Controversial Effects of Vitamin D and Related Genes on Viral Infections, Pathogenesis, and Treatment Outcomes

Vitamin D (VD) plays an essential role in mineral homeostasis and bone remodeling. A number of different VD-related genes (VDRG) are required for the metabolic activation of VD and the subsequent induction of its target genes. They include a set of genes that encode for VD-binding protein, metabolic enzymes, and the VD receptor. In addition to its well-characterized skeletal function, the immunoregulatory activities of VD and the related polymorphisms of VDRG have been reported and linked to its therapeutic and preventive actions for the control of several viral diseases. However, in regards to their roles in the progression of viral diseases, inconsistent and, in some cases, contradictory results also exist. To resolve this discrepancy, I conducted an extensive literature search by using relevant keywords on the PubMed website. Based on the volume of hit papers related to a certain viral infection, I summarized and compared the effects of VD and VDRG polymorphism on the infection, pathogenesis, and treatment outcomes of clinically important viral diseases. They include viral hepatitis, respiratory viral infections, acquired immunodeficiency syndrome (AIDS), and other viral diseases, which are caused by herpesviruses, dengue virus, rotavirus, and human papillomavirus. This review will provide the most current information on the nutritional and clinical utilization of VD and VDRG in the management of the key viral diseases. This information should be valuable not only to nutritionists but also to clinicians who wish to provide evidence-based recommendations on the use of VD to virally infected patients.

The Potential Protective Role of Vitamin D Supplementation on HIV-1 Infection

HIV infection remains a global and public health issue with the incidence increasing in some countries. Despite the fact that combination antiretroviral therapy (cART) has decreased mortality and increased the life expectancy of HIV-infected individuals, non-AIDS conditions, mainly those associated with a persistent inflammatory state, have emerged as important causes of morbidity, and mortality despite effective antiviral therapy. One of the most common comorbidities in HIV-1 patients is Vitamin D (VitD) insufficiency, as VitD is a hormone that, in addition to its physiological role in mineral metabolism, has pleiotropic effects on immune regulation. Several reports have shown that VitD levels decrease during HIV disease progression and correlate with decreased survival rates, highlighting the importance of VitD supplementation during infection. An extensive review of 29 clinical studies of VitD supplementation in HIV-infected patients showed that regardless of cART, when VitD levels were increased to normal ranges, there was a decrease in inflammation, markers associated with bone turnover, and the risk of secondary hyperparathyroidism while the anti-bacterial response was increased. Additionally, in 3 of 7 studies, VitD supplementation led to an increase in CD4+ T cell count, although its effect on viral load was inconclusive since most patients were on cART. Similarly, previous evidence from our laboratory has shown that VitD can reduce the infection of CD4+ T cells in vitro. The effect of VitD supplementation on other HIV-associated conditions, such as cardiovascular diseases, dyslipidemia or hypertension, warrants further exploration. Currently, the available evidence suggests that there is a potential role for VitD supplementation in people living with HIV-1, however, comprehensive studies are required to define an adequate supplementation protocol for these individuals.

Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

The role of UV radiation and vitamin D in the seasonality and outcomes of infectious disease

The seasonality of infectious disease outbreaks suggests that environmental conditions have a significant effect on disease risk. One of the major environmental factors that can affect this is solar radiation, primarily acting through ultraviolet radiation (UVR), and its subsequent control of vitamin D production. Here we show how UVR and vitamin D, which are modified by latitude and season, can affect host and pathogen fitness and relate them to the outcomes of bacterial, viral and vector-borne infections. We conducted a thorough comparison of the molecular and cellular mechanisms of action of UVR and vitamin D on pathogen fitness and host immunity and related these to the effects observed in animal models and clinical trials to understand their independent and complementary effects on infectious disease outcome. UVR and vitamin D share common pathways of innate immune activation primarily via antimicrobial peptide production, and adaptive immune suppression. Whilst UVR can induce vitamin D-independent effects in the skin, such as the generation of photoproducts activating interferon signaling, vitamin D has a larger systemic effect due to its autocrine and paracrine modulation of cellular responses in a range of tissues. However, the seasonal patterns in infectious disease prevalence are not solely driven by variation in UVR and vitamin D levels across latitudes. Vector-borne pathogens show a strong seasonality of infection correlated to climatic conditions favoring their replication. Conversely, pathogens, such as influenza A virus, Mycobacterium tuberculosis and human immunodeficiency virus type 1, have strong evidence to support their interaction with vitamin D. Thus, UVR has both vitamin D-dependent and independent effects on infectious diseases; these effects vary depending on the pathogen of interest and the effects can be complementary or antagonistic.

Does Vitamin D Deficiency Affect the Immunogenic Responses to Influenza Vaccination? A Systematic Review and Meta-Analysis

Influenza virus infection is a major global public health problem, and the efficacy of influenza vaccination is not satisfactory. Vitamin D is involved in many immune-mediated inflammatory processes. The impact of vitamin D levels on the immunogenic response to influenza vaccination is not clear. We performed a comprehensive literature search and systematic review of studies that investigated vitamin D and influenza vaccination. Data pertaining to study population, vaccine components, vitamin D levels, and immunogenic response were analyzed. Nine studies, with a combined study population of 2367 patients, were included in the systematic review. Four studies were included in the meta-analysis to investigate the influence of vitamin D deficiency (VDD) on the seroprotection (SP) rates and seroconversion (SC) rates following influenza vaccination. We found no significant association between vitamin D level and the immunogenic response to influenza vaccination. However, strain-specific differences may exist. We observed lower SP rates of influenza A virus subtype H3N2 (A/H3N2) and B strain in VDD patients than patients with normal vitamin D levels (A/H3N2: 71.8% vs. 80.1%, odds ratio (OR): 0.63, 95% confidence interval (CI): 0.43-0.91, p = 0.01; B strain: 69.6% vs. 76.4%, OR: 0.68, 95% CI: 0.5-0.93, p = 0.01). However, the SP rates of A/H1N1 and SC rates of all three strains were not significantly different in VDD and control groups. In conclusion, no association was observed between VDD and immunogenic response to influenza vaccination.

Vitamin D deficiency in children with recurrent respiratory infections, with or without immunoglobulin deficiency

PURPOSE

The objective of this study was to evaluate thevitamin D concentration in patients with recurrent respiratory infections with or without immunoglobulin G, A or M (IgG, IgA, IgM) deficiency, and to find a correlation between the vitamin D concentration and the response to hepatitis B vaccination.

MATERIALS AND METHOD

The study involved 730 patients with recurrent respiratory infections. The concentration of 25-hydroxyvitamin D (25(OH)D), immunoglobulins G, A and M, anti-HBs was determined.

RESULTS

The tests showed that 11% of patients presented IgG levels below the age related reference values. Children with reduced IgG concentration were also found to have significantly lower vitamin D concentrations in comparison to children with normal IgG. Vitamin D deficiency was observed in schoolchildren between 7 and 18 years of age. No correlation was found between 25(OH)D concentration and Hbs antibody levels.

CONCLUSIONS

An investigation of a large group of patients who have recurrent infection found patients with IgG deficiency to whom special proceeding have to be performed: 1. Significantly lower vitamin D concentration observed in the group of children with IgG deficiency implicated in long-lasting monitoring of vitamin D level require adding to the practice guidelines for Central Europe 2013. 2. Intervention treatment with suitable doses of vitamin D to clarified metabolism of vitamin D has to be plan for children with IgG deficiency and significant lower vitamin D concentration.

Vitamin D, leptin and impact on immune response to seasonal influenza A/H1N1 vaccine in older persons

BACKGROUND

Influenza-related complications are highest in the elderly. Vaccine efficacy is lower due to immunosenescence. Vitamin D's immunomodulatory role was studied in the context of vaccine response.

METHODS

We evaluated the effect of baseline 25-(OH) D on vaccine-induced immunological response in a cohort of 159 healthy subjects ages 50-74 in Rochester, MN, who received one dose of seasonal trivalent 2010-2011 influenza vaccine, containing A/California/H1N1- like virus. We examined correlations between 25-(OH) D, leptin, and leptin-related gene SNPs to understand the role of leptin and vitamin D's effects.

RESULTS

The median (IQR) baseline for total 25-(OH) D was 44.4 ng/mL (36.6-52.2 ng/mL). No correlation was observed with age. No correlation between 25-(OH) D levels and humoral immune outcomes existed at any timepoint. There was a weak positive correlation between 25-(OH) D levels and change (Day 75-Day 0) in influenza-specific granzyme-B response (r=0.16, p=0.04). We found significant associations between 3 SNPs in the PPARG gene and 25-(OH) D levels (rs1151996, p=0.01; rs1175540, p= 0.02; rs1175544, p=0.03).

CONCLUSION

Several SNPs in the PPARG gene were significantly associated with baseline 25-(OH) D levels. Understanding the functional and mechanistic relationships between vitamin D and influenza vaccine-induced immunity could assist in directing new influenza vaccine design.

Effects of calcitriol (1, 25-dihydroxy-vitamin D3) on the inflammatory response induced by H9N2 influenza virus infection in human lung A549 epithelial cells and in mice

Background

H9N2 influenza viruses circulate globally and are considered to have pandemic potential. The hyper-inflammatory response elicited by these viruses is thought to contribute to disease severity. Calcitriol plays an important role in modulating the immune response to viral infections. However, its unknown whether calcitriol can attenuate the inflammatory response elicited by H9N2 influenza virus infection.

Methods

Human lung A549 epithelial cells were treated with calcitriol (100 nM) and then infected with an H9N2 influenza virus, or infected and then treated with calcitriol (30 nM). Culture supernatants were collected every 24 h post infection and the viral growth kinetics and inflammatory response were evaluated. Calcitriol (5 mg/kg) was administered daily by intraperitoneal injection to BABL/c mice for 15 days following H9N2 influenza virus infection. Mice were monitored for clinical signs of disease, lung pathology and inflammatory responses.

Results

Calcitriol treatment prior to and post infection with H9N2 influenza significantly decreased expression of the influenza M gene, IL-6, and IFN-β in A549 cells, but did not affect virus replication. In vivo, we found that calcitriol treatment significantly downregulated pulmonary inflammation in mice 2 days post-infection, but increased the inflammatory response 4 to 6 days post-infection. In contrast, the antiviral cytokine IFN-β was significantly higher in calcitriol-treated mice than in the untreated infected mice at 2 days post-infection, but lower than in untreated infected mice on days 4 and 8 post-infection. The elevated levels of pro-inflammatory cytokines and the decreased levels of antiviral cytokine are consistent with the period of maximum body weight loss and the lung damage in calcitriol-treated mice.

Conclusions

These results suggest that calcitriol treatment might have a negative impact on the innate immune response elicited by H9N2 infection in mice, especially at the later stage of influenza virus infection. This study will provide some novel insights into the use of calcitriol to modulate the inflammatory response elicited by influenza virus infection in humans.

No Positive Association between Vitamin D Level and Immune Responses to Hepatitis B and Streptococcus pneumoniae Vaccination in HIV-Infected Adults

Objective

To assess whether higher 25-hydroxyvitamin D (25OHD) levels are associated with subsequent better immune responses to hepatitis B and Streptococcus pneumoniae vaccination in HIV-infected patients.

Methods

25OHD was measured on stored baseline plasma samples from two randomized vaccine trials in HIV-infected adults: the ANRS HB03 VIHVAC B trial and an immunological sub-study of the ANRS 114-PNEUMOVAC trial. In ANRS HB03 VIHVAC B, participants received three or four doses of recombinant HBV vaccine strategies. Anti-HBs IgG titers were measured four weeks after the last injection. Associations between baseline 25OHD levels and ordered IgG response categories were analyzed in multivariable proportional odds models. In the ANRS 114-PNEUMOVAC sub-study, two strategies of pneumococcal vaccination were tested, cellular immune responses were measured at repeated time points, and IgG responses four weeks after the last vaccine injection. Exploratory statistical analyses were performed on this sub-study data set.

Results

Three hundred and thirty-nine ANRS HB03 VIHVAC B and 25 ANRS 114-PNEUMOVAC sub-study participants were included in the analyses. Median age in each of the two studies was 43 years, 68% were male, and 77–92% on antiretroviral treatment. Median 25OHD level was 18 ng/mL (IQR: 12–25) and 24 ng/mL (IQR: 13–32) in the two trial populations, respectively. In the multivariable model, there was no significant association between baseline 25OHD level and vaccine responses in ANRS HB03 VIHVAC B (proportional odds ratio 0.83 per 10 ng/mL 25OHD increase; 95% confidence interval 0.65–1.07, p = 0.14). Exploratory analyses of ANRS 114-PNEUMOVAC showed consistent results.

Conclusion

This study does not support a positive association between 25OHD and immune responses to hepatitis B or pneumococcal vaccination in HIV-infected patients.

"English Disease": Historical Notes on Rickets, the Bone-Lung Link and Child Neglect Issues

Nutritional or classical rickets (here labeled as "rickets") is a worldwide disease involving mostly infants and young children having inadequate sunlight exposure, often associated with a low dietary intake of Vitamin D. Rickets targets all layers of society independently of economic status with historical information spanning more than two millennia. Vitamin D is critical for the absorption of calcium and prevention of rickets in children as well as osteomalacia in adults. The initial and misleading paradigm of the 19th and 20th centuries that rickets may have been the consequence of infection has been, indeed, reversed following the identification of the Vitamin D molecule's important role in the function of the immune system. Although traditionally considered limited to osteopathology, Vitamin D deficiency is now known to be linked to infection, inflammation, and carcinogenesis. In this review, we consider the key historical (Whistler, pre-Whistler and post-Whistler descriptors) and social facts around rickets; highlight the osteo-pathological features of rickets and the pathology of the upper and lower respiratory tract, stressing the fact that lungs remain the main secondary organ affected by Vitamin D deficiency; and emphasize the public health role in identifying the cases of child neglect or abuse based on the evaluation of the costochondral region.

Vitamin D levels and influenza vaccine immunogenicity among HIV-infected and HIV-uninfected adults

BACKGROUND

Vaccination is the most important preventive strategy against influenza, however post-vaccination antibody responses are often inadequate especially among HIV-infected persons. Vitamin D deficiency has been suggested to adversely influence immune responses and is highly prevalent among HIV-infected adults. Therefore, we evaluated the association between 25-hydroxyvitamin D [25(OH)D] levels and post-influenza vaccination responses.

METHODS

We conducted a prospective cohort study evaluating the immunogenicity of monovalent influenza A (H1N1) vaccination among both HIV-infected and HIV-uninfected adults (18-50years of age) during the 2009-2010 influenza season. Antibody titers were evaluated at baseline, day 28, and 6months post-vaccination using hemagluttination inhibition assays. Serum 25(OH)D levels were measured at day 28. Univariate and multivariate regression analyses examined the association between 25(OH)D levels [categorized as <20ng/ml (deficiency) vs. ⩾20ng/ml] with the primary outcome of seroconversion. Secondary outcomes included seroprotection; a ⩾4-fold increase in titers; and geometric mean titers post-vaccination. Analyses were repeated using 25(OH)D levels as a continuous variable.

RESULTS

A total of 128 adults [64 HIV-infected (median CD4 count 580cells/mm(3)) and 64 HIV-uninfected] were included. Seroconversion at day 28 post-vaccination was achieved in fewer HIV-infected participants compared with HIV-uninfected participants (56% vs. 74%, p=0.03). Vitamin D deficiency was more prevalent among HIV-infected persons vs. HIV-uninfected persons (25% vs. 17%), although not significantly different (p=0.39). There were no associations found between lower 25(OH)D levels and poorer antibody responses at day 28 or 6months for any of the study outcomes among either HIV-infected or HIV-uninfected adults.

CONCLUSION

Vitamin D deficiency was common among both HIV-infected and HIV-uninfected adults, but lower levels did not predict antibody responses after H1N1 (2009) influenza vaccination. Low 25(OH)D levels do not explain poorer post-vaccination responses among HIV-infected persons.

Role of vitamin D in cytotoxic T lymphocyte immunity to pathogens and cancer

The discovery of vitamin D receptor (VDR) expression in immune cells has opened up a new area of research into immunoregulation by vitamin D, a niche that is distinct from its classical role in skeletal health. Today, about three decades since this discovery, numerous cellular and molecular targets of vitamin D in the immune system have been delineated. Moreover, strong clinical associations between vitamin D status and the incidence/severity of many immune-regulated disorders (e.g. infectious diseases, cancers and autoimmunity) have prompted the idea of using vitamin D supplementation to manipulate disease outcome. While much is known about the effects of vitamin D on innate immune responses and helper T (T(H)) cell immunity, there has been relatively limited progress on the frontier of cytotoxic T lymphocyte (CTL) immunity--an arm of host cellular adaptive immunity that is crucial for the control of such intracellular pathogens as human immunodeficiency virus (HIV), tuberculosis (TB), malaria, and hepatitis C virus (HCV). In this review, we discuss the strong historical and clinical link between vitamin D and infectious diseases that involves cytotoxic T lymphocyte (CTL) immunity, present our current understanding as well as critical knowledge gaps in the realm of vitamin D regulation of host CTL responses, and highlight potential regulatory connections between vitamin D and effector and memory CD8 T cell differentiation events during infections.

"Let there be light": the role of vitamin D in the immune response to vaccines

Vitamin D's non-skeletal actions, including immunomodulatory role, have been increasingly recognized. Of significance, many immune cells are able to synthesize a biologically active form of vitamin D from circulating 25-hydroxyvitamin D with subsequent intracrine actions, and the vitamin D receptor is broadly distributed. In this review, we discuss vitamin D's potent role in innate and adaptive immune responses and published studies evaluating the impact of serum vitamin D, vitamin D gene pathway polymorphisms or empiric vitamin D supplementation on vaccine immunogenicity. We highlight existing knowledge gaps and propose the steps needed to advance the science and answer the question of whether vitamin D may prove valuable as a vaccine adjuvant for certain vaccines against infectious diseases.

Modulation of the immune response to respiratory viruses by vitamin D

Background: Vitamin D deficiency has been shown to be independently associated with increased risk of viral acute respiratory infection (ARI) in a number of observational studies, and meta-analysis of clinical trials of vitamin D supplementation for prevention of ARI has demonstrated protective effects. Several cellular studies have investigated the effects of vitamin D metabolites on immune responses to respiratory viruses, but syntheses of these reports are lacking. Scope: In this article, we review the literature reporting results of in vitro experiments investigating immunomodulatory actions of vitamin D metabolites in human respiratory epithelial cells infected with respiratory viruses. Key findings: Vitamin D metabolites do not consistently influence replication or clearance of rhinovirus, respiratory syncytial virus (RSV) or influenza A virus in human respiratory epithelial cell culture, although they do modulate expression and secretion of type 1 interferon, chemokines including CXCL8 and CXCL10 and pro-inflammatory cytokines, such as TNF and IL-6. Future research: More studies are needed to clarify the effects of vitamin D metabolites on respiratory virus-induced expression of cell surface markers mediating viral entry and bacterial adhesion to respiratory epithelial cells.

Can we translate vitamin D immunomodulating effect on innate and adaptive immunity to vaccine response?

Vitamin D (VitD), which is well known for its classic role in the maintenance of bone mineral density, has now become increasingly studied for its extra-skeletal roles. It has an important influence on the body’s immune system and modulates both innate and adaptive immunity and regulates the inflammatory cascade. In this review our aim was to describe how VitD might influence immune responsiveness and its potential modulating role in vaccine immunogenicity. In the first instance, we consider the literature that may provide molecular and genetic support to the idea that VitD status may be related to innate and/or adaptive immune response with a particular focus on vaccine immunogenicity and then discuss observational studies and controlled trials of VitD supplementation conducted in humans. Finally, we conclude with some knowledge gaps surrounding VitD and vaccine response, and that it is still premature to recommend “booster” of VitD at vaccination time to enhance vaccine response.

Does vitamin D protect against respiratory viral infections?

The active form of vitamin D has effects on both innate and adaptive immune responses that may influence the outcome in many infectious diseases. Observational studies conclusively show that a low vitamin D status is associated with an increased occurrence of respiratory viral infections, which globally represent significant health and financial burdens. However, no consistent protective effects are evident in prospective clinical trials carried out to date where vitamin D was provided as a dietary supplement, except possibly in cases where the starting vitamin D status of the individual was considered deficient. Thus far, vitamin D has not been found to enhance the immune response to vaccines. The design of future prospective clinical trials assessing a role for vitamin D in respiratory viral infections requires very careful planning to avoid the uncertainties associated with the data available currently.

Serum 25-hydroxyvitamin d level and influenza vaccine immunogenicity in children and adolescents

Background

Vaccination is an important strategy in the prevention of influenza, but immunologic response to vaccination can vary widely. Recent studies have shown an association between serum 25-hydroxyvitamin D (25[OH]D) levels and immune function. The purpose of this study was to determine if serum 25(OH)D level correlates with influenza vaccine immunogenicity in children and adolescents.

Methods

We conducted a prospective cohort study of children age 3 to 15 years of age vaccinated with trivalent influenza vaccine (A/Brisbane/59/2007[H1N1]-like virus, A/Brisbane/10/2007 [H3N2]-like virus and B/Florida/4/2006-like virus) in Hutterite communities in Alberta, Saskatchewan and Manitoba. Serum 25(OH)D levels were measured at baseline and immunogenicity was assessed using hemagluttination inhibition (HAI) titers done at baseline and 3–5 weeks post vaccination. Logistic regression was used to assess the relationship between serum 25(OH)D level as both a continuous and dichotomous variable and seroprotection, seroconversion, fold increase in geometric mean titer (GMT) and post vaccination titer.

Results

A total of 391 children and adolescents were included in the study and 221 (57% had post-vaccination HAI titers. The median serum 25(OH)D level was 61.0 nmol/L (Interquartile range [IQR] 50.0, 71.0). No relationship was found between serum 25(OH)D level and seroprotection (post-vaccination titer ≥40 and ≥320) or seroconversion (post-vaccination titer ≥40 for participants with pre-vaccine titer <10 or four-fold rise in post-vaccination titer for those with a pre-vaccine titer ≥10).

Conclusion

Serum 25(OH)D level was not associated with influenza vaccine immunogenicity in otherwise healthy children and adolescents. Other strategies to enhance influenza vaccine response should continue to be evaluated in this population.

The role of serum 25(OH)D level in vaccine responsiveness in other populations, especially those hyporesponsive to influenza vaccination, requires further study.

Immune response after a single dose of the 2010/11 trivalent, seasonal influenza vaccine in HIV-1-infected patients and healthy controls

BACKGROUND

Immune response rates following influenza vaccination are often lower in HIV-infected individuals. Low vitamin D levels were correlated with weak immune response in cancer patients and are known to be lower in HIV-infected patients.

METHODS

Diagnostic study to determine immune response against the H1N1v component after a single, intramuscular dose of the 2010/11 seasonal, trivalent influenza vaccine (TIV) in adult HIV-infected and healthy controls scheduled for influenza vaccination (ClinicalTrials.gov Identifier: NCT01017172). Influenza A/H1N1 antibody titers (AB) were determined before and 21 days after vaccination by hemagglutination inhibition assay.

RESULTS

Immune response was not different between HIV-infected patients (n = 36) and healthy controls (n = 42) who were previously naïve to the H1N1v component of the TIV. Comparing HIV-infected patients (n = 55) and healthy controls (n = 63) who had received 1 or 2 doses of an AS03 adjuvanted H1N1 vaccine in the previous winter season (2009/10), seroconversion rate and the geometric mean AB titer after TIV of the HIV-infected patients were more than twice as high compared to healthy controls. This difference was mainly driven by the 2-dose schedule for HIV patients in 2009/10. Vitamin D levels were lower in HIV patients but did not correlate with immune response.

CONCLUSION

HIV-infected patients who had received 1 or 2 doses of an adjuvanted H1N1 vaccine in the previous year (2009/10) had a significant higher seroconversion rate following TIV as compared to healthy controls, indicating a stronger memory cell response due to the 2-dose schedule.

How important is vitamin D in preventing infections?

Interaction with the immune system is one of the most recently established nonclassic effects of vitamin D (VitD). For many years, this was considered to be limited to granulomatous diseases in which synthesis of active 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) or calcitriol is known to be increased. However, recent reports have supported a role for 1,25(OH)2D3 in promoting normal function of the innate and adaptive immune systems. Crucially, these effects seem to be mediated not only by the endocrine function of circulating calcitriol but also via paracrine (i.e., refers to effects to adjacent or nearby cells) and/or intracrine activity (i.e., refers to a hormone acting inside a cell) of 1,25(OH)2D3 from its precursor 25(OH)D3, the main circulating metabolite of VitD. The ability of this vitamin to influence human immune responsiveness seems to be highly dependent on the 25(OH)D3 status of individuals and may lead to aberrant response to infection or even to autoimmunity in those who are lacking VitD. The potential health significance of this has been underlined by increasing awareness of impaired status in populations across the globe. This review will examine the current understanding of how VitD status may modulate the responsiveness of the human immune system. Furthermore, we discuss how it may play a role in host resistance to common pathogens and how effective is its supplementation for treatment or prevention of infectious diseases in humans.

Vitamin D is not associated with serologic response to influenza vaccine in adults over 50 years old

Vitamin D deficiency has been implicated in risk of respiratory illness. We determined whether serum vitamin D levels are related to influenza vaccine response measured by hemagglutination antibody inhibition (HAI) titer in adults aged ≥50 years old. The study was a prospective cohort study conducted over two influenza seasons (fall 2008-spring 2009 and fall 2009-spring 2010) in Marshfield, WI and Nashville, TN including 1103 community-dwelling adult volunteers ≥50 years of age. Pre-vaccination levels of serum vitamin D and HAI titer levels pre- and 21-28 days post-influenza vaccination were measured. Seroprotection was defined as HAI ≥40; seroconversion was defined as ≥4-fold rise in HAI titers from pre- to post-vaccination. More than 25% of participants were vitamin D deficient (<25ng/mL). Vitamin D measured as a continuous variable was not related to pre- or post-vaccination seroprotection or seroconversion for any vaccine strain in any year. Vitamin D deficiency was associated with a greater frequency of post-vaccination seroprotection for seasonal H1N1 in the first year of the study, but was not related to seroprotection or seroconversion for any other strain in either year. No consistent association was found between vitamin D levels or vitamin D deficiency and serologic response to influenza vaccination in older adults. Cell-mediated immune parameters should also be explored in order to further investigate possible relationships between micronutrient status and influenza vaccine response.

Impact of vitamin D administration on immunogenicity of trivalent inactivated influenza vaccine in previously unvaccinated children

As vitamin D (VD) has a significant regulatory effect on innate and adaptive immunity, the aim of this prospective, randomized, single-blinded, placebo-controlled study was to measure the impact of VD administration on the immune response to trivalent influenza vaccination (TIV). A total of 116 children (61 males, 52.6%; mean age 3.0 ± 1.0 y) with a history of recurrent acute otitis media (AOM), who had not been previously vaccinated against influenza, were randomized to receive daily VD 1,000 IU or placebo by mouth for four months. All of them received two doses of TIV (Fluarix, GlaxoSmithKline Biologicals) one month apart, with the first dose administered when VD supplementation was started. There was no difference in seroconversion or seroprotection rates, or antibody titers, in relation to any of the three influenza vaccine antigens between the VD and placebo groups, independently of baseline and post-treatment VD levels. The safety profile was also similar in the two groups. These data indicate that the daily administration of VD 1,000 IU for four months from the time of the injection of the first dose of TIV does not significantly modify the antibody response evoked by influenza vaccine.

Vitamin D and influenza

Vitamin D has become increasingly recognized in the literature for its extra-skeletal roles, including an effect on inflammation and the immune response to infection. Our goal was to describe the role of vitamin D in the immune response and implications for the risk of influenza infection in humans. In this review, we first consider literature that provides molecular and genetic support to the idea that vitamin D is related to the adaptive and innate immune responses to influenza infection in vitro and in animal models. We then discuss observational studies and randomized controlled trials of vitamin D supplementation in humans. Finally, we consider some of the knowledge gaps surrounding vitamin D and immune response that must be filled.