The dynamic immunomodulatory effects of vitamin D3 during Mycobacterium infection

Plasma Vitamin D levels in correlation with circulatory proteins could be a potential biomarker tool for pulmonary tuberculosis and treatment monitoring

BACKGROUND

Tuberculosis (TB), a life-threatening immune challenging disease to the global human community has to be diagnosed earlier and eliminated in the upcoming era. Vitamin D, a fat-soluble micronutrient, mainly from epidermal cells of the skin and a few dietary sources, is associated with the immune system in various disease management. Therefore, a better understanding of vitamin D metabolism and immune function in tuberculosis should be studied for the consideration of biomarkers.

METHODS

The study consist of Pulmonary Tuberculosis (PTB) patients (n = 32) at two-time points: Baseline (PTB BL) and after 6 months of anti-TB treatment (ATT) (PTB PT), latently Mtb infected (IFNγ + ) group (n = 32) and a non-LTB healthy control (IFNγ-) group (n = 32). Vitamin D levels were measured using High-performance liquid chromatography (HPLC). The cytokine data from the same participants assayed by ELISA from our earlier investigations were used to correlate it with serum Vitamin D levels.

RESULTS

The assayed serum Vitamin D levels between the groups showed significantly lowered levels in PTB BL when compared with IFNγ + and IFNγ- groups. And, the Vitamin D levels in the PTB group after ATT were significantly lower than the baseline levels. The Vitamin D data were compared with pro- and anti-inflammatory cytokines and adipokines levels by performing a principal component regression analysis. Based on the PC scores, the study group showed distinct clusters for the TB group and control group. And, the correlation analysis between the study group and immunological indices showed significant correlations. Vitamin D significantly correlated with IFNγ, TNFα, IL17A, IL-4 and Resistin in the TB group, whereas IL-6 and G-CSF in the control group.

CONCLUSION

The baseline measurement of Vitamin D levels was significantly decreased in the PTB group when compared with IFNγ + and IFNγ- groups showing the importance of Vitamin D as a preventive factor against the TB disease progression. The six-month post-treatment of TB showed a further decrease in Vitamin D levels in PTB. The significantly correlated immunological indices with Vitamin D levels are the biomarker profile that could predict TB.

Vitamin D3 and COVID-19 Outcomes: An Umbrella Review of Systematic Reviews and Meta-Analyses

BACKGROUND

The immune system (innate and adaptive) is influenced by vitamin D3, which affects gene expression and inflammatory pathways. An umbrella review was conducted to evaluate the power and accuracy of data connecting vitamin D3 to the outcomes of COVID-19 infection and to appraise the proof provided by published meta-analyses.

METHODS

MEDLINE, Embase, and the Cochrane Library were searched from database inception to 31 May 2022. Meta-analyses of prospective or retrospective observational studies and randomized trials were included. Evidence of association was graded according to the established criteria: strong, highly suggestive, suggestive, weak, or not significant.

RESULTS

From 74 publications, 27 meta-analyses described five associations between vitamin D3 levels and supplementation and COVID-19 outcomes. Low levels of vitamin D3 were significantly associated with severity (highly suggestive evidence; OR = 1.97 [95% CI, 1.55-2.51], p < 0.01; I² = 77%, p < 0.01) and mortality risk due to COVID-19 disease (OR = 1.83 [95% CI, 1.55-2.16], p < 0.01; I² = 50%, p < 0.01). Vitamin D3 supplementation, after a diagnosis of COVID-19 infection, was associated with significantly reduced infection severity (e.g., ICU admission) and mortality.

CONCLUSIONS

This umbrella review of the available evidence suggests that insufficient vitamin D3 may increase COVID-19 infection risk, severity, and mortality, in addition to showing a highly suggestive association between vitamin D3 supplementation and reduced severity and mortality among infected patients.

Evaluation of circulating serum cathelicidin levels as a potential biomarker to discriminate between active and latent tuberculosis in Uganda

Background

Tuberculosis remains a major public health problem worldwide accounting for 1.4 million deaths annually. LL-37 is an effector molecule involved in immunity with both antimicrobial and immunomodulatory properties. The purpose of this study was to compare LL-37 circulatory levels among participants with active and latent tuberculosis and to determine its ability to discriminate between the two infectious states.

Methods

A cross-sectional study was performed among 56 active tuberculosis patients, 49 latent tuberculosis individuals, and 43 individuals without tuberculosis infection. The enzyme-linked immunosorbent assay was used to assess LL-37 levels. Data analysis was performed using STATA software and Graph pad Prism version 8. Mann-Whitney U test was used for correlation between variables with two categories and the Kruskal-Wallis test for three or more categories.

Results

The study had more female participants than males, with similar median ages across the three groups, 29.5, 25.0, and 23.0 years respectively. Active tuberculosis patients had significantly higher LL-37 levels compared to those with latent tuberculosis and without tuberculosis. The median/interquartile ranges were 318.8 ng/ml (157.9–547.1), 242.2 ng/ml (136.2–579.3), 170.9 ng/ml (129.3–228.3); p = 0.002 respectively. Higher LL-37 was found in the male participant with median/interquartile range, 424.8 ng/ml (226.2–666.8) compared to the females 237.7 ng/ml (129.6–466.6); p = 0.045. LL-37 had better discriminatory potential between active tuberculosis and no tuberculosis (AUC = 0.71, sensitivity 71.4% specificity = 69.8%) than with latent tuberculosis (AUC = 0.55, sensitivity = 71.4%, specificity = 44.9%). There was moderate differentiation between latent tuberculosis and no tuberculosis (AUC = 0.63, sensitivity = 44.9% specificity = 90.7%).

Conclusion

Significantly higher LL-37 levels were observed among active tuberculosis patients than those without tuberculosis infection and were, therefore able to discriminate between active tuberculosis and other tuberculosis infectious states, especially with no tuberculosis. Further assessment of this biomarker as a screening tool to exclude tuberculosis is required.

The Role of Diet and Supplements in the Prevention and Progression of COVID-19: Current Knowledge and Open Issues

A healthy diet and dietary supplements have gained attention as potential co-adjuvants in managing and preventing coronavirus disease 2019 (COVID-19). This paper critically reviews the current evidence regarding the impact of diet and supplements on the prevention and progression of COVID-19. According to available data, a healthy diet and normal weight are considered protective factors. Regarding dietary supplementation, the most robust results from human studies are for vitamin C, which appears to decrease inflammatory markers and suppress cytokine storm. A small, randomized trial showed that a high dose of vitamin D significantly reduced the need for intensive care unit treatment of patients requiring hospitalization for COVID-19. According to retrospective human studies, there is limited evidence for vitamin E and selenium supplements. Animal studies have investigated the effects of green tea and curcumin. Xanthohumol and probiotics, interesting for their antiviral, anti-inflammatory, and immunoregulatory properties, need formal clinical study. In summary, there is promising evidence supporting the role of diet and supplements as co-adjuvants in the treatment of COVID-19. Further studies and properly designed clinical trials are necessary to draw more robust conclusions; however, it is not unreasonable to take a pragmatic approach and promote the use of appropriate diet and supplements to counter the effects of COVID-19, ideally with a mechanism to assess outcomes.

Vitamin D receptor gene polymorphism and vitamin D supplementation on clinical/ treatment outcome in tuberculosis: current and future perspectives

INTRODUCTION

Tuberculosis (TB) is a transnational public health concern, which requires more precise treatment strategies than the existing approaches. Vitamin D modulates the inflammatory and immune response to the disease. Robust evidence shows that vitamin D deficiency and its receptor gene polymorphism influence the susceptibility to TB and the outcome of the anti-tubercular treatment (ATT). However, in the different populations, these findings were inconsistent and even contradictory.

AREAS COVERED

The current review focuses on the association between vitamin D receptor (VDR) gene polymorphism with the risk of development of TB disease and response to the ATT. Additionally, it reviews various systematic reviews and meta-analyses on the impact of vitamin D supplements on both clinical and treatment outcomes in TB patients.

EXPERT OPINION

Although the majority of the findings rule out the benefits of the supplementation, sufficient evidence is available to warrant larger epidemiological research that should be aimed to generate possible interaction among the VDR polymorphism, vitamin D status, and the outcome in TB. We conclude that establishing such an association in different ethnic populations will help design nutrigenomics- or pharmacogenomics-based vitamin D supplementation to develop a personalized medicine approach to flatten the curve of TB disease.

Vitamin D and tuberculosis in children: a role in the prevention or treatment of the disease?

Despite the growing number of published studies, the role of vitamin D in the prevention or treatment of tuberculosis remains unclear. In this review we analyze current scientific literature to provide evidence about the relationship between vitamin D and TB, with a special focus on the pediatric population. While in vitro studies have shown relevant antimycobacterial immune-stimulatory and immunosuppressive effects of vitamin D, this has not panned out in vivo with active TB. On the contrary, there is some evidence that this tool could work as prevention - both against TB infection as well as progression from latent to active infection. However, only a few studies have evaluated this correlation in children. The potential link between tuberculosis and vitamin D levels is promising. If effective, vitamin D supplementation of at-risk populations would be an affordable public health intervention, particularly in light of the worldwide increase in identified TB cases and drug-resistance. Vitamin D might represent a new, affordable, safe and easy to access drug for the prevention and treatment of TB. For stronger evidence, considering the features of infection (relative low incidence of reactivation of latent infection in immunocompetent patients) we need clinical trials with large numbers of participants conducted in endemic regions with a prolonged follow-up time.

1α,25(OH)2D3(VD3) promotes Raddeanin A-induced anti-proliferative effects on HeLa cell apoptosis and autophagy through negative regulation of HPV18E6-E7/PD-L1/VDR axis

Raddeanin A (RA) has indicated suppressive effects on various human tumor cells, and insufficient vitamin D was associated with human papillomavirus (HPV) persistence and gynecological tumors. However, combined effects of RA and vitamin D on HPV-positive cells remain elusive. Herein, we aimed to investigate the combined effects of RA and 1ɑ,25(OH)₂D₃ (VD3) on cellular viability and modulation of HPV18E6/E7, programmed cell death 1 ligand (PD-L1) and vitamin D receptor (VDR) expression in HeLa cells in vitro. HeLa cells were treated with RA alone or VD3 combined with RA. Cell viability was measured using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT), and apoptosis was detected by flow cytometry. Real-time PCR (qRT-PCR) and Western blot were used to determine the gene/protein expression levels. The autophagosomes were observed by Transmission electron microscopy (TEM). The result showed that cell viability was inhibited by RA, and apoptosis in HeLa cells treated with RA was elevated accordingly. The expression of Bax, Cleaved-caspase-3, Cleaved-caspase-9 and Cleaved-PARP increased, and Bcl-2 decreased. The autophagy was induced by RA, as evidenced by elevated autophagosomes and the increased LC3-II/I ratio and Beclin-1. The expression of HPV18E6/E7, PD-L1 and VDR was reduced by RA. Moreover, RA combined with VD3 had a stronger effect on HeLa cells than RA alone. In conclusion, RA inhibits HeLa proliferation and induces apoptosis and autophagy via suppressing HPV18E6/E7, PD-L1 and VDR, and VD3 showed reinforced effects of RA on HeLa cells. Therefore, combined usage of VD3 with RA might be a potential novel immunotherapy strategy for HPV-related diseases.

Autophagy and Host Defense in Nontuberculous Mycobacterial Infection

Autophagy is critically involved in host defense pathways through targeting and elimination of numerous pathogens via autophagic machinery. Nontuberculous mycobacteria (NTMs) are ubiquitous microbes, have become increasingly prevalent, and are emerging as clinically important strains due to drug-resistant issues. Compared to Mycobacterium tuberculosis (Mtb), the causal pathogen for human tuberculosis, the roles of autophagy remain largely uncharacterized in the context of a variety of NTM infections. Compelling evidence suggests that host autophagy activation plays an essential role in the enhancement of antimicrobial immune responses and controlling pathological inflammation against various NTM infections. As similar to Mtb, it is believed that NTM bacteria evolve multiple strategies to manipulate and hijack host autophagy pathways. Despite this, we are just beginning to understand the molecular mechanisms underlying the crosstalk between pathogen and the host autophagy system in a battle with NTM bacteria. In this review, we will explore the function of autophagy, which is involved in shaping host–pathogen interaction and disease outcomes during NTM infections. These efforts will lead to the development of autophagy-based host-directed therapeutics against NTM infection.

Relevance of vitamin D3 in COVID-19 infection

SARS-CoV-2 virus, the main culprit for COVID-19 disaster, has triggered a gust of curiosity both in the mechanism of action of this infection as well as potential risk factors for disease generation and regimentation. The prime focus of the present review, which is basically a narrative one, is in utilizing the current concepts of vitamin D₃ as an agent with myriad functions, one of them being immunocompetence and a promising weapon for both innate and adaptive immunity against COVID-19 infection. Some of the manifestations of SARS-CoV-2 virus such as Acute Respiratory Distress Syndrome (ARDS) overlap with the pathophysiological effects that are overcome due to already established role of vitamin D₃ e.g., amelioration of cytokine outburst. Additionally, the cardiovascular complications due to COVID-19 infection may also be connected to vitamin D₃ levels and the activity of its active forms. Eventually, we summarise the clinical, observational and epidemiological data of the respiratory diseases including COVID-19 disease and try to bring its association with the potential role of vitamin D₃, in particular, the activity of its active forms, circulating levels and its supplementation, against dissemination of this disease.

Vitamin D in the Covid-19 era: a review with recommendations from a G.I.O.S.E.G. expert panel

Vitamin D (VITD) is a key hormone for bone health and has relevant extra-skeletal effects that might play a role in the prevention and treatment of COronaVIrus Disease 19 (COVID-19). Literature regarding this scenario is voluminous but controversial. Glucocorticoid Induced Osteoporosis Skeletal Endocrinology Group (G.I.O.S.E.G) has been present in the scientific debate about the use of VITD and has regularly interfaced national regulatory agencies to ensure appropriateness of its employment. Given the current pandemic and the questions on COVID-19 and VITD, G.I.O.S.E.G. appointed an expert panel to advise how to consider this issue best. The results of these deliberations are reported in the current recommendation paper.

Changes in 25-(OH) Vitamin D Levels during the SARS-CoV-2 Outbreak: Lockdown-Related Effects and First-to-Second Wave Difference-An Observational Study from Northern Italy

Simple Summary

Several biological functions, more or less sustained by experimental evidence, have been proposed for vitamin D and in addition to its role in bone health, its optimal status has also been related with a reduced risk of allergy, obesity, and respiratory tract infections. During the SARS-CoV-2 pandemic, vitamin D levels have been put into relation with both the susceptibility to SARS-CoV-2 infection and the severity of COVID-19. The results from different studies are, however, not conclusive, since several variables impact on this relationship. In this study, we investigated the impact of the stringent confinement during the March–April 2020 lockdown on vitamin D levels and the relationship with the recorded sun exposure in the considered area (Milano, Italy). Furthermore, we investigated the eventual relationship between vitamin D levels and SARS-CoV-2 infection in different age groups throughout the pandemic, including the first and second wave, as well as the lockdown and between-lockdown periods. Taken together, our data suggest that 25-(OH)D levels are neither related with sun exposure nor with SARS-CoV-2 infection.

Abstract

Background. We investigated the changes in 25-hydroxy vitamin D [25-(OH)D] concentrations values, during the first and the second pandemic waves and the impact of the lockdown periods, with their different approaches to home confinement, among different age groups. Methods. Daily cloud-modified vitamin D UV dose (UVDVC), for the area of interest (Milano, Italy), was obtained. Single-center 25-(OH)D determinations from 40,996 individuals in a 2019 (pre-pandemic), 32,355 individuals from 1 January to 31 August 2020 (containing the first pandemic wave) and 27,684 individuals from 1 June to 30 November 2020 (containing the second wave) were compared to investigate both the effect of the lockdown on vitamin D status and the association between 25-(OH)D and SARS-CoV-2 positivity. Results. No direct association was found between UVDVC, 25-(OH)D status and SARS-CoV-2 infection. The stringent confinement implemented during the first wave lockdown has not had any effect on 25-(OH)D status, although some peculiar time-restricted profile behaviors can be deduced, possibly due to vitamin D supplementation habits and features of those patients who presented to the hospital during the lockdown period. Conclusions. Although our data do not suggest any direct relationship between 25-(OH)D status, sun exposure, and SARS-CoV-2 infection, an indirect protective role cannot be excluded.

Is there a link between vitamin D status, SARS-CoV-2 infection risk and COVID-19 severity?

The outbreak of COVID-19 emerged in December 2019 rapidly spread across the globe and has become pandemic. Little is known about the protective factors of this infection, which is equally distributed between genders and different ages while severe and poor prognosis cases are strongly associated to old males and the presence of comorbidities. Thus, preventive measures aiming at reducing the number of infection and/or their severity are strongly needed. Vitamin D has got great attention and has been claimed as potentially protective against the infection since it may be associated with immunocompetence, inflammation, aging, and those diseases involved in determining the outcomes of COVID-19. This narrative review aims at collecting the literature available on the involvement of the vitamin D status in the pathogenesis of COVID-19 and the putative utility of vitamin D supplementation in the therapeutics. It emerges that a poor vitamin D status seems to associate with an increased risk of infection whereas age, gender and comorbidities seem to play a more important role in COVID-19 severity and mortality. While randomized control trials are needed to better inquire into this topic, vitamin D supplementation may be useful beside its potential effects on SARS-CoV-2 infection and COVID-19.

MECHANISMS IN ENDOCRINOLOGY: Vitamin D and COVID-19

The SARS-CoV-2 virus responsible for the COVID-19 pandemic has generated an explosion of interest both in the mechanisms of infection leading to dissemination and expression of this disease, and in potential risk factors that may have a mechanistic basis for disease propagation or control. Vitamin D has emerged as a factor that may be involved in these two areas. The focus of this article is to apply our current understanding of vitamin D as a facilitator of immunocompetence both with regard to innate and adaptive immunity and to consider how this may relate to COVID-19 disease. There are also intriguing potential links to vitamin D as a factor in the cytokine storm that portends some of the most serious consequences of SARS-CoV-2 infection, such as the acute respiratory distress syndrome. Moreover, cardiac and coagulopathic features of COVID-19 disease deserve attention as they may also be related to vitamin D. Finally, we review the current clinical data associating vitamin D with SARS-CoV-2 infection, a putative clinical link that at this time must still be considered hypothetical.

Vitamin D increases killing of intracellular Leishmania amazonensis in vitro independently of macrophage oxidative mechanisms

Vitamin D has been reported to activate macrophage microbicidal mechanisms by inducing the production of antimicrobial peptides and nitric oxide (NO), but conversely has been shown to contribute to a greater susceptibility to Leishmania amazonensis infection in mice. Thus, this study aimed to evaluate the role of vitamin D during intracellular infection with L. amazonensis by examining its effect on macrophage oxidative mechanisms and parasite survival in vitro. Vitamins D2 and D3 significantly inhibited promastigote and amastigote growth in vitro. Vitamin D3 was not able to induce NO and reactive oxygen species (ROS) production in uninfected macrophages or macrophages infected with L. amazonensis. In addition, vitamin D3 in combination with interferon (IFN)-γ did not enhance amastigote killing and in fact, significantly reduced NO and ROS production when compared with the effect of IFN-γ alone. In this study, we demonstrated that vitamin D directly reduces parasite growth in infected macrophages (approximately 50-60% at 50 μm) but this effect is independent of the activation of macrophage oxidative mechanisms. These findings will contribute to a better understanding of the role of vitamin D in cutaneous leishmaniasis.

Nuclear Receptors as Autophagy-Based Antimicrobial Therapeutics

Autophagy is an intracellular process that targets intracellular pathogens for lysosomal degradation. Autophagy is tightly controlled at transcriptional and post-translational levels. Nuclear receptors (NRs) are a family of transcriptional factors that regulate the expression of gene sets involved in, for example, metabolic and immune homeostasis. Several NRs show promise as host-directed anti-infectives through the modulation of autophagy activities by their natural ligands or small molecules (agonists/antagonists). Here, we review the roles and mechanisms of NRs (vitamin D receptors, estrogen receptors, estrogen-related receptors, and peroxisome proliferator-activated receptors) in linking immunity and autophagy during infection. We also discuss the potential of emerging NRs (REV-ERBs, retinoic acid receptors, retinoic acid-related orphan receptors, liver X receptors, farnesoid X receptors, and thyroid hormone receptors) as candidate antimicrobials. The identification of novel roles and mechanisms for NRs will enable the development of autophagy-adjunctive therapeutics for emerging and re-emerging infectious diseases.

Host-Directed Therapy as a Novel Treatment Strategy to Overcome Tuberculosis: Targeting Immune Modulation

Tuberculosis (TB) is one of the leading causes of mortality and morbidity, particularly in developing countries, presenting a major threat to the public health. The currently recommended long term treatment regimen with multiple antibiotics is associated with poor patient compliance, which in turn, may contribute to the emergence of multi-drug resistant TB (MDR-TB). The low global treatment efficacy of MDR-TB has highlighted the necessity to develop novel treatment options. Host-directed therapy (HDT) together with current standard anti-TB treatments, has gained considerable interest, as HDT targets novel host immune mechanisms. These immune mechanisms would otherwise bypass the antibiotic bactericidal targets to kill Mycobacterium tuberculosis (Mtb), which may be mutated to cause antibiotic resistance. Additionally, host-directed therapies against TB have been shown to be associated with reduced lung pathology and improved disease outcome, most likely via the modulation of host immune responses. This review will provide an update of host-directed therapies and their mechanism(s) of action against Mycobacterium tuberculosis.

Compounding effect of vitamin D3 diet, supplementation, and alcohol exposure on macrophage response to mycobacterium infection

Vitamin D₃ is known to be a key component in the defense against Mycobacterium tuberculosis (Mtb) infection through the regulation of cytokine and effector molecules. Conversely, alcohol exposure has been recognized as an immune dysregulator. Macrophages were extracted from D₃ deficient and sufficient diet mice and supplemented with D₃ or exposed to ethanol during ex vivo infection using M. bovis BCG, as a surrogate for Mtb. Results of our study indicate that while exogenous supplementation or alcohol exposure did alter immune response, in vivo diet was the greatest determinant of cytokine and effector molecule production. Alcohol exposure was found to profoundly dysregulate primary murine macrophages, with ethanol-exposed cells generally characterized as hyper- or hyporesponsive. Exogenous D₃ supplementation had a normative effect for diet deficient host, however supplementation was not sufficient to compensate for the effects of diet deficiency. Vitamin D₃ sufficient diet resulted in reduced cell cytotoxicity for the majority of time points. Results provide insight into the ramifications of both the individual and combined health risks of D₃ deficiency or alcohol exposure. Given the clinical relevance of D₃ deficiency and alcohol use comorbidities, outcomes of this study have implications in therapeutic approaches for the treatment of tuberculosis disease.

In Silico Model of Vitamin D3 Dependent NADPH Oxidase Complex Activation During Mycobacterium Infection

Mycobacterium tuberculosis (Mtb) is a highly infectious aerosolizable bacterium, which causes upward of 1.5 million deaths per year. Alveolar macrophages, the primary defense cell of the lung, are the preferred host cell of this intracellular bacterium. Vitamin D₃ is a known transcription factor, modulating the transcription of pro- and anti-inflammatory cytokines and immunologically relevant proteins. In a vitamin D₃ deficient host, the immune systems response to infection is greatly impaired. We used a quantitative systems biology approach to model the impact of long-term vitamin D₃ deficiency on macrophage effector response. We then compared our simulation output to our in vitro model of mycobacterium infection of macrophages from vitamin D₃ supplemented hosts. Our in silico model results agreed with in vitro levels of hydrogen peroxide (H₂O₂) production, an antimicrobial effector molecule produced by the host's macrophage, known to be modulated indirectly by vitamin D₃. The current model will provide a foundation for further studies into the effects of micronutrient deficiency on immune response.

Spatiotemporal Analysis of Mycobacterium-Dependent Macrophage Response

There are three main outcomes of Mycobacterium tuberculosis infection: clearance, dissemination, and containment - in which the immune system physically isolates the invading microbes in lesions called granulomas. These structures are a hallmark of the disease and play an important role in the progression of infection. However, current in vitro and in vivo methods are ill adapted for spatial and temporal quantification of host-pathogen dynamics, which are necessary for the development of granulomas. We have developed an integrated 3D in vitro and computational platform with longterm time-lapse confocal imaging to provide a semi-automatic analysis of host-pathogen interaction data. Through exploratory data analysis, we conduct a preliminary investigation of how the intracellular bacterial load of macrophages can impact cellular spatiotemporal dynamics during Mycobacterium infection.

Vitamin D and tuberculosis: where next?

Tuberculosis (TB) has troubled mankind for millennia, but current treatment strategies are long and complicated and the disease remains a major global health problem. The risk of Mycobacterium tuberculosis (Mtb) infection or progression of active TB disease is elevated in individuals with vitamin D deficiency. High-dose vitamin D was used to treat TB in the preantibiotic era, and in vitro experimental data show that vitamin D supports innate immune responses that restrict growth of Mtb. Several randomized controlled trials have tested whether adjunctive vitamin D supplementation enhances the clinical and microbiological response to standard antimicrobial chemotherapy for pulmonary TB. The effects have been modest at best, and attention is turning to the question of whether vitamin D supplementation might have a role in preventing acquisition or reactivation of latent Mtb infection. In this article, we describe the effects of vitamin D on host immune responses to Mtb in vitro and in vivo and review the results of clinical trials in the field. We also reflect on the findings of clinical trials of vitamin D supplementation for the prevention of acute respiratory tract infections, and discuss how these findings might influence the design of future trials to evaluate the role of vitamin D in the prevention and treatment of TB.