No effect of high-dose vitamin D supplementation on glycemic status or cardiovascular risk factors in subjects with prediabetes

A Systematic Review Supporting the Endocrine Society Clinical Practice Guidelines on Vitamin D

CONTEXT

Low vitamin D status is common and is associated with various common medical conditions.

OBJECTIVE

To support the development of the Endocrine Society's Clinical Practice Guideline on Vitamin D for the Prevention of Disease.

METHODS

We searched multiple databases for studies that addressed 14 clinical questions prioritized by the guideline panel. Of the 14 questions, 10 clinical questions assessed the effect of vitamin D vs no vitamin D in the general population throughout the lifespan, during pregnancy, and in adults with prediabetes; 1 question assessed dosing; and 3 questions addressed screening with serum 25-hydroxyvitamin D (25[OH]D). The Grading of Recommendations Assessment, Development and Evaluation approach was used to assess certainty of evidence.

RESULTS

Electronic searches yielded 37 007 citations, from which we included 151 studies. In children and adolescents, low-certainty evidence suggested reduction in respiratory tract infections with empiric vitamin D. There was no significant effect on select outcomes in healthy adults aged 19 to 74 years with variable certainty of evidence. There was a very small reduction in mortality among adults older than 75 years with high certainty of evidence. In pregnant women, low-certainty evidence suggested possible benefit on various maternal, fetal, and neonatal outcomes. In adults with prediabetes, moderate certainty of evidence suggested reduction in the rate of progression to diabetes. Administration of high-dose intermittent vitamin D may increase falls, compared to lower-dose daily dosing. We did not identify trials on the benefits and harms of screening with serum 25(OH)D.

CONCLUSION

The evidence summarized in this systematic review addresses the benefits and harms of vitamin D for the prevention of disease. The guideline panel considered additional information about individuals' and providers' values and preferences and other important decisional and contextual factors to develop clinical recommendations.

Vitamin D and Risk of Incident Type 2 Diabetes in Older Adults: An Updated Systematic Review and Meta-Analysis

Vitamin D deficiency is very common worldwide, particularly in old age, when people are at the highest risk of the negative adverse consequences of hypovitaminosis D. Additionally to the recognized functions in the regulation of calcium absorption, bone remodeling, and bone growth, vitamin D plays a key role as a hormone, which is supported by various enzymatic, physiological, metabolic, and pathophysiological processes related to various human organs and systems. Accruing evidence supports that vitamin D plays a key role in pancreatic islet dysfunction and insulin resistance in type 2 diabetes. From an epidemiological viewpoint, numerous studies suggest that the growing incidence of type 2 diabetes in humans may be linked to the global trend of prevalent vitamin D insufficiency. In the past, this association has raised discussions due to the equivocal results, which lately have been more convincing of the true role of vitamin D supplementation in the prevention of incident type 2 diabetes. Most meta-analyses evaluating this role have been conducted in adults or young older persons (50-60 years old), with only one focusing on older populations, even if this is the population at greater risk of both hypovitaminosis D and type 2 diabetes. Therefore, we conducted an update of the previous systematic review and meta-analysis examining whether hypovitaminosis D (low serum 25OHD levels) can predict incident diabetes in prospective longitudinal studies among older adults. We found that low 25OHD was associated with incident diabetes in older adults even after adjusting for several relevant potential confounders, confirming and updating the results of the only previous meta-analysis conducted in 2017.

Vitamins and Minerals for Blood Pressure Reduction in the General, Normotensive Population: A Systematic Review and Meta-Analysis of Six Supplements

Hypertension is the leading preventable risk factor for cardiovascular disease and all-cause mortality worldwide. However, studies have shown increased risk of mortality from heart disease and stroke even within the normal blood pressure (BP) range, starting at BPs above 110-115/70-75 mm Hg. Nutraceuticals, such as vitamins and minerals, have been studied extensively for their efficacy in lowering BP and may be of benefit to the general, normotensive population in achieving optimal BP. Our study investigated the effects of six nutraceuticals (Vitamins: C, D, E; Minerals: Calcium, Magnesium, Potassium) on both systolic blood pressure (SBP) and diastolic blood pressure (DBP) in this population. We performed a systematic review and pairwise meta-analysis for all six supplements versus placebo. Calcium and magnesium achieved significant reductions in both SBP and DBP of -1.37/-1.63 mm Hg and -2.79/-1.56 mm Hg, respectively. Vitamin E and potassium only yielded significant reductions in SBP with values of -1.76 mm Hg and -2.10 mm Hg, respectively. Vitamins C and D were not found to significantly lower either SBP or DBP. Future studies should determine optimal dosage and treatment length for these supplements in the general, normotensive population.

Systematic comparison of Mendelian randomisation studies and randomised controlled trials using electronic databases

OBJECTIVE

To scope the potential for (semi)-automated triangulation of Mendelian randomisation (MR) and randomised controlled trials (RCTs) evidence since the two methods have distinct assumptions that make comparisons between their results invaluable.

METHODS

We mined ClinicalTrials.Gov, PubMed and EpigraphDB databases and carried out a series of 26 manual literature comparisons among 54 MR and 77 RCT publications.

RESULTS

We found that only 13% of completed RCTs identified in ClinicalTrials.Gov submitted their results to the database. Similarly low coverage was revealed for Semantic Medline (SemMedDB) semantic triples derived from MR and RCT publications -36% and 12%, respectively. Among intervention types that can be mimicked by MR, only trials of pharmaceutical interventions could be automatically matched to MR results due to insufficient annotation with Medical Subject Headings ontology. A manual survey of the literature highlighted the potential for triangulation across a number of exposure/outcome pairs if these challenges can be addressed.

CONCLUSIONS

We conclude that careful triangulation of MR with RCT evidence should involve consideration of similarity of phenotypes across study designs, intervention intensity and duration, study population demography and health status, comparator group, intervention goal and quality of evidence.

Effect of Vitamin D Supplementation on Psoriasis Severity in Patients With Lower-Range Serum 25-Hydroxyvitamin D Levels: A Randomized Clinical Trial

Importance

Topical vitamin D analogues are routine treatment for psoriasis, but the effect of oral supplementation has not been established.

Objective

To examine the effect of vitamin D supplementation on psoriasis severity throughout the winter.

Design, Setting, and Participants

This randomized, double-blind placebo-controlled clinical trial with 2 parallel groups was performed through 2 winter seasons (2017 to 2018 and 2018 to 2019). Randomization was computer generated. All participants, health care clinicians, and outcome assessors were masked to group assignment. Each participant was followed for 4 months. The presented analyses were conducted in May 2022. The trial was conducted at the clinical research unit of the University Hospital of North Norway (Tromsø; Norway). Adults from the general population in Tromsø with active plaque psoriasis and 25-hydroxyvitamin D (25[OH]D) levels of less than 24 ng/mL (to convert to nmol/L, multiply by 2.496) were included.

Intervention

Vitamin D (cholecalciferol, 100 000 IU, loading dose, followed by 20 000 IU/week) or placebo for 4 months.

Main outcomes and Measures

Psoriasis Area Severity Index (PASI) (primary outcome), Physician Global Assessment, self-administered PASI, and Dermatology Life Quality Index scores (secondary outcomes).

Results

A total of 122 participants (46 women [37.7%]; mean [SD] age, 53.6 [10.0] years; mean [SD] PASI score, 3.1 [2.0]; mean [SD] serum 25(OH)D, 14.9 [3.9] ng/mL) were included. Of these, 60 (49.2%) were randomized to the vitamin D group and 62 (50.8%) to the placebo group. A total of 120 participants (59 vitamin D [49.2%]/61 placebo [51.8%]) completed the study. By completion, mean (SD) 25(OH)D levels were 29.7 (5.2) ng/mL (vitamin D) and 12.0 (3.8) ng/mL (placebo). There was no significant difference in change in PASI score between the groups (adjusted difference, 0.11; 95% CI, -0.23 to 0.45). There was no significant difference in change in Physician Global Assessment score (adjusted odds ratio, 0.66; 95% CI, 0.27-1.63), self-administered PASI (adjusted difference, -0.60; 95% CI, -1.76 to 0.55) or Dermatology Life Quality Index (adjusted difference, -0.86; 95% CI, -1.9 to 0.19) between the groups. No adverse effects of the intervention were registered.

Conclusion and Relevance

The results of this randomized clinical trial showed that vitamin D supplementation did not affect psoriasis severity. Low baseline severity scores may explain the lack of measurable effect. Levels of 25(OH)D in the intervention group increased to a less-than-expected degree based on previous experimental data from the same source population, and this may have affected the results.

Trial Registration

ClinicalTrials.gov Identifier: NCT03334136.

The Effect of Vitamin D Supplementation on Incidence of Type 2 Diabetes: A Systematic Review

With the clinical increase in Type 2 Diabetes worldwide, several interventions to decrease its incidence have been investigated. One such intervention is Vitamin D supplementation, as it affects Insulin secretion from the pancreas and Insulin receptors in the cells of the body. This systematic review addresses whether or not Vitamin D supplementation has a role in reducing the risk of developing Type 2 Diabetes. Systematic searches were conducted on PubMed, and Cochrane Library mainly but also checked Google Scholar. Randomized controlled trials, systematic trials and cohort studies were retrieved that included keywords pertaining to Vitamin D supplementation and the incidence of Type 2 Diabetes. Exclusion criteria included studies that looked at different forms of Diabetes, studies including patients aged less than 18 or more than 85 years of age and studies that were not English language. For all the trials identified, the incidence of Type 2 Diabetes among the cohort receiving vitamin D supplementation was compared to the cohort receiving placebo medication. Additionally, the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) was analyzed to observe if there was a difference between Insulin resistance among these two cohorts between the start of the trials and the end. Thirteen randomized controlled trials were identified. Seven of these identified incidences of Type 2 Diabetes as a research outcome, out of which six showed no statistically significant impact of vitamin D on the incidence of Type 2 Diabetes. Out of the 13 trials, 10 analyzed the impact of vitamin D supplementation on patients' HOMA-IR. In six of these trials, patients receiving vitamin D supplementation had a decrease in their HOMA-IR, while it increased in 4 trials. In seven of the ten trials that analyzed for HOMA-IR, the HOMA-IR was less in the vitamin D cohort than the placebo cohort. There is insufficient evidence to suggest that vitamin D supplementation significantly reduces the incidence of Type 2 Diabetes despite its effects on insulin resistance. Further research in this area would be helpful in order to influence clinical guidelines on vitamin D supplementation among patients at risk of Type 2 Diabetes.

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

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

Longitudinal changes in vitamin D concentrations and the association with type 2 diabetes mellitus: the Tromsø Study

AIM

We aimed to investigate the relationship between pre- and post-diagnostic 25-hydroxyvitamin D (25(OH)D) concentrations and type 2 diabetes (T2DM) over a period of 30 years in individuals who developed T2DM compared to healthy controls.

METHODS

This case-control study included 254 participants with blood samples collected at five different time-points (T1-T5) between 1986 and 2016. Of the 254 participants, 116 were diagnosed with T2DM between T3 and T4, and were considered cases; the remaining 138 were controls. Linear mixed regression models were used to examine pre- and post-diagnostic changes in 25(OH)D concentrations, and logistic regression was used to examine associations between these concentrations and T2DM at each time-point.

RESULTS

25(OH)D concentrations at different time-points and the longitudinal change in concentrations differed between cases and controls, and by sex. For women, each 5-nmol/l increase in 25(OH)D concentrations was inversely associated with T2DM at T3 (odds-ratio, OR, 0.79), whereas for men, this same increase was positively associated with T2DM at T1 (OR 1.12). Cases experienced a significant decrease in pre-diagnostic 25(OH)D concentrations (p value < 0.01 for women, p value = 0.02 for men) and a significant increase in post-diagnostic 25(OH)D concentrations (p value < 0.01 for women, p value = 0.01 for men). As such, each 1-unit increase in month-specific z-score change between T1 and T3 was significantly inversely associated with T2DM (OR 0.51 for women, OR 0.52 for men), and each such increase between T3 and T5 was significantly positively associated with T2DM in women (OR 2.48).

CONCLUSIONS

25(OH)D concentrations seem to be affected by disease progression and type 2 diabetes diagnosis.

Combined vitamin D and magnesium supplementation does not influence markers of bone turnover or glycemic control: A randomized controlled clinical trial

High-dose vitamin D supplementation can increase total osteocalcin concentrations that may reduce insulin resistance in individuals at risk for prediabetes or diabetes mellitus. Magnesium is a cofactor in vitamin D metabolism and activation. The purpose of this study was to determine the combined effect of vitamin D and magnesium supplementation on total osteocalcin concentrations, glycemic indices, and other bone turnover markers after a 12-week intervention in individuals who were overweight and obese, but otherwise healthy. We hypothesized that combined supplementation would improve serum total osteocalcin concentrations and glycemic indices more than vitamin D supplementation alone or a placebo. A total of 78 women and men completed this intervention in 3 groups: a vitamin D and magnesium group (1000 IU vitamin D₃ and 360 mg magnesium glycinate), a vitamin D group (1000 IU vitamin D₃), and a placebo group. Despite a significant increase in serum 25-hydroxyvitamin D concentrations in the vitamin D and magnesium group compared with the placebo group (difference = 5.63; CI, -10.0 to -1.21; P = .001) post-intervention, there were no differences in serum concentrations of total osteocalcin, glucose, insulin, and adiponectin or the homeostatic model assessment of insulin resistance (HOMA-IR) among groups (P > .05 for all). Additionally, total osteocalcin (β = -0.310, P = .081), bone-specific alkaline phosphatase (β = 0.004, P = .986), and C-terminal cross-linked telopeptide (β = 0.426, P = .057), were not significant predictors of HOMA-IR after the intervention. Combined supplementation was not associated with short-term improvements in glycemic indices or bone turnover markers in participants who were overweight and obese in our study. This trial was registered at clinicaltrials.gov (NCT03134417).

The enigma of vitamin D supplementation in aging with obesity

INTRODUCTION

The American Geriatrics Society recommends a minimum daily supplement of 1,000 IU and underlines that a dosage lower than 600 IU do not prevent falls in elderly people.

EVIDENCE ACQUISITION

The author searched on PubMed, Medline, Embase, Scopus database the MeSH terms and keywords of "vitamin D," "(25(OH)D)," "elderly" and "obesity." The aim of this study was to support the rationale on the correct vitamin D supplementation in elderly people with obesity and overweight.

EVIDENCE SYNTHESIS

Ten studies were found suitable for consideration in writing this comprehensive evidence-based rapid review. The supplementation of vitamin D included 1500 elderly subjects with Body Mass Index (BMI) over 25 kg/m². This article proved that the daily vitamin D supplementation from 2000 to 4000 UI is highly recommended in elderly people with obesity because of: 1) sequestration of vitamin D by the adipose tissue; 2) increased catabolism of vita-in D in the adipose tissue; 3) decreased synthesis of serum 25 hydroxyvitamin D (25(OH)D) in the liver; 4) reduced sun-exposure; and 5) dosages equal at 1000 UI or lower that did not show any important effect on vitamin D deficiency and on related comorbidities in elderly people with obesity.

CONCLUSIONS

Gender, baseline levels of serum (25(OH)D) concentration, ethnicity and severity of BMI should be accounted for the correct supplementation of vitamin D in elderly population for the precision medicine goal.

The effect of vitamin D supplementation on glycemic status of elderly people with prediabetes: a 12-month open-label, randomized-controlled study

BACKGROUND

Data on the efficacy of vitamin D in improving the glycemic status of elderly people with prediabetes are scarce. This open-label, randomized-controlled trial investigated the effect of vitamin D supplementation on glycemic markers of Greek people with prediabetes aged 60 years or above, over 12 months.

RESEARCH DESIGN AND METHODS

Participants were randomized to a weekly vitamin D₃ dose of 25,000 IU (n = 45) or nothing (n = 45), on top of lifestyle measures. Anthropometric and glycemic markers were assessed at baseline, 3, 6, and 12 months.

RESULTS

Supplemented participants demonstrated a significant increase in 25(OH)D concentrations at 3,      6,      and 12 months     compared to baseline    . In the intervention group, fasting glucose was decreased at 6 months compared to baseline (96.12 ± 5.51 vs 103.40 ± 12.05 mg/dl, p < 0.01) and glycated hemoglobin was significantly lower at 6 and 12 months compared to baseline [5.82 ± 0.21% vs 5.87 ± 0.21%, p = 0.004 and 5.80 ± 0.23% vs 5.87 ± 0.21%, p < 0.001, respectively].

CONCLUSIONS

Vitamin D could be complementary to lifestyle change strategy for the management of prediabetes in the elderly.

CLINICAL TRIAL REGISTRATION

ISRCTN51643592.

Effect of Vitamin D Supplementation on the Regulation of Blood Pressure in Iranian Patients with Essential Hypertension: A Clinical Trial

BACKGROUND

Low serum vitamin D level is associated with both high blood pressure and incidence of primary hypertension. Experimental studies suggest that vitamin D supplements may reduce blood pressure.

OBJECTIVE

The aim of this study was to investigate whether vitamin D supplementation reduces systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) in Iranian patients with essential hypertension.

METHOD

A total of 173 patients with essential hypertension participated in this open-label clinical trial. SBP, DBP, and serum vitamin D levels were measured at baseline and at the end of the study. Vitamin D was administered at a dose of 50,000 IU/week, and 1000 IU/day in patients with serum vitamin D levels <20 ng/mL and 20-30 ng/mL, respectively, for 8 weeks.

RESULTS

Based on serum vitamin D levels, 45.1%, 17.3%, and 29.5% of patients were deficient, insufficient, and sufficient for vitamin D intake, respectively. Baseline serum levels of vitamin D were not correlated with SBP, DBP, and MAP at the beginning of the study (p = ns). Multiple logistic regression analysis revealed that the risk of vitamin D deficiency was 2.5-fold times higher in women than in men (p = 0.03). After 8 weeks of supplementation with vitamin D, mean SBP and MAP were significantly reduced by 5.5 ± 16.16 (p = 0.01) and 3.7 ± 9.24 (p = 0.004) mmHg, respectively. Neither sex nor age could significantly predict BP response to vitamin D supplementation.

CONCLUSION

Vitamin D supplementation may significantly reduce SBP and MAP but not DBP in patients with essential hypertension.

Economic evaluation of a national vitamin D supplementation program among Iranian adolescents for the prevention of adulthood type 2 diabetes mellitus

BACKGROUND

This study aimed to evaluate the cost-effectiveness of vitamin D supplementation in preventing type 2 diabetes mellitus (T2DM) among Iranian adolescents.

METHODS

This analytical observational study was conducted, using the decision tree model constructed in TreeAge Pro to assess the cost per quality-adjusted life-year (QALY) of monthly intake vitamin D supplements to prevent T2DM compared to no intervention from the viewpoint of Iran's Ministry of Health and through an one-year horizon. In the national program of vitamin D supplementation, 1,185,211 Iranian high-school students received 50,000 IU vitamin D supplements monthly for nine months. The costs-related data were modified to 2018. The average cost and effectiveness were compared based on the Incremental Cost-Effectiveness Ratio (ICER).

RESULTS

Our analytical analysis estimated the 4071.25 (USD / QALY) cost per AQALY gained of the monthly intake of 50,000 IU vitamin D for nine months among adolescents over a one-year horizon. Based on the ICER threshold of 1032-2666, vitamin D supplementation was cost-effective for adolescents to prevent adulthood T2DM. It means that vitamin D supplementation costs were substantially less than the costs of T2DM treatments than the no intervention.

CONCLUSIONS

Based on the findings, the national vitamin D supplementation program for Iranian adolescents could be a cost-effective strategy to reduce the risk of diabetes in adulthood. From an economic perspective, vitamin D supplementation, especially in adolescents with vitamin D deficiency, would be administrated.

Effect of Intramuscular Injection of Vitamin D on 25-Hydroxyvitamin D Levels, Glycaemic Control, and Liver Enzymes in Libyan Patients with Type 2 Diabetes Mellitus

Background Vitamin D is a fat-soluble hormone that plays an important role in glycaemic control. In addition, it has a positive effect on improving liver enzyme function.

Aim This study was performed to examine the effect of intramuscular injection of vitamin D on serum 25-hydroxyvitamin D [25(OH)D] levels, glycemic control, and liver enzymes in Libyan patients suffering from type 2 diabetes mellitus (T2DM) with vitamin D deficiency.

Methods and Materials This cross-sectional study enrolled 100 T2DM (50 males and 50 females). Their serum 25(OH)D, fasting blood glucose (FBG), and liver enzymes were measured at the baseline and 12 weeks after treatment with vitamin D (200,000 IU) injection monthly for 3 months. Data analysis involved the estimation of mean ± standard error (SE) and comparison of means between pre and post-treatment values using paired t-test. Independent t-test was used to compare the means between males and females. The level of significance was set at p < 0.05.

Results Females had a lower 25(OH)D blood levels than males at baseline (7.03 ± 0.25 ng/mL versus 7.86 ± 0.26 ng/mL, respectively p < 0.02). 25(OH)D levels in both sexes was increased significantly from 7.45 ± 0.18 ng/mL to 26.69 ± 0.24 ng/mL after 12 weeks of vitamin D injections (p < 0.001), with no significant differences between male and females. FBG levels in both sexes was significantly decreased from 144.68 ± 1.84 mg/dL to 85.96 ± 0.34 mg/dL post treatment (p < 0.001). Alanine aminotransferase (ALT) was increased from 10.24 ± 0.17 U/L at baseline to 20.34 ± 1.15 U/L post treatment (p < 0.001). Similarly, aspartate aminotransferase (AST) was increased from 11.23 ± 0.21 to 20.57 ± 0.22 U/L (p < 0.001), and alkaline phosphatase (ALP) was decreased from 124.95 ± 1.15 U/L to 111.17 ± 1.27 U/L (p < 0.001). There were no significant differences between male and female liver enzymes either pre- or post-vitamin D injections

Conclusion Treatment with vitamin D injection showed a significant increase in 25(OH)D accompanied by decreased FBG and ALP levels and increased ALT and AST levels. Vitamin D levels should be monitored and adjusted in diabetic patients.

Effect of Vitamin D Supplementation on Glycemic Control in Prediabetes: A Meta-Analysis

Clinical research results of vitamin D supplementation in the improvement of prediabetes remain controversial. Accordingly, a literature search was conducted of PubMed, Embase (Ovid), and Web of Science prior to 9 November 2021. Randomized controlled studies reported that the following indicators were included: body mass index (BMI), fasting blood glucose (FBG), 2 h oral glucose tolerance test plasma glucose (2h-PG), hemoglobin A1c (HbA1c), insulin resistance by homeostasis model assessment (HOMA-IR), homeostasis model assessment of β-cell function (HOMA-B), and fasting insulin (FINS). Twenty-nine articles (N = 3792) were included in the present meta-analysis. Intriguingly, vitamin D supplementation resulted in a vast improvement in FBG (standardized mean difference (SMD) = -0.38; 95%CI: -0.59, -0.16), HbA1c (SMD = -0.14; 95%CI: -0.22, -0.06) and FINS (SMD = 0.18; 95%CI: -0.26, -0.09), but not in other outcomes. However, preferred changes were observed in subgroups, as follows: Asia (SMD_2h-PG = -0.25, 95%CI: -0.45, -0.04), study duration ≥1 year (SMD_HOMA-IR = -0.44, 95%CI: -0.81, -0.06) (SMD_HOMA-B = 0.34, 95%CI: 0.01, 0.66), baseline 25(OH)D < 50 nmol/L (SMD_2h-PG = -0.23, 95%CI: -0.39, -0.06), and baseline 25(OH)D ≥ 50 nmol/L (SMD_HOMA-IR = -0.50, 95%CI: -0.96, -0.03). In conclusion, oral supplementation of vitamin D has shown better effects in improving FBG, HbA1c, and FINS compared with controls among prediabetics; long-term vitamin D supplementation could have additional effects in participants with vitamin D deficiency for 2h-PG, HOMA-IR, and HOMA-B.

Safety of Vitamin D Food Fortification and Supplementation: Evidence from Randomized Controlled Trials and Observational Studies

The safety considerations of food-based solutions for vitamin D deficiency prevention, such as fortification and supplementation, are critical. On the basis of collective data from 20 randomized controlled trials (RCTs) and 20 national healthy surveys, as well as prospective cohort studies (PCSs) across the ODIN project (“Food-based solutions for optimal vitamin D nutrition and health through the life cycle”, FP7-613977), we analyzed the potential safety issues arising from vitamin D intakes and/or supplementation. These adverse consequences included high serum 25-hydroxyvitamin D (S-25(OH)D) concentrations (>125 nmol/L), high serum calcium concentrations, and vitamin D intakes in excess of the tolerable upper intake levels (ULs). In the RCTs (n = 3353, with vitamin D doses from 5–175 µg/day), there were no reported adverse effects. The prevalence of high S-25(OH)D was <10% when vitamin D supplements were administered, and <0.1% for fortified foods. Elevated serum calcium was observed among <0.5% in both administration types. No ODIN RCT participants exceeded the age-specific ULs. In observational studies (n = 61,082), the prevalence of high 25(OH)D among children/adolescents, adults, and older adults was <0.3%, with no evidence of adverse effects. In conclusion, high S-25(OH)D concentrations >125 nmol/L were rare in the RCTs and PCSs, and no associated adverse effects were observed.

Mechanisms Involved in the Relationship between Vitamin D and Insulin Resistance: Impact on Clinical Practice

Recent evidence has revealed anti-inflammatory properties of vitamin D as well as extra-skeletal activity. In this context, vitamin D seems to be involved in infections, autoimmune diseases, cardiometabolic diseases, and cancer development. In recent years, the relationship between vitamin D and insulin resistance has been a topic of growing interest. Low 25-hydroxyvitamin D (25(OH)D) levels appear to be associated with most of the insulin resistance disorders described to date. In fact, vitamin D deficiency may be one of the factors accelerating the development of insulin resistance. Vitamin D deficiency is a common problem in the population and may be associated with the pathogenesis of diseases related to insulin resistance, such as obesity, diabetes, metabolic syndrome (MS) and polycystic ovary syndrome (PCOS). An important question is the identification of 25(OH)D levels capable of generating an effect on insulin resistance, glucose metabolism and to decrease the risk of developing insulin resistance related disorders. The benefits of 25(OH)D supplementation/repletion on bone health are well known, and although there is a biological plausibility linking the status of vitamin D and insulin resistance supported by basic and clinical research findings, well-designed randomized clinical trials as well as basic research are necessary to know the molecular pathways involved in this association.

Association Between Serum 25-hydroxyvitamin D Concentrations and Mortality Among Adults With Prediabetes

OBJECTIVES

To investigate the association of circulating 25-hydroxyvitamin D [25(OH)D] levels with mortality among adults with prediabetes.

METHODS

This retrospective cohort study included 15,195 adults with prediabetes (aged ≥20 years) from the National Health and Nutrition Examination Survey (NHANES) III and NHANES 2001-2014. Mortality from all causes, cardiovascular disease (CVD), and cancer was linked to National Death Index mortality data.

RESULTS

The median (interquartile range) concentration of serum 25(OH)D was 60.5 (45.3, 77.4) nmol/L, and only 23.1% had sufficient vitamin D (≥75 nmol/L). Elevated serum 25(OH)D concentrations were significantly associated with lower levels of insulin, homeostasis model assessment of insulin resistance, triglyceride, and C-reactive protein, and higher levels of high-density lipoprotein at baseline (all Ptrend < 0.05). During a median follow up of 10.7 years, 3765 deaths (including 1080 CVD deaths and 863 cancer deaths) were identified. Compared with participants with 25(OH)D <30 nmol/L, the multivariate-adjusted hazard ratios and 95% confidence intervals for participants with 25(OH)D ≥ 75 nmol/L were 0.66 (0.53, 0.82) for all-cause mortality (Ptrend < 0.001), 0.66 (0.48, 0.89) for CVD mortality (Ptrend = 0.001), and 0.82 (0.49, 1.35) for cancer mortality (Ptrend = 0.32). For per-unit increment in ln-transformed 25(OH)D, there was a 27% lower risk of all-cause mortality and a 34% lower risk of CVD mortality (both P < 0.01).

CONCLUSIONS

These findings suggested that higher serum 25(OH)D concentrations were associated with lower all-cause and CVD mortality among individuals with prediabetes.

The effects of vitamin D supplementation on inflammatory biomarkers in patients with abnormal glucose homeostasis: A systematic review and meta-analysis of randomized controlled trials

FINDINGS

on the level of inflammatory cytokines following vitamin D supplementation among individuals with abnormal glucose homeostasis (AGH) are controversial. Therefore, the present study was conducted on AGH patients to assess the impact of vitamin D on inflammatory cytokines such as CRP, TNF-α and IL-6. A systematic search up to September 2020 was performed through PubMed and Scopus databases. All clinical studies which evaluated the effect of oral vitamin D supplementation on inflammation in patients with AGH were included. The random-effects model was applied to obtain pooled results. For dose-response analysis, we used a fractional polynomial model. Overall, 38 studies, with 46 effect sizes, were included in this study. Combining effect sizes, we found that vitamin D considerably decrease serum concentrations of CRP (weight mean difference (WMD): - 0.67 mg/l; 95%CI: - 0.92, - 0.43; P < 0.001), IL-6 (WMD: -1.93 pg/mL; 95%CI: -2.80, -1.07; P < 0.001) and TNF-α (WMD: -0.81 pg/mL; 95%CI: -1.59, -0.03; P = 0.04). In the dose-response analysis, we failed to find any correlation between dosage of supplements and inflammatory biomarkers concentrations. Summarizing earlier studies, we demonstrated that circulating concentrations of inflammatory cytokines such as CRP, TNF-α, and IL-6 might be decreased following vitamin D supplementation among individuals with AGH.

Effects of Vitamin D Supplementation on Cardiovascular and Glycemic Biomarkers

Background Experimental and observational studies have suggested a link between vitamin D and cardiovascular and metabolic disease, but this has not been confirmed in randomized controlled trials. We sought to determine whether vitamin D supplementation reduces biomarkers of insulin resistance, inflammation, neurohormonal activation, and lipids. Methods and Results This was a prespecified, secondary analysis of the DAYLIGHT (Vitamin D Therapy in Individuals at High Risk of Hypertension) randomized controlled trial. We measured circulating homeostatic model assessment of insulin resistance, hs-CRP (high-sensitivity C-reactive protein), N-terminal pro-B-type natriuretic peptide, renin, aldosterone, and lipids at baseline and at 6 months in 289 individuals with low vitamin D status (25-hydroxyvitamin-D [25-OH-D] ≤25 ng/mL) receiving low-dose (400 IU/d) versus high-dose (4000 IU/d) vitamin D3 for 6 months. A meta-analysis of randomized controlled trials reporting biomarker changes after vitamin D supplementation was then performed. Levels of 25-OH-D increased in the high-dose relative to the low-dose vitamin D group (+15.5 versus +4.6 ng/mL, P<0.001). Changes in biomarkers of glycemia, inflammation, and neurohormonal activation did not differ by dose. Lipids did not differ between groups, other than triglycerides, which increased in the high-dose compared with the low-dose group (+11.3 versus -6.2 mg/dL, P<0.001). The meta-analysis showed potential modest decreases in homeostatic model assessment of insulin resistance and hs-CRP, but no changes in low-density lipoprotein, after vitamin D supplementation compared with control groups. Conclusions In the DAYLIGHT randomized controlled trial, high-dose vitamin D supplementation did not improve biomarkers of glycemia, inflammation, neurohormonal activation, or lipids. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT01240512.

Tracking of serum 25-hydroxyvitamin D during 21 years

BACKGROUND/OBJECTIVES

Our objective was to evaluate the degree of tracking for serum levels of 25-hydroxyvitamin D [25(OH)D] over time, by using data from three previously conducted surveys of the Tromsø study collected in the years 1994/1995 (Tromsø 4), 2007/2008 (Tromsø 6), and 2015/2016 (Tromsø 7).

SUBJECTS/METHODS

Subjects with valid 25(OH)D measurements in all three surveys were included. 25(OH)D z-scores were used to adjust for seasonal variation. Z-scores and sextiles were used to illustrate tracking of 25(OH)D.

RESULTS

1702 subjects (572 males, 1130 females) fulfilled the inclusion criteria. Median (5th, 95th percentiles) age for these subjects was 55 (33, 65) years in Tromsø 4, and mean (SD) 25(OH)D levels were 57 (18) nmol/L, 59 (19) nmol/L, and 72 (21) nmol/L for Tromsø 4, Tromsø 6, and Tromsø 7, respectively. There was significant tracking of serum 25(OH)D over the 21 years period between the surveys of the Tromsø study. The correlation coefficient r between 25(OH)D z-scores from Tromsø 4 and Tromsø 6 was 0.40, and declined to 0.29 for the correlation between Tromsø 4 and Tromsø 7. Twenty-six percent of the subjects in the lowest 25(OH)D z-score sextile in Tromsø 4 were in the three highest sextiles of 25(OH)D in Tromsø 7. Similarly, 35% of those in the highest sextile in Tromsø 4 were in the lowest three sextiles in Tromsø 7.

CONCLUSIONS

The degree of tracking for serum 25(OH)D declines over time, and the use of a single serum 25(OH)D measurement as an indicator of the vitamin-D status is questionable if used in long-lasting observational studies.

Increased calcium intake is associated lower serum 25-hydroxyvitamin D levels in subjects with adequate vitamin D intake: a population-based observational study

BACKGROUND

There are indications that an increased intake of calcium has a vitamin D sparing effect, which might be explained by a decreased catabolism of 25-hydroxyvitamin D (25(OH)D). However, there are only a few studies where this has been examined.

METHOD

In the seventh survey of the Tromsø study, serum 25(OH)D and parathyroid hormone were measured, and questionnaires on calcium and vitamin D intakes filled in.

RESULTS

There were significant interactions between sex, calcium and vitamin D intakes regarding serum 25(OH)D level. The analyses were therefore done stratified. In males there was, regardless of vitamin D intake, a significant decrease in serum 25(OH)D with increasing calcium intake. The difference in serum 25(OH)D between those with the highest and lowest calcium intakes was approximately 10%. In the females, there was in subjects with low vitamin D intake (< 7 μg/d) a significant increase in serum 25(OH)D with increasing calcium intake, which could not be explained by secondary hyperparathyroidism. In females with higher vitamin D intakes, increasing calcium intake was associated with lower serum 25(OH)D levels.

CONCLUSIONS

There is, at least in subjects with an adequate vitamin D intake, a negative association between calcium intake and serum 25(OH)D.

Nutritional Strategies in Prediabetes: A Scoping Review of Recent Evidence

Nutritional therapy has been conventionally recommended for people with prediabetes as a method to delay or halt progression to type 2 diabetes. However, recommended nutritional strategies evolve over time. Hence, we performed a scoping review on recently reported nutritional interventions for individuals with prediabetes. Ovid MEDLINE, PubMed, Embase, Scopus, CINAHL and PsycINFO databases were searched to identify relevant research articles published within the past 10 years. Ninety-five articles involving a total of 11,211 participants were included in this review. Nutritional strategies were broadly classified into four groups: low calorie diet, low glycemic index diet, specific foods, and a combination of diet and exercise. The most frequently assessed outcomes were plasma glucose, serum insulin, serum lipid profile, body mass index and body weight. More than 50% of reported interventions resulted in significant improvements in these parameters. Nutritional interventions have demonstrated feasibility and practicality as an effective option for prediabetes management. However, the intervention variability demonstrates the challenges of a 'one-size-fits-all' approach. Investigations in genetically diverse populations and objective assessment of progression rate to diabetes are necessary to better comprehend the impact of these nutritional strategies in prediabetes.

Delta-like 1 (DLK1) is a possible mediator of vitamin D effects on bone and energy metabolism

Vitamin D effects on bone and mineral metabolism are well recognized, and its anti-inflammatory actions are gaining particular interest. Delta-like 1 (DLK1) is a protein, expressed by progenitor cells of different tissues, and increases the size of progenitor cell population during the inflammatory phase of tissue regeneration. DLK1 also plays a role in energy metabolism as it antagonizes insulin signaling in bone. In this one-year randomized clinical trial of overweight elderly individuals that received either 600 or 3750 IU daily cholecalciferol we assessed the effect of vitamin D supplementation on pre-specified secondary outcomes: DLK1, leptin, adiponectin, C-Reactive Protein (CRP) and Vascular Cell Adhesion Molecule (VCAM). We also examined correlations between DLK1 and bone (BMD, bone markers), fat (adipokines, body composition), insulin sensitivity and inflammatory markers. Multivariate analyses were conducted to further explore these associations. Overall, there was a significant increase in serum DLK1 and leptin and a decrease in VCAM, but no change in CRP, after 12 months of vitamin D supplementation. DLK1 was negatively correlated with BMD and positively correlated with bone markers, associations that persisted after adjusting for age, gender and BMI. DLK1 was also positively associated with indices of insulin resistance and negatively with indices of insulin sensitivity. Correlations between DLK1 and fat parameters, such as adipokines, and DXA derived fat mass were less consistent. There were no correlations between DLK1 and inflammatory markers. In conclusion, twelve months supplementation of vitamin D3 increased serum DLK1. DLK1 was negatively associated with indices of bone health and fuel metabolism, and with 1,25(OH)2D levels. Similar to the role of DLK1 in animal models, our findings support the hypothesis that DLK1 can be targeted to regulate bone and energy metabolism and develop drugs to improve BMD and insulin sensitivity. However, further studies are needed to explore the role of DLK1 and its relationship to vitamin D metabolites in vivo.

Effects of Vitamin D Supplementation on Prevention of Type 2 Diabetes in Patients With Prediabetes: A Systematic Review and Meta-analysis

BACKGROUND

While observational studies have shown an association between vitamin D insufficiency and diabetes, it is unclear whether intervention with vitamin D supplements can lower the risk of type 2 diabetes mellitus (T2DM).

PURPOSE

To assess whether vitamin D supplementation reduces the risk of T2DM in people with prediabetes.

DATA SOURCES

We searched MEDLINE, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) from inception to 5 July 2019.

STUDY SELECTION

We included randomized controlled trials assessing vitamin D supplementation versus placebo in relation to new-onset T2DM in people with prediabetes.

DATA EXTRACTION

We screened studies and extracted data from published trials independently.

DATA SYNTHESIS

We identified eight eligible trials with a total of 4,896 subjects. Vitamin D supplementation significantly reduced the risk of T2DM (risk ratio [RR] 0.89 [95% CI 0.80-0.99]; I ² = 0%). Benefit was found in nonobese subjects (RR 0.73 [95% CI 0.57-0.92]) but not in obese subjects (RR 0.95 [95% CI 0.84-1.08]) (P _interaction = 0.048). The reversion of prediabetes to normoglycemia occurred in 116 of 548 (21.2%) participants in the vitamin D group and 75 of 532 (14.1%) in the control group. Vitamin D supplementation increased reversion rate of prediabetes to normoglycemia (RR 1.48 [95% CI 1.14-1.92]; I ² = 0%.) LIMITATIONS: Definitions of prediabetes and new-onset diabetes in eligible studies were different, and long-term data on outcomes of T2DM prevention were lacking.

CONCLUSIONS

In persons with prediabetes, vitamin D supplementation reduces the risk of T2DM and increases the reversion rate of prediabetes to normoglycemia. The benefit of the prevention of T2DM could be limited to nonobese subjects. Individual participant data meta-analyses are needed to confirm these findings.

Effects of vitamin D supplementation on 25(OH)D levels and blood pressure in the elderly: a systematic review and meta-analysis

Background: Hypertension and vitamin D deficiency are prevalent among the elderly. This study evaluated the effects of vitamin D supplementation on changes in serum 25-hydroxyvitamin D (25(OH)D) levels and blood pressure (BP) in the elderly (age > 60 years). Methods: Randomized controlled trials from electronic databases on the elderly taking oral vitamin D, until the end of March 2019, were selected. Two reviewers independently screened the literature on the basis of specific inclusion criteria. The primary outcomes were serum 25(OH)D level, systolic BP (SBP), and diastolic BP (DBP) changes. Results: Our analysis revealed significant differences in serum 25(OH)D level changes between the vitamin D and control groups (mean difference [MD] = 13.84; 95% confidence interval [CI] = 10.21-17.47; P < 0.000). There were no significant differences in SBP and DBP changes between the vitamin D and control groups. Subgroup analysis revealed significant differences in SBP changes between the hypertensive and vitamin D-deficient subgroups (MD = -4.01; 95% CI = -7.45 to -0.57; P = 0.02 and MD = -1.91; 95% CI = -3.48 to -0.34; P = 0.02, respectively), and DBP changes only in the hypertensive subgroup (MD = -2.22; 95% CI = -4.1 to -0.34; P = 0.02). Conclusions: Vitamin D supplementation significantly increases 25(OH)D levels and seems beneficial in lowering BP, specifically in the elderly with elevated BP and vitamin D deficiency.

Effects of vitamin D supplementation on 25(OH)D concentrations and blood pressure in the elderly: a systematic review and meta-analysis

Background: Hypertension and vitamin D deficiency are prevalent among the elderly. This study evaluated the effects of vitamin D supplementation on changes in serum 25-hydroxyvitamin D (25(OH)D) concentrations and blood pressure (BP) in the elderly (age > 60 years). Methods: Randomized controlled trials from electronic databases on the elderly taking oral vitamin D, until the end of March 2019, were selected. Two reviewers independently screened the literature on the basis of specific inclusion criteria. The primary outcomes were serum 25(OH)D level, systolic BP (SBP), and diastolic BP (DBP) changes. Results: Our analysis revealed significant differences in serum 25(OH)D concentrations changes between the vitamin D and control groups (mean difference [MD] = 13.84; 95% confidence interval [CI] = 10.21-17.47; P < 0.000). There were no significant differences in SBP and DBP changes between the vitamin D and control groups. Subgroup analysis revealed significant differences in SBP changes between the hypertensive and vitamin D-deficient subgroups (MD = -4.01; 95% CI = -7.45 to -0.57; P = 0.02 and MD = -1.91; 95% CI = -3.48 to -0.34; P = 0.02, respectively), and DBP changes only in the hypertensive subgroup (MD = -2.22; 95% CI = -4.1 to -0.34; P = 0.02). Conclusions: Vitamin D supplementation significantly increases 25(OH)D concentrations and seems beneficial in lowering BP, specifically in the elderly with elevated BP and vitamin D deficiency.

Effects of vitamin D supplementation on 25(OH)D levels and blood pressure in the elderly: a systematic review and meta-analysis

Background: Hypertension and vitamin D deficiency are prevalent among the elderly. This study evaluated the effects of vitamin D supplementation on changes in serum 25-hydroxyvitamin D (25(OH)D) levels and blood pressure (BP) in the elderly (age > 60 years). Methods: Randomized controlled trials from electronic databases on the elderly taking oral vitamin D, until the end of March 2019, were selected. Two reviewers independently screened the literature on the basis of specific inclusion criteria. The primary outcomes were serum 25(OH)D level, systolic BP (SBP), and diastolic BP (DBP) changes. Results: Our analysis revealed significant differences in serum 25(OH)D level changes between the vitamin D and control groups (mean difference [MD] = 13.84; 95% confidence interval [CI] = 10.21-17.47; P < 0.000). There were no significant differences in SBP and DBP changes between the vitamin D and control groups. Subgroup analysis revealed significant differences in SBP changes between the hypertensive and vitamin D-deficient subgroups (MD = -4.01; 95% CI = -7.45 to -0.57; P = 0.02 and MD = -1.91; 95% CI = -3.48 to -0.34; P = 0.02, respectively), and DBP changes only in the hypertensive subgroup (MD = -2.22; 95% CI = -4.1 to -0.34; P = 0.02). Conclusions: Vitamin D supplementation significantly increases 25(OH)D levels and seems beneficial in lowering BP, specifically in the elderly with elevated BP and vitamin D deficiency.

Effect of vitamin D3 supplementation on vascular and metabolic health of vitamin D-deficient overweight and obese children: a randomized clinical trial

BACKGROUND

Obese children are vulnerable to vitamin D deficiency and impaired cardiovascular health; vitamin D replenishment might improve their cardiovascular health.

OBJECTIVES

The aims were to determine, in vitamin D-deficient overweight and obese children, whether supplementation with vitamin D3 1000 or 2000 IU/d is more effective than 600 IU/d in improving arterial endothelial function, arterial stiffness, central and systemic blood pressure (BP), insulin sensitivity (1/fasting insulin concentration), fasting glucose concentration, and lipid profile and to explore whether downregulation of adipocytokines and markers of systemic inflammation underlies vitamin D effects.

METHODS

We conducted a randomized, double-masked, controlled clinical trial in 225 10- to 18-y-old eligible children. Change in endothelial function at 6 mo was the primary outcome.

RESULTS

Dose-response increases in serum 25-hydroxyvitamin D concentrations were significant and tolerated without developing hypercalcemia. Changes at 3 and 6 mo in endothelial function, arterial stiffness, systemic-systolic BP, lipids, and inflammatory markers did not differ between children receiving 1000 or 2000 IU vitamin D and children receiving 600 IU. Some secondary outcomes differed between groups. Compared with the 600-IU group, central-systolic, central-diastolic, and systemic-diastolic BP was lower at 6 mo in the 1000-IU group [-2.66 (95% CI: -5.27, -0.046), -3.57 (-5.97, -1.17), and -3.28 (-5.55, -1.00) mm Hg, respectively]; insulin sensitivity increased at 3 and 6 mo and fasting glucose concentration declined at 6 mo (-2.67; 95% CI: -4.88, -0.46 mg/dL) in the 2000-IU group.

CONCLUSIONS

Correction of vitamin D deficiency in overweight and obese children by vitamin D3 supplementation with 1000 or 2000 IU/d versus 600 IU/d did not affect measures of arterial endothelial function or stiffness, systemic inflammation, or lipid profile, but resulted in reductions in BP and fasting glucose concentration and in improvements in insulin sensitivity. Optimization of children's vitamin D status may improve their cardiovascular health. This trial was registered at clinicaltrials.gov as NCT01797302.

Association between vitamin D and prediabetes: A PRISMA-compliant meta-analysis

BACKGROUND

Previous studies showed conflicting results for associations between vitamin D and prediabetes. The study aimed to make a systematic review and meta-analysis for the association between vitamin D and prediabetes.

METHODS

We searched for articles identifying associations between vitamin D and prediabetes published in English until July 2019 in following databases (PubMed, Web of Science, EMBASE, Medline, Google Scholar, and Cochrane databases). Finally, we conducted these analyses (heterogeneities examination, meta-regression analyses, sensitivity analysis, and publication bias examination) using STATA 12.0 software (Stata Corporation, College Station, TX, USA). Q test and I were applied to examine heterogeneities between studies.

RESULTS

Twelve studies were finally included in the present study. The study included 4 studies to explore the association between serum levels of 25-hydroxy (OH) vitamin D and risks of prediabetes (including 3094 participants). Additionally, the present study included 8 studies (including 865 individuals with prediabetes treated with vitamin D supplementation and 715 patients treated with placebo) to assess differences in therapeutic effects between individuals with prediabetes treated with vitamin D supplementation and those treated with placebo. The present study showed no significant associations between low serum levels of 25(OH) vitamin D and high risk of prediabetes. Additionally, the study showed no significant differences in changes of hemoglobin A1c (HbA1c), fasting plasma glucose (FPG), and homeostatic model assessment of insulin resistance (HOMA-IR) between individuals with prediabetes treated with vitamin D and those patients given placebo, whereas meta-analysis showed significantly greater changes in 2-hour oral glucose tolerance test (2HPG) in individuals with prediabetes treated with vitamin D, compared with individuals with prediabetes treated with placebo.

CONCLUSION

The study supported that low serum levels of 25(OH) vitamin D increased the risk of prediabetes. In addition, vitamin D supplementation improves impaired glucose tolerance in prediabetes. However, more large-scale clinical trials are essential to explore the association between vitamin D and prediabetes.

Vitamin D Supplementation in Overweight/obese Asian Indian Women with Prediabetes Reduces Glycemic Measures and Truncal Subcutaneous Fat: A 78 Weeks Randomized Placebo-Controlled Trial (PREVENT-WIN Trial)

Vitamin D deficiency may contribute to etiology of type 2 diabetes in Asian Indians. The objectives of this study was to evaluate effect of vitamin D supplementation on glycemic profile and body composition in prediabetic and vitamin D deficient overweight/obese Asian Indian women. In this open-label randomized placebo-controlled trial (78 weeks duration), 121 females (aged 20–60 years) with prediabetes and vitamin D deficiency were randomly allocated in intervention (n, 61) and placebo (n, 60) groups. The primary outcome variables were fasting blood glucose (FBG), 2-h blood glucose post OGTT (2-h BG), hemoglobin A1c (HbA1C), and reversal to normoglycemia. In Intention-to-treat analysis, at the end of intervention, we observed significant decrease in FBG [−5.0 (−12.6–2.4), p = 0.04], 2-h blood glucose post OGTT [−11(−49.3–26.9), p = 0.02], hemoglobin A1c [−0.41 (5.89, 6.55), p = 0.05] and increase in 25(OH) D [7.5 (−6.0–20.9), p = 0.002] levels in intervention as compared to the placebo group. Changes in glycemic category based on FBG were as follows; intervention group: normal FBG, 58.6%; impaired fasting glucose (IFG), 39%; and type 2 diabetes mellitus (T2DM), 2.4%; placebo group: normal FBG, 48.8%; IFG, 46.3%; and T2DM, 4.9%. Changes in category of 2-hour glucose post OGTT after intervention were as follows; intervention group: normal glucose tolerance (NGT) 51.2% and prediabetes, 48.8%; placebo group: NGT, 43.9%; prediabetes, 53.7% and T2DM, 2.4%. After intervention, subscapular skinfold (visit I^st compared to visit III^rd) and suprailiac skinfold (visit II^nd compared to visit III^rd) were significantly lower in intervention group vs. control group. In conclusion, we observed significant reduction in FBG, 2-hour glucose post OGTT, HbA1c, and truncal subcutaneous fat and reversal to normoglycemia in overweight/obese prediabetic vitamin D deficient Asian Indian women after 78 weeks of vitamin D supplementation.

Establishing Benefit from Vitamin D Supplementation - Adherence to Defined Criteria and Targeting of High-Risk Groups Essential?

BACKGROUND

Vitamin D is the one of the most common nutritional deficiencies worldwide, and insufficiency or deficiency can be associated with musculoskeletal and non-skeletal conditions such as cancer, cardiovascular disease and diabetes mellitus.

OBJECTIVE

Recent data suggests that Vitamin D is relatively safe and toxicity is rarer than previously indicated. However, international guidelines regarding dosage and target plasma levels are conflicting. Moreover multiple well-designed studies of healthy older adults, unselected in terms of Vitamin D status, have revealed largely negative results (with the possible exception of older patients in care homes/hospitals) in terms of improvement in musculoskeletal and non-skeletal conditions to date.

CONCLUSION

On that basis, it is suggested that future trials regarding Vitamin D supplementation should be carried out in high-risk groups. The use of published criteria for evaluating the effect of nutrients and targeting of individuals with Vitamin D insufficiency and deficiency for inclusion in such studies is also proposed. The identification of specific subgroups that will benefit from supplementation and replacement, and the establishment of a scientific basis for such therapy, should be possible with this approach.

The Latest Evidence from Vitamin D Intervention Trials for Skeletal and Non-skeletal Outcomes

Vitamin D has long been considered a central part of the treatment paradigm for osteoporosis. Initial studies in high-risk populations with widespread vitamin D deficiency found a reduction of both vertebral and non-vertebral fractures. Subsequent studies in the general population have yielded mixed but mostly disappointing results both for skeletal and especially non-skeletal outcomes. Recent sequential trial meta-analyses suggest that future studies are likely to be futile given the overall disappointing result. However, mega-trials are still in progress, and additional results have been released. This narrative review aims to evaluate new literature to determine if there has been any substantial change in the message. In conclusion, there is no longer a strong case for initiating vitamin D alone trials in the general adult population, irrespective of age and gender, for significant health outcomes such as fractures, cardiovascular disease and cancer. New studies should focus on risk groups and take directions from the Heaney criteria for evaluation of threshold nutrients. Indeed, real benefits may still be reaped by directing vitamin D supplementation to persons with proven or likely vitamin D deficiency. Further, the role of dietary calcium as a critical co-nutrient remains controversial and could contribute to the discrepancy between studies in terms of cancer outcomes and possibly falls and fractures.

The effect of omega-3 and vitamin D co-supplementation on glycemic control and lipid profiles in reproductive-aged women with pre-diabetes and hypovitaminosis D: a randomized controlled trial

BACKGROUND

Prediabetes can predispose the individual to type 2 diabetes in the long-term. The present study was conducted to determine the effectiveness of vitamin D and omega-3 co-supplementation on glycemic control and serum lipid profiles in women of reproductive age with prediabetes and hypovitaminosis D.

METHODS

The present factorial, triple-blind, clinical trial was conducted on 168 women of reproductive age with prediabetes and hypovitaminosis D. The participants were assigned to four groups based on block randomization method: the placebo group received omega-3 and vitamin D placebos; the omega-3 group took omega-3 supplements and vitamin D placebos; the vitamin D group received omega-3 placebos and vitamin D supplements and the co-supplementation group. The groups received every 2 weeks 50,000 IU pearls of vitamin D and twice-daily doses of 1000-mg omega-3 tablets or placebos for 8 weeks. Dietary intake, physical activity, anthropometric indices and blood biochemical tests were measured at the beginning and end of the study. Analysis was performed using two-way mixed ANOVA.

RESULTS

A significant reduction was observed in fasting glucose, insulin, homeostasis model assessment-beta cell function, weight and waist circumference in the co-supplementation group compared to the other three groups (P < 0.05). Moreover, high-density lipoprotein-cholesterol levels increased significantly in the co-supplementation group compared to the other three groups (P < 0.05). Despite the fact that homeostasis model assessment-insulin resistance, total cholesterol, triglyceride and low-density lipoprotein-cholesterol levels decreased after intervention in the co-supplementation group, there was no significant difference between the groups in these outcomes.

CONCLUSION

Vitamin D and omega-3 co-supplementation improved fasting serum glucose, insulin, high-density lipoprotein-cholesterol level, homeostasis model assessment-beta cell function, weight and waist circumference in women of reproductive age with prediabetes and hypovitaminosis D. This co-supplementation can therefore be recommended for glycemic control in these women.Trial registration Iranian Registry of Clinical Trials Code: IRCT20100130003226N17. Registered on 9 Feb. 2019.

Four months vitamin D supplementation to vitamin D insufficient individuals does not improve muscular strength: A randomized controlled trial

Main objective

The inconsistent results on the effects of vitamin D on muscle strength reported by intervention trials may partly be explained by inclusion of vitamin D sufficient individuals. The main objective was to study whether vitamin D supplementation will improve muscle strength in men and women with low serum vitamin D status, as measured by 25-hydroxyvitamin D (25(OH)D) at baseline.

Methods

417 men and women aged 40–80 years were included and randomized to receive a loading dose of 100 000 IU (2500 ug) vitamin D₃ followed by 20 000 IU (500 ug)/week, or placebo. Muscle strength was tested by dynamometers at baseline and after four months.

Results

Serum 25(OH)D levels increased from 32.6±11.1 nmol/l to 88.8±19.4 nmol/l (p<0.01) in the vitamin D group, while remaining low in the placebo group (baseline and final levels at 35.1±13.6 nmol/l and 30.7 ±9.7 nmol/l respectively). Muscle strength (hip flexion, biceps flexion, pectorals and handgrip strength) did not change in any of the groups. The results were the same in analyses stratified on sex, 25(OH)D above/below 25 nmol/L (10 ng/ml); smoking status; and BMI above/below 27 kg/m².

Conclusion

These data does not support vitamin D supplementation for improving muscle strength.

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 cause-specific vascular disease and mortality: a Mendelian randomisation study involving 99,012 Chinese and 106,911 European adults

BACKGROUND

Randomised control trials and genetic analyses have demonstrated that vitamin D or 25-hydroxyvitamin D (25[OH]D) levels may not play a causal role in the development of cardiovascular disease. However, it is unclear if 25(OH)D is causally associated with cause-specific vascular disease and lipids. Therefore, we examined the causal association of 25(OH)D with myocardial infarction, stroke, ischaemic heart disease, ischaemic stroke, subarachnoid haemorrhage, intracerebral haemorrhage, and lipid levels among both Chinese and Europeans.

METHODS

We used a Mendelian randomisation (MR) design in the China Kadoorie Biobank, the Copenhagen City Heart Study, and the Copenhagen General Population Study. The 25(OH)D-related genetic variants in the CYP2R1 and DCHR7 genes were genotyped in 99,012 Chinese adults and 106,911 Danish adults.

RESULTS

In Chinese adults, plasma 25(OH)D levels were not significantly associated with cause-specific vascular disease or mortality, with the exception of intracerebral haemorrhage (HR, 1.09 [95% CI, 1.01,1.18] per 25 nmol/L higher plasma 25(OH)D). In Europeans, plasma 25(OH)D levels were inversely associated with all types of vascular diseases and mortality. However, MR analysis did not demonstrate causal associations of genetically increased 25(OH)D levels with cause-specific vascular diseases, or mortality in both Chinese and European adults. In addition, each 25 nmol/L higher 25(OH)D was observationally associated with lower total cholesterol and low-density lipoprotein cholesterol levels, but higher high-density lipoprotein cholesterol levels. Likewise, MR analysis showed that 25(OH)D levels were not causally associated with lipids in both Chinese and European adults after Bonferroni correction.

CONCLUSIONS

We found no evidence to support that genetically increased 25(OH)D was associated with a lower risk of ischaemic stroke, intracerebral haemorrhage, subarachnoid haemorrhage, and lipid levels in both Chinese and European adults. These results suggest that the inverse associations of vitamin D with vascular disease could be the result of confounding.

Effects of vitamin D supplementation on bone turnover markers and other bone-related substances in subjects with vitamin D deficiency

In observational studies, vitamin D deficiency is a risk factor for low bone density and future fractures, whereas a causal relation has been difficult to show in randomized controlled trials (RCTs). Similarly, vitamin D deficiency has been associated with increased bone turnover, but RCTs with vitamin D have not shown conclusive effects. This could be due to inclusion of vitamin D sufficient subjects and low vitamin D doses. In the present study 399 subjects with mean baseline serum 25-hydroxyvitamin D (25(OH)D) 34.0 nmol/L completed a four months intervention with vitamin D₃ 20,000 IU per week versus placebo. Mean serum 25(OH)D increased to 89.0 nmol/L in the vitamin D group and decreased slightly in the placebo group. A small, but significant, decrease in the bone formation marker procollagen of type 1 amino-terminal propeptide (P1NP) was seen in the vitamin D group as compared to the placebo group (mean delta P1NP -1.2 pg/mL and 1.5 ng/mL, respectively, P < 0.01). No significant effects were seen on serum carboxyl-terminal telopeptide of type 1 collagen (CTX-1), Dickkopf-1, sclerostin, tumor necrosis factor-alpha, osteoprotegerin, receptor activator of nuclear factor ĸB ligand, or leptin. Subgroup analyses on subjects with low baseline serum 25(OH)D did not yield additional, significant results. In subjects with high baseline serum parathyroid hormone (PTH) > 6.5 pmol/L and post-intervention decrease in PTH, the decrease in P1NP was more pronounced, they also exhibited significantly reduced serum CTX-1 and increased serum sclerostin. In conclusion, supplementation with vitamin D appears to suppress bone turnover, possibly mediated by PTH reduction. Our findings need to be confirmed in even larger cohorts with vitamin D insufficient subjects.

Vitamin D Status, Calcium Intake and Risk of Developing Type 2 Diabetes: An Unresolved Issue

The relationship between vitamin D status, calcium intake and the risk of developing type 2 diabetes (T2D) is a topic of growing interest. One of the most interesting non-skeletal functions of vitamin D is its potential role in glucose homeostasis. This possible association is related to the secretion of insulin by pancreatic beta cells, insulin resistance in different tissues and its influence on systemic inflammation. However, despite multiple observational studies and several meta-analyses that have shown a positive association between circulating 25-hydroxyvitamin D concentrations and the risk of T2D, no randomized clinical trials supplementing with different doses of vitamin D have confirmed this hypothesis definitively. An important question is the identification of what 25-hydroxyvitamin D levels are necessary to influence glycemic homeostasis and the risk of developing T2D. These values of vitamin D can be significantly higher than vitamin D levels required for bone health, but the currently available data do not allow us to answer this question adequately. Furthermore, a large number of observational studies show that dairy consumption is linked to a lower risk of T2D, but the components responsible for this relationship are not well established. Therefore, the importance of calcium intake in the risk of developing T2D has not yet been established. Although there is a biological plausibility linking the status of vitamin D and calcium intake with the risk of T2D, well-designed randomized clinical trials are necessary to answer this important question.

No improvement in depressive symptoms by vitamin D supplementation: results from a randomised controlled trial

In observational studies, vitamin D deficiency is associated with depressive symptoms. However, randomised controlled trials (RCT) with vitamin D supplementation have not been conclusive. In the present study 206 subjects were randomised to vitamin D (100 000 IU (2500 µg) as a bolus dose followed by 20 000 IU (500 µg) per week) and 202 to placebo. The Beck Depression Inventory-II (BDI-II) was filled in at baseline and after 4 months at the end of the study. At baseline the mean age was 51·4 and 52·5 years and mean serum 25-hydroxyvitamin D (25(OH)D) 32·5 and 35·1 nmol/l in the vitamin D and placebo groups, respectively. Among the 408 subjects, 193 had a BDI-II score >4, and forty-five had a score >13. Twenty-three subjects were using anti-depressant or mood-stabilising drugs. At the end of the study, there were no significant differences in Δ BDI-II score (score at the end of the study minus score at baseline), regardless of analysing all subjects, subjects with or without psycopharmaca, or if performing subgroup analyses based on baseline and final serum 25(OH)D levels combined with categories of baseline BDI-II scores >4 or >13. In conclusion, we have not been able to demonstrate any significant effect of vitamin D supplementation on depressive symptoms. However, few of our subjects were clinically depressed. Future RCT should include subjects with more severe vitamin D deficiency as well as more depressed subjects than in our study. In such a setting vitamin D may probably be more relevant as an augmenter of standard antidepressant medication/treatment.

Vitamin D Supplementation, Serum 25(OH)D Concentrations and Cardiovascular Disease Risk Factors: A Systematic Review and Meta-Analysis

Background: Cardiovascular disease (CVD) risk factors are associated with low serum 25 hydroxyvitamin D (25(OH)D) concentrations in observational studies; however, clinical trial findings are inconsistent.

Objective: We assessed the effect of vitamin D supplementation and increased serum 25(OH)D concentrations on CVD risk factors in a systemic review and meta-analysis of randomized controlled trials (RCTs).

Design: MEDLINE, CINAHL, EMBASE, and Google Scholar were searched for RCTs that evaluated vitamin D supplementation and cardiovascular outcomes [blood pressure, parathyroid hormone (PTH), serum high-sensitivity C-reactive protein (hs-CRP), total cholesterol, high and low density lipoprotein (HDL and LDL, respectively), triglycerides, peak wave velocity (PWV) and Augmentation Index (AI)] from 1992 through 2017. Meta-analysis was based on a random-effects model and inverse variance method to calculate standardized mean difference (SMD) as effect sizes, followed by a leave-one-out method for sensitivity analysis. Risk of publication bias was assessed using Cochrane checklist and Begg funnel plots. The systematic review is registered as CRD42015025346.

Results: We identified 2341 studies from which 81 met inclusion criteria. The meta-analysis indicated a significant reduction in systolic blood pressure (SMD = −0.102 ± 0.04 mmHg, 95% confidence interval (CI), −0.20 to −0.03), diastolic blood pressure (SMD = −0.07 ± 0.03 mmHg, 95% CI, −0.14 to −0.006), serum PTH (SMD = −0.66 ± 0.08 ng/L, 95% CI, −0.82 to −0.49), hs-CRP (SMD = −0.20 ± 0.07 mg/L, 95% CI, −0.34 to −0.06), total cholesterol (SMD = −0.15 ± 0.06 mmol/L, 95% CI, −0.25 to −0.04), LDL (SMD = −0.10 ± 0.05 mmol/L, 95% CI, −0.20 to −0.003), triglycerides (SMD = −0.12 ± 0.06 mmol/L, 95% CI, −0.23 to −0.003) and a significant increase in HDL (SMD = 0.09 ± 0.04 mmol/L, 95% CI, 0.00 to 0.17) with vitamin D supplementation. These findings remained significant in sensitivity analyses for blood pressure, lipid profile, serum PTH, and serum hs-CRP. There was no significant effect of vitamin D supplementation on PWV (SMD = −0.20 ± 0.13 m/s, 95% CI, −0.46 to 0.06, p = 0.14) and AI (SMD = −0.09 ± 0.14%, 95% CI, −0.37 to 0.19, p = 0.52) for vitamin D supplemented groups.

Conclusion: These findings suggest that vitamin D supplementation may act to protect against CVD through improving risk factors, including high blood pressure, elevated PTH, dyslipidemia, and inflammation.

Vitamin D Supplementation, Glycemic Control, and Insulin Resistance in Prediabetics: A Meta-Analysis

Diabetes prevention is a public health priority. Vitamin D supplementation may help prevent the development of diabetes in persons at increased risk. We performed a meta-analysis of controlled clinical trials that assessed glycemic outcome measures among adults at risk for type 2 diabetes, including prediabetes, overweight, or obesity. We searched PUBMED/ MEDLINE, CINAHL, and Google Scholar databases for trials published prior to April 2017. Placebo-controlled clinical trials with random allocation to vitamin D with or without calcium supplementation were selected. Data collection included country, study design, inclusion criteria, sample size, form, and dose of vitamin D, supplementation interval, control group, duration, participant characteristics, comorbidities, baseline and follow-up serum 25-hydroxyvitamin D [25(OH)D] concentration, and available outcome measures [glycosylated hemoglobin (HbA1c), fasting plasma glucose, plasma glucose after 2-hour oral glucose tolerance test, and homeostatic model assessment of insulin resistance (HOMA-IR)]. Data synthesis was conducted using random-effect models (PROSPERO registration no. CRD42017055326). Twenty-eight trials, representing 3848 participants, met the eligibility criteria. Compared with the control group, vitamin D supplementation significantly reduced HbA1c level by -0.48% (95% CI, -0.79 to -0.18), fasting plasma glucose level by -0.46 mmol/L (95% CI, -0.74 to -0.19), and HOMA-IR level by -0.39 (95% CI, -0.68 to -0.11). Subgroup analysis revealed that the effects of vitamin D supplementation on different glycemic measures were influenced by age, calcium coadministration, vitamin D deficiency, serum 25(OH)D level after supplementation, and duration of supplementation. Vitamin D supplementation and improved vitamin D status improved glycemic measures and insulin sensitivity and may be useful as part of a preventive strategy for type 2 diabetes.

CORRELATIONS OF SERUM VITAMIN D WITH METABOLIC PARAMETERS IN ADULT OUTPATIENTS WITH DIFFERENT DEGREES OF OVERWEIGHT / OBESITY COMING FROM AN URBAN COMMUNITY

OBJECTIVE

To describe the correlations between serum 25(OH) vitamin D and anthropometric and metabolic parameters in adult outpatients of both sexes with different BMI coming from an urban community.

SUBJECTS AND METHODS

264 subjects referred for obesity assessment participated - 109 men and 155 women (20-60 years). Body weight and height, waist circumference (WC), blood pressure were recorded. Body composition was assessed by bioelectrical impedance (BIA) on a Tanita BC 420 MA analyzer (Tanita Inc., Japan). Serum 25(OH)D Total, Insulin, High-sensitivity C-reactive protein, blood glucose, total, HDL-cholesterol and triglycerides were measured. The insulin resistance index was calculated (HOMA-IR). Participants with BMI>25.0 kg/m2 underwent standard 75 g OGTT. Statistical analysis was performed on an IBM SPSS Statistics 19.0 for Windows platform (Chicago, IL).

RESULTS

Normal weight was found in 27.2 % of the participants, 24.6 % had overweight, 29.2 % -class I obesity, and 18.9 % - class II or III. Vitamin D was weakly and inversely correlated to different variables in the whole group - such as weight, WC, WC/Height, % body fat and HOMA-IR index (r=-0.231, -0.283, -0.307, -0.339, -0.328 respectively, all p<0.001). Building subgroups based on BMI led to loss of significance. Backward analysis revealed Total-C/LDL-C ratio, and LDL-C/HDL-C ratio as strongest predictors of serum vitamin D (p=0.001; R2=0.204).

CONCLUSION

The association of vitamin D with blood pressure, plasma lipids, glucose and insulin is very weak on an individual level. However, several obesity indices (WC, WC/height ratio, % Body fat from BIA) might be used as a screening tool for subjects at risk for vitamin D deficiency.

Effects of vitamin D supplementation on markers for cardiovascular disease and type 2 diabetes: an individual participant data meta-analysis of randomized controlled trials

Background

Evidence from randomized controlled trials (RCTs) for the causal role of vitamin D on noncommunicable disease outcomes is inconclusive.

Objective

The aim of this study was to investigate whether there are beneficial or harmful effects of cholecalciferol (vitamin D3) supplementation according to subgroups of remeasured serum 25-hydroxyvitamin D [25(OH)D] on cardiovascular and glucometabolic surrogate markers with the use of individual participant data (IPD) meta-analysis of RCTs.

Design

Twelve RCTs (16 wk to 1 y of follow-up) were included. For standardization, 25(OH)D concentrations for all participants (n = 2994) at baseline and postintervention were re-measured in bio-banked serum samples with the use of a certified liquid chromatography-tandem mass spectrometry method traceable to a reference measurement procedure. IPD meta-analyses were performed according to subgroups of remeasured 25(OH)D. Main outcomes were blood pressure and glycated hemoglobin (HbA1c). Secondary outcomes were LDL, HDL, and total cholesterol and triglycerides; parathyroid hormone (PTH); fasting glucose, insulin, and C-peptide; and 2-h glucose. In secondary analyses, other potential effect modifiers were studied.

Results

Remeasurement of 25(OH)D resulted in a lower mean 25(OH)D concentration in 10 of 12 RCTs. Vitamin D supplementation had no effect on the main outcomes of blood pressure and HbA1c. Supplementation resulted in 10-20% lower PTH concentrations, irrespective of the 25(OH)D subgroups. The subgroup analyses according to achieved 25(OH)D concentrations showed a significant decrease in LDL-cholesterol concentrations after vitamin D supplementation in 25(OH)D subgroups with <75, <100, and <125 nmol of -0.10 mmol/L (95% CI: -0.20, -0.00 mmol/L), -0.10 mmol/L (95% CI: -0.18, -0.02 mmol/L), and -0.07 mmol/L (95% CI: -0.14, -0.00 mmol/L), respectively. Patient features that modified the treatment effect could not be identified.

Conclusions

For the main outcomes of blood pressure and HbA1c, the data support no benefit for vitamin D supplementation. For the secondary outcomes, in addition to its effect on PTH, we observed indications for a beneficial effect of vitamin D supplementation only on LDL cholesterol, which warrants further investigation. This trial was registered at www.clinicaltrials.gov as NCT02551835.

Vitamin D supplementation does not improve CVD risk factors in vitamin D-insufficient subjects

OBJECTIVE

Low serum 25(OH)D levels are associated with cardiovascular disease (CVD) and some of its risk factors. However, in interventional studies, the effects of vitamin D supplementation have been uncertain, possibly due to inclusion of vitamin D-sufficient subjects. Our aim was therefore to examine effects of vitamin D supplementation on CVD risk factors in vitamin D-insufficient subjects.

DESIGN

Double-blinded randomized controlled trial.

METHODS

A 4-month interventional study with high-dose vitamin D (100,000 IU loading dose, followed by 20,000 IU/week) or placebo with measurements of blood pressure, lipids (total-, LDL- and HDL-cholesterol, triglycerides, apolipoproteins A1 and B), and glucose metabolism parameters (blood glucose, HbA_1c, serum human receptors for advanced glycation end products (sRAGE), insulin, C-peptide and HOMA-IR).

RESULTS

A total of 422 subjects with mean serum 25(OH)D level 34 nmol/L were included, with 411 subjects completing the study. Serum 25(OH)D levels increased with 56 nmol/L and decreased with 4 nmol/L in the vitamin D and placebo group, respectively. We found no statistically significant differences between the two groups in any of the measured CVD risk factors, except for a minor increase in sRAGE in the vitamin D group. Stratified analyses of subjects with low baseline serum 25(OH)D levels alone, or combined with blood pressure, lipid and HOMA-IR values above the median for the cohort, did not skew the results in favour of vitamin D supplementation.

CONCLUSION

Supplementation with vitamin D in subjects with baseline vitamin D insufficiency does not improve CVD risk factor profile.

Effect of vitamin D supplementation on fasting plasma glucose, insulin resistance and prevention of type 2 diabetes mellitus in non-diabetics: A systematic review and meta-analysis

Increasing epidemiological studies suggest that there is an association between vitamin D deficiency and risk of type 2 diabetes mellitus (T2DM). Therefore, randomized clinical trials (RCTs) have been performed to observe the effect of vitamin D supplementation on preventing T2DM, decreasing fasting plasma glucose (FPG) and improving insulin resistance to confirm the association between vitamin D and T2DM. However, the results of RCTs on controlling FPG level, improving insulin resistance and preventing T2DM in non-diabetics are inconsistent. In the present study, a systematic meta-analysis considering individual variation and intervention strategy was conducted to establish an objective and definitive conclusion. The results suggested that vitamin D supplementation had no significant effect on controlling FPG level, improving insulin resistance or preventing T2DM in non-diabetics in a pooled meta-analysis of 23 articles (containing 28 RCTs). However, stratified analysis indicated that supplementation of vitamin D had differential effects on FPG control, insulin sensitivity improvement and T2DM prevention in individuals with different baseline states: FPG was decreased for those with BMI <25 (P=0.048) or 20≤ 25(OH)D <30 ng/ml (P=0.002); insulin resistance was improved for those with 25(OH)D ≥30 ng/ml (P=0.021); and risk of T2DM was lower for pre-diabetic individuals (P=0.047) or for those with 25≤ BMI <30 (P=0.032). Additionally, the effect on T2DM prevention was improved when the supplement dose was >2,000 IU/day (P=0.047) and with intervention without calcium (P=0.047). Thus, further trials should focus on individual baselines and the supplementation strategy of vitamin D in the prevention of T2DM.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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