Serum 25-hydroxyvitamin D, calcium intake, and risk of type 2 diabetes after 5 years: results from a national, population-based prospective study (the Australian Diabetes, Obesity and Lifestyle study)

A randomised controlled trial of high dose vitamin D in recent-onset type 2 diabetes

AIMS

Vitamin D insufficiency has been associated with impaired pancreatic beta-cell function. We aimed to determine if high dose oral vitamin D3 (D) improves beta-cell function and glycaemia in type 2 diabetes.

METHODS

Fifty adults with type 2 diabetes diagnosed less than 12 months, with normal baseline serum 25-OH D (25D), were randomised to 6000 IU D (n=26) or placebo (n=24) daily for 6 months. Beta-cell function was measured by glucagon-stimulated serum C-peptide (delta C-peptide [DCP], nmol/l). Secondary outcome measures were fasting plasma glucose (FPG), post-prandial blood glucose (PPG), HbA1c and insulin resistance (HOMA-IR).

RESULTS

In the D group, median serum 25D (nmol/l) increased from 59 to 150 (3 months) and 128 (6 months) and median serum 1,25D (pmol/l) from 135 to 200 and 190. After 3 months, change in DCP from baseline in D (+0.04) and placebo (-0.08) was not different (P=0.112). However, change in FPG (mmol/l) was significantly lower in D (-0.40) compared to placebo (+0.1) (P=0.007), as was the change in PPG in D (-0.30) compared to placebo (+0.8) (P=0.005). Change in HbA1c (%) between D (-0.20) and placebo (-0.10) was not different (P=0.459). At 6 months, changes from baseline in DCP, FPG, PPG and HbA1c were not different between groups.

CONCLUSION

Oral D3 supplementation in type 2 diabetes was associated with transient improvement in glycaemia, but without a measurable change in beta-cell function this effect is unlikely to be biologically significant. High dose D3 therefore appears to offer little or no therapeutic benefit in type 2 diabetes.

The effects of progressive resistance training combined with a whey-protein drink and vitamin D supplementation on glycaemic control, body composition and cardiometabolic risk factors in older adults with type 2 diabetes: study protocol for a randomized controlled trial

Background

While physical activity, energy restriction and weight loss are the cornerstone of type 2 diabetes management, less emphasis is placed on optimizing skeletal muscle mass. As muscle is the largest mass of insulin-sensitive tissue and the predominant reservoir for glucose disposal, there is a need to develop safe and effective evidence-based, lifestyle management strategies that optimize muscle mass as well as improve glycaemic control and cardiometabolic risk factors in people with this disease, particularly older adults who experience accelerated muscle loss.

Methods/Design

Using a two-arm randomized controlled trial, this 6-month study builds upon the community-based progressive resistance training (PRT) programme Lift for Life® to evaluate whether ingestion of a whey-protein drink combined with vitamin D supplementation can enhance the effects of PRT on glycaemic control, body composition and cardiometabolic health in older adults with type 2 diabetes. Approximately 200 adults aged 50 to 75 years with type 2 diabetes, treated with either diet alone or oral hypoglycaemic agents (not insulin), will be recruited. All participants will be asked to participate in a structured, supervised PRT programme based on the Lift for Life® programme structure, and randomly allocated to receive a whey-protein drink (20 g daily of whey-protein plus 20 g after each PRT session) plus vitamin D supplements (2000 IU/day), or no additional powder and supplements. The primary outcome measures to be collected at baseline, 3 and 6 months will be glycated haemoglobin (HbA_1c) and insulin sensitivity (homeostatic model assessment). Secondary outcomes will include changes in: muscle mass, size and intramuscular fat; fat mass; muscle strength and function; blood pressure; levels of lipids, adipokines and inflammatory markers, serum insulin-like growth factor-1 and 25-hydroxyvitamin D; renal function; diabetes medication; health-related quality of life, and cognitive function.

Discussion

The findings from this study will provide new evidence on whether increased dietary protein achieved through the ingestion of a whey-protein drink combined with vitamin D supplementation can enhance the effects of PRT on glycaemic control, muscle mass and size, and cardiometabolic risk factors in older adults with type 2 diabetes.

Trial registration

Australian New Zealand Clinical Trials ACTRN12613000592741.

Electronic supplementary material

The online version of this article (doi:10.1186/1745-6215-15-431) contains supplementary material, which is available to authorized users.

Effects of combined calcium and vitamin D supplementation on insulin secretion, insulin sensitivity and β-cell function in multi-ethnic vitamin D-deficient adults at risk for type 2 diabetes: a pilot randomized, placebo-controlled trial

OBJECTIVES

To examine whether combined vitamin D and calcium supplementation improves insulin sensitivity, insulin secretion, β-cell function, inflammation and metabolic markers.

DESIGN

6-month randomized, placebo-controlled trial.

PARTICIPANTS

Ninety-five adults with serum 25-hydroxyvitamin D [25(OH)D] ≤55 nmol/L at risk of type 2 diabetes (with prediabetes or an AUSDRISK score ≥15) were randomized. Analyses included participants who completed the baseline and final visits (treatment n = 35; placebo n = 45).

INTERVENTION

Daily calcium carbonate (1,200 mg) and cholecalciferol [2,000-6,000 IU to target 25(OH)D >75 nmol/L] or matching placebos for 6 months.

MEASUREMENTS

Insulin sensitivity (HOMA2%S, Matsuda index), insulin secretion (insulinogenic index, area under the curve (AUC) for C-peptide) and β-cell function (Matsuda index x AUC for C-peptide) derived from a 75 g 2-h OGTT; anthropometry; blood pressure; lipid profile; hs-CRP; TNF-α; IL-6; adiponectin; total and undercarboxylated osteocalcin.

RESULTS

Participants were middle-aged adults (mean age 54 years; 69% Europid) at risk of type 2 diabetes (48% with prediabetes). Compliance was >80% for calcium and vitamin D. Mean serum 25(OH)D concentration increased from 48 to 95 nmol/L in the treatment group (91% achieved >75 nmol/L), but remained unchanged in controls. There were no significant changes in insulin sensitivity, insulin secretion and β-cell function, or in inflammatory and metabolic markers between or within the groups, before or after adjustment for potential confounders including waist circumference and season of recruitment. In a post hoc analysis restricted to participants with prediabetes, a significant beneficial effect of vitamin D and calcium supplementation on insulin sensitivity (HOMA%S and Matsuda) was observed.

CONCLUSIONS

Daily vitamin D and calcium supplementation for 6 months may not change OGTT-derived measures of insulin sensitivity, insulin secretion and β-cell function in multi-ethnic adults with low vitamin D status at risk of type 2 diabetes. However, in participants with prediabetes, supplementation with vitamin D and calcium may improve insulin sensitivity.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12609000043235.

Evidence Gap on the Prevalence of Non-conventional Risk Factors for Type 2 Diabetes in Iran

OBJECTIVES

Robust scientific evidence exists about the role of non-conventional risk factors in type 2 diabetes worldwide. The current epidemiological pattern of the disease in Iran suggests a precipitating role for these non-conventional risk factors. This review was performed to examine the research evidence suggesting a higher prevalence of non-conventional type 2 diabetes risk factors in Iran.

METHODS

MeSH keywords were applied to search several databases, including PUBMED, MEDLINE, AMED, EMBASE, Iran DOC, and the Scientific Information Database without a time limit from inception to September 2011. The quality of the non-interventional and population-based studies on Iranians included in these databases was assessed by the authors and any disagreement was resolved with consensus.

RESULTS

The literature search yielded 1847 publications, of which 62 were included in this study after eliminating non-relevant and overlapping papers. No study was found that verified a higher prevalence of the non-conventional type 2 diabetes risk factors in the Iranian population.

CONCLUSION

The identified evidence gap about the role of prominent non-conventional risk factors of type 2 diabetes in the Iranian population could be a major caveat in the application of an evidence-based approach to endorse or reject existing hypothesis about these risk factors. Studies on the prevalence of non-conventional biomarkers of type 2 diabetes among Iranians could be a promising area of research.

Effects of calcium-vitamin D co-supplementation on metabolic profiles in vitamin D insufficient people with type 2 diabetes: a randomised controlled clinical trial

AIMS/HYPOTHESIS

This study was performed to assess the effects of vitamin D and calcium supplementation on the metabolic profiles of vitamin D insufficient persons with type 2 diabetes.

METHODS

In a parallel designed randomised placebo-controlled clinical trial, a total of 118 non-smoker individuals with type 2 diabetes and insufficient 25-hydroxyvitamin D, aged >30 years, were recruited from the Isfahan Endocrine and Metabolism Research Centre. Participants were randomly assigned to four groups receiving: (1) 50,000 U/week vitamin D + calcium placebo; (2) 1,000 mg/day calcium + vitamin D placebo; (3) 50,000 U/week vitamin D + 1,000 mg/day calcium; or (4) vitamin D placebo + calcium placebo for 8 weeks. A study technician carried out the random allocations using a random numbers table. All investigators, participants and laboratory technicians were blinded to the random assignments. All participants provided 3 days of dietary records and 3 days of physical activity records throughout the intervention. Blood samples were taken to quantify glycaemic and lipid profiles at study baseline and after 8 weeks of intervention.

RESULTS

30 participants were randomised in each group. During the intervention, one participant from the calcium group and one from the vitamin D group were excluded because of personal problems. Calcium-vitamin D co-supplementation resulted in reduced serum insulin (changes from baseline: -14.8 ± 3.9 pmol/l, p = 0.01), HbA1c [-0.70 ± 0.19% (-8.0 ± 0.4 mmol/mol), p = 0.02], HOMA-IR (-0.46 ± 0.20, p = 0.001), LDL-cholesterol (-10.36 ± 0.10 mmol/l, p = 0.04) and total/HDL-cholesterol levels (-0.91 ± 0.16, p = 0.03) compared with other groups. We found a significant increase in QUICKI (0.025 ± 0.01, p = 0.004), HOMA of beta cell function (HOMA-B; 11.8 ± 12.17, p = 0.001) and HDL-cholesterol (0.46 ± 0.05 mmol/l, p = 0.03) in the calcium-vitamin D group compared with others.

CONCLUSIONS/INTERPRETATION

Joint calcium and vitamin D supplementation might improve the glycaemic status and lipid profiles of vitamin D insufficient people with type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01662193 FUNDING: Clinical Research Council, Isfahan University of Medical Sciences, Isfahan, Iran.

Vitamin D levels in an Australian population

BACKGROUND

Levels of vitamin D in the population have come under increasing scrutiny, however there are only a few studies in Australia which measure levels in the general population. The aim of this study was to measure the levels of vitamin D within a large population cohort and examine the association with seasons and selected demographic and health risk factors.

METHODS

A longitudinal cohort study of 2413 participants in the northwest suburbs of Adelaide, South Australia conducted between 2008 and 2010 was used to examine serum levels of 25-hydroxy vitamin D (25(OH)D) in relation to demographic characteristics (age, sex, income, education and country of birth), seasons, the use of vitamin D supplements and selected health risk factors (physical activity, body mass index and smoking). Both unadjusted and adjusted mean levels of serum 25(OH)D were examined, as were the factors associated with the unadjusted and adjusted prevalence of serum 25(OH)D levels below 50 and 75 nmol/L.

RESULTS

Overall, the mean level of serum 25(OH)D was 69.2 nmol/L with 22.7% of the population having a serum 25(OH)D level below 50 nmol/L, the level which is generally recognised as vitamin D deficiency. There were significantly higher levels of 25(OH)D among males compared to females (t = 4.65, p < 0.001). Higher levels of 25(OH)D were also measured in summer and autumn compared with winter and spring. Generally, mean levels of 25(OH)D were lower in those classified as obese. Smokers and those undertaking no or less than 150 minutes/week of physical activity also had lower levels of serum vitamin D. Obesity (as classified by body mass index), season and undertaking an insufficient level of physical activity to obtain a health benefit were significantly associated with the prevalence of vitamin D deficiency.

CONCLUSIONS

Vitamin D deficiency is prevalent in South Australia, affecting almost one quarter of the population and levels are related to activity, obesity and season even when adjusted for confounding factors. Improved methods of addressing vitamin D levels in population are required.

Measurements of 25-hydroxyvitamin D concentrations in archived dried blood spots are reliable and accurately reflect those in plasma

CONTEXT

Recognition that vitamin D might be associated with many chronic diseases has led to large-scale epidemiological and clinical studies. Dried blood spots (DBS) are a useful resource for these studies. Consequently, accurate, efficient, and inexpensive assays to quantify 25-hydroxyvitamin D (25OHD) in DBS are required.

OBJECTIVE

This study evaluated the validity and reliability of a liquid chromatography-tandem mass spectrometry assay for measuring 25OHD in archived DBS and compared measurements of 25OHD in DBS with those in plasma.

DESIGN AND PARTICIPANTS

Sixty-two participants in the Melbourne Collaborative Cohort Study who had plasma and matching DBS stored since study entry in the early 1990s were randomly selected for a study calibrating 25OHD concentrations in DBS with plasma. As part of a study of vitamin D and mortality, cancer, and diabetes, we also assessed the reliability of measurements from DBS using 500 replicates placed randomly within 31 batches run over 15 months.

OUTCOME MEASURE

25OHD concentrations were measured by liquid chromatography-tandem mass spectrometry.

RESULTS

There was good agreement between measurements of 25OHD from DBS and plasma; R(2) = 0.73 from a regression of plasma concentration on DBS concentration. The within-batch and between-batch intraclass correlations from the 500 replicate measurements were 0.82 (95% confidence interval, 0.80, 0.85) and 0.73 (95% confidence interval, 0.68, 0.78), respectively.

CONCLUSIONS

Measuring 25OHD in DBS is a valid and reliable alternative to measuring 25OHD in sera or plasma. A simple calibration model was developed to convert measurements from DBS to equivalent plasma measurements, thus enabling comparisons against clinical reference ranges and with studies using sera or plasma samples.

Bioavailability of vitamin D2 from enriched mushrooms in prediabetic adults: a randomized controlled trial

BACKGROUND/OBJECTIVES

Based on the growing evidence of risk reduction from fresh fruit and vegetable consumption and an inverse relationship between serum 25-hydroxyvitamin D (25OHD) and the risk of type 2 diabetes (T2D), we determined the benefits of regularly consuming vitamin D-enriched mushrooms in a prediabetic cohort. Exposing edible mushrooms to ultraviolet B (UVB) light increases vitamin D2 (D2) and raises serum 25OHD2 in healthy young adults; however, their benefit to deficient prediabetics and glucose metabolism remains untested.

SUBJECTS/METHODS

Forty-three prediabetic, D-deficient adults (25OHD≤20 ng/ml), BMI>25 were randomized to four groups consuming daily entrées containing 100 g fresh sliced cooked mushrooms prepared by a chef for 16 weeks. Two groups were fed UVB-treated mushrooms initially containing: 600 IU D2 or 4000 IU D2; each one also received one capsule of placebo daily. Two control groups were fed untreated mushrooms and D3 dietary supplements at two label doses: 600 IU D3 and 4000 IU D3. D2 and D3 content were analyzed in mushrooms, before and after cooking and in over-the-counter supplements.

RESULTS

After 16 weeks, both D2-UVB-mushroom entrée doses, which were significantly lower after cooking, produced modest or no increases in 25OHD2 or total 25OHD relative to the positive control subjects who actually consumed about 1242 and 7320 IU per day of D3 (higher than stated on the label).

CONCLUSIONS

Unanticipated D2 cooking loss from fresh UVB mushrooms and probable low absorption and/or hydroxylation may explain the smaller increase in 25OHD2 in our prediabetic overweight/obese cohort compared with past findings in younger, healthy subjects. Moreover, no dose or vitamin D source was associated with modifying T2D risk factors.

Lower vitamin D levels at first trimester are associated with higher risk of developing gestational diabetes mellitus

The progressive increase of insulin resistance observed in pregnancy contributes to the pathophysiology of gestational diabetes mellitus (GDM). There is controversy whether vitamin D deficiency contributes to abnormal glycemic regulation in pregnancy. We tested the associations between first trimester 25-hydroxyvitamin D (25OHD) levels and: 1) the risk of developing GDM; 2) insulin resistance/sensitivity, beta cell function and compensation indices in a large population-based prospective cohort of pregnant women. Participants (n = 655) were seen at first (6-13 weeks) and second (24-28 weeks) trimesters for blood samples. At first trimester, 25OHD levels were measured. At second trimester, glucose and insulin were measured 3 times during the oral glucose tolerance test to estimate insulin resistance (HOMA-IR), beta cell function (HOMA-B), insulin sensitivity (Matsuda index), insulin secretion (AUCins/gluc) and beta cell compensation (ISSI-2). Based on IADPSG criteria, 54 participants (8.2 %) developed GDM. Lower first trimester 25OHD levels were associated with higher risk of developing GDM even after adjustment for vitamin D confounding factors and GDM risk factors (OR = 1.48 per decrease of one SD in 25OHD levels; P = 0.04). Lower first trimester 25OHD levels were associated with higher HOMA-IR (r = - 0.08; P = 0.03), lower Matsuda index (r = 0.13; P = 0.001) and lower ISSI-2 (r = 0.08; P = 0.04). After adjustment for confounders, we found no significant association with HOMA-B and AUCins/gluc. Our results suggest that low levels of 25OHD at first trimester are (1) an independent risk factor for developing GDM and (2) associated with insulin resistance at second trimester.

TCF2 attenuates FFA-induced damage in islet β-cells by regulating production of insulin and ROS

Free fatty acids (FFAs) are cytotoxic to pancreatic islet β-cells and play a crucial role in the diabetes disease process. A recent study revealed a down-regulation of transcription factor 2 (TCF2) levels during FFA-mediated cytotoxicity in pancreatic β-cells. However, its function during this process and the underlying mechanism remains unclear. In this study, treatment with palmitic acid (PA) at high levels (400 and 800 μM) decreased β-cell viability and TCF2 protein expression, along with the glucose-stimulated insulin secretion (GSIS). Western and RT-PCR analysis confirmed the positive regulatory effect of TCF2 on GSIS through promotion of the key regulators pancreatic duodenal homeobox-1 (PDX1) and glucose transporter 2 (GLUT2) in β-cells. In addition, both PI3K/AKT and MEK/ERK showed decreased expression in PA (800 μM)-treated β-cells. Overexpression of TCF2 could effectively restore the inhibitory effect of PA on the activation of PI3K/AKT and MEK/ERK as well as β-cell viability, simultaneously, inhibited PA-induced reactive oxygen species (ROS) generation. After blocking the PI3K/AKT and MAPK/ERK signals with their specific inhibitor, the effect of overexpressed TCF2 on β-cell viability and ROS production was obviously attenuated. Furthermore, a protective effect of TCF2 on GSIS by positive modulation of JNK-PDX1/GLUT2 signaling was also confirmed. Accordingly, our study has confirmed that TCF2 positively modulates insulin secretion and further inhibits ROS generation via the PI3K/AKT and MEK/ERK signaling pathways. Our work may provide a new therapeutic target to achieve prevention and treatment of diabetes.

Environmental, personal, and genetic determinants of response to vitamin D supplementation in older adults

CONTEXT AND OBJECTIVE

Suboptimal vitamin D status can be corrected by vitamin D supplementation, but individual responses to supplementation vary. We aimed to examine genetic and nongenetic determinants of change in serum 25-hydroxyvitamin D (25(OH)D) after supplementation.

DESIGN AND PARTICIPANTS

We used data from a pilot randomized controlled trial in which 644 adults aged 60 to 84 years were randomly assigned to monthly doses of placebo, 30 000 IU, or 60 000 IU vitamin D3 for 12 months. Baseline characteristics were obtained from a self-administered questionnaire. Eighty-eight single-nucleotide polymorphisms (SNPs) in 41 candidate genes were genotyped using Sequenom MassArray technology. Serum 25(OH)D levels before and after the intervention were measured using the Diasorin Liaison platform immunoassay. We used linear regression models to examine associations between genetic and nongenetic factors and change in serum 25(OH)D levels.

RESULTS

Supplement dose and baseline 25(OH)D level explained 24% of the variability in response to supplementation. Body mass index, self-reported health status, and ambient UV radiation made a small additional contribution. SNPs in CYP2R1, IRF4, MC1R, CYP27B1, VDR, TYRP1, MCM6, and HERC2 were associated with change in 25(OH)D level, although only CYP2R1 was significant after adjustment for multiple testing. Models including SNPs explained a similar proportion of variability in response to supplementation as models that included personal and environmental factors.

CONCLUSION

Stepwise regression analyses suggest that genetic variability may be associated with response to supplementation, perhaps suggesting that some people might need higher doses to reach optimal 25(OH)D levels or that there is variability in the physiologically normal level of 25(OH)D.

Effect of moderate-dose vitamin D supplementation on insulin sensitivity in vitamin D-deficient non-Western immigrants in the Netherlands: a randomized placebo-controlled trial

BACKGROUND

Low serum 25-hydroxyvitamin D [25(OH)D] concentrations have been associated with insulin resistance, the metabolic syndrome, and type 2 diabetes. Because many non-Western immigrants in the Netherlands are vitamin D deficient, obese, and at high risk of diabetes, vitamin D supplementation may contribute to prevent diabetes and insulin resistance.

OBJECTIVE

We examined the effect of vitamin D supplementation on insulin sensitivity and β cell function in overweight, vitamin D-deficient, non-Western immigrants at high risk of diabetes.

DESIGN

The study was a 16-wk, randomized, placebo-controlled trial. A total of 130 non-Western immigrants with prediabetes (fasting glucose concentration >5.5 mmol/L or random glucose concentration from 7.8 to 11.1 mmol/L) and vitamin D deficiency (serum 25[OH]D concentration <50 nmol/L) were randomly assigned after stratification by sex to receive either cholecalciferol (1200 IU/d) or a placebo for 16 wk. All participants received 500 mg Ca/d as calcium carbonate. The primary outcome was the difference in the area under the curve of insulin and glucose after a 75-g oral-glucose-tolerance test after 4 mo of treatment. Secondary outcomes were insulin-sensitivity variables, β cell-function variables, and metabolic syndrome.

RESULTS

Mean serum 25(OH)D concentrations increased significantly in the vitamin D compared with placebo groups. After 4 mo of therapy, the mean between-group difference was 38 nmol/L (95% CI: 32.1, 43.9 nmol/L; P < 0.001). There was no significant effect on insulin sensitivity and β cell function. In a post hoc analysis, when patients with diabetes at baseline were excluded, a significant increase in the insulinogenic index was observed in participants who obtained a 25(OH)D concentration ≥60 nmol/L (P = 0.040).

CONCLUSIONS

Vitamin D supplementation in non-Western vitamin D-deficient immigrants with prediabetes did not improve insulin sensitivity or β cell function or change the incidence of metabolic syndrome. However, after the exclusion of diabetic subjects, an improvement in the insulinogenic index was observed in participants who obtained a 25(OH)D concentration ≥60 nmol/L. This trial was registered at trialregister.nl as NTR1827.

Vitamin D levels and microvascular complications in type 2 diabetes

BACKGROUND

Vitamin D has important actions on glucose metabolism. These include improved insulin exocytosis, direct stimulation of insulin receptor, improved uptake of glucose by peripheral tissues, improving insulin resistance. It has got various pleiotropic effects like suppression of cell mediated immunity, regulation of cell proliferation, stimulation of neurotropic factors such as nerve growth factor, Glial cell line-derived neurotrophic factor, neurotropin, suppression of RAAS, reduction of albuminuria, immunomodulatory effects, and anti-inflammatory effects. Thus, vitamin D is implicated in many ways in the pathogenesis of retinopathy, neuropathy and nephropathy.

OBJECTIVES

To study the correlation of vitamin D levels with microvascular complications in type 2 diabetes.

MATERIALS AND METHODS

Cross-sectional case-control study of 18 patients (18-70 years), who met the American Diabetes Association 2011 criteria for type 2 diabetes, was conducted. Age and sex matched healthy controls were taken. Subjects were evaluated for the presence of microvascular complications by clinical evaluation, urine examination, fundus examination, nerve conduction studies, and various biochemical tests. 25-OH cholecalciferol levels were done for each. Cut off level for vitamin D deficiency was 20 ng/ml.

RESULTS

Mean vitamin D was lower in type 2 diabetics than healthy subjects (19.046 vs. 27.186 ng/ml). Prevalence of vitamin D deficiency and insufficiency was found to significantly higher in diabetics when compared to healthy subjects (P = 0.0001). Vitamin D deficiency was found to be significantly associated with neuropathy (χ(2) = 5.39, df = 1, P = 0.020), retinopathy, (χ(2) = 6.6, df = 1, P = 0.010) and nephropathy (χ(2) = 10. 52, df = 1, P = 0.001). Lower levels of vitamin D were found to be associated with increasing prevalence of combinations of microvascular complications namely neuropathy with retinopathy (P = 0.036), neuropathy with nephropathy (P = 0.029), retinopathy with nephropathy (P = 0.022) and neuropathy with retinopathy with nephropathy (P = 0.0001).

Serum 25-hydroxyvitamin D and incidence of diabetes in elderly people: the PRO.V.A. study

CONTEXT

Increasing research has shown that low levels of serum 25-hydroxyvitamin (25OHD) predict the onset of diabetes, but no research is available on this issue in elderly people.

OBJECTIVE

Our objective was to examine whether low serum levels of 25OHD are associated with a higher risk of incident type 2 diabetes over a lengthy follow-up in a representative group of elderly people.

DESIGN AND SETTING

This was a population-based cohort study as part of the Progetto Veneto Anziani (Pro.V.A.) Study over a follow-up of 4.4 years in the general community.

PARTICIPANTS

PARTICIPANTS included 2227 participants (1728 with follow-up visits and 499 died during the follow-up) over 65 years of age without diabetes at baseline, of 2352 initially included.

MAIN OUTCOME MEASURE

The main outcome measure was incident diabetes.

RESULTS

There were no baseline differences in known factors for the onset of diabetes (body mass index, waist circumference, total cholesterol, renal function, and hemoglobin A1c levels) between the groups with different serum 25OHD levels (≤ 25, 25-50, 50-75, and ≥ 75 nmol/L). Over a 4.4-year follow-up, 291 individuals developed diabetes, with an incidence of 28 events per 1000 person-years. No significant difference in the incidence of diabetes emerged between the baseline 25OHD groups. Cox's regression analysis, adjusted for potential confounders, revealed no relationship between low vitamin D levels and incident diabetes during the follow-up (hazard ratio [HR] = 1.05, 95% confidence interval [CI] = 0.76-1.45, P = .77; HR = 1.44, 95% CI = 0.95-1.98, P = .12; and HR = 1.37, 95% CI = 0.87-2.16, P = .17 for those with 25OHD ≤25, 25-50, and 50-75 nmol/L, respectively).

CONCLUSION

Baseline serum concentrations of 25OHD were not associated with the incidence of diabetes in community-dwelling elderly people over a follow-up of 4.4 years.

Maternal, umbilical arterial and umbilical venous 25-hydroxyvitamin D and adipocytokine concentrations in pregnancies with and without gestational diabetes

OBJECTIVE

Gestational diabetes mellitus (GDM) has been associated with inflammation as well as Vitamin D insufficiency. While Vitamin D has anti-inflammatory properties, relationships between Vitamin D and inflammatory markers remain unexplored in GDM. Therefore, this case--control study investigated adipocytokine and Vitamin D [25(OH)D] concentrations and correlations in GDM and control women, as well as their neonates.

DESIGN/PARTICIPANTS/MEASUREMENTS

seventy-three women participated: 36 GDM and 37 controls. Maternal samples were drawn at 31 weeks. Umbilical arterial and venous samples were collected at birth. 25(OH)D and adipocytokine concentrations were compared for GDM vs control maternal, umbilical arterial and venous samples. Correlations were explored between biochemical results, maternal and neonatal demographics.

RESULTS

Compared with age- and weight-matched control participants, GDM women had significantly lower concentrations of 25(OH)D (77·3 ± 24·3 vs 93·2 ± 19·2 nm/l; P = 0·009); adiponectin (17·5 ± 11·8 vs 34·1 ± 20·3 μg/ml, P < 0·001); resistin (25·4 ± 9·1 vs 31·9 ± 12·1 ng/ml, P = 0·045); and plasminogen activator inhibitor-1 (PAI-1) 13·9 ± 10·0 vs 21·0 ± 12·6 ng/ml, P = 0·038), while delivering 1 week earlier (38·2 ± 1·2 vs 39·5 ± 0·9 weeks, P < 0·001). GDM maternal 25(OH)D concentrations positively correlated with PAI-1, IL-8 and TNF-α concentrations. Umbilical 25(OH)D concentrations were not significantly different in GDM vs control offspring, whereas adiponectin, resistin and PAI-1 concentrations were significantly lower in GDM offspring.

CONCLUSIONS

GDM women had lower 25(OH)D concentrations than controls, while neonatal umbilical concentrations of 25(OH)D did not differ. GDM maternal and GDM offspring had lower adiponectin, resistin and PAI-1 concentrations compared with controls. Results suggest that both GDM women and their offspring demonstrate abnormal adipocytokine patterns.

Inverse relationship between vitamin D status and insulin resistance and the risk of impaired fasting glucose in Korean children and adolescents: the Korean National Health and Nutrition Examination Survey (KNHANES) 2009-2010

OBJECTIVE

To investigate whether low vitamin D status was related to insulin resistance (IR) or impaired fasting glucose (IFG) in Korean adolescents, after adjusting for total body fat mass (FM).

DESIGN

A cross-sectional study.

SETTING

Korea National Health and Nutrition Examination Survey (KNAHNES) 2009-2010.

SUBJECTS

In total, 1466 participants (769 males) aged 10-19 years were assessed for serum 25-hydroxyvitamin D (25(OH)D) levels, for FM by whole-body dual-energy X-ray absorptiometry and for IR by homeostasis model assessment (HOMA-IR) after an 8 h fast.

RESULTS

Age-, sex-, season- and physical-activity-adjusted regression models showed that serum 25(OH)D levels were significantly related to markers of adiposity (P = 0.016 for FM (g), P = 0.023 for FM (%) and P = 0.035 for fat mass index). When the participants were stratified into three 25(OH)D categories (<37.5 nmol/l (n 553), 37.5 to < 50 nmol/l (n 543) and ≥ 50 nmol/l (n 370)), significantly decreasing trends were observed for fasting insulin (all P < 0.001), HOMA-IR (all P < 0.001) and the odds ratios for IFG (all P for trend < 0.05) from the lowest to the highest 25(OH)D category, after adjustments for age, sex, physical activity and all markers of adiposity. In the multivariate logistic regression analysis, the likelihood of participants in the lowest serum 25(OH)D category having IFG was 2.96-3.15 compared with those in the highest 25(OH)D category (all P < 0.05).

CONCLUSIONS

There was a significant inverse relationship between vitamin D status and IR and the risk of IFG, independent of adiposity, in Korean adolescents.

Prospective association of 25(OH)D with metabolic syndrome

CONTEXT

Vitamin D may play a role in the aetiology of the metabolic syndrome (MetS), yet the majority of previous studies have been cross-sectional, and the limited number of prospective studies has yielded inconsistent results.

OBJECTIVE

To examine the prospective association of vitamin D [25-hydroxyvitamin D, 25(OH)D] with MetS in a multi-ethnic cohort of adults in Ontario, Canada.

DESIGN

Nondiabetic individuals with pre-existing MetS risk factors were recruited for participation in the PROspective Metabolism and ISlet cell Evaluation (PROMISE) cohort study, a longitudinal study of the determinants of insulin resistance and MetS.

METHODS

Of the 654 participants enrolled at baseline, 489 attended a 3-year follow-up visit. There were 301 participants eligible for the analysis of 25(OH)D with incident MetS (age 49·2 ± 9·3 years old, 75·4% female), after excluding 188 (38·5%) prevalent MetS cases at baseline. Longitudinal change in MetS components was assessed in the entire follow-up cohort.

RESULTS

There were 76 (15·5%) participants who developed MetS over the 3-years of follow-up. Multivariate logistic regression analyses indicated a decreased risk of MetS at follow-up per standard deviation increase in baseline 25(OH)D after adjustment for sociodemographics, season, baseline and change in supplement use and physical activity and insulin resistance (OR = 0·63, 95% CI 0·44-0·90). Multivariate linear regression analyses revealed a significant inverse association of baseline 25(OH)D with fasting glucose at follow-up (β = -0·0005, P = 0·025).

CONCLUSIONS

There was a significant inverse association of baseline 25(OH)D with incident MetS, which may be partly driven by its association with glucose homoeostasis.

Vitamin D and diabetes

There has been increasing evidence that vitamin D may have a role in modifying risk of diabetes. Vitamin D has both direct and indirect effects on various mechanisms related to the pathophysiology of type 2 diabetes, including pancreatic beta cell dysfunction, impaired insulin action and systemic inflammation. This article describes the biologic plausibility behind the potential association between vitamin D and type 2 diabetes and summarizes the current evidence from human studies that suggests but does not prove a relation between vitamin D and type 2 diabetes, and briefly reports on the potential association between vitamin D and type 1 diabetes.

Associations between serum 25-hydroxyvitamin D concentrations and multiple health conditions, physical performance measures, disability, and all-cause mortality: the Concord Health and Ageing in Men Project

OBJECTIVES

To explore associations between serum 25-hydroxyvitamin D (25(OH)D) levels and a wide range of health conditions, physical performance measures, disability, and mortality in a large epidemiological study to identify an optimum range for 25(OH)D concentrations.

DESIGN

Cross-sectional study, with additional prospective data on falls and mortality.

SETTING

Concord Health and Ageing in Men Project, Sydney, Australia.

PARTICIPANTS

Community-dwelling men aged 70 and older (N = 1,659).

MEASUREMENTS

Serum 25(OH)D levels, general health status, self-reported diseases, physical performance measures, disability (activities of daily living and instrumental activities of daily living) and falls.

RESULTS

Fair, poor, and very poor health; self-reported diabetes mellitus; hyperglycemia; depression; muscle weakness; poor balance; and all-cause mortality were all associated with serum 25(OH)D levels less than 50 nmol/L, even after adjustment for confounding. The findings also suggest that, in older men, for a wide range of health conditions, physical performance measures, disability, falls, and mortality, the optimum range of 25(OH)D is between 50.0 and 74.9 nmol/L, with no additional benefit for 25(OH)D levels of 75.0 nmol/L or greater.

CONCLUSION

Programs aimed at achieving an optimum range of serum 25(OH)D at levels between 50.0 and 74.9 nmol/L may have overall health benefits and such levels are adequate for older men.

Vitamin D and 1-hour post-load plasma glucose in hypertensive patients

Background

A plasma glucose value ≥155 mg/dl for 1-hour post-load plasma glucose during an oral glucose tolerance test (OGTT) is able to identify subjects with normal glucose tolerance (NGT) at high-risk for type-2 diabetes and with subclinical organ damage. We designed this study to address if 25-hydroxyvitamin D [25(OH)D] circulating levels are associated with glucose tolerance status, and in particular with 1-hour post-load plasma glucose levels.

Methods

We enrolled 300 consecutive Caucasian hypertensive never-treated outpatients (160 men and 140 women, aged 52.9 ± 9.2 years). Subjects underwent OGTT and measurements of 25(OH)D and standard laboratory tests. Estimated glomerular filtration rate (e-GFR) was calculated by CKD-EPI formula and insulin sensitivity was assessed by Matsuda-index.

Results

Among participants, 230 were NGT, 44 had impaired glucose tolerance (IGT) and 26 had type-2 diabetes. According to 1-h post-load plasma glucose cut-off point of 155 mg/dL, we divided NGT subjects into: NGT < 155 (n = 156) and NGT > 155 mg/dL (n = 74).

NGT ≥ 155 had higher significant fasting and post-load glucose and insulin, parathyroid hormone and hs-CRP levels than NGT < 155. On the contrary, Matsuda-index, e-GFR, and 25(OH)D were significantly lower in NGT ≥ 155 than NGT < 155 subjects. In the multiple regression analysis, 25(OH)D levels resulted the major determinant of 1-h post-load plasma glucose in all population and in the four groups of glucose tolerance status. In the whole population, Matsuda-index, hs-CRP and e-GFR explained another 12.2%, 6.7% and 1.7% of its variation.

Conclusions

Our data demonstrate a significant and inverse relationship between 25(OH)D levels and glucose tolerance status, particularly with 1-h post-load glucose.

Effects of vitamin D in skeletal muscle: falls, strength, athletic performance and insulin sensitivity

Accompanying the high rates of vitamin D deficiency observed in many countries, there is increasing interest in the physiological functions of vitamin D. Vitamin D is recognized to exert extra-skeletal actions in addition to its classic roles in bone and mineral homeostasis. Here, we review the evidence for vitamin D's actions in muscle on the basis of observational studies, clinical trials and basic research. Numerous observational studies link vitamin D deficiency with muscle weakness and sarcopaenia. Randomized trials predominantly support an effect of vitamin D supplementation and the prevention of falls in older or institutionalized patients. Studies have also examined the effect of vitamin D in athletic performance, both inferentially by UV radiation and directly by vitamin D supplementation. Effects of vitamin D in muscle metabolic function, specifically insulin sensitivity, are also addressed in this review. At a mechanistic level, animal studies have evaluated the roles of vitamin D and associated minerals, calcium and phosphate, in muscle function. In vitro studies have identified molecular pathways by which vitamin D regulates muscle cell signalling and gene expression. This review evaluates evidence for the various roles of vitamin D in skeletal muscle and discusses controversies that have made this a dynamic field of research.

The Association between 25-Hydroxyvitamin D and Hemoglobin A1c Levels in Patients with Type 2 Diabetes and Stage 1-5 Chronic Kidney Disease

Aim. To examine the relationship between plasma 25-hydroxyvitamin D (25(OH)D) levels and blood hemoglobin A1c (HbA1c) levels in diabetic patients at various stages of chronic kidney disease (CKD). Methods. We screened for data collected between 2003 and 2012. The correlation between 25(OH)D and HbA1c levels was studied in patients categorized according to the severity of CKD and their vitamin D status. A multivariate linear regression model was used to determine whether 25(OH)D and HbA1c levels were independently associated after adjustment for a number of covariates (including erythrocyte metformin levels). Results. We identified 542 reports from 245 patients. The mean HbA1c value was 6.7 ± 1.0% in vitamin D sufficiency, 7.3 ± 1.5% in insufficiency, and 8.4 ± 2.0% in deficiency (P < 0.0001). There was a negative correlation between 25(OH)D and HbA1c levels for the population as a whole (r = -0.387, P < 0.0001) and in the CKD severity subgroups (r = -0.384, P < 0.0001 and r = -0.333, P < 0.0001 for CKD stages 1-3 and 4-5, resp.). In the multivariate analysis, the 25(OH)D level was the only factor associated with HbA1c (P < 0.0001). Conclusion. 25(OH)D levels were negatively correlated with HbA1c levels independently of study covariates.

Serum vitamin D levels, diabetes and cardio-metabolic risk factors in Aboriginal and Torres Strait Islander Australians

BACKGROUND

Low levels of serum 25-hydroxy vitamin D (25(OH)D), have been associated with development of type 2 diabetes and cardiovascular disease (CVD); however there are limited data on serum 25(OH)D in Indigenous Australians, a population at high risk for both diabetes and CVD. We aimed to assess levels of serum 25(OH)D in Aboriginal and Torres Strait Islander Australians and to explore relationships between 25(OH)D and cardio-metabolic risk factors and diabetes.

METHODS

592 Aboriginal and/or Torres Strait Islander Australian participants of The eGFR (estimated glomerular filtration rate) Study, a cross-sectional analysis of a cohort study performed in 2007-2011, from urban and remote centres within communities, primary care and tertiary hospitals across Northern Territory, Far North Queensland and Western Australia. Assessment of serum 25(OH)D, cardio-metabolic risk factors (central obesity, diabetes, hypertension, history of cardiovascular disease, current smoker, low HDL-cholesterol), and diabetes (by history or HbA1c ≥6.5%) was performed. Associations were explored between 25(OH)D and outcome measures of diabetes and number of cardio-metabolic risk factors.

RESULTS

The median (IQR) serum 25(OH)D was 60 (45-77) nmol/L, 31% had 25(OH)D <50 nmol/L. For participants with 25(OH)D < 50 vs ≥50 nmol/L, cardio-metabolic risk profile differed for: diabetes (54%, 36% p < 0.001), past history of cardiovascular disease (16%, 9%, p = 0.014), waist-hip ratio (0.98, 0.92, p < 0.001), urine albumin-creatinine ratio (2.7, 1.5 mg/mmol, p < 0.001). The OR (95% CI) for diabetes was 2.02 (1.03 - 3.95) for people in the lowest vs highest tertiles of 25(OH)D (<53 vs >72 nmol/L, respectively) after adjusting for known cardio-metabolic risk factors.

CONCLUSION

The percentage of 25(OH)D levels <50 nmol/L was high among Aboriginal and Torres Strait Islander Australians from Northern and Central Australia. Low 25(OH)D level was associated with adverse cardio-metabolic risk profile and was independently associated with diabetes. These findings require exploration in longitudinal studies.

Vitamin D status and its relationship with metabolic markers in persons with obesity and type 2 diabetes in the UAE: a cross-sectional study

AIM

To report vitamin D status and its impact on metabolic parameters in people in the United Arab Emirates with obesity and type 2 diabetes (T2D).

METHODOLOGY

This cross-sectional study included 309 individuals with obesity and T2D who were randomly selected based on study criteria. Serum concentrations of 25-hydroxy vitamin D (s-25(OH)D), calcium, phosphorus, parathyroid hormone, alkaline phosphatase, glycemic profile, and cardiometabolic parameters were assessed in fasting blood samples, and anthropometric measurements were recorded.

RESULTS

Vitamin D deficiency (s-25(OH)D < 50 nmol/L) was observed in 83.2% of the participants, with a mean s-25(OH)D of 33.8 ± 20.3 nmol/L. Serum 25(OH)D correlated negatively (P < 0.01) with body mass index, fat mass, waist circumference, parathyroid hormone, alkaline phosphatase, triglycerides, LDL-cholesterol, and apolipoprotein B and positively (P < 0.01) with age and calcium concentration. Waist circumference was the main predictor of s-25(OH)D status. There was no significant association between serum 25(OH)D and glycemic profile.

CONCLUSION

There is an overwhelming prevalence of vitamin D deficiency in our sample of the Emirati population with obesity and T2D. Association of s-25(OH)D with body mass index, waist circumference, fat mass, markers of calcium homeostasis and cardiometabolic parameters suggests a role of vitamin D in the development of cardiometabolic disease-related process.

Status of Vitamin-D in diabetic patients

BACKGROUND

Vitamin D (vit D) deficiency has been found to have an inverse relationship with the occurrence of type-2 diabetes mellitus (DM). The aim of this study was to assess the vit D level in type-2 diabetic patients.

METHODS

One hundred-twenty DM patients selected as case group and 120 healthy individuals as control group were investigated in this study from October 2011 to September 2012 in Shahid Beheshti and Ayatollah Rouhani teaching hospital in Babol, North of Iran. Both groups were matched regarding age and gender. Serum levels of 25(OH)-vitamin D were measured in both groups. The data were collected and analyzed.

RESULTS

The mean age of the case group was 51.2±7.98 and in control group was 50.6±7.73 years. The mean concentration of vit D in the case group was 18.7±10.2 and in the control group was 24.6±13.5 ng/dl (p=0.002). The mean concentration of vit D in male subjects in both groups were equal but in women with diabetes was lower than the healthy women (19.3±11.9 versus 27.03±10.28 ng/dl, respectively) (p=0.0001). In diabetic patient vit D level was deficient in 77 (64.2%), insufficient in 30 (25%) and sufficient in 13 (10.3%) patients. In the healthy group, these parameters were seen in 44 (36.6%), in 46 (38.4%) and in 30 (25%) patients.

CONCLUSION

The results show that vit D concentration was significantly lower in diabetic patients than the healthy individuals. Although the mean concentration of vit D in males in both groups was equal but in the women with diabetes was lower than the healthy women.

Primary hyperparathyroidism and metabolic risk factors, impact of parathyroidectomy and vitamin D supplementation, and results of a randomized double-blind study

BACKGROUND

Vitamin D insufficiency may increase the risk for cardio metabolic disturbances in patients with primary hyperparathyroidism (PHPT).

OBJECTIVE

To analyze the vitamin D status and indices of the metabolic syndrome in PHPT patients and the effect of vitamin D supplementation after parathyroid adenomectomy (PTX).

DESIGN AND METHODS

Double-blinded, randomized clinical trial (ClinicalTrials.gov identifier: NCT00982722) performed at Karolinska University Hospital, Sweden, April 2008 to November 2011. One hundred and fifty consecutive patients with PHPT (119 women) were randomized after PTX, 75 to oral treatment with calcium carbonate 1000 mg daily and 75 to calcium carbonate 1000 mg and cholecalciferol 1600 IU daily over 12 months. Changes in metabolic profile and ambulatory blood pressure (BP) were analyzed. Main outcome measures were changes in metabolic factors, BP, and body composition.

RESULTS

The 25-hydroxyvitamin D (25-OH-D)-level was <50 nmol/l in 76% of the patients before PTX. After PTX, glucose, insulin, and IGF1 decreased, while the 25-OH-D and the IGF-binding protein 1 increased and remained unchanged at follow-up after study medication. One year of vitamin D supplementation resulted in lower parathyroid hormone (PTH) (40 (34-52) vs 49 (38-66) ng/l) and higher 25-OH-D (76 (65-93) vs 49 (40-62) nmol/l; P<0.05). Other laboratory parameters were stable compared with after PTX. Systolic BP decreased and total bone mineral content increased in both groups.

CONCLUSION

Except for the lowering of the PTH level, no additive effect of vitamin D supplementation was seen. However, PTX proved effective in reducing insulin resistance.

Vitamin D in youth with Type 1 diabetes: prevalence of insufficiency and association with insulin resistance in the SEARCH Nutrition Ancillary Study

AIMS

To determine the prevalence of plasma vitamin D (25-dihydroxyvitamin D) insufficiency in individuals with Type 1 diabetes and to determine the cross-sectional and longitudinal associations of plasma vitamin D with insulin resistance.

METHODS

Participants from the SEARCH for Diabetes in Youth Study [n = 1426; mean age 11.2 years (sd 3.9)] had physician-diagnosed Type 1 diabetes [diabetes duration mean 10.2 months (sd 6.5)] with data available at baseline and follow-up (approximately 12 and 24 months after baseline). Insulin resistance was estimated using a validated equation. Cross-sectional and longitudinal multivariate logistic regression models were used to determine the association of plasma vitamin D with insulin resistance, adjusting for potential confounders.

RESULTS

Forty-nine per cent of individuals had plasma vitamin D < 50 nmol/l and 26% were insulin resistant. In cross-sectional multivariate analyses, participants who had higher plasma vitamin D (65 nmol/l) had lower odds of prevalent insulin resistance than participants with lower plasma vitamin D (25 nmol/l) (odds ratio 0.70, 95% CI 0.57-0.85). This association was attenuated after additional adjustment for BMI z-score, which could be a confounder or a mediator (odds ratio 0.81, 95% CI 0.64-1.03). In longitudinal multivariate analyses, individuals with higher plasma vitamin D at baseline had lower odds of incident insulin resistance, but this was not significant (odds ratio 0.85, 95% CI 0.63-1.14).

CONCLUSIONS

Vitamin D insufficiency is common in individuals with Type 1 diabetes and may increase risk for insulin resistance. Additional prospective studies are needed to determine the association between plasma vitamin D and insulin resistance, and to further examine the role of adiposity on this association.

Plasma 25-hydroxyvitamin D and its genetic determinants in relation to incident type 2 diabetes: a prospective case-cohort study

It is unclear whether vitamin D lowers risk of type 2 diabetes (T2D). In an observational study, we assessed the prospective association between plasma 25-hydroxyvitamin D (25(OH)D) and incident T2D, and evaluated whether it holds up for genetically determined elevated 25(OH)D. We used a case-cohort study nested within the German arm of the European Prospective Investigation into Cancer. From a total cohort of 53,088 participants with a mean follow-up of 6.6 years, we identified a random subcohort of 2,121 participants (57% women) and 1,572 incident cases of T2D. 25(OH)D was measured in baseline plasma samples retrieved from frozen storage. Mean plasma 25(OH)D in the subcohort was 47.1 (5th-95th percentile 19.6-80.7) nmol/L. After controlling for age, sex, center, season of blood draw, education, and lifestyle, the hazard of T2D decreased across increasing plasma concentrations of 25(OH)D (P linear trend<0.0001). The association became non-linear after adjustment for BMI and waist circumference (P non-linearity<0.0001), with the inverse association being restricted to participants with 25(OH)D concentrations below ~45 nmol/L (hazard ratio per 5 nmol/L higher 25(OH)D 0.91, 95% CI 0.84-0.98). A score predicting genetically determined plasma 25(OH)D by weighting four independent single-nucleotide polymorphisms by their effect on 25(OH)D, explained 3.7% of the variance in 25(OH)D. The hazard ratio (95% CI) per 5 nmol/L higher genetically predicted 25(OH)D was 0.98 (0.89-1.08) in the entire study sample and 1.06 (0.93-1.21) in the sub-sample with 25(OH)D<45 nmol/L. This latter finding casts doubt on a strong causal association of 25(OH)D with T2D, but further research in large-scale consortia is needed.

Vitamin D, calcium, and atherosclerotic risk: evidence from serum levels and supplementation studies

Vitamin D and calcium have traditionally been viewed in relation to bone health. However, recent research has suggested relations between these nutrients and cardiovascular disease (CVD). Specifically, evidence from both observational studies and clinical trials suggests that vitamin D may be related to lower risk of CVD. The picture for calcium is more complex. Dietary intake of calcium may be associated with lower CVD risk, while calcium supplementation may elevate CVD risk. In this review, we summarize evidence of these relations, and comment on the recent Institute of Medicine (IOM) recommendations regarding use of vitamin D and calcium supplements.

Vitamin D and cardiovascular disease: is there evidence to support the bandwagon?

In the last 3 years, more evidence accumulated that vitamin D (vitD)deficiency associates with cardiovascular disease (CVD) and risk factors. The association with higher cardiovascular (CV) mortality was stronger than with nonfatal CVD events. A higher incidence of type 2 diabetes was also shown. Many factors related to lifestyle (physical activity in particular) influence both vitD levels and CVD, and may contribute to explain these observational data. Whether the association between vitD and CVD is causal can only be established through randomized controlled trials (RCTs), and to date the results of the randomized trials, which were not designed for investigating CV outcomes, do not support the association data. Answers on the effects of vitD supplementation on primary and secondary prevention of CV may be found in the specifically designed ongoing RCTs. In the mean time, low vitamin D levels should be regarded as a marker of unhealthy lifestyle, requiring a more aggressive attempt at modifying individual lifestyle.

Metabolic syndrome, vitamin D deficiency and hypoadiponectinemia among nondiabetic patients early after kidney transplantation

BACKGROUND AND AIMS

Metabolic syndrome (MetS) is common among kidney transplant patients. We studied the relationship between MetS, vitamin D deficiency/insufficiency and hypoadiponectinemia early posttransplantation and their impact on clinical outcomes.

METHODS

Seventy-four previously nondiabetic kidney transplant patients were enrolled in a prospective cohort study between February and November 2008. Participants underwent a 2-hour oral glucose tolerance test and had their plasma levels of 25-hydroxyvitamin D (25[OH]D), adiponectin, insulin, intact parathyroid hormone and lipids measured at 11 weeks posttransplantation. Clinical events including cardiovascular events, new-onset diabetes after transplantation, acute rejection, graft loss and death were recorded during the follow-up to December 2012.

RESULTS

Thirty-four study patients (45.9%) had MetS. Patients with MetS had lower plasma concentrations of 25[OH]D (20.5 ± 7.2 vs. 24.8 ± 11.1 ng/ml, p = 0.049) and adiponectin (8.2 ± 4.5 vs. 14.6 ± 8.0 μg/ml, p < 0.0001) early on, and higher composite clinical event rate (61.8 vs. 27.5%, p = 0.003) during the follow-up. Multivariate analysis showed that the presence of MetS early after transplantation was independently associated with 25[OH]D deficiency/insufficiency (OR: 14.0, 95% CI: 1.8, 107.5; p = 0.011), depressed plasma adiponectin levels (β -6.39, r(2) 0.195, p < 0.0001) and increased risk for clinical events (OR: 5.6, 95% CI: 1.9, 16.5; p = 0.002).

CONCLUSION

Kidney transplant patients with MetS early after transplantation had lower levels of 25[OH]D and adiponectin, and unfavorable clinical outcomes.

Plasma 25 hydroxyvitamin D level and blood gene expression profiles: a cross-sectional study of the Norwegian Women and Cancer Post-genome Cohort

BACKGROUND/OBJECTIVES

Vitamin D deficiency has been associated with increased risk of developing several diseases, but much is unknown about the molecular effects involved. Gene expression technology is increasingly being used to elucidate molecular mechanisms related to nutritional factors, and in this study of free-living, middle-aged Norwegian women, we aimed at identifying gene expression pathways in the blood associated with vitamin D status.

SUBJECTS/METHODS

Blood samples and questionnaires were collected as a part of the Norwegian Women and Cancer Post-genome Cohort (500 invited subjects, 218 included). Plasma 25 hydroxyvitamin D (25(OH)D) concentrations were measured using high-performance liquid chromatography, and we compared groups with sufficient versus deficient vitamin D status (25(OH)D >50 nmol/l (n=66) versus <37.5 nmol/l (n=83)), to identify differences in gene expression profiles obtained using full-genome microarrays.

RESULTS

In a targeted pathway-level analysis, several immunological processes, immune cell functions and major signaling pathways were differentially regulated according to vitamin D status (P<0.01). To a certain degree, results from in vitro studies reported in the literature were reflected in this population setting.

CONCLUSIONS

We conclude that vitamin D status measured as 25(OH)D was associated with molecular pathways that may ultimately affect the potential onset of diseases. The use of gene expression analysis in a population setting may give valuable input to the study of effects of nutritional factors.

Association of vitamin D deficiency with incidence of type 2 diabetes in high-risk Asian subjects

BACKGROUND

Recent studies suggest an association between 25-hydroxyvitamin D [25(OH)D] and type 2 diabetes (T2D) risk. However, prospective studies investigating the relation between vitamin D inadequacy and incidence of T2D incorporating obesity and dynamic measures of insulin resistance (IR) and pancreatic β cell function are limited.

OBJECTIVE

We tested the hypothesis that baseline 25(OH)D is associated with the incidence of T2D in high-risk subjects for up to 5 y of follow-up, independently of obesity, baseline IR, and β cell function.

DESIGN

We recruited 1080 nondiabetic Korean subjects [mean ± SD age: 49.5 ± 11.4 y] based on the presence of one or more risk factors for T2D, including obesity, hypertension, dyslipidemia, and/or family history of T2D. We measured anthropometric and biochemical indicators, HOMA2-IR, and the insulinogenic index (IGI; calculated as change in insulin at 30 min/change in glucose at 30 min) from a 75-g oral-glucose-tolerance test.

RESULTS

Of the participants, 10.5% had a serum 25(OH)D deficiency (<10 ng/mL), 51.6% had an insufficiency (10.0-19.9 ng/mL), and 38.0% had a sufficiency (≥20 ng/mL), and the incidence of T2D at 32.3 ± 15.6 mo (±SD) declined accordingly: 15.9%, 10.2%, and 5.4%, respectively (P < 0.001). After adjustment for age, sex, blood pressure, lifestyles, family history, season, parathyroid hormone, and high-sensitivity C-reactive protein, the participants with 25(OH)D deficiency had an increased risk of T2D independently of BMI, HOMA2-IR, and IGI; the HRs were 2.06 (95% CI: 1.22, 3.49) for 25(OH)D 10-19.9 ng/mL compared with ≥20 ng/mL and 3.23 (95% CI: 1.66, 6.30) for 25(OH)D <10 ng/mL compared with ≥20 ng/mL.

CONCLUSION

The current prospective study suggests that vitamin D metabolism may play a role in T2D pathogenesis independently of known risk factors. This trial was registered at clinicaltrials.gov as NCT01508481.

High-dose vitamin D supplementation in people with prediabetes and hypovitaminosis D

OBJECTIVE

Low vitamin D levels predict the development of diabetes. This double-blind, randomized, control study in subjects with prediabetes and hypovitaminosis D evaluated whether high doses of vitamin D for 1 year affected insulin secretion, insulin sensitivity, and the development of diabetes.

RESEARCH DESIGN AND METHODS

A total of 1,551 subjects ≥40 years of age not known to have diabetes were screened with A1C levels. Subjects with A1C levels of 5.8-6.9% underwent an oral glucose tolerance test (OGTT). Subjects with prediabetes and 25-OH vitamin D (25-OHD) levels <30 ng/mL were randomized to receive weekly placebo (n = 53) or vitamin D (n = 56) with doses based on body weight and baseline 25-OHD levels. OGTTs were performed 3, 6, 9, and 12 months later. Insulin secretion and sensitivity were measured, and the proportion of subjects developing diabetes was assessed.

RESULTS

25-OHD levels rapidly rose from 22 to nearly 70 ng/mL after vitamin D supplementation with a mean weekly dose of 88,865 IU. There were no differences between the placebo and vitamin D groups regarding fasting plasma glucose, 2-h glucose, or insulin secretion and sensitivity or in the percent developing diabetes or returning to normal glucose tolerance. No subjects experienced increased serum or urinary calcium levels. At 12 months, A1C levels were significantly slightly less (0.2%) in the vitamin D group.

CONCLUSIONS

In individuals with prediabetes and hypovitaminosis D, doses of vitamin D supplementation designed to raise serum 25-OHD levels into the upper-normal range for 1 year had no effect on insulin secretion, insulin sensitivity, or the development of diabetes compared with placebo administration.

The roles of vitamin D in skeletal muscle: form, function, and metabolism

Beyond its established role in bone and mineral homeostasis, there is emerging evidence that vitamin D exerts a range of effects in skeletal muscle. Reports of profound muscle weakness and changes in the muscle morphology of adults with vitamin D deficiency have long been described. These reports have been supplemented by numerous trials assessing the impact of vitamin D on muscle strength and mass and falls in predominantly elderly and deficient populations. At a basic level, animal models have confirmed that vitamin D deficiency and congenital aberrations in the vitamin D endocrine system may result in muscle weakness. To explain these effects, some molecular mechanisms by which vitamin D impacts on muscle cell differentiation, intracellular calcium handling, and genomic activity have been elucidated. There are also suggestions that vitamin D alters muscle metabolism, specifically its sensitivity to insulin, which is a pertinent feature in the pathophysiology of insulin resistance and type 2 diabetes. We will review the range of human clinical, animal, and cell studies that address the impact of vitamin D in skeletal muscle, and discuss the controversial issues. This is a vibrant field of research and one that continues to extend the frontiers of knowledge of vitamin D's broad functional repertoire.

Variability and reproducibility of circulating vitamin D in a nationwide U.S. population

CONTEXT

Most studies examining associations between circulating vitamin D and disease are based on a single measure of vitamin D, which may not reflect levels over time, particularly because vitamin D concentrations vary by season. Few studies evaluated how well multiple 25-hydroxyvitamin D [25(OH)D] measures track within the same individual over time.

OBJECTIVE

This study examined variability and reproducibility of vitamin D by evaluating repeat measurements of plasma 25(OH)D concentrations while accounting for determinants of circulating concentrations including dietary supplement use and latitude of residence from a population of U.S. radiologic technologists.

DESIGN AND PARTICIPANTS

We analyzed circulating 25(OH)D in blood samples taken from 538 men and women from a prospective, nationwide study at two time points within a 1-yr period, most measured in different seasons. Inter- and intra-individual variability, reliability coefficients, and measurement error were examined.

RESULTS

The spearman rank correlation between two measurements of 25(OH)D concentrations was moderate (r = 0.75, P < 0.001) and did not vary significantly by participant characteristics including age, race, or latitude. The intraclass correlation coefficient was 0.72 (95% confidence interval = 0.68-0.76). The deattenuation factor of plasma 25(OH)D levels was 1.39, suggesting that a single measure of vitamin D on a continuous scale in regression analyses may result in attenuated relationships of about 40%.

CONCLUSION

Our results suggest that a single blood sample obtained in spring or fall provides a reasonable average for 25(OH)D over a 1-yr period, but additional studies are needed to estimate variability and agreement in plasma 25(OH)D measurements over longer intervals and younger populations.

Fish and marine omega-3 polyunsatured Fatty Acid consumption and incidence of type 2 diabetes: a systematic review and meta-analysis

Objective. To examine the association between fish and marine long-chain omega-3 polyunsaturated fatty acid (LC n-3 PUFA) consumption and incidence of type 2 diabetes (T2D) in prospective cohort studies. Methods. Meta-analytic procedures were used to estimate the relative risk (RR) using random effects or fixed effects generic inverse variance model. Publication bias and study heterogeneity were assessed using Egger's test and I(2) statistic. Results. We found no significant association between the intake of fish/seafood (pooled RR: 1.04; P = 0.63, 95% CI: 0.9 to 1.2, 549, 955 participants) or marine LC n-3 PUFA (pooled RR: 1.08, P = 0.39, 95% CI: 0.90 to 1.30, 346, 710 participants) and T2D risk. Significant study heterogeneity was observed in fish/seafood and marine LC n-3 PUFA studies (P < 0.00001). Subgroup analysis revealed no obvious sources for high heterogeneity. We also found a significant protective effect of oily fish intake on T2D risk (pooled RR = 0.89, P = 0.005, 95% CI: 0.82 to 0.96). Dose-response analysis suggested that every 80 g per day intake of oily fish may reduce 20% risk of T2D. Conclusion. We found no significant effect of fish/seafood or marine LC n-3 PUFA intake on risk of T2D but a significant effect of oily fish intake on risk of T2D.

Plasma vitamin D and parathormone are associated with obesity and atherogenic dyslipidemia: a cross-sectional study

Background

Low concentrations of plasma vitamin D (25(OH)D) have been associated with the development of metabolic syndrome (MetS), obesity, diabetes and cardiovascular disease. The objective of this study was to quantify the associations between 25(OH)D and parathormone (PTH) plasma levels and obesity, the presence of MetS, diabetes or atherogenic dyslipidemia (AD) in a large sample of individuals with different degrees of adiposity.

Methods

Retrospective study of all patients who had attended the obesity clinics in a Spanish hospital between 2009 and 2011, and whose concentrations of PTH, 25(OH)D, calcium and alkaline phosphatase had been determined (n=316, 75.9% women). Individuals were categorized by degree of adiposity, presence of MetS, and other comorbidities.

Results

PTH increased but 25(OH)D and calcium decreased with increasing adiposity. The prevalence of 25(OH)D deficiency or insufficiency increased with obesity (<10% when BMI<45kg/m², and 26% when >50). The prevalence of hyperparathyroidism increased from 12% in non-obese to 47.5% in morbidly obese individuals with BMI>50 kg/m². Low plasma 25(OH)D and high PTH concentrations were associated with an increased risk of MetS and AD. These associations disappeared, except in the case of AD for 25(OH)D when adjusting for BMI. Regression analysis revealed that BMI and age or seasonality were independent predictors of PTH and 25(OH)D levels, respectively.

Conclusions

BMI was the variable most strongly associated with plasma 25(OH)D and PTH concentrations in our study. Low 25(OH)D and high PTH concentrations were not independently associated with an increased risk of MetS, or diabetes. Our data support a possible contribution of plasma 25(OH)D to the pathogenesis of hypertriglyceridemia and AD through inflammation.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Relation of obesity with serum 25 hydroxy vitamin D3 levels in type 2 diabetic patients

BACKGROUND

Hypovitaminosis D is associated with diabetes mellitus (DM). Aim of our study was to determine the relation of obesity with vitamin D levels in type 2 diabetic patients.

MATERIALS AND METHODS

We examined 101 type 2 diabetic patients and made a correlation analysis in all parameters. Then we classified our diabetics according to their body-mass indices and compared their 25 hdroxy vitamin D3 levels.

RESULTS

We found negative correlation between 25O HD and body mass index (BMI) (P: <0.001, r: -0.23). When we classified our diabetics according to their body mass indices as normal, overweight and obese, and compared their 25 hydroxy vitamin D3 levels, we determined that in every BMI group 25 hydroxy vitamin D levels were not found to be significantly different.

CONCLUSION

These results suggest that at least in a Turkish population with type 2 DM vitamin D levels are low and correlate with BMI, but when vitamin D levels are so low, as obesity worsens vitamin D levels does not lessen.

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

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

Vitamin D status, incident diabetes and prospective changes in glucose metabolism in older subjects: the Hoorn study

BACKGROUND AND AIMS

Vitamin D deficiency may contribute to impaired glucose metabolism and type 2 diabetes, especially in the elderly population. We aimed to evaluate whether baseline 25-hydroxyvitamin D (25[OH]D) levels are prospectively associated with deterioration of glucose metabolism and the incidence of diabetes.

METHODS AND RESULTS

We examined a subsample from the population based Hoorn study among older men and women. Physical examinations were performed from 2000 to 2001 and included measurements of 25(OH)D. Glucose tolerance tests and HbA1c measurements were performed at baseline and at a follow-up between 2007 and 2009. We included 351 study participants (51% females; 67.9 ± 5.7 years). Baseline 25(OH)D levels were 56.7 ± 18.8 nmol/L and follow-up visits were performed after 7.5 ± 0.5 years. Among 280 study participants without diabetes at baseline we recorded 45 cases of incident diabetes. There was no significant association of 25(OH)D with the incidence of diabetes and with fasting and 2h postload glucose levels at follow-up. In analyses adjusted for age, sex, and baseline HbA1c there was, however, a significant association of 25(OH)D with follow-up HbA1c levels (beta coefficient=-0.085, p=0.085). This association was attenuated after further adjustments for BMI (beta coefficient=-0.079, p=0.064).

CONCLUSIONS

In this study among the older population we observed no significant association of baseline 25(OH)D with glucose metabolism and incident diabetes. We found, however, a non-significant trend towards an inverse association of 25(OH)D with prospective changes in HbA1c that deserves further investigations.

Extraskeletal effects of vitamin D

The presence of vitamin D receptors in diverse tissues like immune cells, beta-cells in the pancreas, and cardiac myocytes has prompted research to evaluate the impact of vitamin D deficiency on the occurrence of immune diseases, diabetes, and cardiovascular disease (CVD). The expression of receptors not only in normal cells, but also in cancer cells including breast, prostate, and colon cancer cells has moreover opened the path to therapeutic exploitation of vitamin D or its metabolites and hypocalcemic structural analogues as pharmaceutical tools in the fight against chronic non-communicable diseases like diabetes, CVD, and cancer.