Vitamin D replacement in Asians with diabetes may increase insulin resistance

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

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

Vitamin D status in children and adolescents with type 1 diabetes in a specialized diabetes care centre in Bangladesh

OBJECTIVES

High prevalence of vitamin D deficiency (VDD) in children and adolescents with type 1 diabetes (T1D) was found in several epidemiological studies. The current study aimed to assess the Vitamin D status in children and adolescents with T1D and to examine the influence of the disease characteristics on vitamin D status in a specialized care centre in a tertiary hospital in Bangladesh.

METHODS

Participants were enrolled in the cross-sectional study at the time of a regularly scheduled visit to the CDiC Paediatric Diabetes Center in BIRDEM 2(Bangladesh Institute of Research and Rehabilitation of Diabetes Endocrine and Metabolic Disorders), a tertiary care hospital in Bangladesh. The demographic and clinical data were collected through medical records with a structured questionnaire.

RESULTS

Among sixty study participants, most had inadequate levels of vitamin D: deficiency 31 (51.7%), insufficiency 14 (23.3%) and sufficiency 15 (25.0%). Participants with vitamin D deficiency (VDD) were significantly older compared to the sufficient and insufficient group (p = .029), and were residing in urban areas (p = .036) and from higher socioeconomic status (p = .014). BMI was significantly higher in VDD compared to the sufficient group (p = .040). Although we observed higher median values of daily insulin requirements and HbA1c values in patients with VDD compared to patients with vitamin D insufficiency or vitamin D sufficiency, these differences did not reach statistical significance.

CONCLUSIONS

The present study revealed that the prevalence of vitamin D deficiency and insufficiency among T1 diabetes children was very high. Future studies in large sample are required to assess hypovitaminosis D in youth with T1D and also the possible relating factors of vitamin D deficiency.

Vitamin D supplementation improves SIRT1, Irisin, and glucose indices in overweight or obese type 2 diabetic patients: a double-blind randomized placebo-controlled clinical trial

BACKGROUND

Vitamin D (VD) may increase sirtuin 1 (SIRT1) and subsequently PPAR-γ coactivator 1α (PGC-1α) and irisin levels and these improvements may reduce insulin resistance (IR). The aim was to assess the effects of vitamin D supplementation on SIRT1, irisin, and IR in overweight/obese type 2 diabetes (T2D) patients.

METHODS

Ninety T2D males and females were recruited as a clinical trial study (mean of age and body mass index (BMI) of intervention and placebo groups were 50.05 ± 10.17 and 50.36 ± 10.2 yrs. and 31.37 ± 3.4 and 30.43 ± 3.2 kg/m², respectively). The inclusion criteria were T2D, VD deficient, BMI > 25 kg/m², and serum HbA1c < 8.5%. The exclusion criteria were using vitamin and mineral supplements, having any acute disease, recent modifying dose or type of drugs. The supplementation was 50,000 IU/week VD or placebo for 8 weeks. The demographic characteristics, anthropometrics, dietary intakes and physical activity status, sun exposure status, fasting blood sugar (FBS) and insulin, glycosylated hemoglobin (HbA1c), irisin, SIRT1, 25-hydroxy D3 (25(OH)VD), homeostasis model assessment of insulin resistance (HOMA-IR), and quantitative insulin sensitivity check index (QUICKI) were determined. The significant P-value was ≤0.05.

RESULTS

The increase of serum VD, SIRT1, and irisin in the intervention group was significant (p < 0.001). HbA1c was decreased significantly by 1%. The changes in the other glucose indices (FBS, insulin, and IR) were non-significant.

CONCLUSIONS

VD supplementation may improve T2D by decreasing HbA1c and increasing SIRT1 and irisin in VD deficient T2D patients. Further trials are suggested.

TRIAL REGISTRATION

Iranian Registry of Clinical Trials, IRCT201604202365N11. Registered 21/08/2016, http://en.irct.ir/trial/2019.

Correlation Between Vitamin D Deficiency and Diabetic Ketoacidosis

Both type 1 and type 2 diabetes mellitus have been associated with vitamin D deficiency. Diabetic ketoacidosis, which is a complication of type 1 and, rarely, type 2 diabetes, is also found to be associated with vitamin D levels. This review discusses studies on the correlation between diabetic ketoacidosis and vitamin D levels. Studies show that vitamin D deficiency is associated with the occurrence of diabetic ketoacidosis. Diabetic ketoacidosis is also found to affect vitamin D levels. The possible explanation of diabetic ketoacidosis affecting vitamin D levels is the inactivity of the 1-alpha-hydroxylase enzyme and an increase in the renal excretion of vitamin D binding proteins. The presence of vitamin D receptors on pancreatic beta cells explains the role of vitamin D in the causation of diabetic ketoacidosis.

Diabetic regulation of subjects with type 2 diabetes mellitus is associated with serum vitamin D levels

OBJECTIVE

Vitamin D deficiency is not only associated with bone metabolism but also with diabetes mellitus. We aimed to study the possible association between serum vitamin D concentration and HbA1c level in patients with type 2 diabetes mellitus (T2DM) in this retrospective report.

METHODS

Patients with T2DM were enrolled to the study either in regulated or non-regulated T2DM groups, according to HbA1c levels. An HbA1c level of <8% was considered as relatively controlled and others were considered as poorly controlled T2DM.

RESULTS

Serum vitamin D levels in poorly controlled T2DM subjects (9.4 (4.9-34) ng/ml) were significantly lower than that of the relatively well regulated T2DM patients (13.5 (3.4-36) ng/ml) (p=0.03). Vitamin D was strongly and inversely correlated with HbA1c levels (r= -0.295, p=0.005).

CONCLUSION

Whatever the cause or result of the diabetes mellitus, it is clear that lower vitamin D is strongly associated with worse diabetic regulation in T2DM subjects. Randomized controlled larger studies, which research the relation between diabetic regulation and vitamin D status, are needed to claim whether it could be a therapeutic target in future in diabetic subjects.

Vitamin D and Metabolic Diseases: Growing Roles of Vitamin D

Vitamin D, a free sunshine vitamin available for mankind from nature, is capable to avert many health-related critical circumstances. Vitamin D is no more regarded as a nutrient involved in bone metabolism alone. The presence of vitamin D receptor in a number of tissues implies that vitamin D has various physiological roles apart from calcium and phosphorus metabolism. Low serum vitamin D has been found to be associated with various types of metabolic illness such as obesity, diabetes mellitus, insulin resistance, cardiovascular diseases including hypertension. Various studies reported that vitamin D insufficiency or deficiency in linked with metabolic syndrome risk. This review focuses on various metabolic diseases and its relationship with serum vitamin D status.

1,25-Dihydroxyvitamin D3 protects obese rats from metabolic syndrome via promoting regulatory T cell-mediated resolution of inflammation

Vitamin D₃ has been found to produce therapeutic effects on obesity-associated insulin resistance and dyslipidemia through its potent anti-inflammatory activity, but the precise immunomodulatory mechanism remains poorly understood. In the present study we found that 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], the biologically active form of vitamin D₃, significantly attenuated monosodium glutamate (MSG)-induced obesity and insulin resistance as indicated by body weight reduction, oral glucose tolerance improvement, and a glucose infusion rate increase as detected with hyperinsulinemic-euglycemic clamp. Moreover, 1,25(OH)₂D₃ not only restored pancreatic islet functions but also improved lipid metabolism in insulin-targeted tissues. The protective effects of 1,25(OH)₂D₃ on glycolipid metabolism were attributed to its ability to inhibit an obesity-activated inflammatory response in insulin secretory and targeted tissues, as indicated by reduced infiltration of macrophages in pancreas islets and adipose tissue while enhancing the expression of Tgf-β1 in liver tissue, which was accompanied by increased infiltration of Treg cells in immune organs such as spleen and lymph node as well as in insulin-targeted tissues such as liver, adipose, and muscle. Together, our findings suggest that 1,25(OH)₂D₃ serves as a beneficial immunomodulator for the prevention and treatment of obesity or metabolic syndrome through its anti-inflammatory effects.

Role of Vitamin D on glycemic control and oxidative stress in type 2 diabetes mellitus

Background:

Vitamin D deficiency may play a key role in the development of impaired glucose tolerance, type 2 diabetes mellitus (T2DM), and metabolic syndrome. Several studies have shown that Vitamin D has an antioxidant property. We aimed to investigate 25-hydroxy Vitamin D (25[OH]D) levels in patients with T2DM and in nondiabetic healthy controls and to ascertain the impact of 25(OH)D levels on glycemic control and oxidative stress in T2DM patients.

Materials and Methods:

Thirty male patients with T2DM and twenty age- and socioeconomic status-matched male healthy controls were included in the study. Fasting and postprandial blood sugar and glycated hemoglobin (HbA1c) were measured. Enzyme activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) was determined by spectrophotometric assay, and serum levels of 25(OH)D were measured using radioimmunoassay.

Results:

Serum Vitamin D levels were significantly lower in patients with T2DM than healthy controls (P = 0.015). There was a significantly lower GPx activity in patients with T2DM than controls (P = 0.048), but the difference in SOD activity did not reach statistical significance. There was a significant negative correlation between serum Vitamin D levels and HbA1c (P = 0.016), but no statistical correlation was shown between serum Vitamin D levels and GPx and SOD.

Conclusion:

We conclude that low level of Vitamin D might play a significant role in T2DM pathogenesis. Hence, Vitamin D supplementation may improve glycemic control and oxidative stress in T2DM.

Effect of vitamin D on stress-induced hyperglycaemia and insulin resistance in critically ill patients

AIM

Effects of vitamin D supplementation on the glycaemic indices and insulin resistance in diabetic and non-diabetic patients were studied. In this study, effects of vitamin D supplementation on stress-induced hyperglycaemia and insulin resistance were evaluated in non-diabetic surgical critically ill patients.

METHODS

Adult surgical patients with stress-induced hyperglycaemia within the first 24 h of admission to the ICU were recruited. The patients randomly assigned to receive either vitamin D or placebo. Patients in the vitamin D group received a single dose of 600,000 IU vitamin D3 as intramuscular injection at time of recruitment. Besides demographic and clinical characteristics of the patients, plasma glucose, insulin, 25(OH) D and adiponectin levels were measured at the time of ICU admission and day 7. Homoeostasis model assessment for insulin resistance (HOMA-IR) and homestasis model assessment adiponectin (HOMA-AD) ratio were considered at the times of assessment.

RESULTS

Comparing with the baseline, plasma 25(OH) D level significantly increased in the subjects who received vitamin D (p = 0.04). Improvement in fasting plasma glucose levels was detected in day 7 of the study compared with the baseline status in both groups. HOMA-IR showed a decrement pattern in vitamin D group (p = 0.09). Fasting plasma adiponectin levels increased significantly in the vitamin D group (p = 0.007), but not in the placebo group (p = 0.38). Finally, changes in HOMA-AD ratio were not significant in the both groups.

CONCLUSION

Vitamin D supplementation showed positive effect on plasma adiponectin level, as a biomarker of insulin sensitivity in surgical critically ill patients with stress-induced hyperglycaemia. However, effects of vitamin D supplementation on HOMA-IR and HOMA-AD as indicators of insulin resistance were not significant.

Vitamin D, inflammation, and relations to insulin resistance in premenopausal women with morbid obesity

OBJECTIVE

In this study, the associations between vitamin D, insulin sensitivity, and inflammation and their relationships with adipose tissue expression of vitamin D receptor (VDR) and inflammatory markers in women with morbid obesity were determined.

METHODS

An oral glucose tolerance test prior to surgery was completed by healthy premenopausal women (n = 76) seeking bariatric surgery. Abdominal subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) were collected during surgery.

RESULTS

Approximately, 70% of our subjects were vitamin D sufficient or optimal, and 80% had normal glucose tolerance. No significant association between serum 25-hydroxyvitamin D [25(OH)D] with circulating inflammatory markers or insulin sensitivity was identified. In subjects with waist circumference of <139 cm (n = 42), log25(OH)D positively predicted VAT logIL-6 mRNA expression (P = 0.003). LogVDR expression was positively correlated with the expression of inflammatory markers in both SAT (logIL-1β mRNA: r = 0.95, P < 0.0001; logTNF mRNA: r = 0.82, P < 0.0001) and VAT (logIL-1β mRNA: r = 0.89, P < 0.0001; logTNF mRNA: r = 0.75, P < 0.0001). VAT logVDR expression positively predicted logHOMA-IR in non-African American subjects (P = 0.05).

CONCLUSIONS

The beneficial effects of vitamin D on inflammation and insulin sensitivity were not supported by our findings. VDR does not appear to possess a protective effect in adipose tissue.

Effect of therapeutic dose of vitamin d on serum adiponectin and glycemia in vitamin d-insufficient or deficient type 2 diabetic patients

Background:

Lower vitamin D status has been reported in diabetic patients. Serum 25-hydroxyvitamin D and adiponectin were inversely associated with type 2 diabetes and insulin resistance. Vitamin D may involve in regulation of the adiponectin levels, which is directly related to insulin sensitivity.

Objectives:

The aim of this study was to investigate the effect of therapeutic dose of vitamin D on serum adiponectin and insulin resistance in vitamin D-insufficient or deficient type 2 diabetic patients.

Materials and Methods:

This double-blind, randomized, clinical trial was conducted on 81 type 2 diabetic patients with vitamin D level of 10-30 ng/mL. Intervention was 50000 IU vitamin D or placebo once a week for 8 weeks. At the beginning and end of the study, blood samples were collected after 12 hours of fasting and serum glucose, insulin, 25-hydroxyvitamin D, and adiponectin were measured. Insulin resistance was calculated by homeostasis model assessment (HOMA-IR).

Results:

After 8-week intervention, serum 25-hydroxyvitamin D significantly increased and reached the normal levels in patients receiving vitamin D (P < 0.001) and the levels of fasting serum glucose, insulin, and HOMA-IR were significantly decreased (P = 0.04, 0.02 and 0.007, respectively). No significant changes were observed in these levels in the placebo group. Significant differences were observed in mean changes in the above-mentioned variables between the two groups (P = 0.01, 0.04 and 0.006, respectively). No significant changes were found in serum adiponectin in the vitamin D and placebo groups (P = 0.83).

Conclusions:

Therapeutic dose of vitamin D can improve vitamin D status and glycemic indicators. But it seems that an 8-week intervention period was not sufficient to reveal the possible effects of vitamin D on serum adiponectin levels.

Does the intramuscular injection of vitamin D increase insulin resistance?

Objective:

Considering the physiologic roles of vitamin D on insulin regulation, the effects of vitamin D treatment on insulin sensitivity and resistance indexes and beta cell function in pre-diabetic vitamin D deficient patients were investigated.

Methods:

In a randomized open clinical trial, 61 pre-diabetic vitamin D deficient patients who were the first degree relatives of type 2 diabetic patients, were enrolled and randomized into three groups (A, B and C). Group A (n = 21) were treated with intramuscular injection of 300,000 units of vitamin D at the beginning of the study and one month later. In group B (n = 20), injection of vitamin D plus 500 mg/d calcium and in group C (n = 20), just calcium was administered for two months. At baseline and two months later, oral glucose tolerance test was done. Homeostasis Model of Assessment-Insulin Resistance (HOMA-IR), insulin resistance index, Homeostasis Model of Assessment-B (HOMA-B) which is a beta cell function index, and Matsuda index, an insulin sensitivity index, were calculated and compared before and after intervention and between three groups.

Findings:

In vitamin D treated groups (A + B), the mean (SD) of HOMA-IR increased from 2.46 (1.36) to 3.1 (2.3) (P = 0.02), and Matsuda index decreased from 11 (3) to 9.0 (2.3) (P = 0.001).

Conclusion:

Injection of vitamin D increased insulin resistance and decreased insulin sensitivity indexes.

Biochemical efficacy of vitamin D in ameliorating endocrine and metabolic disorders in diabetic rats

CONTEXT

Due to the biochemical role of vitamin D (Vit D) in the endocrine system, especially its potential anti-inflammatory and immune-modulating properties, there is an increased interest in its potential role in the prevention and control of diabetes mellitus.

OBJECTIVE

This study evaluated the potential therapeutic efficacy of Vit D in averting the detrimental effects of both types of diabetes mellitus.

MATERIALS AND METHODS

A total of 50 male Wistar rats were allotted into five groups: a placebo group; a nongenetic model of type 1 diabetes in rats (T1D), injected with a single dose of streptozotocin (STZ; 65 mg/kg, ip); a nongenetic model of type 2 diabetes in rats (T2D), given a short-term high-fat diet followed by a single low dose of STZ (35 mg/kg, ip); fourth and fifth groups that were gastrogavaged with Vit D (10 IU/kg) three days after the induction of T1D and T2D, respectively, which was continued daily throughout the experiment.

RESULTS

Vit D (10 IU/kg/60 days) significantly (p < 0.05) decreased fasting plasma glucose, ketoacidosis (decreased non-esterified fatty acid and β-hydroxyl butyric acid), pro-inflammatory interleukin-6, HbA1c in T1D and T2D and insulin resistance index by 33% in T2D. Interestingly, Vit D significantly (p < 0.05) increased fasting plasma insulin by 144% in T1D, plasma Ca level, insulin sensitivity index, and β-cell function index in T1D and T2D.

DISCUSSION AND CONCLUSION

Vit D ameliorated the deleterious biochemical impact of diabetes mellitus, likely by increasing insulin secretion and sensitivity, ameliorating the β-cell function, and decreasing the number of pro-inflammatory cytokines and insulin resistance.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

The effects of oral vitamin D on insulin resistance in pre-diabetic patients

BACKGROUND

Some epidemiological and interventional studies have shown the role of vitamin D on insulin secretion and resistance. A previous study in our center showed that intramuscular vitamin D decreases insulin sensitivity in pre-diabetic patients. We investigated the role of oral vitamin D on the insulin sensitivity index and insulin resistance in pre-diabetic patients.

MATERIALS AND METHODS

In a randomized clinical trial, we divided 45 people with pre-diabetes aged 47.4 ± 6.6 (range 33-61) years into three groups: group A subjects treated with 50,000 IU oral vitamin D and 500 mg calcium carbonate (n = 21), group B subjects treated with a single 300,000 IU intramuscular vitamin D and 500 mg calcium carbonate (n = 9), and group C subjects treated with 500 mg calcium carbonate alone (n = 15). Serum 25-hydroxyvitamin D [25(OH) D] was measured at baseline. If it was less than 75 nmol/l, 50,000 IU vitamin D was given weekly, and if serum 25(OH) D was more than that, vitamin D was administered every 2 weeks. Before and after 12 weeks of treatment, a 75-g glucose tolerance test was performed. We used paired t-test and analysis of variance (ANOVA) to analyze the data. P values less than 0.05 were considered significant.

RESULTS

Mean (SD) of serum vitamin D increased from 77.5 ± 39.2 to 118.8 ± 56.3 nmol/l (P = 0.009) in group A and from 80 ± 36 to 102.8 ± 43.3 nmol/l (P = 0.053) in group B, and decreased from 44.8 ± 18.3 to 34.6 ± 13.9 nmol/l (P = 0.06) in group C. Insulin sensitivity index (Matsuda) decreased from 11.4 ± 3 to 9.9 ± 3.2 (P = 0.046) in group A, but in comparison with other groups, it was not significant.

CONCLUSION

Oral vitamin D had no effect on insulin sensitivity in pre-diabetes patients in 12 weeks treatment. A randomized double-blind study with a longer duration of treatment is suggested to investigate the effect of vitamin D on insulin resistance.

Role of vitamin D in insulin resistance

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

A randomized, placebo-controlled trial of vitamin D supplementation to improve glycaemia in overweight and obese African Americans

AIMS

Vitamin D deficiency may increase the risk for type 2 diabetes. African Americans tend to have poor vitamin D status and increased risk of diabetes, but effects of vitamin D supplementation on components of diabetes risk have not been tested in this group. This study was conducted to determine whether vitamin D supplementation improves insulin secretion, insulin sensitivity and glycaemia in African Americans with prediabetes or early diabetes.

METHODS

In this randomized, placebo-controlled trial, we examined the effect of 4000 IU/day vitamin D(3,) on glycaemia and contributing measures including insulin secretion, insulin sensitivity and the disposition index over 12 weeks in 89 overweight or obese African Americans with prediabetes or early diabetes. Outcome measures were derived from oral glucose tolerance testing.

RESULTS

Mean plasma 25-hydroxyvitamin D was about 40 nmol/l in the placebo and vitamin D groups at baseline and increased to 81 nmol/l with supplementation. Insulin sensitivity decreased by 4% in the vitamin D group compared with a 12% increase in the placebo group (p = 0.034). Insulin secretion increased by 12% in the vitamin D group compared with a 2% increase in the placebo group (p = 0.024), but changes in the disposition index were similar across groups. There was no effect of supplementation on post-load glucose or other measures of glycaemia.

CONCLUSIONS

Supplementation with 4000 IU/day vitamin D(3) successfully corrected vitamin D insufficiency and had divergent effects on insulin secretion and sensitivity with no overall effect on disposition index or glycaemia. In this study, vitamin D supplementation for 3 months did not change the pathophysiology of prediabetes in overweight and obese African Americans.

Effect of vitamin D on insulin resistance and anthropometric parameters in Type 2 diabetes; a randomized double-blind clinical trial

Background & the purpose of the study

Prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide. To reduce its risk and progression, preventive strategies are needed. Vitamin supplementation such as vitamin D is one of the strategies. This study was designed to investigate the effect of injection of vitamin D on insulin resistance and anthropometric parameters in T2DM.

Methods

This randomized double-blind clinical trial was conducted with 42 diabetic patients in two groups; intervention group with single intramuscular injection of 300,000 International Unit (IU) of vitamin D3 and the placebo group. After recording demographic and anthropometric factors (waist circumference, blood pressure and body mass index), fasting blood samples was taken for measurement of blood glucose, 25-hydroxyvitamin D3 (25-OHD3), insulin, glycosylated hemoglobin A1c (HbA1c) and estimation of Homeostasis Model Assessment Index (HOMA) in two times; before study and after three months.

Results

Two groups had similar baseline characteristics (each group = 21 subjects). Three months after vitamin D injection, HbA1c, anthropometric factors and HOMA index in intervention group stayed constant, however, serum 25- OHD3 was significantly increased (p = 0.007).

Conclusion

The present data is not convincing and further studies with large sample sizes are needed to show the definite effect of injection of vitamin D on control of diabetes and its risk.

Vitamin D and diabetes

There is no doubt that vitamin D deficiency is the cause of several metabolic bone diseases, but vitamin D status is also linked to many major human diseases including immune disorders. Mounting data strengthen the link between vitamin D and diabetes, in particular T1D and T2D. Despite some inconsistencies between studies that associate serum 25(OH)D levels with the risk of developing T1D or T2D, there seems to be an overall trend for an inverse correlation between levels of 25(OH)D and both disorders. There is also compelling evidence that 1,25(OH)2D regulates b-cell function by different mechanisms, such as influencing insulin secretion by regulating intracellular levels of Ca2+, increasing β-cell resistance to apoptosis, and perhaps also increasing β-cell replication. The capacity of vitamin D, more specifically 1,25(OH)2D, to modulate immune responses is of particular interest for both the therapy and prevention of diabetes. In the case of T1D, vitamin D supplementation in prediabetic individuals could help prevent or reduce the initiation of autoimmune processes possibly by regulating thymic selection of the T-cell repertoire, decreasing the numbers of autoreactive T cells, and inducing Treg cells. Although immune modulation is generally discussed for the treatment of T1D, it is also relevant for T2D. Indeed, recent studies have shown that T2D patients have increased systemic inflammation and that this state can induce β-cell dysfunction and death. Supplementation trials with regular vitamin D for the protection against the development of T1D and T2D have generated some contradictory data, but many weaknesses can be identified in these trials as most were underpowered or open-labeled. However, the overwhelming strength of preclinical data and of the observational studies make vitamin D or its analogues strong candidates for the prevention or treatment of diabetes or its complications. However, proof of causality needs well-designed clinical trials and if positive, adequate dosing, regimen, and compound studies are needed to define the contribution of vitamin D status and therapy in the global diabetes problem. There are many confounding factors that need to be taken into consideration when translating successful vitamin D therapies in animal models into humans, for example, gender, age, lifestyle, and genetic background. To come to solid conclusions on the potential of vitamin D or its analogues in the prevention of or therapy for all forms of diabetes, it is clear that large prospective trials with carefully selected populations and end points will be needed, but should also receive high priority.

Effects of a single post-partum injection of a high dose of vitamin D on glucose tolerance and insulin resistance in mothers with first-time gestational diabetes mellitus

AIM

This study was performed to determine the effect of a single, large, intramuscular injection of vitamin D post-partum on glucose tolerance and insulin resistance in women with gestational diabetes.

METHODS

Forty-five participants in a randomized controlled trial on gestational diabetes mellitus were divided into an intervention group and a control group. Only subjects in the intervention group received one intramuscular injection of 300,000 IU of vitamin D3. HbA(1c), serum 25-hydroxyvitamin D3, fasting insulin and blood glucose, C-peptide, homeostasis model assessment insulin resistance index (HOMA-IR), β-cell function, insulin sensitivity and the Quantitative Insulin Sensitivity Check Index (QUICKI) were measured at baseline and after 3 months of intervention.

RESULTS

Approximately 80% of the mothers had a degree of vitamin D deficiency. Post-intervention, this was found in 4.2 and 71.4% in the intervention and control groups, respectively. The medians of HOMA-IR indices before and after intervention were 0.6 and 0.5 (P = 0.7), respectively, in subjects in the intervention group, and 0.5 and 0.9 (P = 0.01) in subjects in the control group. The mean of the QUICKI fell only in the control group (P = 0.008). In the control group, β-cell function increased by ~8% (P = 0.01) and insulin sensitivity decreased after 3 months (P = 0.002). Post-intervention, the median C-peptide decreased in the intervention group and increased in the control group, but the change was significant only in the control group (P = 0.03).

CONCLUSIONS

A single injection of 300,000 IU of vitamin D3 achieves a 3-month serum 25-hydroxyvitamin D range of 50-80 nmol/l and is an efficient, effective and safe procedure for improving the vitamin status and indices of insulin resistance in mothers with gestational diabetes after delivery.

Does Vitamin D deficiency play a role in peripheral neuropathy in Type 2 diabetes?

AIM

Despite recent reports linking vitamin D deficiency with increased risk of diabetes mellitus and complications, there is limited data on patients with diabetic peripheral neuropathy. We aimed to evaluate the incidence and associations of vitamin D deficiency in 210 patients with Type 2 diabetes with and without diabetic peripheral neuropathy.

METHODS

Renal, liver, lipid profile and HbA(1c) were measured. Vitamin D status was determined by measuring 25-dihydroxyvitamin D. Presence or absence of coronary heart disease was determined and early-morning urine microalbumin:creatinine ratio was measured. All patients were assessed clinically using neuropathy symptom score, neuropathy disability score and nerve conduction study.

RESULTS

Eighty-seven patients had diabetic peripheral neuropathy and these patients had significantly longer duration of diabetes and higher HbA(1c). Age, gender, incidence of retinopathy and coronary heart disease were not significantly different from those without neuropathy. Mean (SD) vitamin D was significantly lower in those with neuropathy [36.9 (39.9) nmol/l] compared with those without [58.32 (58.9) nmol/l] and 81.5% of patients with neuropathy had vitamin D deficiency compared with 60.4% of those without. Vitamin D showed significant (P < 0.05) correlations with total cholesterol, LDL-cholesterol and urine microalbumin:creatinine ratio. Binary logistic regression analysis showed that diabetic peripheral neuropathy was significantly associated with vitamin D deficiency (odds ratio = 3.47; 95% CI = 1.04-11.56, P = 0.043) after inclusion of potential confounders such as duration of diabetes, HbA(1c) and LDL-cholesterol.

CONCLUSION

Vitamin D deficiency is an independent risk factor for diabetic peripheral neuropathy, and further studies are required to confirm if Vitamin D supplementation could prevent or delay the onset.

Efficacy of vitamin D3-fortified-yogurt drink on anthropometric, metabolic, inflammatory and oxidative stress biomarkers according to vitamin D receptor gene polymorphisms in type 2 diabetic patients: a study protocol for a randomized controlled clinical trial

BACKGROUND

Development of type 2 diabetes mellitus (T2DM) is determined by the interactions of genetic and environmental factors. This study was designed to evaluate the possible role of VDR single nucleotide polymorphisms (SNPs) on different aspects of diabetic host response (anthropometric, metabolic, oxidative stress and inflammatory) to daily intake of vitamin D through fortified yogurt drink for 12 weeks.

METHODS/DESIGN

This study comprises two parts: (i) a case-control study; and (ii) an intervention trial. In the first part, VDR polymorphisms (Taq1, FokI, Apa1, Bsm1, and Cdx2) are determined in 350 T2DM patients and 350 non-diabetic subjects. In the second part, the possible effects of daily intake of two servings of vitamin D3-fortified yogurt drink (FYD; 500 IU vitamin D/250 mL) on some selected metabolic (including insulin resistance), inflammatory and oxidative stress biomarkers in 135 T2DM patients are assessed. To relate the resulted changes in the biomarkers to vitamin D replenishment, another group of diabetic patients (n = 45) are also included in the study who receive 2 servings of plain yogurt drink (PYD) a day. The primary outcome is serum level of 25(OH) D, which it is expected to be elevated only in FYD group. Secondary outcomes include improvements in glycemic, metabolic, inflammatory and oxidative stress biomarkers in FYD group compared to PYD group. Three VDR FokI polymorphisms are determined only in FYD group followed by comparison of changes in the biomarkers among these genotypic variants.

DISCUSSION

The present study, at least in part, elucidates the discrepancies in the results of different vitamin D-diabetes studies pertaining to the genetic variations of the population. If VDR polymorphisms are found to influence the response to our intervention, then knowing distribution of VDR polymorphisms in both diabetic and non-diabetic populations can give a picture of the proportion of the community in whom up to 1000 IU/d vitamin D may not be effective enough to improve insulin resistance and related morbidities. Therefore, they should ideally receive further nutritional support according to their genotype.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01236846.

Glycemic changes after vitamin D supplementation in patients with type 1 diabetes mellitus and vitamin D deficiency

BACKGROUND

A prospective, nonblinded and nonrandomized controlled trial was conducted to test the hypothesis that vitamin D supplementation would improve glycemic control in patients with type 1 diabetes mellitus who have vitamin D deficiency.

PATIENTS AND METHODS

Eighty patients with type 1 diabetes mellitus who had 25-hydroxyvitamin D levels less than 50 nmol/L were assigned to receive 4000 IU of vitamin D3. Calcium supplements were provided to ensure a total calcium intake of 1200 mg/d. Glycosylated hemoglobin and 25-hydroxyvitamin D levels were measured at baseline and at 12 weeks.

RESULTS

There was a significant difference in mean (SD) glycosylated hemoglobin level (%) between the groups that achieved 25-hydroxyvitamin D levels of <35.4 nmol/L, 35.4-51 nmol/L and >51 nmol/L at 12 weeks (P=.02). There was a significant difference in glycosylated hemoglobin change from baseline between the groups that achieved 25-hydroxyvitamin D levels of <35.4 nmol/L, 35.4-51 nmol/L and >51 nmol/L at 12 weeks (P=.04). There was a significant difference in 25-hydroxyvitamin D level between the groups that achieved glycosylated hemoglobin levels of <7.8, 7.8-9.9 and >9.9 at 12 weeks (P=.001). Patients were more likely to achieve lower glycosylated hemoglobin levels at 12 weeks if they had higher 25-hydroxyvitamin D levels at 12 weeks (r=-0.4, P=.001).

CONCLUSIONS

There was an observed effect of vitamin D supplementation on glycemic control in vitamin D-replete, type 1 diabetes mellitus patients. Further studies are needed to determine if these findings are applicable.

Baseline serum 25-hydroxyvitamin D concentrations in the Tromsø Study 1994-95 and risk of developing type 2 diabetes mellitus during 11 years of follow-up

AIMS

We wanted to test the hypothesis that low serum 25-hydroxyvitamin D (25(OH)D) concentrations are associated with increased risk of developing Type 2 diabetes mellitus (DM) in a population-based cohort during 11 years of follow-up.

METHODS

The analyses included 4157 non-smokers and 1962 smokers from the Tromsø Study 1994-95 without diabetes at baseline. Subsequent Type 2 DM was defined using a hospital journal-based end-point registry, completed through the year 2005. Participants were allocated into quartiles of serum 25(OH)D within each month to account for seasonal variation, and serum 25(OH)D values both as a continuous variable and in quartiles were used in Cox regression models. The analyses were stratified by smoking. Adjustments were made for age, sex, body mass index (BMI), physical activity and, in non-smokers, former smoking.

RESULTS

Type 2 DM was registered in 183 non-smoking and 64 smoking participants. Using the fourth (highest) quartile of serum 25(OH)D as the reference, non-smoking participants in the third, second and first quartiles had age- and sex-adjusted hazard ratios (95% confidence intervals) of incident Type 2 DM of 1.00 (0.62-1.61), 1.50 (0.97-2.31) and 1.89 (1.25-2.88), respectively, whereas the corresponding values for smokers were 1.79 (0.77-4.19), 2.33 (1.02-5.35) and 2.68 (1.18-6.08). Adjustment for BMI attenuated the hazard ratios, and they were no longer significant.

CONCLUSIONS

Baseline serum 25(OH)D was inversely associated with subsequent Type 2 DM in a population-based 11 year follow-up study, but not after adjustment for BMI. Randomized trials are needed to define the possible role of serum 25(OH)D status, and thereby the role of supplementation, in the prevention of Type 2 DM.

Vitamin D role and use in prediabetes

OBJECTIVE

To review the role of vitamin D in prediabetes on the basis of evidence from human studies.

METHODS

English-language literature in MEDLINE (January 1969-July 2009) was searched for observational studies and randomized controlled trials of vitamin D deficiency and treatment in prediabetes, including impaired fasting glucose, impaired glucose tolerance, and metabolic syndrome. Search terms included hyperglycemia, glucose, glycohemoglobin, insulin resistance, diabetes, homeostasis model assessment, insulin secretion, vitamin D, and related terms. Publications were also identified from review articles and references in the found articles. Abstracts, conference proceedings, case reports, and letters were excluded. Articles concerning only type 1 and type 2 diabetes, hemodialysis, or hyperparathyroidism and studies in children were also excluded.

RESULTS

Vitamin D insufficiency is defined by a circulating 25-hydroxyvitamin D concentration less than 30 ng/mL, and it is prevalent in the United States (77% of the population). Most cross-sectional and prospective studies in various populations show inverse association between circulating 25-hydroxyvitamin D and fasting plasma glucose, impaired glucose tolerance, hemoglobin A1c, metabolic syndrome, and incidence of prediabetes. A few clinical trials suggest beneficial effect of vitamin D supplementation in prediabetes, including improved insulin secretion, basal fasting insulin sensitivity, and postprandial peripheral insulin resistance. The limitations of the studies are small sample size, short duration of follow-up, lack of control groups, and inability to achieve vitamin D sufficiency with treatment.

CONCLUSION

Available data suggest that achieving vitamin D sufficiency may be beneficial in patients with prediabetes, although clinical trials are needed to provide evidence-based recommendations.

Effect of oral vitamin D and calcium replacement on glycaemic control in South Asian patients with type 2 diabetes

BACKGROUND

Vitamin D deficiency is associated with a greater risk of developing type 2 diabetes mellitus (T2DM). Studies looking at the effect of vitamin D replacement on glycaemic control in type 2 diabetics are few and conflicting. In addition, none have been published looking at the South Asian population despite both T2DM and vitamin D deficiency being gross burdens in this population. The aim of this study was to determine the effect of using vitamin D and calcium replacement therapy on glycaemic control in South Asian patients with T2DM and vitamin D inadequacy.

MATERIALS AND METHODS

Data were collected retrospectively from patients' records focusing on South Asians with established T2DM treated with combined oral vitamin D(3) and calcium supplementation. Vitamin D, parathyroid hormone (PTH), HbA1c and weight were recorded before and after 3 months on this therapy.

RESULTS

Post-treatment, all patients' (n = 52) vitamin D levels were normalised (> 50nmol/l). There was a mean decrease in HbA1c of 0.70 +/- 0.77% (p < 0.001) in the vitamin D deficient group (n = 29) and 0.21 +/- 0.28% (p = 0.001) in the vitamin D insufficient group (n = 23). The change in weight post-treatment was only significant in the vitamin D deficient group at -0.80 +/- 1.11 kg (p = 0.001). Overall, there were negative correlations between the changes in HbA1c and weight with the change in vitamin D (p < 0.05).

CONCLUSION

This study shows that vitamin D and calcium replacement therapy in South Asian patients with T2DM causes a significant decrease in both HbA1c and weight, which may be attributed to the increase in vitamin D levels post-treatment.

Vitamin D and diabetes

Type 1 (T1D) and type 2 (T2D) diabetes are considered multifactorial diseases in which both genetic predisposition and environmental factors participate in their development. Many cellular, preclinical, and observational studies support a role for vitamin D in the pathogenesis of both types of diabetes including: (1) T1D and T2D patients have a higher incidence of hypovitaminosis D; (2) pancreatic tissue (more specifically the insulin-producing beta-cells) as well as numerous cell types of the immune system express the vitamin D receptor (VDR) and vitamin D-binding protein (DBP); and (3) some allelic variations in genes involved in vitamin D metabolism and VDR are associated with glucose (in)tolerance, insulin secretion, and sensitivity, as well as inflammation. Moreover, pharmacologic doses of 1,25-dihydroxyvitamin D (1,25(OH)(2)D), the active form of vitamin D, prevent insulitis and T1D in nonobese diabetic (NOD) mice and other models of T1D, possibly by immune modulation as well as by direct effects on beta-cell function. In T2D, vitamin D supplementation can increase insulin sensitivity and decrease inflammation. This article reviews the role of vitamin D in the pathogenesis of T1D and T2D, focusing on the therapeutic potential for vitamin D in the prevention/intervention of T1D and T2D as well as its complications.

Addressing vitamin D deficiency in Canada: a public health innovation whose time has come

There is disturbing evidence of widespread vitamin D deficiency in many population groups, particularly within nations at high latitude. Numerous recent studies in the scientific literature associate vitamin D deficiency with a colossal increase in morbidity and mortality. Since Canada is at higher latitude, this review assesses the vitamin D status within the Canadian population. This review was prepared by assessing available medical and scientific literature from Medline, as well as by reviewing several books and conference proceedings. A standard 25(OH)D level of 75-80nmol/l or more was used to indicate vitamin D sufficiency. Between 70% and 97% of Canadians demonstrate vitamin D insufficiency. Furthermore, studies assessing 25(OH)D levels of vitamin D at 25-40nmol/l reveal that many Canadians have profoundly deficient levels. Repletion of vitamin D3 with 2000IU/day for those not receiving judicious sun exposure and those with no contra-indications would likely achieve normalized levels in more than 93% of patients, without risk of toxicity. Explicit directives regarding vitamin D assessment and management are urgently required.

The effect of vitamin D replacement therapy on insulin resistance and androgen levels in women with polycystic ovary syndrome

Insulin resistance (IR) is one of the common features of the polycystic ovary syndrome (PCOS), and recent studies indicate the possible role of vitamin D in the pathogenesis of IR and glucose metabolism. Aim of this study was aimed to determine the effect of vitamin D replacement therapy on glucose metabolism, insulin, and androgen levels in obese, insulin-resistant women with PCOS. Eleven women with PCOS were included in the study. Mean age of the patients was 23.6+/-5.7 yr, body mass index 33.9+/-5.1 kg/m(2). Six patients (54.5%) had acantosis nigricans and 10 (90.9%) oligoamenorrhea. The mean Ferriman Gallwey score was 14.1+/-4.6. Only 2 women were within the normal limits of vitamin D levels as >20 ng/ml. Three weeks after the administration of the single dose of 300,000 units of vitamin D3 orally, 25-hydroxyvitamin D3 significantly increased from 16.9+/-16 ng/ml to 37.1+/-14.6 ng/ml (p: 0.027) and only 2 women were detected to have vitamin D3 levels <20 ng/ml. Although glucose and insulin levels were decreased non-significantly, homeostasis model assessment (HOMA)-IR significantly decreased from 4.41+/-1.38 to 3.67+/-1.48 (p: 0.043). No significant alterations were witnessed at the levels of DHEAS, total and free testosterone, androstenedione. No correlation was found between vitamin D with HOMA and other hormonal parameters. In conclusion, women with PCOS have mostly insufficient vitamin D levels, and vitamin D replacement therapy may have a beneficial effect on IR in obese women with PCOS.

The prevalence of vitamin D abnormalities in South Asians with type 2 diabetes mellitus in the UK

BACKGROUND

The high prevalence of both hypovitaminosis D and type 2 diabetes (T2DM) in the Asian community is well recognised, but the impact of diabetes on vitamin D status and vice versa, has not been well reported.

AIMS

To determine the prevalence of hypovitaminosis D in Asian patients with T2DM and its impact on glycaemic control.

METHODS

A cross-sectional study was conducted in a tertiary referral centre in the UK. Two hundred and ten Asian patients aged more than 40 years were included (170 with and 40 without T2DM). Each had a standard bone profile (serum calcium, phosphate and alkaline phosphatase), serum parathyroid hormone and 25-hydroxycholecalciferol.

RESULTS

The prevalence of low serum 25-hydroxyvitamin D (< 50 nmol/l) was high in the group as a whole (> 80%) and more common in diabetics compared with controls (83% vs. 70%; p = 0.07). This was particularly so in men (82.5% vs. 57.9%; p = 0.02). HbA1c was higher in women with vitamin D deficiency (< 12.5 nmol/l) (8.11 +/- 1.11% vs. 7.33 +/- 1.32%, p = 0.046). In logistic regression analysis, T2DM was an independent predictor of hypovitaminosis D. In linear regression analysis, vitamin D deficiency was independently related to HbA1c in women with T2DM.

CONCLUSIONS

Hypovitaminosis D remains a major public health issue in the Asian population and is exaggerated in patients with T2DM. The fact that vitamin D deficient women had higher HbA1c levels raises the possibility that vitamin D replacement may improve glycaemic control.

Marked Transaminase Elevations and Worsening Glycemic Control Associated With Counterfeit Polyherbal Use in a Patient With Diabetes

Dietary and herbal supplements, a US$20.3 billion entity, are used by more than half of the adult population in the United States. Since weight loss is beneficial in obese patients at high risk for cardiovascular disease, many obese Americans are ingesting herbal weight loss supplements under the assumption that they are inherently safe. We report the case of a 55-year-old morbidly obese Caucasian female with diabetes, who started multiple polyherbal supplements. Six months after starting several herbal products, the patient’s A1C increased from 7.8% to 9.4% and the AST/ALT were markedly elevated. After discontinuation, transaminases normalized in 28 days. On follow-up visit, the patient reported compliance with prescribed medications and denied use of herbal products. The patient’s A1C approached target goal. The potential for counterfeit herbal supplement production exists. Our patient’s products were analyzed for purity, and 0% Hoodia gordonii was found. A misconception of herbal products is that they are safe because they are natural. Unfortunately, many natural products can act in the same capacity as drugs, educing both benefit and harm. Health care providers, particularly pharmacists, should be aware of counterfeit herbal supplements and closely monitor for dangers of herbal supplement use.

Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient - a randomised, placebo-controlled trial

Low serum 25-hydroxyvitamin D (25(OH)D) has been shown to correlate with increased risk of type 2 diabetes. Small, observational studies suggest an action for vitamin D in improving insulin sensitivity and/or insulin secretion. The objective of the present study was to investigate the effect of improved vitamin D status on insulin resistance (IR), utilising randomised, controlled, double-blind intervention administering 100 microg (4000 IU) vitamin D(3) (n 42) or placebo (n 39) daily for 6 months to South Asian women, aged 23-68 years, living in Auckland, New Zealand. Subjects were insulin resistant - homeostasis model assessment 1 (HOMA1)>1.93 and had serum 25(OH)D concentration < 50 nmol/l. Exclusion criteria included diabetes medication and vitamin D supplementation >25 microg (1000 IU)/d. The HOMA2 computer model was used to calculate outcomes. Median (25th, 75th percentiles) serum 25(OH)D(3) increased significantly from 21 (11, 40) to 75 (55, 84) nmol/l with supplementation. Significant improvements were seen in insulin sensitivity and IR (P = 0.003 and 0.02, respectively), and fasting insulin decreased (P = 0.02) with supplementation compared with placebo. There was no change in C-peptide with supplementation. IR was most improved when endpoint serum 25(OH)D reached > or = 80 nmol/l. Secondary outcome variables (lipid profile and high sensitivity C-reactive protein) were not affected by supplementation. In conclusion, improving vitamin D status in insulin resistant women resulted in improved IR and sensitivity, but no change in insulin secretion. Optimal vitamin D concentrations for reducing IR were shown to be 80-119 nmol/l, providing further evidence for an increase in the recommended adequate levels. Registered Trial No. ACTRN12607000642482.

Potential for vitamin D receptor agonists in the treatment of cardiovascular disease

Vitamin D(3) is made in the skin and modified in the liver and kidney to form the active metabolite, 1,25-dihydroxyvitamin D(3) (calcitriol). Calcitriol binds to a nuclear receptor, the vitamin D receptor (VDR), and activates VDR to recruit cofactors to form a transcriptional complex that binds to vitamin D response elements in the promoter region of target genes. During the past three decades the field has focused mainly on the role of VDR in the regulation of parathyroid hormone, intestinal calcium/phosphate absorption and bone metabolism; several VDR agonists (VDRAs) have been developed for the treatment of osteoporosis, psoriasis and hyperparathyroidism secondary to chronic kidney disease (CKD). Emerging evidence suggests that VDR plays important roles in modulating cardiovascular, immunological, metabolic and other functions. For example, data from epidemiological, preclinical and clinical studies have shown that vitamin D and/or 25(OH)D deficiency is associated with increased risk for cardiovascular disease (CVD). However, VDRA therapy seems more effective than native vitamin D supplementation in modulating CVD risk factors. In CKD, where decreasing VDR activation persists over the course of the disease and a majority of the patients die of CVD, VDRA therapy was found to provide a survival benefit in both pre-dialysis and dialysis CKD patients. Although VDR plays an important role in regulating cardiovascular function and VDRAs may be potentially useful for treating CVD, at present no VDRA is approved for CVD, and also no serum markers, beside parathyroid hormone in CKD, exist to indicate the efficacy of VDRA in CVD.

Vitamin D and human health: lessons from vitamin D receptor null mice

The vitamin D endocrine system is essential for calcium and bone homeostasis. The precise mode of action and the full spectrum of activities of the vitamin D hormone, 1,25-dihydroxyvitamin D [1,25-(OH)(2)D], can now be better evaluated by critical analysis of mice with engineered deletion of the vitamin D receptor (VDR). Absence of a functional VDR or the key activating enzyme, 25-OHD-1alpha-hydroxylase (CYP27B1), in mice creates a bone and growth plate phenotype that mimics humans with the same congenital disease or severe vitamin D deficiency. The intestine is the key target for the VDR because high calcium intake, or selective VDR rescue in the intestine, restores a normal bone and growth plate phenotype. The VDR is nearly ubiquitously expressed, and almost all cells respond to 1,25-(OH)(2)D exposure; about 3% of the mouse or human genome is regulated, directly and/or indirectly, by the vitamin D endocrine system, suggesting a more widespread function. VDR-deficient mice, but not vitamin D- or 1alpha-hydroxylase-deficient mice, and man develop total alopecia, indicating that the function of the VDR and its ligand is not fully overlapping. The immune system of VDR- or vitamin D-deficient mice is grossly normal but shows increased sensitivity to autoimmune diseases such as inflammatory bowel disease or type 1 diabetes after exposure to predisposing factors. VDR-deficient mice do not have a spontaneous increase in cancer but are more prone to oncogene- or chemocarcinogen-induced tumors. They also develop high renin hypertension, cardiac hypertrophy, and increased thrombogenicity. Vitamin D deficiency in humans is associated with increased prevalence of diseases, as predicted by the VDR null phenotype. Prospective vitamin D supplementation studies with multiple noncalcemic endpoints are needed to define the benefits of an optimal vitamin D status.

Glucose tolerance and vitamin D: effects of treating vitamin D deficiency

OBJECTIVE

We investigated the effects of vitamin D treatment on plasma glucose, serum insulin, and insulin sensitivity in vitamin D-deficient individuals without diabetes mellitus.

METHODS

Thirty-three adults with vitamin D insufficiency (serum 25-hydroxyvitamin D concentration < or = 50 nmol/L) and without diabetes (12 with impaired glucose tolerance) were given two oral doses of 100 000 IU of cholecalciferol, 2 wk apart. Before the first dose and 2 wk after the second dose, a 75-g oral glucose tolerance test was performed. Plasma glucose, serum insulin, 25-hydroxyvitamin D, and parathyroid hormone concentrations were measured and insulin sensitivity was calculated from the oral glucose tolerance test.

RESULTS

Mean serum 25-hydroxyvitamin D increased from 39.9 +/- 1.5 (SEM) to 90.3 +/- 4.3 nmol/L (P < 0.0001) and mean serum parathyroid hormone decreased from 6.7 +/- 1.2 to 4.5 +/- 0.6 pmol/L (P = 0.055). There was no change in blood glucose mean of 0-120 min (6.1 +/- 0.3 before versus 6.2 +/- 0.3 mmol/L, P = 0.63) or insulin mean of 0-120 min (47.8 +/- 5.35 versus 48.9 +/- 5.22 mU/L, P = 0.67) concentrations, and no change in insulin sensitivity (Avignon's insulin sensitivity index [SiM], P = 0.97; insulin sensitivity index at 0 and 120 min [ISI(0,120)], P = 0.74; Quantitative Insulin Sensitivity Check Index [QUICKI], P = 0.88; homeostasis model assessment [HOMA], P = 0.99) after vitamin D treatment. Results did not differ between subjects, with and without, impaired glucose tolerance.

CONCLUSION

In adults without diabetes, correction of vitamin D deficiency is not associated with any effect on blood glucose or insulin concentrations or insulin sensitivity as assessed during an oral glucose tolerance test. These observations do not support an association between glucose/insulin homeostasis and vitamin D, at least in the short term.

Study protocol--metabolic syndrome, vitamin D and bone status in South Asian women living in Auckland, New Zealand: a randomised, placebo-controlled, double-blind vitamin D intervention

Background

The identification of the vitamin D receptor in the endocrine pancreas suggests a role for vitamin D in insulin secretion. There is also some limited evidence that vitamin D influences insulin resistance, and thus the early stages of the development of type 2 diabetes.

Methods

Eighty-four women of South Asian origin, living in Auckland, New Zealand, were randomised to receive either a supplement (4000IU 25(OH)D₃ per day) or a placebo for 6 months. At baseline, all participants were vitamin D deficient (serum 25(OH)D₃ <50 nmol/L), insulin resistant (HOMA-IR > 1.93) and/or hyperinsulinaemic, hyperglycemic or had clinical signs of dislipidaemia. Changes in HOMA-IR, lipids, parathyroid hormone, calcium and bone markers were monitored at 3 months and 6 months.

Discussion

This randomised, controlled trial will be the first to investigate the effect of vitamin D supplementation on insulin resistance in non-diabetic subjects. It will subsequently contribute to the growing body of evidence about the role of vitamin D in metabolic syndrome.Registered clinical.

Trial registration

Registered clinical trial – Registration No. ACTRN12607000642482

The complex role of vitamin D in autoimmune diseases

Vitamin D, besides having well-known control functions of calcium and phosphorus metabolism, bone formation and mineralization, also has a role in the maintenance of immune-homeostasis. The immune-regulatory role of vitamin D affects both the innate and adaptive immune system contributing to the immune-tolerance of self-structures. Impaired vitamin D supply/regulation, amongst other factors, leads to the development of autoimmune processes in animal models of various autoimmune diseases. The administration of vitamin D in these animals leads to improvement of immune-mediated symptoms. Moreover, in human autoimmune diseases, such as multiple sclerosis, or rheumatoid arthritis the pathogenic role of vitamin D has been described. The review aims at describing the complex immune-regulatory role of vitamin D from the cellular level through autoimmune animal models and depicting the known contribution of vitamin D in the pathogenesis of human autoimmune diseases.

Role of vitamin D in the pathogenesis of type 2 diabetes mellitus

Vitamin D deficiency has been shown to alter insulin synthesis and secretion in both humans and animal models. It has been reported that vitamin D deficiency may predispose to glucose intolerance, altered insulin secretion and type 2 diabetes mellitus. Vitamin D replenishment improves glycaemia and insulin secretion in patients with type 2 diabetes with established hypovitaminosis D, thereby suggesting a role for vitamin D in the pathogenesis of type 2 diabetes mellitus. The presence of vitamin D receptors (VDR) and vitamin D-binding proteins (DBP) in pancreatic tissue and the relationship between certain allelic variations in the VDR and DBP genes with glucose tolerance and insulin secretion have further supported this hypothesis. The mechanism of action of vitamin D in type 2 diabetes is thought to be mediated not only through regulation of plasma calcium levels, which regulate insulin synthesis and secretion, but also through a direct action on pancreatic beta-cell function. Therefore, owing to its increasing relevance, this review focuses on the role of vitamin D in the pathogenesis of type 2 diabetes mellitus.

Vitamin D, glucose, insulin, and insulin sensitivity

This review examines available evidence of links between abnormalities of glucose and insulin metabolism and vitamin D deficiency. Possible mechanisms of action of vitamin D include stimulation of insulin secretion and effects on insulin sensitivity. Sun exposure usually implies greater outdoor physical activity, which in itself may have beneficial effects on insulin sensitivity, unrelated to serum 25-hydroxyvitamin D concentrations. The observed associations in humans among vitamin D, insulin, and glucose metabolism have not yet been confirmed by intervention studies and, hence, a causal association has not been established. Clinical trials are needed to determine whether vitamin D treatment of vitamin D-deficient individuals is able to prevent or treat diabetes mellitus.

The effects of calcium and vitamin D supplementation on blood glucose and markers of inflammation in nondiabetic adults

OBJECTIVE

We sought to compare the effects of combined calcium and vitamin D supplementation versus placebo on blood glucose and markers of inflammation in nondiabetic adults aged > or =65 years.

RESEARCH DESIGN AND METHODS

A total of 314 Caucasian adults without diabetes received either 500 mg calcium citrate and 700 IU vitamin D(3) or placebos daily for 3 years in a double-blind, randomized, controlled trial designed for bone-related outcomes. In a post hoc analysis, fasting plasma glucose (FPG), insulin sensitivity (estimated by homeostasis model assessment of insulin resistance [HOMA-IR]), plasma C-reactive protein, and interleukin-6, were measured at baseline and 3 years.

RESULTS

The effects of combined calcium-vitamin D supplementation on 3-year change in FPG depended on baseline FPG (P = 0.02 for interaction). Therefore, we conducted analyses separately in participants with normal fasting glucose (NFG) (FPG <5.6 mmol/l, n = 222) and impaired fasting glucose (IFG) (FPG 5.6-6.9 mmol/l, n = 92) at baseline. Among participants with IFG at baseline, those who took combined calcium-vitamin D supplements had a lower rise in FPG at 3 years compared with those on placebo (0.02 mmol/l [0.4 mg/dl] vs. 0.34 mmol/l [6.1 mg/dl], respectively, P = 0.042) and a lower increase in HOMA-IR (0.05 vs. 0.91, P = 0.031). In the NFG subgroup, there was no difference in the change in FPG or HOMA-IR between the two treatment arms. There were no differences in C-reactive protein or interleukin-6 between the two treatment arms in either subgroup.

CONCLUSIONS

In healthy, older adults with IFG, supplementation with calcium and vitamin D may attenuate increases in glycemia and insulin resistance that occur over time. However, our findings should be considered hypothesis generating and need to be confirmed in randomized trials specifically designed for the outcomes of interest.

Algorithm for Complementary and Alternative Medicine Practice and Research in Type 2 Diabetes

OBJECTIVE

To develop a model to direct the prescription of nutritional and botanical medicines in the treatment of type 2 diabetes for both clinical and research purposes.

METHODS

Available literature on nutritional and botanical medicines was reviewed and categorized as follows: antioxidant/anti-inflammatory; insulin sensitizer; and beta-cell protectant/insulin secretagogue. Literature describing laboratory assessment for glycemic control, insulin resistance, and beta-cell reserve was also reviewed and a clinical decision tree was developed.

RESULTS

Clinical algorithms were created to guide the use of nutritional and botanic medicines using validated laboratory measures of glycemic control, insulin sensitivity, and beta-cell reserve. Nutrient and botanic medicines with clinical trial research support include coenzyme Q10, carnitine, alpha-lipoic acid, N-acetylcysteine, vitamin D, vitamin C, vitamin E, chromium, vanadium, omega-3 fatty acids, cinnamon (Cinnamomum cassia), fenugreek (Trigonella foenum-graecum), and gymnema (Gymnema sylvestre).

CONCLUSIONS

Clinical algorithms can direct supplementation in clinical practice and provide research models for clinical investigation. Algorithms also provide a framework for integration of future evidence as it becomes available. Research funding to investigate potentially beneficial practices in complementary medicine is critically important for optimal patient care and safety.

Vitamin D and diabetes

Vitamin D deficiency predisposes individuals to type 1 and type 2 diabetes, and receptors for its activated form-1alpha,25-dihydroxyvitamin D3-have been identified in both beta cells and immune cells. Vitamin D deficiency has been shown to impair insulin synthesis and secretion in humans and in animal models of diabetes, suggesting a role in the development of type 2 diabetes. Furthermore, epidemiological studies suggest a link between vitamin D deficiency in early life and the later onset of type 1 diabetes. In some populations, type 1 diabetes is associated with certain polymorphisms within the vitamin D receptor gene. In studies in nonobese diabetic mice, pharmacological doses of 1alpha,25-dihydroxyvitamin D3, or its structural analogues, have been shown to delay the onset of diabetes, mainly through immune modulation. Vitamin D deficiency may, therefore, be involved in the pathogenesis of both forms of diabetes, and a better understanding of the mechanisms involved could lead to the development of preventive strategies.