Vitamin D Determinants, Status, and Antioxidant/Anti-inflammatory-Related Effects in Cardiovascular Risk and Disease: Not the Last Word in the Controversy

Synergistic Activation of VDR-RXR Heterodimers by Vitamin D and Rexinoids in Human Kidney and Brain Cells

The active form of vitamin D, 1,25-dihydroxyvitamin D (1,25D), binds to the vitamin D receptor (VDR) with high affinity. The VDR then heterodimerizes with the retinoid X receptor (RXR) and associates with vitamin D response elements (VDREs) to regulate the transcription of target genes. Bexarotene (Bex) is an RXR ligand (rexinoid) developed to treat cutaneous T-cell lymphoma and is a putative therapeutic for other diseases. We postulate that VDR ligands (1,25D) and RXR ligands (Bex/analogs) can "synergize" to "super-activate" the VDR-RXR heterodimer. This "cross-talk" could allow disorders treated with high-dose Bex therapy (leading to significant adverse side effects) to instead be treated using both low-dose Bex and vitamin D. Thus, we designed experiments to examine the effect of both VDR and RXR ligands, alone and in combination, to activate VDR-RXR-mediated transcription. The goal was to determine if selected RXR-specific ligands can synergize with vitamin D to amplify RXR-VDR activity. The results demonstrate a synergistic effect with both Bex and 1,25D which could be further modulated by (1) the protein levels (or polymorphic version) of VDR present in the cell, (2) the concentration of the ligands, (3) the cellular "background" (e.g., brain cells versus kidney cells), (4) the nature of the VDRE platform, or (5) the type of rexinoid (Bex analogs). Our findings suggest that diseases that respond to treatment with either vitamin D, or with rexinoids, may be amenable to enhanced therapeutic potential by employing multi-ligand dosing via combinatorial therapy.

The Impact of Neutrophil-to-High-Density Lipoprotein Ratio and Serum 25-Hydroxyvitamin D on Ischemic Heart Disease

Background: This study describes the complex association between the neutrophil-to-high-density lipoprotein cholesterol ratio (NHR), 25-hydroxyvitamin D (25(OH)D) levels, and cardiovascular disease (CVD), such as stable ischemic heart disease (IHD), ST elevation myocardial infarction (STEMI), non-ST-segment elevation myocardial infarction (NSTEMI), and unstable angina (UA). Methods: The serum 25(OH)D concentration and NHR values were analyzed in groups of patients with chronic coronary syndrome (CCS) and acute coronary syndrome (ACS). The severity of coronary artery atherosclerosis was determined using the Coronary Artery Surgery Study (CASS) scale. Results: Significant differences in 25(OH)D and NHR concentrations were observed between CCS and (ACS)/STEMI patients (p < 0.01). Higher 25(OH)D concentrations were associated with the diagnosis of CCS, and higher NHR values with the diagnosis of ACS/STEMI. The NHR threshold for ACS was set at 0.10 (p < 0.001). Patients without significant coronary artery stenosis showed significantly higher 25(OH)D levels and lower NHR values (p < 0.01). Conclusions: The significant correlation between 25(OH)D, HDL, and the NHR suggests that vitamin D, through its influence on inflammatory processes and lipid metabolism, may play a role in the pathogenesis of chronic and acute coronary syndromes. The suggested bidirectional relationship between the NHR and 25(OH)D and the role of the NHR as a predictor of vitamin D levels require further well-designed studies.

How Follow-Up Period in Prospective Cohort Studies Affects Relationship Between Baseline Serum 25(OH)D Concentration and Risk of Stroke and Major Cardiovascular Events

Background/Objectives: Prospective cohort studies are useful for studying how biomolecular status affects risk of adverse health outcomes. Less well known is that the longer the follow-up time, the lower the association (or "apparent effect") due to "regression dilution". Here, we evaluate how follow-up interval from baseline to "event" affects the relationship between baseline serum 25-hydroxyvitamin D [25(OH)D] concentration and the later incidence of stroke and major cardiovascular events (MACEs). Methods: Findings for the relative risk (RR) of stroke and MACEs with respect to serum 25(OH)D concentrations at baseline from prospective cohort studies were plotted against mean follow-up time. Fifteen studies from mainly European countries and the United States were used for stroke and nine studies for MACEs. Linear regression analyses were used to study data for follow-up periods of up to 10 years and for more than 10 years. Results: For stroke, the linear regression fit for 1-10 years is RR = 0.34 + (0.065 × follow-up [years]), r = 0.84, adjusted r2 = 0.67, p < 0.001. No significant variations in association were found for studies with follow-up periods of 10-20 years. For MACEs, the linear fit for 1-8.1 years is RR = 0.61 + (0.055 × follow-up [years]), r = 0.81, adjusted r2 = 0.59, p = 0.03. Discussion: The shorter the follow-up period, the greater the apparent effect of better vitamin D status in reducing risk of stroke and MACEs. In addition, the apparent effect of higher 25(OH)D concentration found for the shortest follow-up time is more than twice as great as the estimate based on average follow-up intervals for all studies. Mechanisms have been found to explain how higher serum 25(OH)D concentrations could reduce risk of stroke and MACEs. Randomized controlled trials have not shown that vitamin D supplementation significantly reduces risk of either stroke or MACEs, probably because risk of both outcomes increases rapidly below 15 ng/mL (38 nmol/L) and it is difficult in Western developed countries to enroll enough participants with concentrations that low. Nonetheless, vitamin D's role in reducing risk of stroke and MACEs could be considered causal on the basis of an evaluation of the evidence using Hill's criteria for causality in a biological system. Conclusions: Serum 25(OH)D concentrations above 20 ng/mL are associated with significantly reduced risk of stroke and MACEs prospectively and in an apparent causal manner. Raising serum 25(OH)D concentrations to >20 ng/mL should, therefore, be recommended for everyone likely to be at risk for stroke or MACEs and indeed in the general population.

Effect of a Phytochemical-Rich Olive-Derived Extract on Anthropometric, Hematological, and Metabolic Parameters

BACKGROUND

Extra virgin olive oil is a fundamental component of the Mediterranean diet. It contains several molecules that sustain human well-being by modulating cellular metabolism and exerting antioxidant, anti-inflammatory, and anti-ageing effects to protect normal tissues, and it can exert anti-angiogenic and pro-apoptotic effects on cancer cells. Metabolites found in different parts of the olive tree, including leaves, also possess properties that might help in cancer prevention and promote wellness in aging. Olive mill wastewater (OMWW), a liquid residue produced during olive oil extraction, represents an environmental issue. However, it is rich in phytochemicals with potential beneficial properties. Dietary supplements based on OMWW can be produced for nutritional supplementation with advantages to the ecology.

PURPOSE

This work aims to measure hematochemical, anthropometric, and metabolomic parameters in volunteers taking an OMWW dietary supplement, Oliphenolia® (OMWW-OL).

METHODS

The supplementation of OMWW-OL 25 mL twice daily for 30 days was tested on a pilot cohort of volunteers with characteristics close to metabolic syndrome. Hematochemical, anthropometric, serum biomarkers and serum metabolomic parameters were analyzed before the intervention, at 30 days, and 30 days after stopping consumption.

RESULTS

A total of 29 volunteers were enrolled, and 23 completed the study. The participants' parameters at baseline were measured, and then twice daily at 30 days of treatment and 30 days after assumption discontinuation. Although treatment was with an olive derivative, their weight did not increase. Their body mass index, instead of augmenting, slightly decreased, particularly in the women. Also, hydration increased, especially in the women, while blood pressure, glycemia, and insulin decreased. Cholesterol, high-density lipoproteins, and triglycerides were stable, and LDL levels decreased, while vitamin D levels, alongside calcium, perceptibly increased. Albumin also increased. All the values were in support of an equilibrium, with no damaging effects. By mass spectrometry analysis, we also found favorable changes in the vitamin D/histamine and homocysteine/methionine ratios, an increase in a new metabolite of unknown formula, and the vitamin D/unknown metabolite ratio.

CONCLUSIONS

Supplementation of OMWW-OL has no detrimental effects and might imply the beneficial modulation of several biological parameters. Although this is a small pilot study, with limited potency, it preliminarily suggests that the OMWW extract use could be potentially valuable for people at risk of metabolic syndrome. Some of these parameters could also be relevant in supporting healthy ageing and in cancer prevention.

Confronting the global obesity epidemic: investigating the role and underlying mechanisms of vitamin D in metabolic syndrome management

The escalating prevalence of MetS, driven by global obesity trends, underscores the urgent need for innovative therapeutic strategies. To gain a deeper understanding of the therapeutic potential of vitamin D in addressing MetS, we embarked on a targeted literature review that thoroughly examines the scientific underpinnings and pivotal discoveries derived from pertinent studies, aiming to unravel the intricate mechanisms through which vitamin D exerts its effects on MetS and its components. This article explores the multifunctional role of vitamin D in the management of MetS, focusing on its regulatory effects on insulin sensitivity, lipid metabolism, inflammation, and immune response. Through an extensive review of current research, we unveil the complex mechanisms by which vitamin D influences MetS components, highlighting its potential as a therapeutic agent. Our analysis reveals that vitamin D's efficacy extends beyond bone health to include significant impacts on cellular and molecular pathways critical to MetS. We advocate for further research to optimize vitamin D supplementation as a component of precision medicine for MetS, considering the safety concerns related to dosage and long-term use.

Effects of vitamin D signaling in cardiovascular disease: centrality of macrophage polarization

Among the leading causes of natural death are cardiovascular diseases, cancer, and respiratory diseases. Factors causing illness include genetic predisposition, aging, stress, chronic inflammation, environmental factors, declining autophagy, and endocrine abnormalities including insufficient vitamin D levels. Inconclusive clinical outcomes of vitamin D supplements in cardiovascular diseases demonstrate the need to identify cause-effect relationships without bias. We employed a spectral clustering methodology capable of analyzing large diverse datasets for examining the role of vitamin D's genomic and non-genomic signaling in disease in this study. The results of this investigation showed the following: (1) vitamin D regulates multiple reciprocal feedback loops including p53, macrophage autophagy, nitric oxide, and redox-signaling; (2) these regulatory schemes are involved in over 2,000 diseases. Furthermore, the balance between genomic and non-genomic signaling by vitamin D affects autophagy regulation of macrophage polarization in tissue homeostasis. These findings provide a deeper understanding of how interactions between genomic and non-genomic signaling affect vitamin D pharmacology and offer opportunities for increasing the efficacy of vitamin D-centered treatment of cardiovascular disease and healthy lifespans.

Vitamin D: An Essential Nutrient in the Dual Relationship between Autoimmune Thyroid Diseases and Celiac Disease-A Comprehensive Review

Autoimmune thyroid diseases (AITD) are among the most frequent autoimmune disorders, with a multifactorial etiology in which both genetic and environmental determinants are probably involved. Celiac disease (CeD) also represents a public concern, given its increasing prevalence due to the recent improvement of screening programs, leading to the detection of silent subtypes. The two conditions may be closely associated due to common risk factors, including genetic setting, changes in the composition and diversity of the gut microbiota, and deficiency of nutrients like vitamin D. This comprehensive review discussed the current evidence on the pivotal role of vitamin D in modulating both gut microbiota dysbiosis and immune system dysfunction, shedding light on the possible relevance of an adequate intake of this nutrient in the primary prevention of AITD and CeD. While future technology-based strategies for proper vitamin D supplementation could be attractive in the context of personalized medicine, several issues remain to be defined, including standardized assays for vitamin D determination, timely recommendations on vitamin D intake for immune system functioning, and longitudinal studies and randomized controlled trials to definitely establish a causal relationship between serum vitamin D levels and the onset of AITD and CeD.

High-Volume Liposuction in Lipedema Patients: Effects on Serum Vitamin D

Background: Lipedema is a subcutaneous adipose tissue disorder characterized by increased pathological adipocytes mainly in the extremities. Vitamin D is stored in adipocytes, and serum levels inversely correlate with BMI. As adipocytes are removed during liposuction, lipedema patients might be prone to further substantial vitamin D loss while their levels are already decreased. Therefore, we examined the effect of liposuction on perioperative serum 25-hydroxyvitamin D levels. Methods: In patients undergoing lipedema liposuction, blood samples were obtained pre- and postoperatively. Statistical analyses were performed to correlate the volume of lipoaspirate, patients' BMI and number of sessions to vitamin D levels. Results: Overall, 213 patients were analyzed. Mean liposuction volume was 6615.33 ± 3884.25 mL, mean BMI was 32.18 ± 7.26 kg/m2. mean preoperative vitamin D levels were 30.1 ± 14.45 ng/mL (borderline deficient according to the endocrine society) and mean postoperative vitamin D levels were 21.91 ± 9.18 ng/mL (deficient). A significant decrease in serum vitamin D was seen in our patients (p < 0.001) of mean 7.83 ng/mL. The amount of vitamin D loss was not associated with BMI or aspiration volume in our patients (p > 0.05). Interestingly, vitamin D dynamics showed a steady drop regardless of volume aspirated or preoperative levels. Conclusions: Many lipedema patients have low vitamin D levels preoperatively. Liposuction significantly reduced these levels additionally, regardless of aspirated volume or BMI. However, vitamin D loss was constant and predictable; thus, patients at risk are easily identified. Overall, lipedema patients undergoing liposuction are prone to vitamin D deficiency, and the long-term effects in this population are currently unknown.

Exploring the Interplay between Vitamin D, Insulin Resistance, Obesity and Skeletal Health

Vitamin D (ViD), plays an important role in calcium absorption and bone mineralization, is associated with bone mineral density. Severe deficiency in ViD has long been linked to conditions such as rickets in children and osteomalacia in adults, revealing its substantial role in skeletal health. Additionally, investigations show an existing interconnection between ViD and insulin resistance (Ins-R), especially in patients with type 2 diabetes mellitus (T2DM). Obesity, in conjunction with Ins-R, may augment the risk of osteoporosis and deterioration of skeletal health. This review aims to examine recent studies on the interplay between ViD, Ins-R, obesity, and their impact on skeletal health, to offer insights into potential therapeutic strategies. Cochrane Library, Google Scholar, and Pubmed were searched to investigate relevant studies until December 2023. Current research demonstrates ViD's impact on pancreatic β-cell function, systemic inflammation, and insulin action regulation. Our findings highlight an intricate association between ViD, Ins-R, obesity, and skeletal health, providing a perspective for the prevention and/or treatment of skeletal disorders in patients with obesity, Ins-R, and T2DM.

Vitamin D and Ceramide Metabolomic Profile in Acute Myocardial Infarction

Sphingolipids (SLs) influence several cellular pathways, while vitamin D exerts many extraskeletal effects in addition to its traditional biological functions, including the modulation of calcium homeostasis and bone health. Moreover, Vitamin D and SLs affect the regulation of each others' metabolism; hence, this study aims to evaluate the relationship between the levels of 25(OH)D and ceramides in acute myocardial infarction (AMI). In particular, the blood abundance of eight ceramides and 25(OH)D was evaluated in 134 AMI patients (aged 68.4 ± 12.0 years, 72% males). A significant inverse correlation between 25(OH)D and both Cer(d18:1/16:0) and Cer(d18:1/18:0) was found; indeed, patients with severe hypovitaminosis D (<10 ng/mL) showed the highest levels of the two investigated ceramides. Moreover, diabetic/dyslipidemic patients with suboptimal levels of 25(OH)D (<30 ng/mL) had higher levels of both the ceramides when compared with the rest of the population. On the other hand, 25(OH)D remained an independent determinant for Cer(d18:1/16:0) (STD Coeff -0.18, t-Value -2, p ≤ 0.05) and Cer(d18:1/18:0) (-0.2, -2.2, p < 0.05). In light of these findings, the crosstalk between sphingolipids and vitamin D may unravel additional mechanisms by which these molecules can influence CV risk in AMI.

Oxidative Stress and Cerebral Vascular Tone: The Role of Reactive Oxygen and Nitrogen Species

The brain's unique characteristics make it exceptionally susceptible to oxidative stress, which arises from an imbalance between reactive oxygen species (ROS) production, reactive nitrogen species (RNS) production, and antioxidant defense mechanisms. This review explores the factors contributing to the brain's vascular tone's vulnerability in the presence of oxidative damage, which can be of clinical interest in critically ill patients or those presenting acute brain injuries. The brain's high metabolic rate and inefficient electron transport chain in mitochondria lead to significant ROS generation. Moreover, non-replicating neuronal cells and low repair capacity increase susceptibility to oxidative insult. ROS can influence cerebral vascular tone and permeability, potentially impacting cerebral autoregulation. Different ROS species, including superoxide and hydrogen peroxide, exhibit vasodilatory or vasoconstrictive effects on cerebral blood vessels. RNS, particularly NO and peroxynitrite, also exert vasoactive effects. This review further investigates the neuroprotective effects of antioxidants, including superoxide dismutase (SOD), vitamin C, vitamin E, and the glutathione redox system. Various studies suggest that these antioxidants could be used as adjunct therapies to protect the cerebral vascular tone under conditions of high oxidative stress. Nevertheless, more extensive research is required to comprehensively grasp the relationship between oxidative stress and cerebrovascular tone, and explore the potential benefits of antioxidants as adjunctive therapies in critical illnesses and acute brain injuries.

Association of the ESR1 (rs9340799), OLR1 (rs3736234), LIPC (rs2070895), VDR (rs2228570), and CETP (rs708272) Polymorphisms With Risk of Coronary Artery Disease in Iranian Patients

BACKGROUND

Coronary artery disease (CAD) is a devastating illness and a leading cause of death worldwide, primarily caused by atherosclerosis resulting from a genetic-environmental interaction. This study aimed to investigate the relationship between the ESR1 (rs9340799), OLR1 (rs3736234), LIPC (rs2070895), VDR (rs2228570), and CETP (rs708272) polymorphisms, lipid profile parameters, and CAD risk in a southeast Iranian population.

METHODS

A total of 400 subjects (200 CAD patients with hyperlipidemia and 200 healthy controls) were enrolled in this case-control study. Five selected polymorphisms were genotyped using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique.

RESULTS

For all single nucleotide polymorphisms (SNPs), the population under study was in the Hardy-Weinberg equilibrium. The T-risk allele frequency of rs2228570 was associated with an increased risk of CAD. The TT and CT genotypes of rs2228570 had also been associated with the risk of CAD. Additionally, the TT genotype was associated with higher serum low-density lipoprotein cholesterol (LDL-c) and high-density lipoprotein cholesterol (HDL-c) levels. The GG genotype of the rs3736234 was associated with higher body mass index (BMI) and triglyceride (TG) levels, and the AA genotype of the rs708272 was associated with higher HDL-c levels. Based on these findings, we propose that the VDR (rs2228570) polymorphism was associated with serum HDL-c and LDL-c levels and may serve as potential risk factors for CAD within the Iranian population. Moreover, rs3736234 and rs708272 influence the concentrations of TG and HDL-c, respectively.

CONCLUSION

These findings provided insights into the complex interplay between genetic variations, cardiovascular risk, and lipid metabolism.

The imprecision of micronutrient requirement values: the example of vitamin D

Food, not nutrients, is the fundamental unit in nutrition. Nutrient requirement values and recommended daily intakes have long been determined and organized in tables by several regulators. These figures, however, overlook the complexity of mixing different foods in a diet and the mediation by human gut microbiota on digestion, metabolism, and health. The microbiome molecular mechanisms and its potential influence on nutrient requirements are far from clear. Guidelines should depend on the sort of intake, along with the dietary habits, rather than focusing on single nutrients. Despite many decades of attempts to investigate the proximate nutrient composition of foods consumed by different world populations, there are still neither standardization of food composition databases nor harmonized dietary intake methods of assessment of nutrients. No all-inclusive attempt was yet made to emphasize the requirements of the various micronutrients, phytonutrients, and non-nutrients on gut microbiota and vice versa, and thereafter reflected into dietary guidelines. New multifaceted methods have been advanced to reevaluate the way nutrients and nutrient requirements are assessed within the intricate biological systems. Our main goal here was to enhance the fact that existing food guidelines hold inherent strengths and limitations but fail, in many aspects, namely, in not taking into account essential geographical, ethnic and cultural differences, and the different stages of life, infant nutrition, and the microbiota impact on several micronutrient requirements. Vitamin D is given as an illustration on present inaccuracy of its requirements. Defining dietary reference intakes is therefore an ongoing process specific for each population.

From the Sun to the Cell: Examining Obesity through the Lens of Vitamin D and Inflammation

Obesity affects more than one billion people worldwide and often leads to cardiometabolic chronic comorbidities. It induces senescence-related alterations in adipose tissue, and senescence is closely linked to obesity. Fully elucidating the pathways through which vitamin D exerts anti-inflammatory effects may improve our understanding of local adipose tissue inflammation and the pathogenesis of metabolic disorders. In this narrative review, we compiled and analyzed the literature from diverse academic sources, focusing on recent developments to provide a comprehensive overview of the effect of vitamin D on inflammation associated with obesity and senescence. The article reveals that the activation of the NF-κB (nuclear factor kappa B subunit 1) and NLRP3 inflammasome (nucleotide-binding domain, leucine-rich-containing, pyrin domain-containing-3) pathways through the toll-like receptors, which increases oxidative stress and cytokine release, is a common mechanism underlying inflammation associated with obesity and senescence, and it discusses the potential beneficial effect of vitamin D in alleviating the development of subclinical inflammation. Investigating the main target cells and pathways of vitamin D action in adipose tissue could help uncover complex mechanisms of obesity and cellular senescence. This review summarizes significant findings related to opportunities for improving metabolic health.

Interplay between Vitamin D and Sphingolipids in Cardiometabolic Diseases

Sphingolipids (SLs) are structural, bioactive molecules with several key cellular roles, whereas 1,25-dihydroxyvitamin D (1,25(OH)D), the active form of vitamin D, is considered the major regulator of calcium homeostasis, although it also exerts other extraskeletal effects. Many studies reported the physiological connection between vitamin D and SLs, highlighting not only the effects of vitamin D on SL metabolism and signaling but also the influence of SLs on vitamin D levels and function, thus strongly suggesting a crosstalk between these molecules. After a brief description of 1,25(OH)D and SL metabolism, this review aims to discuss the preclinical and clinical evidence on the crosstalk between SLs and 1,25(OH)D, with a special focus on cardiometabolic diseases.

Three-stage pattern of rapid increase, plateau, and subsequent decline in vitamin D concentration during pregnancy among Chinese women: a large-scale survey

Background

There is an incomplete understanding of fluctuations in vitamin D (VitD) concentration during pregnancy among Chinese women. Furthermore, previous research has yielded conflicting results in this area. This study aims to investigate the changes in VitD status and deficiency in Chinese pregnant women across various age groups, gestational weeks, and as well as seasonal variations through conducting a large-scale survey.

Methods

A toal of 11,220 Chinese pregnant women between 2021 and April 2023 were included in this study. Generalized additive models (GAM), stratified analysis, and restricted cubic splines (RCS) were used to analyze changes in VitD status and deficiency risk during pregnancy.

Results

Of the participants, 45.2% had deficient concentration of 25-hydroxyvitamin D. VitD concentration and deficiency rate do not show linear changes with age and gestational weeks. With increasing gestational weeks, VitD concentration rapidly increased in women with gestational age < 20 weeks, remained stable between 20 and 30 weeks, and decreased beyond 30 weeks; however, the odds of VitD deficiency showed three different patterns: a rapid decline, a stable period, and a mild increase, respectively. Based on the stratified regression analysis, VitD deficiency odds increased by 16% with each additional week of gestation in pregnant women with gestational age > 30 weeks, OR = 1.16 (1.10-1.22), p < 0.001. Interaction effect analysis indicated that pregnant women over 35 years with gestational weeks between 20 and 30 had the lowest odds of VitD deficiency.

Conclusion

VitD concentration undergo three phases during pregnancy: rapid increase, plateau, and subsequent decrease. VitD deficiency odds was highest in pregnant women under 25 with gestational ages <20 and lowest in pregnant women over 35 with gestational ages between 20 and 30. The odds of deficiency increase slightly in pregnant women with gestational ages beyond 30 weeks, indicating that they may require additional VitD supplementation.

The Role of Vitamin D in Neuroprotection in Multiple Sclerosis: An Update

Multiple sclerosis (MS) is a complex neurological condition that involves both inflammatory demyelinating and neurodegenerative components. MS research and treatments have traditionally focused on immunomodulation, with less investigation of neuroprotection, and this holds true for the role of vitamin D in MS. Researchers have already established that vitamin D plays an anti-inflammatory role in modulating the immune system in MS. More recently, researchers have begun investigating the potential neuroprotective role of vitamin D in MS. The active form of vitamin D, 1,25(OH)₂D₃, has a range of neuroprotective properties, which may be important in remyelination and/or the prevention of demyelination. The most notable finding relevant to MS is that 1,25(OH)₂D₃ promotes stem cell proliferation and drives the differentiation of neural stem cells into oligodendrocytes, which carry out remyelination. In addition, 1,25(OH)₂D₃ counteracts neurodegeneration and oxidative stress by suppressing the activation of reactive astrocytes and M1 microglia. 1,25(OH)₂D₃ also promotes the expression of various neuroprotective factors, including neurotrophins and antioxidant enzymes. 1,25(OH)₂D₃ decreases blood-brain barrier permeability, reducing leukocyte recruitment into the central nervous system. These neuroprotective effects, stimulated by 1,25(OH)₂D₃, all enhance neuronal survival. This review summarizes and connects the current evidence supporting the vitamin D-mediated mechanisms of action for neuroprotection in MS.