Expression of 25-hydroxyvitamin D3-1alpha-hydroxylase in pancreatic islets

Evidence-based non-skeletal actions of vitamin D

Vitamin D is a major regulator of mineral homeostasis through its action in the kidney, intestine, bone and parathyroid glands. On these tissues, its active form, calcitriol, acts by binding to a specific nuclear receptor that belongs to the steroid/thyroid hormone receptor family. This receptor, however, has also been identified in several additional human tissues. So, apart from its traditional actions related to calcium, vitamin D and its synthetic analogs are being increasingly recognized for their anti-proliferative, pro-differentiative and immunomodulatory activities. Low levels of vitamin D have been linked to many chronic diseases. Decreased muscle function and increased fall risk in elderly people; prostate, breast and colorectal cancers; diabetes mellitus; and other health problems have been associated to low circulating levels of 25-hydroxyvitamin D. This paper presents an overview of the available scientific evidence for the non-calcemic actions of vitamin D in humans.

Effect of vitamin D supplementation in type 2 diabetes patients with pulmonary tuberculosis

AIM

Diabetes and vitamin D deficiency are widely prevalent in India. Studies have proven correlation between low vitamin D levels and pulmonary tuberculosis (PTB) and low vitamin D levels and insulin resistance. We evaluated the effects of vitamin D supplementation on type 2 diabetes mellitus patients with pulmonary tuberculosis (PTB).

METHODS

Forty-five subjects (M:F=34:11) were screened. Inclusion criteria were age >15 years, newly diagnosed PTB cases with uncontrolled diabetes, serum vitamin D<20 ng/ml. The patients with vitamin D level<20 ng/ml were randomly assigned to 2 groups. Group 1 subjects received oral cholecalceferol (60,000 units/week) and calcium carbonate (1g/day) along with anti tubercular treatment (ATT), while group 2 subjects did not. Sputum was checked at interval of 2 weeks for 12 weeks. Primary end point was time to achieve sputum smear conversion.

RESULTS

Fifteen patients having vitamin D>20 ng/ml were excluded. Age of the patients was 42.9±13.2 years and serum vitamin D levels were 18.4±15.3 ng/ml. Sputum smear conversion was 6 weeks in group 1 versus 8 weeks in group 2 (p=0.067). Glycated hemoglobin levels reduced from 11.1±1.3 to 7.7±0.9 in group 1 versus 10.3±1.2 to 7.8±1.1 (p>0.1).

CONCLUSION

Vitamin D can serve as adjuvant treatment of tuberculosis in diabetics with vitamin D deficiency. Further studies are required to validate this observation and define a cut off for vitamin D level to prevent immunological alterations.

Daily consumption of vitamin D- or vitamin D + calcium-fortified yogurt drink improved glycemic control in patients with type 2 diabetes: a randomized clinical trial

BACKGROUND

Low serum concentrations of 25-hydroxyvitamin D [25(OH)D] have been associated with impaired glucose tolerance and diabetes.

OBJECTIVE

This study aimed to compare the effects of daily intake of vitamin D- or vitamin D(3) + calcium-fortified yogurt drink on glycemic status in subjects with type 2 diabetes (T2D).

DESIGN

Ninety diabetic subjects were randomly allocated to 3 groups to consume plain yogurt drink (PY; containing no vitamin D and 150 mg Ca/250 mL), vitamin D-fortified yogurt drink (DY; containing 500 IU vitamin D(3) and 150 mg Ca/250 mL), or vitamin D + calcium-fortified yogurt drink (DCY; containing 500 IU vitamin D(3) and 250 mg Ca/250 mL) twice per day for 12 wk. Fasting serum glucose (FSG), glycated hemoglobin (Hb A(1c)), homeostasis model assessment of insulin resistance (HOMA-IR), serum lipid profile, and percentage fat mass (FM) were assessed before (baseline) and after the intervention.

RESULTS

In both the DY and DCY groups, mean serum 25(OH)D(3) improved (+32.8 ± 28.4 and +28.8 ± 16.1 nmol/L, respectively; P < 0.001 for both), but FSG [-12.9 ± 33.7 mg/dL (P = 0.015) and -9.6 ± 46.9 mg/dL (P = 0.035)], Hb A(1c) [-0.4 ± 1.2% (P < 0.001) and -0.4 ± 1.9% (P < 0.001)], HOMA-IR [-0.6 ± 1.4 (P = 0.001) and -0.6 ± 3.2 (P < 0.001)], waist circumference (-3.6 ± 2.7 and -2.9 ± 3.3; P < 0.001 for both), and body mass index [in kg/m(2); -0.9 ± 0.6 (P < 0.001) and -0.4 ± 0.7 (P = 0.005)] decreased significantly more than in the PY group. An inverse correlation was observed between changes in serum 25(OH)D(3) and FSG (r = -0.208, P = 0.049), FM (r = -0.219, P = 0.038), and HOMA-IR (r = -0.219, P = 0.005).

CONCLUSION

Daily intake of a vitamin D-fortified yogurt drink, either with or without added calcium, improved glycemic status in T2D patients. This trial was registered at clinicaltrials.gov as NCT01229891.

Pilot study to evaluate the effect of short-term improvement in vitamin D status on glucose tolerance in patients with type 2 diabetes mellitus

OBJECTIVE

To study the effect of improvement in vitamin D status on glucose tolerance in Asian Indian patients with moderately controlled type 2 diabetes mellitus (T2DM).

METHODS

This randomized, double-blind, placebo-controlled pilot study was conducted in 28 Asian Indian patients with T2DM. Study participants were randomly assigned to a vitamin D-treated group (group D) or a placebo group (group P). Serum 25-hydroxyvitamin D, hemoglobin A1c, and serum fructosamine levels were measured, and an oral glucose tolerance test (OGTT) was performed in all patients at baseline and 4 weeks after intervention. During the OGTT, plasma glucose and serum insulin levels were measured at 0, 30, 60, 90, and 120 minutes. The unpaired t test was used to compare the groups at baseline and to compare the differences in changes from baseline to 4 weeks between the 2 study groups.

RESULTS

Group D and group P were similar with respect to their fasting plasma glucose and serum insulin concentrations, post-OGTT plasma glucose and serum insulin levels, and hemoglobin A1c and fructosamine values at baseline. Serum 25-hydroxyvitamin D levels increased significantly in group D at 4 weeks. No significant differences were found between the groups at baseline and 4 weeks with respect to serum fructosamine, fasting plasma glucose and serum insulin, post-OGTT plasma glucose and serum insulin levels, and homeostasis model assessment of insulin resistance.

CONCLUSION

In this study, short-term improvement in vitamin D status was not associated with improvement in glucose tolerance, insulin secretion, or insulin sensitivity in Asian Indian patients with moderately controlled T2DM.

Vitamin D and cardiometabolic health: a review of the evidence

The cardiometabolic syndrome (MetS) is a clustering of related metabolic abnormalities including abdominal adiposity, insulin resistance, hypertension, dyslipidaemia and increased inflammatory and thrombotic markers, which is linked to increased risk of type 2 diabetes, CVD and overall mortality. Several cross-sectional and prospective studies have shown an association between low vitamin D status, as indicated by concentrations of serum 25-hydroxyvitamin D (s25(OH)D), and increased prevalence of the MetS and individual CVD risk factors. These epidemiological observations are supported by mechanistic studies but experimental data are limited. The available data from intervention studies are largely confounded as most vitamin D supplementation trials were mainly carried out to explore the role of Ca in CVD and include Ca in the treatment arms. Inadequate consideration of seasonal effects on s25(OH)D concentrations is also a common design flaw in most studies. Further complications arise from shared risk factors such as adiposity and ageing, which predispose individuals to exhibit both a more pronounced risk profile and relatively lower s25(OH)D concentrations. In conclusion, while epidemiological associations are promising and a rationale for low vitamin D status as a potentially modifiable risk factor for CVD is supported by mechanistic data, suitable experimental data from appropriately designed trials are just beginning to emerge. As yet, this body of literature is too immature to draw firm conclusions on the role of vitamin D in CVD prevention. Carefully controlled vitamin D trials in well-described population groups using intervention doses that are titrated against target s25(OH)D concentrations could yield potentially valuable outcomes that may have a positive impact on CVD risk modification.

Should vitamin D status be assessed in patients with congestive heart failure?

For decades the vitamin D biological system has been considered almost exclusively as the master integrator of calcium-phosphate homeostasis and bone metabolism. More recently, the discovery that many human tissues and cells, which do not directly participate in mineral ion homeostasis, express the vitamin D receptor (VDR) and are able to convert the circulating pro-hormone 25-hydroxyvitamin D in its active form, 1,25-dihydroxyvitamin D, has provided new insights into the biological function of this peculiar endocrine system. Several reports have highlighted a variety of human diseases possibly related to vitamin D insufficiency or deficiency (respectively defined as 25-hydroxyvitamin D serum levels lower than 30 or lower than 20 ng/ml). In particular, experimental and observational studies, including those published in this journal issue, support the concept that vitamin D deficiency is involved in the pathogenesis of congestive heart failure, a disabling condition affecting over 15 million of patients worldwide. Considering that circulating levels of 25-hydroxyvitamin D represent the accepted clinical indicator of individual vitamin D status, the measurement of this pro-hormone can be regarded as an appropriate and cost-effective screening tool in patients with chronic heart failure.

Rethinking the genetic basis for comorbidity of schizophrenia and type 2 diabetes

The co-occurrence of schizophrenia (SCZ) and type 2 diabetes mellitus (T2D) has been well documented. This review article focuses on the hypothesis that the co-occurrence of SCZ and T2D may be, at least in part, driven by shared genetic factors. Previous genetic studies of T2D and SCZ evidence have disclosed a number of overlapped risk loci. However, the putative common genetic factors for SCZ and T2D remain inconclusive due to inconsistent findings. A systemic review of methods of identifying genetic loci contributing to the comorbidity link between SCZ and T2D is hence needed. In the current review article, we have discussed several different approaches to localizing the shared susceptibility genes for these two diseases. To begin with, one could start with probing the gene involved in both glucose and dopamine metabolisms. Additionally, hypothesis-free genome-wide association studies (GWAS) may provide more clues to the common genetic basis for these two diseases. Genetic similarities inferred from GWAS may shed some light on the genetic mechanism underlying the comorbidity link between SCZ and T2D. Meanwhile, endophenotypes (e.g., adiponectin level in T2D and working memory in SCZ) may serve as alternative phenotypes that are more directly influenced by genes than target diseases. Hence, endophenotypes of these diseases may be more tractable to identification. To summarize, novel approaches are needed to dissect the complex genetic basis of the comorbidity of SCZ and T2D.

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.

Associations among 25-hydroxyvitamin D, diet quality, and metabolic disturbance differ by adiposity in adults in the United States

CONTEXT

Recent evidence indicates that a higher plasma level of 25-hydroxyvitamin D [25(OH)D] is associated with lower adiposity and a reduced number of metabolic disturbances (MetD).

OBJECTIVES

We examined associations among dietary quality, 25(OH)D, percent body fat (%BF), and MetD, and a pathway linking them, across central obesity.

DESIGN

This cross-sectional nationally representative study used extensive data from the National Health and Nutrition Examination Surveys of 2001-2004.

PARTICIPANTS

U.S. adults aged at least 20 yr were stratified by central obesity (CO) status. Sample sizes ranged from 1943 (all MetD combined) to 7796 (each component).

MAIN OUTCOME MEASURES

%BF was measured using dual-energy x-ray absorptiometry, and MetD was measured with individual continuous nonadiposity outcomes (e.g. fasting plasma glucose) and with a composite count index of binary MetD with prespecified cutoff points (Index I).

RESULTS

A higher 25(OH)D was associated with better dietary quality, lower %BF, and lower number of MetD. These inverse 25(OH)D-%BF and 25(OH)D-MetD associations (i.e. fasting blood glucose, homeostatic model assessment of insulin resistance, C-reactive protein, and Index I) were significantly stronger among the CO+ group. Finally, the pathway linking the dairy component of the Healthy Eating Index (HEIdairy) to Index I through 25(OH)D and %BF indicated complete mediation among the CO- group, but HEIdairy and 25(OH)D had direct inverse associations with Index I among the CO+ group.

CONCLUSIONS

Due to potential genetic differences between CO- and CO+ groups, empowering U.S. adults with central obesity to make related behavioral changes may be especially effective in improving their vitamin D status and metabolic profile.

Effects of uranium depletion on 1α-hydroxylase in kidney of rats

This study was designed to evaluate the effects of depleted uranium (DU) on 1α-hydroxylase in the kidney of rats and to delinerate the mechanism of damage to kidneys and bones by DU. Male Sprague-Dawley rats were surgically implanted with DU fragments at three dose levels (0.1 g, 0.2 g and 0.3 g). After 3, 6 or 12 months, the concentration of 1α,25(OH)2D3 in the kidney was measured by radioimmunoassay. The activity of 1α-hydroxylase was shown by the production of 1α,25(OH)2D3 after incubation. The results showed that the 1α-hydroxylase activity in the kidney was decreased after 3 months (27.2% at the medium dose DU group, p < 0.05; 33.4% at the high dose DU group, p < 0.01). In contrast, at 6 months and 12 months after implantation of DU, the activity of renal 1α-hydroxylase in DU-treated animals was not decreased significantly in comparison with the controls (p > 0.05). On the other hand, the activity of renal 1α-hydroxylase was decreased by 33.1% (p < 0.05) and 34.4% (p < 0.01) in blank control groups at 6 and 12 months, respectively, when compared with the blank control group at 3 months. In conclusion, this study showed that chronic DU exposure could induce renal damages and inhibit the synthesis of biologically active form of vitamin D, which may be the underlying mechanism of bone metabolic disorder caused by renal injury after DU exposure.

Circulating 25-hydroxyvitamin D and risk of pancreatic cancer: Cohort Consortium Vitamin D Pooling Project of Rarer Cancers

Results from epidemiologic studies examining pancreatic cancer risk and vitamin D intake or 25-hydroxyvitamin D (25(OH)D) concentrations (the best indicator of vitamin D derived from diet and sun) have been inconsistent. Therefore, the authors conducted a pooled nested case-control study of participants from 8 cohorts within the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers (VDPP) (1974-2006) to evaluate whether prediagnostic circulating 25(OH)D concentrations were associated with the development of pancreatic cancer. In total, 952 incident pancreatic adenocarcinoma cases occurred among participants (median follow-up, 6.5 years). Controls (n = 1,333) were matched to each case by cohort, age, sex, race/ethnicity, date of blood draw, and follow-up time. Conditional logistic regression analysis was used to calculate smoking-, body mass index-, and diabetes-adjusted odds ratios and 95% confidence intervals for pancreatic cancer. Clinically relevant 25(OH)D cutpoints were compared with a referent category of 50-<75 nmol/L. No significant associations were observed for participants with lower 25(OH)D status. However, a high 25(OH)D concentration (> or =100 nmol/L) was associated with a statistically significant 2-fold increase in pancreatic cancer risk overall (odds ratio = 2.12, 95% confidence interval: 1.23, 3.64). Given this result, recommendations to increase vitamin D concentrations in healthy persons for the prevention of cancer should be carefully considered.

No improvement in cardiovascular risk factors in overweight and obese subjects after supplementation with vitamin D3 for 1 year

BACKGROUND AND AIM

Cross-sectional studies indicate vitamin D to be of importance for glucose tolerance, blood pressure and serum lipids, but whether supplementation with vitamin D would improve cardio-vascular risk factors is not known.

DESIGN AND SETTING

The study was a 1 year, double blind placebo-controlled intervention trial performed at the University Hospital of North Norway from November 2005 to October 2007. Subjects. A total of 438 overweight or obese subjects, 21-70 years old, were included and 330 completed the study.

INTERVENTIONS

The subjects were randomized to vitamin D (cholecalciferol, vitamin D(3)) 40 000 IU per week (DD group), vitamin D 20 000 IU per week (DP group), or placebo (PP group). All subjects were given 500 mg calcium daily.

MAIN OUTCOME MEASURES

Fasting serum lipids and blood pressure were measured and an oral glucose tolerance test performed at start and end of the study.

RESULTS

At baseline the mean serum 25(OH)D levels were 58 nmol L(-1) (all subjects) and increased to 140 and 101 nmol L(-1) in the DD and DP groups, respectively. No significant differences were found between the three groups regarding change in measures of glucose metabolism or serum lipids. In the DP group, there was a slight but significant increase in systolic blood pressure compared with the placebo group.

CONCLUSIONS

Our results do not support a positive effect of vitamin D on glucose tolerance, blood pressure or serum lipids. Further studies in subjects with low serum 25(OH)D levels combined with impaired glucose tolerance, hypertension or dyslipidaemia are needed.

Infant feeding and the risk of type 1 diabetes

Type 1 diabetes is generally considered to be a chronic, immune-mediated disease with a subclinical prodrome during which beta cell autoimmunity becomes overt disease at a variable rate in genetically susceptible individuals. Accumulated evidence supports a critical role of environmental factors in its development. Prospective birth cohort studies show that the first signs of beta cell autoimmunity may be initiated during the first year of life. This implies that risk factors for beta cell autoimmunity and type 1 diabetes must be operative in infancy. Early nutrition provides essential exogenous exposures in that period. This article discusses the role of factors related to infant nutrition in the development of beta cell autoimmunity and type 1 diabetes and the potential mechanistic pathways involved. So far, no specific dietary factor has been shown to be an unequivocal risk factor for beta cell autoimmunity or type 1 diabetes, and there are a number of contradictory observations with regard to the effect of various foods. This may reflect geographic and cultural differences in infant-feeding practices. Most studies suggest that the early introduction of complex foreign proteins may be a risk factor for beta cell autoimmunity, and a pilot intervention trial has implied that weaning to a highly hydrolyzed formula may decrease the risk of beta cell autoimmunity. Lack of vitamin D supplementation and accelerated growth might increase the risk of type 1 diabetes. Additional work, which includes the application of modern approaches such as metabolomics and epigenomics, is needed to discern the contribution of dietary factors in infancy to the diabetic disease process.

Role of vitamin d in insulin secretion and insulin sensitivity for glucose homeostasis

Vitamin D functions are not limited to skeletal health benefits and may extend to preservation of insulin secretion and insulin sensitivity. This review summarizes the literature related to potential vitamin D influences on glucose homeostasis and insulin sensitivity. Cross-sectional data provide some evidence that circulating 25-hydroxyvitamin D (25(OH)D) is inversely associated with insulin resistance, although direct measurements of insulin sensitivity are required for confirmation. Reported associations with insulin secretion, however, are contradictory. Available prospective studies support a protective influence of high 25(OH)D concentrations on type 2 diabetes mellitus risk. There is a general lack of consistency in vitamin D intervention outcomes on insulin secretion and sensitivity, likely due to differences in subject populations, length of interventions, and forms of vitamin D supplementation. Vitamin D receptor gene polymorphisms and vitamin D interactions with the insulin like growth factor system may further influence glucose homeostasis. The ambiguity of optimal vitamin D dosing regimens and optimal therapeutic concentrations of serum 25(OH)D limit available intervention studies. Future studies, including cross-sectional and prospective, should be performed in populations at high risk for both vitamin D deficiency and type 2 diabetes mellitus. Well-designed, placebo-controlled, randomized intervention studies are required to establish a true protective influence of vitamin D on glucose homeostasis.

Baseline serum 25-hydroxy vitamin D in predicting glycemic status and insulin levels

Vitamin D may have a protective role in insulin secretion and an effect on insulin resistance. Low levels of vitamin D are indicated as a risk factor for both type 1 and type 2 diabetes, however, clinical evidence that increased vitamin D levels benefit diabetic patients has not yet been established.

Vitamina D e doenças endocrinometabólicas

Atualmente, a insuficiência/deficiência de vitamina D tem sido considerada um problema de saúde pública no mundo todo, em razão de suas implicações no desenvolvimento de diversas doenças, entre elas, o diabetes melito tipo 2 (DMT2), a obesidade e a hipertensão arterial. A deficiência de vitamina D pode predispor à intolerância à glicose, a alterações na secreção de insulina e, assim, ao desenvolvimento do DMT2. Esse possível mecanismo ocorre em razão da presença do receptor de vitamina D em diversas células e tecidos, incluindo células-β do pâncreas, no adipócito e no tecido muscular. Em indivíduos obesos, as alterações do sistema endócrino da vitamina D, caracterizada por elevados níveis de PTH e da 1,25(OH)2D3 são responsáveis pelo feedback negativo da síntese hepática de 25-OHD3 e também pelo maior influxo de cálcio para o meio intracelular, que pode prejudicar a secreção e a sensibilidade à insulina. Na hipertensão, a vitamina D pode atuar via sistema renina-angiotensina e também na função vascular. Há evidências de que a 1,25(OH)2D3 inibe a expressão da renina e bloqueia a proliferação da célula vascular muscular lisa. Entretanto, estudos prospectivos e de intervenção em humanos que comprovem a efetividade da adequação do status da vitamina D sob o aspecto "prevenção e tratamento de doenças endocrinometabólicas" são ainda escassos. Mais pesquisas são necessárias para se garantir o benefício máximo da vitamina D nessas situações.

Milk intake and the risk of type 2 diabetes mellitus, hypertension and prostate cancer

Milk intake is widely recommended for a healthy diet. Recent evidences suggest that milk/dairy products are associated with a lower risk of type 2 diabetes and hypertension. On the other hand, high calcium intake has been associated with a higher risk of prostate cancer. The calcium and vitamin D content in dairy foods could have beneficial effects on glucose metabolism and renin/angiotensin system as well regulates body weight. The association between high dairy/calcium consumption and prostate cancer risk are related to the presence of estrogens and insulin like growth factor (IGF-I) in milk. Based on the current evidence, it is possible that milk/dairy products, when consumed in adequate amounts and mainly with reduced fat content, has a beneficial effect on the prevention of hypertension and diabetes. Its potential role in the pathogenesis of prostate cancer is not well supported and requires additional study.

Vitamin D: emerging new roles in insulin sensitivity

The growing incidence of prediabetes and clinical type 2 diabetes, in part characterised by insulin resistance, is a critical health problem with consequent devastating personal and health-care costs. Vitamin D status, assessed by serum 25-hydroxyvitamin D levels, is inversely associated with diabetes in epidemiological studies. Several clinical intervention studies also support that vitamin D, or its active metabolite 1,25-dihydroxyvitamin D (1,25(OH)2D), improves insulin sensitivity, even in subjects with glucose metabolism parameters classified within normal ranges. The mechanisms proposed which may underlie this effect include potential relationships with improvements in lean mass, regulation of insulin release, altered insulin receptor expression and specific effects on insulin action. These actions may be mediated by systemic or local production of 1,25(OH)2D or by suppression of parathyroid hormone, which may function to negatively affect insulin sensitivity. Thus, substantial evidence supports a relationship between vitamin D status and insulin sensitivity; however, the underlying mechanisms require further exploration.

Supplementation with cholecalciferol does not improve glycaemic control in diabetic subjects with normal serum 25-hydroxyvitamin D levels

BACKGROUND

Studies have suggested that vitamin D may be important for both insulin sensitivity and insulin secretion, and that supplementation with vitamin D may subsequently prevent development of type 2 diabetes.

AIM OF THE STUDY

The objective of the current study was to test the hypothesis that supplementation with vitamin D would improve glycaemic control in subjects with type 2 diabetes.

METHODS

Thirty-six subjects with type 2 diabetes, treated with metformin and bed-time insulin, were randomised to supplementation with cholecalciferol (40,000 IU per week) versus placebo for 6 months. Thirty-two subjects participated throughout the entirety of the study. Fasting blood samples were drawn before and at the end of the 6 month study without the previous bed-time insulin injection. The insulin and metformin doses were not changed throughout the study.

RESULTS

After 6 months, the fasting glucose, insulin, C-peptide, fructosamine, and HbA(1c) levels were not significantly different from baseline values. In addition, changes in these parameters (values at 6 months minus values at baseline) did not differ between the vitamin D and the placebo group.

CONCLUSIONS

We were not able to demonstrate that vitamin D supplementation had a significant effect on glucose metabolism in subjects with type 2 diabetes but without vitamin D deficiency. Further studies are needed in larger groups of subjects with type 2 diabetes or impaired glucose tolerance, who also exhibit low serum 25-hydroxyvitamin D levels.

Serum vitamin D and risk of pancreatic cancer in the prostate, lung, colorectal, and ovarian screening trial

Experimental evidence suggests that vitamin D has anticarcinogenic properties; however, a nested case-control study conducted in a population of male Finnish smokers found that higher 25-hydroxyvitamin D [25(OH)D], the best indicator of vitamin D status as determined by the sun and diet, was associated with a significant 3-fold increased risk for pancreatic cancer. We conducted a nested case-control study in the Prostate, Lung, Colorectal, and Ovarian Screening Trial cohort of men and women 55 to 74 years of age at baseline to test whether prediagnostic serum 25(OH)D concentrations were associated with pancreatic cancer risk. Between 1994 and 2006, 184 incident cases of pancreatic adenocarcinoma occurred (follow-up to 11.7 years). Two controls (n = 368) who were alive at the time the case was diagnosed were selected for each case and matched by age, race, sex, and calendar date of blood draw (to control for seasonal variation). We calculated odds ratios (OR) and 95% confidence intervals (95% CI) using conditional logistic regression, adjusting for smoking and body mass index. Vitamin D concentrations were not associated with pancreatic cancer overall (highest versus lowest quintile, >82.3 versus <45.9 nmol/L: OR, 1.45; 95% CI, 0.66-3.15; P trend = 0.49). However, positive associations were observed among subjects with low estimated annual residential solar UBV exposure, but not among those with moderate to high annual exposure (P interaction = 0.015). We did not confirm the previous strong positive association between 25(OH)D and pancreatic cancer; however, the increased risk among participants with low residential UVB exposure is similar.

Vitamin D and diabetes mellitus

Better understanding of the physiological role of the vitamin-D system, in particular its potential effects on inflammatory and autoimmune conditions as well as on insulin secretion and possibly also on insulin resistance, increased the interest in its potential role in prevention and control of the diabetic condition, both type-1 and -2 diabetes. Both these conditions are associated with inflammation and type-1 diabetes also with an autoimmune pathology. Indeed, animal and human studies support the notion that adequate vitamin-D supplementation may decrease the incidence of type-1 and possibly also of type-2 diabetes mellitus and may improve the metabolic control in the diabetes state. However, the exact mechanisms by which vitamin-D and calcium supplementation exert their beneficial effects are not clear and need further investigation.

1alpha,25-Dihydroxyvitamin D hydroxylase in adipocytes

High vitamin D intake is associated with reduced insulin resistance. Expression of extra-renal 1alpha,25-dihydroxyvitamin D hydroxylase (1alpha-hydroxylase) has been reported in several tissues and contributes to local synthesis of 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D) from the substrate 25-hydroxyvitamin D (25OHD). Expression and dietary regulation of 1alpha-hydroxylase in tissues associated with energy metabolism, including adipose tissue, has not been assessed. Male Wistar rats were fed a high calcium (1.5%) and high vitamin D (10,000IU/kg) or a low calcium (0.25%), low vitamin D (400IU/kg) with either a high fat (40% energy) or high sucrose (66% energy) dietary background for 14 weeks. Expression of 1alpha-hydroxylase, assessed by real time PCR, was detected in adipose tissue and did not differ with dietary level of calcium and vitamin D. 1alpha-Hydroxylase mRNA was also detected in 3T3-L1 preadipocytes and 25OHD treatment at 10nM levels induced 1,25(OH)(2)D responsive gene, CYP24, and this response was reduced in the presence of the p450 inhibitor, ketoconazole. In addition, (3)H 25OHD was converted to (3)H 1,25(OH)(2)D in intact 3T3-L1 preadipocytes. Cumulatively, these results demonstrate that 1alpha-hydroxylase is expressed in adipose tissue and is functional in cultured adipocytes. Thus, the capacity for local production may play a role in regulating adipocyte growth and metabolism.

Diabetes and the vitamin d connection

Vitamin D deficiency, which is common in children and adults, causes rickets, osteomalacia, and osteoporosis. Most organs and immune cells have a vitamin D receptor, and some also have the capacity to metabolize 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. 1,25-Dihydroxyvitamin D is a potent immunomodulator that also enhances the production and secretion of several hormones, including insulin. Vitamin D deficiency has been associated with increased risk of type 1 diabetes. Glycemic control and insulin resistance are improved when vitamin D deficiency is corrected and calcium supplementation is adequate. 25-Hydroxyvitamin D (measure of vitamin D status) of less than 20 ng/mL is vitamin D deficiency and 21 to 29 ng/mL is insufficiency. Children and adults need at least 1000 IU of vitamin D per day to prevent deficiency when there is inadequate sun exposure.

Vitamin D: a growing perspective

Vitamin D deficiency has been widely reported in all age groups in recent years. Rickets has never been eradicated in developed countries, and it most commonly affects children from recent immigrant groups. There is much evidence that current vitamin D guidelines for the neonatal period, 5-10 microg (200-400 IU)/day, prevent rickets at the typical calcium intakes in developed countries. The annual incidence of vitamin D-deficiency rickets in developed countries ranges between 2.9 and 7.5 cases per 100,000 children. The prevalence of vitamin D deficiency in mothers and their neonates is remarkable, and the results of one study suggest that third-trimester 25-hydroxyvitamin D (25(OH)D) is associated with fetal bone mineral accrual that may affect prepubertal bone mass accumulation. Beyond infancy, the evidence indicates that 5 microg (200 IU)/day of vitamin D has little effect on vitamin D status as measured by the serum 25(OH)D concentration. Two randomized clinical trials show that higher vitamin D intake improves one-year gain in bone density in adolescent girls. The functions of vitamin D extend beyond bone to include immune system regulation and anti-proliferative effects on cells. Early life vitamin D inadequacy is implicated in the risk of bone disease, autoimmune disease, and certain cancers later in life; however, long-term interventional studies do not exist to validate the widespread implementation of greater vitamin D consumption. Here we review the available data concerning vitamin D status and health effects of vitamin D in pregnancy through to and including adolescence.

Relation of 25-hydroxyvitamin D and parathyroid hormone levels with metabolic syndrome among US adults

OBJECTIVE

Previous research on the combined association of 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH) with metabolic syndrome may have been limited by restricted age variability and a lack of representation of the general population. This study examined the combined association of 25(OH)D and PTH with Adult Treatment Panel III-defined MetSyn among a nationally representative sample of US adults.

DESIGN AND METHODS

This population-based cross-sectional study included 834 men and 820 women aged > or =20 years without diagnosed diabetes who completed a physical examination as part of the 2003-2004 US National Health and Nutrition Examination Survey.

RESULTS

After adjusting for age, sex, race/ethnicity, income, lifestyle factors, total calcium, and energy intake, the odds ratio (OR) for MetSyn in the highest quintile of 25(OH)D (median 88.0 nmol/l) compared with the lowest quintile (median 26.8 nmol/l) was 0.27 (0.15, 0.46; P(trend)<0.001). This relation was unchanged after additional adjustment for PTH level (OR, 0.26; 0.15, 0.44; P(trend)<0.001) and did not differ by sex (P interaction 0.6) or age (< or > or =50 years; P interaction 0.2). In contrast, the multivariable-adjusted odds for MetSyn increased with increasing PTH among older men (P(trend) 0.004), but not younger men (P(trend) 0.4) or women regardless of age (P(trend) 0.4 in younger and older women).

CONCLUSIONS

These data suggest an inverse association of 25(OH)D with MetSyn, independent of potential confounding factors, calcium intake, and PTH, and a positive association of PTH with MetSyn among older men.

Unexpected actions of vitamin D: new perspectives on the regulation of innate and adaptive immunity

Knowledge about the ability of vitamin D to function outside its established role in skeletal homeostasis is not a new phenomenon. Nonclassical immunomodulatory and antiproliferative responses triggered by active 1,25-dihydroxyvitamin D were first reported more than a quarter of a century ago. It is only in recent years, however, that there has been a significant improvement in our understanding of how these nonclassical effects of vitamin D can influence the pathophysiology and possible prevention of human disease. Three particular strands of evidence have been prominent: firstly, population studies have revised our interpretation of normal vitamin D status in humans, suggesting, in turn, that vitamin D insufficiency is a clinical problem of global proportions; secondly, epidemiology has linked vitamin D status with disease susceptibility and/or mortality; and, thirdly, expression of the machinery required to synthesize 1,25-dihydroxyvitamin D in normal human tissue seems to be much more widespread than originally thought. Collectively, these observations suggest that nonclassical metabolism and response to vitamin D might have a significant role in human physiology beyond skeletal and calcium homeostasis. Specific examples of this will be detailed in the current Review, with particular emphasis on the immunomodulatory properties of vitamin D.

Vitamin D and pancreatic cancer

Sun exposure has been associated with lower death rates for pancreatic cancer in ecological studies. Skin exposure to solar ultraviolet B radiation induces cutaneous production of precursors to 25-hydroxy (OH) vitamin D (D) and is considered the primary contributor to vitamin D status in most populations. Pancreatic islet and duct cells express 25-(OH) D(3)-1alpha-hydroxylase that generates the biologically active 1,25-dihydroxy(OH)(2) D form. Thus, 25(OH)D concentrations could affect pancreatic function and possibly pancreatic cancer etiology. Serum 25-(OH)D is the major circulating vitamin D metabolite and is considered the best indicator of vitamin D status as determined by the sun and diet. Although recent prospective epidemiologic studies of higher predicted vitamin D status score and vitamin D intake and pancreatic cancer risk suggest protective associations, a nested case-control study showed a significant 3-fold increased risk for pancreatic cancer with higher vitamin D status. Limitations of these studies include the former do not measure vitamin D status on pancreatic cancer cases and the later was conducted in a male smoker population. More research is needed, particularly examination of pre-diagnostic vitamin D status and risk of pancreatic cancer, prior to conclusions for vitamin D's potential role in the etiology of this highly fatal cancer.

The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis

CONTEXT

Altered vitamin D and calcium homeostasis may play a role in the development of type 2 diabetes mellitus (type 2 DM). EVIDENCE ACQUISITION AND ANALYSES: MEDLINE review was conducted through January 2007 for observational studies and clinical trials in adults with outcomes related to glucose homeostasis. When data were available to combine, meta-analyses were performed, and summary odds ratios (OR) are presented.

EVIDENCE SYNTHESIS

Observational studies show a relatively consistent association between low vitamin D status, calcium or dairy intake, and prevalent type 2 DM or metabolic syndrome [OR (95% confidence interval): type 2 DM prevalence, 0.36 (0.16-0.80) among nonblacks for highest vs. lowest 25-hydroxyvitamin D; metabolic syndrome prevalence, 0.71 (0.57-0.89) for highest vs. lowest dairy intake]. There are also inverse associations with incident type 2 DM or metabolic syndrome [OR (95% confidence interval): type 2 DM incidence, 0.82 (0.72-0.93) for highest vs. lowest combined vitamin D and calcium intake; 0.86 (0.79-0.93) for highest vs. lowest dairy intake]. Evidence from trials with vitamin D and/or calcium supplementation suggests that combined vitamin D and calcium supplementation may have a role in the prevention of type 2 DM only in populations at high risk (i.e. glucose intolerance). The available evidence is limited because most observational studies are cross-sectional and did not adjust for important confounders, whereas intervention studies were short in duration, included few subjects, used a variety of formulations of vitamin D and calcium, or did post hoc analyses.

CONCLUSIONS

Vitamin D and calcium insufficiency may negatively influence glycemia, whereas combined supplementation with both nutrients may be beneficial in optimizing glucose metabolism.

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.

A prospective nested case-control study of vitamin D status and pancreatic cancer risk in male smokers

Sun exposure is associated with lower death rates for pancreatic cancer in some ecological studies. Skin exposure to UVB light induces cutaneous production of precursors to 25-hydroxyvitamin D [25(OH)D]. Pancreatic islet and duct cells express 25(OH)D(3)-1alpha-hydroxylase that generates the biologically active 1,25(OH)(2) vitamin D form. Thus, 25(OH)D concentrations could affect pancreatic function and possibly pancreatic cancer etiology. We conducted a prospective nested case-control study in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention cohort of male Finnish smokers, ages 50 to 69 years at baseline, to test whether more adequate vitamin D status, as determined by prediagnostic serum 25(OH)D concentrations, was associated with lower pancreatic cancer risk. Two hundred incident exocrine pancreatic cancer cases that occurred between 1985 and 2001 (up to 16.7 years of follow-up) were matched by age and date of blood draw to 400 controls who were alive and free of cancer at the time the case was diagnosed. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using conditional logistic regression. Higher vitamin D concentrations were associated with a 3-fold increased risk for pancreatic cancer (highest versus lowest quintile, >65.5 versus <32.0 nmol/L: OR, 2.92; 95% CI, 1.56-5.48, P(trend) = 0.001) that remained after excluding cases diagnosed early during follow-up. Contrary to expectations, subjects with higher prediagnostic vitamin D status had an increased pancreatic cancer risk compared with those with lower status. Our findings need to be replicated in other populations and caution is warranted in their interpretation and implication. Our results are intriguing and may provide clues that further the understanding of the etiology of this highly fatal cancer.

Vitamin D and its binding protein Gc: long-term variability in peri- and postmenopausal women with and without hormone replacement therapy

OBJECTIVE

Measurement of plasma 25-hydroxyvitamin D (25OHD) level is often used to evaluate a patient's vitamin D status. The purpose of this study was to investigate the variability in individual plasma 25OHD- and vitamin D-binding protein- (Gc) levels over a 5-year period in postmenopausal women with and without hormone replacement therapy (HRT).

MATERIAL AND METHODS

A total of 187 women were followed-up for 5 years. At baseline, 89 women were allocated to treatment with HRT, given orally. Measurements were performed at baseline and after 1, 2 and 5 years of follow-up.

RESULTS

At baseline, 25OHD levels were positively associated with sunbathing and use of vitamin D supplements, and inversely associated with smoking. HRT therapy increased plasma levels of Gc (+8 %) but did not affect 25OHD levels or the free 25OHD index (molar ratio of 25OHD- to Gc levels). Among those classified in the lowest 25OHD tertile at baseline, 40 % remained in the lowest tertile during all subsequent measurement time-points. Similarly, 32 % of those classified in the highest baseline tertile remained in the highest tertile during all subsequent measurements. Use of the free 25OHD index showed similar results. No independent predictors of changes in vitamin D tertiles during follow-up were identified, which suggests that the observed variation was caused by the intra-individual variation in measured parameters. For all participants, the within-patient variability in 25OHD measurements was between 13 % and 19 %.

CONCLUSIONS

In healthy postmenopausal women, HRT increases Gc levels. Owing to the high intra-individual variation in plasma 25OHD, it seems questionable to use a single estimate as a predictor of individual vitamin D status.

Biological actions of extra-renal 25-hydroxyvitamin D-1alpha-hydroxylase and implications for chemoprevention and treatment

The Vitamin D-activating enzyme 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-hydroxylase) is now known to be expressed in a much wider range of tissues that previously thought, suggesting a role for 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), which is more in keeping with a cytokine than a hormone. In this capacity, the function of 1alpha-hydroxylase in tumors is far from clear. Studies from several groups including ours have shown altered expression of 1alpha-hydroxylase in different types of neoplasm including breast, prostate and colon cancers. However, functional analysis of Vitamin D metabolism in cancer is complicated by the heterogenous composition of tumors. Immunohistochemical analysis of breast tumors has shown that 1alpha-hydroxylase is expressed by both epithelial cells and by tumor-infiltrating macrophages, suggesting an immunomodulatory component to 1,25(OH)(2)D(3) production in some types of cancer. The demonstration of 1alpha-hydroxylase activity in tumors and their equivalent normal tissues has implications for both the treatment and prevention of cancers. For example, in tumors chemotherapy options may include the use of non-1alpha-hydroxylated Vitamin D analogs to increase local concentrations of active metabolites without systemic side-effects. The role of 1alpha-hydroxylase in protection against cancer is likely to be more complicated and may involve anti-tumor immune responses.

Effect of cholecalciferol supplementation on blood glucose in an experimental model of type 2 diabetes mellitus in spontaneously hypertensive rats and Wistar rats

BACKGROUND

Vitamin D might have an influence on glucose concentrations, due to the presence of VDR receptors on the pancreas. We established an experimental model of type 2 diabetes in spontaneously hypertensive rats (SHR) and Wistar rats in order to investigate the glycemic response.

METHODS

SHR males (n=6) and Wistar rats (n=6) weighing approximately 89+/-5.5 g and 123.5+/-6.5 g, respectively, after 7 days of basal period, had the chow pattern substituted (350 kcal/100 g) for a hypercaloric/hyperlipidic (HC/HL) diet (490 kcal/100g) and then injected with 40 mg/kg (SHR) and 20 mg/kg (Wistar) streptozotocin I.P. After the creation of diabetes, the rats suffered daily gavage of cholecalciferol (12.5 microg/kg(-) (1)) for 14 days. The blood glucose was assessed twice a week with a glucometer. The data were analyzed by ANOVA.

RESULTS

SHR and Wistar rats fed on a HC/HL diet gained 60 g and 32 g in once week, vs. the basal period, where they only gained 23 g and 13 g, respectively. The cholecalciferol supplementation did not change the glucose concentration in all of the SHR animals. About 40% of the group responded by treatment with reduction of about 60% in glucose concentrations. We did find a 40% of the blood glucose levels in all Wistar rats.

CONCLUSIONS

Cholecalciferol is able to reduce blood glucose in this experimental diabetes model.

Relationship between fasting serum glucose, age, body mass index and serum 25 hydroxyvitamin D in postmenopausal women

OBJECTIVE

Because it has been reported that vitamin D, given to mother or infant, can prevent type I diabetes in children, that diabetes is more common in adults with low serum vitamin D and that insulin secretion and action are related to vitamin D levels in healthy young adults we examined the relationship between serum vitamin D metabolites and fasting serum glucose in patients attending our outpatient clinics.

DESIGN

Retrospective examination of convenience sample of postmenopausal women attending our osteoporosis clinics.

PATIENTS

A total of 753 postmenopausal women attending a university hospital outpatient clinic and not on any treatment known to affect glucose metabolism.

MEASUREMENTS

Body weight and height, serum 25-hydroxyvitamin D [25(OH)D], serum 1,25-dihydroxyvitamin D [1,25(OH)2D], serum PTH and fasting serum glucose.

RESULTS

On simple correlation fasting serum glucose was a positive function of age (P < 0.05), weight (P < 0.001) and body mass index (BMI) (P < 0.001) and a negative function of serum 25(OH)D (P < 0.001), but it was not significantly related to either serum 1,25(OH)2D, PTH or creatinine. When fasting serum glucose was regressed simultaneously on age, BMI and 25(OH)D, glucose was still an inverse function of 25(OH)D (P = 0.006).

CONCLUSIONS

Fasting serum glucose increased as 25(OH)D levels fell throughout the range of serum 25(OH)D measured but the greatest increase was observed in those with 25(OH)D below 40 nmol/l.