Association of Vitamin D deficiency with peripheral arterial disease: a meta-analysis of literature studies

Integrating Endocrine, Genomic, and Extra-Skeletal Benefits of Vitamin D into National and Regional Clinical Guidelines

BACKGROUND/OBJECTIVES

Vitamin D is essential for bone health, immune function, and overall well-being. Numerous ecological, observational, and prospective studies, including randomized controlled clinical trials (RCTs), report an inverse association between higher serum 25-hydroxyvitamin D [25(OH)D; calcifediol] levels in various conditions, including cardiovascular disease, metabolic disorders such as diabetes and obesity, susceptibility to infection-related complications, autoimmune diseases, and all-cause mortality.

RESULTS

Vitamin D operates through two distinct systems. The endocrine system comprises the renal tubular cell-derived circulatory calcitriol, which primarily regulates calcium homeostasis and muscular functions. In contrast, intracellularly generated calcitriol in peripheral target cells is responsible for intracrine/paracrine system signaling and calcitriol-vitamin D receptor-mediated genomic effects. Government-appointed committees and health organizations have developed various clinical practice guidelines for vitamin D supplementation and management. However, these guidelines heavily relied on the 2011 Institute of Medicine (IoM) report, which focused solely on the skeletal effects of vitamin D, ignoring other body systems. Thus, they do not represent maintaining good overall health and aspects of disease prevention. Additionally, the IoM report was intended as a public health recommendation for the government and is not a clinical guideline.

DISCUSSION

New country- and regional-specific guidelines must focus on healthy nations through disease prevention and reducing healthcare costs. They should not be restricted to bone effect and must encompass all extra-skeletal benefits. Nevertheless, due to misunderstandings, medical societies and other governments have used faulty IoM report as a foundation for creating vitamin D guidelines. Consequently, they placed disproportionate emphasis on bone health while largely overlooking its benefits for other bodily systems, making current guidelines, including 2024, the Endocrine Society less applicable to the public. As a result, the utility of published guidelines has been significantly reduced for clinical practice and RCTs that designed on bone-centric are generate misleading information and remain suboptimal for public health and disease prevention.

CONCLUSIONS

This review and its recommendations address the gaps in current vitamin D clinical practice guidelines and propose a framework for developing more effective, country and region-specific recommendations that capture the extra-skeletal benefits of vitamin D to prevent multiple diseases and enhance public health.

The Relationship Between Bone Metabolism and Peripheral Artery Disease in Patients on Hemodialysis: The Potential Role of Osteocalcin

Introduction

To examine the factors associated with PAD, with a specific focus on bone metabolism factors such as osteocalcin.

Methods

This cross-sectional study examined factors about demographic, clinical, and laboratory parameters including bone metabolism biomarkers in hemodialysis patients. The ankle-brachial index (ABI) was measured in all patients, with PAD diagnosed as an ABI <0.9.

Results

Out of the 71 patients, PAD was found in 23 individuals. These patients had an average age of 63.5±13.0 years, with 59.2% being male. Compared to non-PAD patients, those with PAD were older, had a lower proportion of males, and had a higher prevalence of diabetes and coronary artery disease. Among the factors related to bone metabolism, only osteocalcin exhibited a significant increase in the PAD group compared to the non-PAD group.

Conclusion

PAD in patients on hemodialysis was independently linked to high levels of osteocalcin in the bloodstream, indicating the presence of bone metabolism disorders.

Non-classical monocytes frequency and serum vitamin D3 levels are linked to diabetic foot ulcer associated with peripheral artery disease

AIMS/INTRODUCTION

Peripheral artery disease (PAD) serves as a risk factor for diabetic foot ulcers (DFUs). PAD pathology involves atherosclerosis and impaired immunity. Non-classical monocytes are believed to have an anti-inflammatory role. 1,25-Dihydroxy vitamin D (vitamin D3 ) is claimed to have immune-modulating and lipid-regulating roles. Vitamin D receptor is expressed on monocytes. We aimed to investigate if circulating non-classical monocytes and vitamin D3 were implicated in DFUs associated with PAD.

MATERIALS AND METHODS

There were two groups of DFU patients: group 1 (n = 40) included patients with first-degree DFUs not associated with PAD, and group 2 (n = 50) included patients with DFU with PAD. The monocyte phenotypes were detected using flow cytometry. Vitamin D3 was assessed by enzyme-linked immunosorbent assay.

RESULTS

DFU patients with PAD showed a significant reduction in the frequency of non-classical monocytes and vitamin D3 levels, when compared with DFU patients without PAD. The percentage of non-classical monocytes positively correlated with vitamin D3 level (r = 0.4, P < 0.01) and high-density lipoprotein (r = 0.5, P < 0.001), whereas it was negatively correlated with cholesterol (r = -0.5, P < 0.001). Vitamin D3 was negatively correlated with triglyceride/high-density lipoprotein (r = -0.4, P < 0.01). Regression analysis showed that a high vitamin D3 serum level was a protective factor against PAD occurrence.

CONCLUSIONS

Non-classical monocytes frequency and vitamin D3 levels were significantly reduced in DFU patients with PAD. Non-classical monocytes frequency was associated with vitamin D3 in DFUs patients, and both parameters were linked to lipid profile. Vitamin D3 upregulation was a risk-reducing factor for PAD occurrence.

Vitamin D and Multiple Health Outcomes: An Umbrella Review of Observational Studies, Randomized Controlled Trials, and Mendelian Randomization Studies

Observational studies, randomized controlled trials (RCTs), and Mendelian randomization (MR) studies have yielded inconsistent results on the associations of vitamin D concentrations with multiple health outcomes. In the present umbrella review we aimed to evaluate the effects of low vitamin D concentrations and vitamin D supplementation on multiple health outcomes. We summarized current evidence obtained from meta-analyses of observational studies that examined associations between vitamin D concentrations and multiple health outcomes, meta-analyses of RCTs that investigated the effect of vitamin D supplementation on multiple health outcomes, and MR studies that explored the causal associations of vitamin D concentrations with various diseases (international prospective register of systematic reviews PROSPERO registration number CRD42018091434). A total of 296 meta-analyses of observational studies comprising 111 unique outcomes, 139 meta-analyses of RCTs comprising 46 unique outcomes, and 73 MR studies comprising 43 unique outcomes were included in the present umbrella review. Twenty-eight disease outcomes were identified by both meta-analyses of observational studies and MR studies. Seventeen of these reported disease outcomes had consistent results, demonstrating that lower concentrations of vitamin D were associated with a higher risk for all-cause mortality, Alzheimer's disease, hypertension, schizophrenia, and type 2 diabetes. The combinations of consistent evidence obtained by meta-analyses of observational studies and MR studies together with meta-analyses of RCTs showed that vitamin D supplementation was associated with a decreased risk for all-cause mortality but not associated with the risk for Alzheimer's disease, hypertension, schizophrenia, or type 2 diabetes. The results indicated that vitamin D supplementation is a promising strategy with long-term preventive effects on multiple chronic diseases and thus has the potential to decrease all-cause mortality. However, the current vitamin D supplementation strategy might not be an efficient intervention approach for these diseases, suggesting that new strategies are highly needed to improve the intervention outcomes.

Insulin Resistance and Vitamin D Deficiency: A Link Beyond the Appearances

Vitamin D is a steroid hormone that plays a key role in the regulation of body homeostasis, including cardiovascular function. Although the chronic deficiency of vitamin D is associated with cardiovascular risk factors, as well as with an adverse prognosis, randomized controlled trials have failed in demonstrating that dietary vitamin D supplementation could ameliorate the prognosis of patients with cardiovascular diseases, and suggested that vitamin D deficiency is the expression of the effects of other determinants of cardiovascular risk. Thus, the supplementation of vitamin D is not sufficient to improve the cardiovascular risk profile and prognosis. Insulin resistance is a complex phenomenon that plays a key role in the pathogenesis of conventional cardiovascular risk factors. Interestingly, defects of vitamin D and insulin resistance have a superimposable epidemiological distribution. According to the common view, Insulin resistance is considered the direct or indirect consequence of vitamin D deficiency. However, it is also reasonable to speculate that the deficit or the impaired action of vitamin D, in some circumstances, could be the result of the same pathogenic mechanisms responsible of insulin resistance development. In this case, vitamin D deficiency could be considered an epiphenomenon of insulin resistance. Insulin resistance is a reversible condition, being possibly ameliorated by physical activity and hypocaloric diets. Notably, both physical exercise and energy-restricted dietary regimens are associated with an increase of vitamin D levels. These findings indicate that improving insulin resistance condition is a necessary step to ameliorate vitamin D supplementation-based strategies in cardiovascular prevention.

Vitamin D and Vascular Disease

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Vitamin D deficiency has been identified as a potential risk factor for a number of diseases unrelated to the classical skeletal pathophysiology, such as cancer and CVD, but the effects of vitamin D supplementation are less clear. Purpose of this narrative review is to discuss the evidence suggesting an association between vitamin D status and CVD as well as the results of supplementation studies. Vitamin D deficiency has been associated with CVD risk factors such as hypertension, dyslipidemia and diabetes mellitus as well as with cardiovascular events such as myocardial infarction, stroke and heart failure. While vitamin D deficiency might contribute to the development of CVD through its association with risk factors, direct effects of vitamin D on the cardiovascular system may also be involved. Vitamin D receptors are expressed in a variety of tissues, including cardiomyocytes, vascular smooth muscle cells and endothelial cells. Moreover, vitamin D has been shown to affect inflammation, cell proliferation and differentiation. While observational studies support an association between low plasma vitamin D levels and increased risk of CVD, Mendelian randomization studies do not support a causal association between the two. At present, high quality randomized trials do not find evidence of significant effects on CVD endpoints and do not support supplementation of vitamin D to decrease CVD events.

The Relationship Between Serum Level of Vitamin D3 and Osseointegration Around the Dental Implant

At present, dental implants are used more than before, and their high success rate is attributed to sufficient osseointegration, which depends on prosthetic-, implant-, and patient-related factors. The quality and quantity of bone and the host response are the main patient-related factors. Vitamin D3 affects bone metabolism by stimulating both osteoclasts and osteoblasts. This study aimed to review the human studies on the efficacy of vitamin D3 for dental implant osseointegration. Search of the literature yielded only 4 studies on human models, of which 2 showed the optimal efficacy of vitamin D3 for dental implant osseointegration, whereas the remaining 2 did not report any positive effect. However, this finding may be related to the small sample size of the vitamin D3-deficient group, which can compromise statistical analyses. In conclusion, vitamin D3 seems to be effective for dental implant osseointegration, although further research is required on human models.

Targeting Uremic Toxins to Prevent Peripheral Vascular Complications in Chronic Kidney Disease

Chronic kidney disease (CKD) exhibits progressive kidney dysfunction and leads to disturbed homeostasis, including accumulation of uremic toxins, activated renin-angiotensin system, and increased oxidative stress and proinflammatory cytokines. Patients with CKD are prone to developing the peripheral vascular disease (PVD), leading to poorer outcomes than those without CKD. Cumulative evidence has showed that the synergy of uremic milieu and PVD could exaggerate vascular complications such as limb ischemia, amputation, stenosis, or thrombosis of a dialysis vascular access, and increase mortality risk. The role of uremic toxins in the pathogenesis of vascular dysfunction in CKD has been investigated. Moreover, growing evidence has shown the promising role of uremic toxins as a therapeutic target for PVD in CKD. This review focused on uremic toxins in the pathophysiology, in vitro and animal models, and current novel clinical approaches in reducing the uremic toxin to prevent peripheral vascular complications in CKD patients.

The relationship of 25-hydroxyvitamin D concentrations and individual-level socioeconomic status

Socioeconomic status (SES), defined as the ability to access desired resources, is associated with behaviors that may affect vitamin D status. Most studies of the effect of vitamin D status on outcomes do not account for individual-level SES. The ability to adjust for SES in epidemiologic studies, when data on conventional SES measures have not been obtained, would be advantageous. We identified all serum 25(OH)D measurements in adults age 18 years and older residing in Olmsted County, MN, a mixed urban-rural setting, between January 1, 2005 and December 31, 2011, through the Rochester Epidemiology Project. The first 25(OH)D measurement was considered the index measurement for each subject. SES was determined for each subject by the HOUsing-based SocioEconomic Status (HOUSES) index, derived from real property data. The HOUSES index is an aggregated z-score of assessed housing value, area of living space, number of bedrooms, and number of bathrooms, with higher scores indicating higher SES. Multivariable analyses were adjusted for age, BMI, sex, race, season of 25(OH)D measurement, and Charlson comorbidity index. HOUSES was matched for 10,378 of 11,002 subjects (94 %) with 25(OH)D measurements available. The mean (SD) age was 54.3 (17.1) years with 26.9 % ≥65 years; 77.3 % were women, and 12.1 % were non-white. The mean 25(OH)D concentration was 30.0 (12.9) ng/mL, and 598 (5.8 %) had a 25(OH)D value <12 ng/mL. The mean (SD) HOUSES was -1.55 (3.09),-0.97 (3.34), 0.14 (3.52), 0.24 (3.51) for serum 25(OH)D categories of <12, 12-19, 20-50, and >50 ng/mL, respectively (P = 0.12 for trend). 25(OH)D increased by 0.43 (95 % CI 0.36-0.50) ng/mL for each unit increase in HOUSES in univariate analysis and by 0.28 (0.21-0.35; P < 0.001) ng/mL in multivariable analysis. This represents a change of 4 ng/mL across the entire range of observed HOUSES, an effect similar in magnitude to the seasonal variation of 25(OH)D values. SES was independently associated with serum 25(OH)D concentrations in a dose-response manner after adjustment for important covariates. HOUSES is a useful tool to assess the role of individual-level SES in health outcomes when other SES measures are unavailable and to control for confounding by SES in examining the effect of 25(OH)D on clinical and metabolic outcomes.

Vitamin D and health in the Mediterranean countries

Vitamin D, traditionally well known for its role in maintaining optimal health through its contribution to calcium metabolism and skeletal health, has received increased attention over the past two decades, with considerable focus being placed on its nonskeletal benefits. This paper is a narrative review of the nonskeletal health benefits of vitamin D, of particular interest to inhabitants of Mediterranean countries, namely, autism, cancer, cardiovascular disease, chronic obstructive pulmonary disease, dental caries, diabetes mellitus, erectile dysfunction, hypertension, metabolic syndrome, respiratory tract infections, all-cause mortality, and pregnancy and birth outcomes, because of the relatively high incidence and/or prevalence of these disorders in this region. Currently, the best evidence is coming out of observational studies related to serum 25-hydroxyvitamin D [25(OH)D] concentrations. Vitamin D clinical trials have generally been poorly designed and conducted, usually being based on vitamin D dose rather than 25(OH)D concentration. The optimal 25(OH)D concentration is above 75 nmol/l (30 ng/ml), with even better health outcomes in the range of 100-150 nmol/l. Achieving these concentrations with vitamin D₃ supplements will require 1000-4000 IU/day of vitamin D₃. Sensible sun exposure should also be encouraged. Countries should also consider fortifying grain and dairy products with vitamin D₃.

Serum vitamin D and diabetic foot complications

Background: Foot complications such as ulceration and neuropathy are common complications of diabetes mellitus (DM). Previous reports have demonstrated a possible increased risk of these complications in diabetic patients with low levels of serum vitamin D.Objectctive: The purpose of this study is to compare serum vitamin D levels in diabetic patients with and without Charcot neuroarthropathy (CN), peripheral arterial disease (PAD), infection (DFI), ulceration (DFU), and peripheral neuropathy (DPN). Design: A retrospective chart review of all patients undergoing foot and ankle surgery with a history of DM over a 13 month period was performed. From this cohort, fifty subjects with CN were matched with 50 without CN and preoperative lab values were compared. A secondary evaluation was performed on the subjects' other comorbidities including PAD, DFI, DFU, and DPN. Results: Seventy-eight percent of our patients had vitamin D deficiency or insufficiency. Preoperative serum vitamin D levels were not significantly different between diabetic patients with and without CN (p = 0.55). Diabetic patients with PAD (p = 0.03), DFI (p = 0.0006), and DFU (p = 0.04) were all found to have significantly lower serum vitamin D levels than diabetic patients without these complications. Lower levels of serum albumin and higher serum creatinine were also noted with subjects with PAD, DFI, DPN, and DFU. While seasonal serum vitamin D level fluctuation was noted, this difference did not reach statistical significance with the numbers available. Conclusion: We found various lower extremity complications to be associated with low serum vitamin D including PAD, DFI, and DFU. While other studies have questioned the role of vitamin D and CN, we were unable to identify any significant difference between diabetic patients with and without Charcot neuroarthropathy. Level of evidence: Level 2.

1α,25(OH)2D3 attenuates IL-6 and IL-1β-mediated inflammatory responses in macrophage conditioned medium-stimulated human white preadipocytes by modulating p44/42 MAPK and NF-κB signaling pathways

BACKGROUND

Metabolic syndrome is characterized by macrophage infiltration and inflammatory responses-metaflammation in adipose tissue. IL-6 and IL-1β could mediate the inflammatory responses in macrophage stimulated-preadipocytes by modulating MAPK and NF-κB pathways. To test this hypothesis we used antibodies to block IL-6 and IL-1β action in macrophage conditioned medium (MacCM)-stimulated human white preadipocytes. Moreover, as interventions that prevent this could potentially be used to treat or prevent metabolic syndrome, and 1α,25(OH)₂D₃ has previously been reported to exert an anti-inflammatory action on macrophage-stimulated adipocytes, in this study we also investigated whether 1α,25(OH)₂D₃ could attenuate inflammatory responses in MacCM-stimulated preadipocytes, and explored the potential anti-inflammatory mechanisms.

METHODS

Human white preadipocytes were cultured with 25% MacCM for 24 h to elicit inflammatory responses. This was confirmed by measuring the concentrations and mRNA levels of major pro-inflammatory factors [IL-1β, IL-6, IL-8, monocyte chemoattractant protein (MCP)-1 and regulated on activation, normal T cell expressed and secreted (RANTES)] by ELISA and qPCR, respectively. IL-6 and IL-1β actions were blocked using IL-6 antibody (300 ng/ml) and IL-1β antibody (15 μg/ml), respectively. Potential anti-inflammatory effects of 1α,25(OH)₂D₃ were investigated by pre-treatment and treatment of 1α,25(OH)₂D₃ (0.01 to 10 nM) for 48 h in MacCM-stimulated preadipocytes. In parallel, western blotting was used to determine inflammatory signaling molecules including relA of the NF-κB pathway and p44/42 MAPK modified during these processes.

RESULTS

MacCM enhanced the secretion and gene expression of IL-1β, IL-6, IL-8, MCP-1 and RANTES by increasing the phosphorylation levels of relA and p44/42 MAPK in preadipocytes, whereas blocking IL-6 and IL-1β action inhibited the inflammatory responses by decreasing p44/42 MAPK and relA phosphorylation, respectively. Furthermore, 10 nM of 1α,25(OH)₂D₃ generally inhibited the IL-6 and IL-1β-mediated inflammatory responses, and reduced both p44/42 MAPK and relA phosphorylation in MacCM-stimulated preadipocytes.

CONCLUSIONS

1α,25(OH)₂D₃ attenuates IL-6 and IL-1β-mediated inflammatory responses, probably by inhibiting p44/42 MAPK and relA phosphorylation in MacCM-stimulated human white preadipocytes.

Low serum vitamin D and early dental implant failure: Is there a connection? A retrospective clinical study on 1740 implants placed in 885 patients

Background. Since osseointegration depends on bone metabolism, low levels of vitamin D in the blood may negatively affect bone formation around dental implants. To date, only a few studies have investigated the possible connection between serum levels of vitamin D and early dental implant failure (EDIF), i.e. failure that occurs within 4 months after placement, before the connection of the prosthetic abutment. The aim of this study was to investigate whether there is a relationship between low serum levels of vitamin D and EDIF.

Methods. Data used for this retrospective study were derived from the records of a private dental clinic. Inclusion criteria were patients who had been treated with dental implants, inserted with a submerged technique from January 2003 to December 2017. EDIF was the outcome of this study. Chi-squared test was used to investigate the effect of patient-related variables (age, gender, smoking habit, history of periodontal disease and serum levels of vitamin D) on EDIF.

Results. Originally, 885 patients treated with 1,740 fixtures were enrolled in this study. Overall, 35 EDIFs (3.9%) were reported. No correlation was found between EDIF and the patients' gender (P=0.998), age (P=0.832), smoking habit (P=0.473) or history of periodontal disease (P=0.386). Three EDIFs (11.1%) were reported in 27 patients with serum levels of vitamin D <10 ng/mL, 20 EDIFs (4.4%) in 448 patients with levels between 10 and 30 ng/mL, and 12 EDIFs (2.9%) in 410 patients with levels >30 ng/mL. Although there was a clear trend toward an increased incidence of EDIF with lowering of serum vitamin D levels, no statistically significant difference (P=0.105) was found among these three groups.

Conclusion. Within its limitations (retrospective design, low number of patients with severe blood levels of vitamin D enrolled), this study failed to demonstrate a significant relationship between low serum levels of vitamin D and increased risk of EDIF. However, since a dramatic increase in EDIFs with lowering of vitamin D levels in the blood has been reported, further clinical studies with appropriate design (prospective or randomized controlled studies on a larger sample of severely deficient patients) are needed to better investigate this topic