. Large number of, but not all, variable samples cross sectional human trials have demonstrated an inverse relation between vitamin D status and impaired glucose tolerance, insulin resistance or diabetes. To compliment this conclusively, evidence from intervention studies is critically warranted before we can frankly state that vitamin D plays a role in diabetes prevention or treatment. Absence of both sizable prospective observational trials utilizing 25(OH)D as the main variable and the non-availability of randomized studies specifically designed to assess the effects of vitamin D on pre-diabetes and diabetes states, are the main obstacles to draw solid and conclusive relationships.