An Overview of Systematic Reviews of the Role of Vitamin D on Inflammation in Patients with Diabetes and the Potentiality of Its Application on Diabetic Patients with COVID-19.

Almost two years have passed since the outbreak reported for the first time in Wuhan of coronavirus disease 2019 (COVID-19), due to severe acute respiratory syndrome (SARS)-CoV-2 coronavirus, rapidly evolved into a pandemic. This infectious disease has stressed global health care systems. The mortality rate is higher, particularly in elderly population and in patients with comorbidities such as hypertension, diabetes mellitus, cardiovascular disease, chronic lung disease, chronic renal disease, and malignancy. Among them, subjects with diabetes have a high risk of developing severe form of COVID-19 and show increased mortality. How diabetes contributes to COVID-19 severity remains unclear. It has been hypothesized that it may be correlated with the effects of hyperglycemia on systemic inflammatory responses and immune system dysfunction. Vitamin D (VD) is a modulator of immune-response. Data from literature showed that vitamin D deficiency in COVID-19 patients increases COVID-19 severity, likely because of its negative impact on immune and inflammatory responses. Therefore, the use of vitamin D might play a role in some aspects of the infection, particularly the inflammatory state and the immune system function of patients. Moreover, a piece of evidence highlighted a link among vitamin D deficiency, obesity and diabetes, all factors associated with COVID-19 severity. Given this background, we performed an overview of the systematic reviews to assess the association between vitamin D supplementation and inflammatory markers in patients with diabetes; furthermore, vitamin D's possible role in COVID-19 patients was assessed as well. Three databases, namely MEDLINE, PubMed Central and the Cochrane Library of Systematic Reviews, were reviewed to retrieve the pertinent data. The aim of this review is to provide insight into the recent advances about the molecular basis of the relationship between vitamin D, immune response, inflammation, diabetes and COVID-19.

Consumption of Food Supplements during the Three COVID-19 Waves in Poland-Focus on Zinc and Vitamin D.

Food supplements (FS) are a concentrated source of vitamins, minerals, or other ingredients with nutritional or other physiological effects. Due to their easy availability, widespread advertising, and sometimes low price, increased consumption of this group of preparations has been observed. Therefore, the aim of the study was to assess the knowledge and intake of FS during the COVID-19 pandemic in Poland, with particular reference to FS containing zinc and vitamin D. It was noted that both of the above ingredients were used significantly more often by people with higher education (59.0%), with a medical background or related working in the medical field (54.5%), and/or exercising at home (60.1%). Preparations containing vitamin D were used by 22.8% of the respondents in the first wave, 37.6% in the second wave, and 32.9% in the third wave. To sum up, we showed the highest consumption of vitamin and mineral supplements, and preparations containing zinc and vitamin D were taken significantly more often by people with higher medical and related education. This indicates a high awareness of health aspects and the need for preventive measures in these groups.

[Importance of nutrition for immune defense. The role of milk and its natural components]. / Importancia de la nutrición en la defensa inmunitaria. Papel de la leche y sus componentes naturales.

INTRODUCTION: The immune system is a complex and integrated system whose main function is to protect the body from external aggression by microorganisms, allergens, or toxic agents. Different studies show that maintaining optimal amounts of different nutrients in the body is essential to ensure the synthesis of different factors related to the immune system. Most interesting nutrients and bioactive compounds include: vitamins A, B6, B12, C, D, E, folic acid (B9) and biotin (B7); minerals such as zinc, iron, selenium, magnesium and copper; proteins (lactoferrin) and bioactive peptides; omega-3 fatty acids; and other nutrients and bioactive compounds such as fiber, polyphenols, carotenoids, probiotics, etc. Following a varied and balanced diet, including the servings recommended by food guides for each food group, is essential to achieve nutrient requirements. Food groups to which special attention should be paid are: fruits and vegetables (because of their high content in micronutrients and antioxidant compounds), fatty fish (because it contains omega-3 fatty acids), and dairy products (because this group contains a large number of nutrients). In particular, milk-especially enriched milk-contains many of the nutrients mentioned above. Moreover, their daily consumption, within a balanced diet, can help significantly cover their nutrient reference values. Finally, it is important to consider kind of milks as a good dietary alternative to increase the intake of some important nutrients for the proper functioning of the immune system, most especially some of them such as vitamin D, since a large percentage of the population have nutritional deficiencies.

INTRODUCCIÓN: El sistema inmunitario es un sistema complejo e integrado cuya función principal es proteger al organismo de agresiones externas provocadas por microorganismos, alergenos o agentes tóxicos. Diferentes estudios ponen de manifiesto que el mantenimiento de las cantidades óptimas de diferentes nutrientes es esencial para garantizar la síntesis de diferentes factores y mediadores de este sistema. Entre los nutrientes y compuestos bioactivos con mayor interés destacan: las vitaminas A, B6, B12, C, D, E, ácido fólico (B9) y biotina (B7); minerales como el zinc, hierro, selenio, magnesio y cobre; proteínas (lactoferrina) y péptidos bioactivos; ácidos grasos omega-3, y otros nutrientes y compuestos bioactivos como fibra, polifenoles, carotenoides, probióticos, etc. El seguimiento de una dieta variada y equilibrada que incluya las raciones recomendadas por las guías alimentarias para cada grupo de alimentos es fundamental para alcanzar los requerimientos de estos nutrientes. Y entre los grupos de alimentos a los que se debe prestar especial atención están: las frutas y verduras (por su alto contenido en micronutrientes y compuestos antioxidantes), los pescados azules (por contener omega-3) y los lácteos (por ser alimentos con gran cantidad de nutrientes). En concreto, la leche, especialmente enriquecida, contiene muchos de los nutrientes anteriormente mencionados y su consumo diario, dentro de una dieta equilibrada, puede contribuir a cubrir cantidades importantes de sus valores de referencia. Por último, es importante considerar las leches enriquecidas como una buena alternativa dietética para aumentar la ingesta de muchos nutrientes importantes para el buen funcionamiento del sistema inmune y, en especial, de algunos de ellos, como la vitamina D, en los que un gran porcentaje de la población presenta deficiencias nutricionales.

The contribution of gut bacterial metabolites in the human immune signaling pathway of non-communicable diseases.

The interaction disorder between gut microbiota and its host has been documented in different non-communicable diseases (NCDs) such as metabolic syndrome, neurodegenerative disease, and autoimmune disease. The majority of these altered interactions arise through metabolic cross-talk between gut microbiota and host immune system, inducing a low-grade chronic inflammation that characterizes all NCDs. In this review, we discuss the contribution of bacterial metabolites to immune signaling pathways involved in NCDs. We then review recent advances that aid to rationally design microbial therapeutics. A deeper understanding of these intersections between host and gut microbiota metabolism using metabolomics-based system biology platform promises to reveal the fundamental mechanisms that drive metabolic predispositions to disease and suggest new avenues to use microbial therapeutic opportunities for NCDs treatment and prevention. Abbreviations: NCDs: non-communicable disease, IBD: inflammatory bowel disease, IL: interleukin, T2D: type 2 diabetes, SCFAs: short-chain fatty acids, HDAC: histone deacetylases, GPCR: G-protein coupled receptors, 5-HT: 5-hydroxytryptamine receptor signaling, DCs: dendritic cells, IECs: intestinal epithelial cells, T-reg: T regulatory cell, NF-κB: nuclear factor κB, TNF-α: tumor necrosis factor alpha, Th: T helper cell, CNS: central nervous system, ECs: enterochromaffin cells, NSAIDs: non-steroidal anti-inflammatory drugs, AhR: aryl hydrocarbon receptor, IDO: indoleamine 2,3-dioxygenase, QUIN: quinolinic acid, PC: phosphatidylcholine, TMA: trimethylamine, TMAO: trimethylamine N-oxide, CVD: cardiovascular disease, NASH: nonalcoholic steatohepatitis, BAs: bile acids, FXR: farnesoid X receptor, CDCA: chenodeoxycholic acid, DCA: deoxycholic acid, LCA: lithocholic acid, UDCA: ursodeoxycholic acid, CB: cannabinoid receptor, COBRA: constraint-based reconstruction and analysis.

Vitamin D deficiency and graft-versus-host disease in hematopoietic stem cell transplant population.

Vitamins are the organic compounds that have long been known to play a significant role in our body by functioning as hormones and antioxidants. Vitamin D, a fat-soluble vitamin, is the main regulator of calcium hemostasis in our body. At the same time, it is also known to show its potential effects on the immune system by modulating the differentiation, activation, and proliferation of T and B lymphocytes. The immunomodulatory properties of vitamin D are also known to have a crucial role in the prevention and treatment of graft-versus-host disease. Patients undergoing hematopoietic stem cell transplantation are particularly at risk of vitamin D deficiency. This review article expands our understanding of vitamin D, its immunomodulatory effects, and its role in prevention and treatment of graft-versus-host disease.

Vitamin D: Effect on Haematopoiesis and Immune System and Clinical Applications.

Vitamin D is a steroid-like hormone which acts by binding to vitamin D receptor (VDR). It plays a main role in the calcium homeostasis and metabolism. In addition, vitamin D display other important effects called "non-classical actions." Among them, vitamin D regulates immune cells function and hematopoietic cells differentiation and proliferation. Based on these effects, it is currently being evaluated for the treatment of hematologic malignancies. In addition, vitamin D levels have been correlated with patients' outcome after allogeneic stem cell transplantation, where it might regulate immune response and, accordingly, might influence the risk of graft-versus-host disease. Here, we present recent advances regarding its clinical applications both in the treatment of hematologic malignancies and in the transplant setting.

Vitamin D and the Skin: An Update for Dermatologists.

Vitamin D plays a key role in skeletal and cardiovascular disorders, cancers, central nervous system diseases, reproductive diseases, infections, and autoimmune and dermatological disorders. The two main sources of vitamin D are sun exposure and oral intake, including vitamin D supplementation and dietary intake. Multiple factors are linked to vitamin D status, such as Fitzpatrick skin type, sex, body mass index, physical activity, alcohol intake, and vitamin D receptor polymorphisms. Patients with photosensitive disorders tend to avoid sun exposure, and this practice, along with photoprotection, can put this category of patients at risk for vitamin D deficiency. Maintaining a vitamin D serum concentration within normal levels is warranted in atopic dermatitis, psoriasis, vitiligo, polymorphous light eruption, mycosis fungoides, alopecia areata, systemic lupus erythematosus, and melanoma patients. The potential determinants of vitamin D status, as well as the benefits and risks of vitamin D (with a special focus on the skin), will be discussed in this article.

Vitamin D Status and the Host Resistance to Infections: What It Is Currently (Not) Understood.

PURPOSE: Vitamin D is increasingly thought to play a role in regulating immunity. This comprehensive review updates the current understanding regarding ways in which we believe that vitamin D regulates responsiveness of the immune system and how serum status modulates the host defense against pathogens. METHODS: The literature was searched by using PubMed and Scopus with the following key words: vitamin D, immunity, innate and adaptive immunity, infectious disease, and vaccine response. FINDINGS: Vitamin D deficiency remains a major public health concern worldwide. The overall body of evidence confirms that vitamin D plays an important role in modulating the immune response to infections. Epidemiologic studies suggest a clear association between vitamin D deficiency and susceptibility to various pathogens. However, translation of vitamin D use into the clinic as a means of controlling infections is fraught with methodologic and epidemiologic challenges. The recent discovery of alternative activation pathways, different active forms of vitamin D, and possible interaction with non-vitamin D receptors provide further complications to an already complex interaction between vitamin D and the immune system. Moreover, it has become apparent that the individual responsiveness to supplementation is more dynamic than presumed from the static assessment of 25-hydroxy vitamin D status. Furthermore, the epigenetic response at the level of the individual to environmental changes and lifestyle or health conditions provides greater variation than those resulting from vitamin D receptor polymorphisms. IMPLICATIONS: To understand the future of vitamin D with respect to clinical applications in the prevention and better control of infectious diseases, it is necessary to determine all aspects of vitamin D metabolism, as well as the mechanisms by which active forms interact with the immune system globally. For the most part, we are unable to identify tissue-specific applications of supplementation except for those subjects at high risk of osteomalacia and osteoporosis.

Vitamin D and Sjögren syndrome.

The immunomodulatory effects of vitamin D have been extensively studied in the context of autoimmunity. Multiple studies have demonstrated a high prevalence of vitamin D deficiency in autoimmune diseases. Recently, a possible protective role of vitamin D in autoimmunity has been described; however, this function remains controversial. Few studies have investigated the role of vitamin D in patients with Sjögren syndrome (SS). In this review, we compiled the main features of SS pathogenesis, the vitamin D immunomodulatory effects and the possible interaction between both. Data suggests that vitamin D may play a role in the SS pathogenesis. In addition, vitamin D low levels have been found in SS patients, which are associated with extra-glandular manifestations, such as lymphoma or neuropathy, suggesting a possible benefit effect of vitamin D in SS.

The Physiological/Pathophysiological Significance of Vitamin D in Cancer, Cardiovascular Disorders and Beyond.

BACKGROUND: Vitamin D, a molecular precursor of the potent steroid hormone calcitriol, has crucial functions and roles in physiology and pathophysiology. Tellingly, calcitriol has been shown to regulate various cellular signalling networks and cascades that have crucial role in cancer biology and diagnostics. Mounting lines of evidences from previous clinical and preclinical investigations indicate that the deficiency of vitamin D may contribute to the carcinogenesis risk. Concomitantly, recent reports suggested that significant reduction in the cancer occurrence and progression is more likely to appear after vitamin D supplementation. Furthermore, a pivotal role functioned by vitamin D in cardiovascular physiology indicates that the deficiency of vitamin D is significantly correlated with enhanced prevalence of stroke, hypertension and myocardial infarction. Notably, vitamin D status is more likely to be used as a lifestyle biomarker, since poor and unhealthy lifestyles are correlated with the deficiency of vitamin D, a feature which may result in cardiovascular complications. Moreover, recent reports revealed that the effect of vitamin D is to cover not only cardiovascular system but also skeletal system. OBJECTIVE: Herein, we are highlighting the recent knowledge of vitamin D roles and functions with respect to pathophysiological disorders such as cancer, cardiovascular diseases, rheumatoid arthritis (RA) and debate the potential avails of vitamin D on slowing cancer, cardiovascular disease and RA progression. CONCLUSION: The findings of this review confirm that the importance of vitamin D metabolites or analogues which can provide a helpful platform to target some kinds of cancer, particularly when used in combination with existing therapies. Moreover, the correlation between vitamin D deficiencies with cardiovascular diseases and rheumatoid arthritis (RA) progression might suggest a pivotal role of vitamin D in either initiation or progression of these diseases.

Does Vitamin D3 Have an Impact on Clinical and Biochemical Parameters Related to Third Molar Surgery.

The purpose of this study was to evaluate the clinical effect on the biochemical inflammatory markers of a single oral high dose of cholecalciferol in vitamin D-deficient patients undergoing the surgical removal of lower third molars.A randomized, split-mouth, single-blind study was conducted on 25 vitamin D-deficient patients ranging between 18 and 40 years of age requiring lower third molars extraction and referred at the Oral Surgery Unit of the School of Dentistry of the University of Messina.All patients, with vitamin D3 blood levels ≦30 ng/mL, underwent bilateral surgical removal. The first extraction (control group) being conducted with the administration of a placebo, the second one (test group) being conducted with the preliminary administration of 300,000 IU of cholecalciferol 4 days before the procedure.At each surgery, clinical indexes, such as pain, edema and any functional limitation have been recorded. Clinical and biochemical parameters were registered 4 days before, immediately after, 3 and 7 days after the surgical procedure. The data obtained were processed using paired t-test. The clinical outcome parameters showed a slight to moderate improvement between the control and the vitamin-D treatment group, with statistical significance being obtained regarding the edema at defined time points. Interleukin-1-beta, interleukin-6, and tumor necrosis factor-alpha values were significantly lower (P < 0.01) for the test group after the surgery. The increase of vitamin D serum levels showed an impact on the outcome of the third molar surgery, eliciting a reduced inflammatory response and leading to a more favorable clinical course.

Regulatory Dendritic Cells Restrain NK Cell IFN-γ Production through Mechanisms Involving NKp46, IL-10, and MHC Class I-Specific Inhibitory Receptors.

Cross-talk between mature dendritic cells (mDC) and NK cells through the cell surface receptors NKp30 and DNAM-1 leads to their reciprocal activation. However, the impact of regulatory dendritic cells (regDC) on NK cell function remains unknown. As regDC constrain the immune response in different physiological and pathological conditions, the aim of this work was to investigate the functional outcome of the interaction between regDC and NK cells and the associated underlying mechanisms. RegDC generated from monocyte-derived DC treated either with LPS and dexamethasone, vitamin D3, or vitamin D3 and dexamethasone instructed NK cells to secrete lower amounts of IFN-γ than NK cells exposed to mDC. Although regDC triggered upregulation of the activation markers CD69 and CD25 on NK cells, they did not induce upregulation of CD56 as mDC, and silenced IFN-γ secretion through mechanisms involving insufficient secretion of IL-18, but not IL-12 or IL-15 and/or induction of NK cell apoptosis. Blocking experiments demonstrated that regDC curb IFN-γ secretion by NK cells through a dominant suppressive mechanism involving IL-10, NK cell inhibitory receptors, and, unexpectedly, engagement of the activating receptor NKp46. Our findings unveil a previously unrecognized cross-talk through which regDC shape NK cell function toward an alternative activated phenotype unable to secrete IFN-γ, highlighting the plasticity of NK cells in response to tolerogenic stimuli. In addition, our findings contribute to identify a novel inhibitory role for NKp46 in the control of NK cell function, and have broad implications in the resolution of inflammatory responses and evasion of antitumor responses.

Vitamin D3 in cancer prevention and therapy: the nutritional issue.

The action of vitamin D3, in its biological form 1α,25(OH)2vitD3 or calcitriol, may be summarized as a steroid-like hormone able to modulate basic functions of cell encompassing energy balance, stress response, mitochondria biogenesis, intracellular calcium oscillations, and replication/apoptosis mechanisms leading to cell survival. Moreover, calcitriol exerts a potent role as an innate and adaptive immune cytokine as immunity is closely related to self-maintenance through its energetic/metabolic balance and homeostasis of cell turnover. Therefore, vitamin D might be the ancestral form of survival hormones developed with calcified vertebrate bearing skeleton in order to survive far from water. This characteristic may suggest that the role of dietary vitamin D in preventing cancer is simply ancillary to the many factors playing a major role in contrasting impairment in energy balance and cell survival. Most probably, the immune role of calcitriol might be included in the maintenance, mostly by adipose tissue, of an anti-inflammatory, tolerant immune status, depending on the immune tolerance and modulation from the gut. A balance closely modulated by the leptin axis, which when impairments in metabolism occur, such as in insulin resistance or obesity, calcitriol is unable to face at this imbalance, while leptin plays a major role and cancer progression may be promoted. Furthermore, this mechanism promotes epithelial/mesenchymal transition-mediated fibrosis, leading to cancer resistance to immune control and drug action. Interestingly, this pathologic picture is triggered by deficiency in vitamin D from the diet. Therefore, a dietary habit including vitamin D sources, besides flavonoids, may ameliorate lifestyle and health span in most individuals, depending on their genetic background.

Cellular metabolism and macrophage functional polarization.

Macrophages are a functionally heterogeneous cell population that is mainly shaped by a variety of microenvironmental stimuli. Interferon γ (IFN-γ), interleukin-1ß (IL-1ß), and lipopolysaccharide (LPS) induce a classical activation of macrophages (M1), whereas IL-4 and IL-13 induce an alternative activation program in macrophages (M2). Reprogramming of intracellular metabolisms is required for the proper polarization and functions of activated macrophages. Similar to the Warburg effect observed in tumor cells, M1 macrophages increase glucose consumption and lactate release and decreased oxygen consumption rate. In comparison, M2 macrophages mainly employ oxidative glucose metabolism pathways. In addition, fatty acids, vitamins, and iron metabolisms are also related to macrophage polarization. However, detailed metabolic pathways involved in macrophages have remained elusive. Understanding the bidirectional interactions between cellular metabolism and macrophage functions in physiological and pathological situations and the regulatory pathways involved may offer novel therapies for macrophage-associated diseases.

Vitamin C treatment of mouse bone marrow-derived dendritic cells enhanced CD8(+) memory T cell production capacity of these cells in vivo.

Vitamin C has been found to stimulate dendritic cells (DCs) to secrete more IL-12 and thereby drive naïve CD4(+) T cells to differentiate into Th1 cells. In the present study, we evaluated the effect of these vitamin C-treated DCs on CD8(+) T cell differentiation both in vitro and in vivo. Mouse bone marrow-derived DCs were prepared in the presence of GM-CSF and IL-15. With vitamin C treatment, these DCs, when LPS-stimulated, secreted more IL-12p70 and IL-15 than did untreated DCs. And when co-cultured with T cells, they yielded a higher frequency of IFN-γ(+) CD8(+) T cells. Moreover, we found that administering vitamin C-treated and tumor lysate-loaded DCs into mice yielded a higher frequency of CD44(high) CD62L(low) CD8(+) effector and effector memory T cells, which showed an increased ex vivo killing effect of the tumor cells. These DCs also elicited enhanced protective effects against inoculated tumor cells, most probably by way of the increased cytotoxic T cells, as was revealed by the decreased growth of the inoculated tumor cells in these mice. This ex vivo vitamin C treatment effect on DCs can be considered as a strategy for boosting DC vaccination potency against tumors.

Re-evaluating the role of vitamin D in the periodontium.

The importance of vitamin D in maintaining skeletal health via the regulation of calcium has long been recognized as a critical function of this secosteroid. An abundance of literature shows an association between oral bone mineral density and some measure of systemic osteoporosis and suggests that osteoporosis/low bone mass may be a risk factor for periodontal disease. Recently, nonskeletal functions of vitamin D have gained notoriety for several reasons. Many cells that are not associated with calcium homeostasis have been demonstrated to possess membrane receptors for vitamin D. These include activated T and B lymphocytes, and skin, placenta, pancreas, prostate and colon cancer cells. In addition, vitamin D "insufficiency" is a worldwide epidemic and epidemiologic evidence has linked this condition to multiple chronic health problems, including cardiovascular and autoimmune diseases, hypertension and a variety of cancers. Interestingly, there is mounting evidence connecting diminished serum levels of vitamin D with increased gingival inflammation and supporting the concept of "continual vitamin D sufficiency" in maintaining periodontal health. The ability of vitamin D to regulate both the innate and the adaptive components of the host response may play an important role in this process. This review will examine the skeletal and nonskeletal functions of vitamin D, and explore its potential role in protecting the periodontium as well as in regulating periodontal wound healing.

[Vitamin D level in Hungarian patients with inflammatory bowel diseases]. / D-vitamin-szint mérése hazai gyulladásos bélbetegekben.

INTRODUCTION: Vitamin D has an important role in the immune regulation. Vitamin D is essential for innate and adaptive immune systems and it plays a significant role in the formation of immune tolerance, as well. AIM: Vitamin D deficiency has been observed in patients with inflammatory bowel diseases in Western Europe, but there is no data available from Eastern Europe. METHOD: The study included 169 patients with inflammatory bowel disease. RESULTS: The median vitamin D level was 22.7±10.6 ng/ml. Only 20% of the patients had adequate vitamin D level (>30 ng/ml), 52% had vitamin D insufficiency (15-30 ng/ml), and 28% of them had severe vitamin D deficiency (<15 ng/ml). Vitamin D concentration failed to correlate with clinical activity indexes (partial Mayo score: r = -0.143; Crohn's disease activity index: r = -0.253) and with inflammatory parameters (C-reactive protein: r = 0.008; erythrocyte sedimentation rate: r = 0.012). CONCLUSIONS: Since vitamin D deficiency can be frequently observed in Hungarian patients with inflammatory bowel disease, its level should be tested in these patients.

Toll-like receptor 8 ligands activate a vitamin D mediated autophagic response that inhibits human immunodeficiency virus type 1.

Toll-like receptors (TLR) are important in recognizing microbial pathogens and triggering host innate immune responses, including autophagy, and in the mediation of immune activation during human immunodeficiency virus type-1 (HIV) infection. We report here that TLR8 activation in human macrophages induces the expression of the human cathelicidin microbial peptide (CAMP), the vitamin D receptor (VDR) and cytochrome P450, family 27, subfamily B, polypeptide 1 (CYP27B1), which 1α-hydroxylates the inactive form of vitamin D, 25-hydroxycholecalciferol, into its biologically active metabolite. Moreover, we demonstrate using RNA interference, chemical inhibitors and vitamin D deficient media that TLR8 agonists inhibit HIV through a vitamin D and CAMP dependent autophagic mechanism. These data support an important role for vitamin D in the control of HIV infection, and provide a biological explanation for the benefits of vitamin D. These findings also provide new insights into potential novel targets to prevent and treat HIV infection.

Role of vitamin D in immune responses and autoimmune diseases, with emphasis on its role in multiple sclerosis.

Vitamin D is a seco-steroid involved in calcium and phosphorus metabolism, and bone formation and mineralization, through binding to a specific nuclear receptor, vitamin D receptor (VDR). Besides its well-established functions on bone health, multiple lines of evidence have indicated the immunomodulatory roles of vitamin D. Vitamin D can affect both innate and adaptive immunity, and prevent autoimmune responses efficiently. Vitamin D regulates the immune responses by suppressing T cell proliferation and modulating macrophage functions. Epidemiological studies have shown that vitamin D deficiency is associated with multiple diseases such as rickets and cancer. Moreover, associations between vitamin D and autoimmune diseases have been confirmed in multiple sclerosis (MS), rheumatoid arthritis (RA), etc. The present review mainly summarized the recent findings on the immunomodulatory role of vitamin D in various disorders, with special focus on its role in MS, an autoimmune disease of the nervous system.