The immunomodulatory and antiviral function of vitamin D

Recently, scientists reviewed the available literature to higher understand vitamin D’s immunomodulatory and antiviral function.

The study explores how vitamin D influences the pediatric respiratory system after acute respiratory tract infections (ARTI), comparable to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which is the causal agent of the continued coronavirus disease 2019 (COVID-19) pandemic. This review is offered in Nutrients.

Study: Immunomodulatory Effects of Vitamin D in Respiratory Tract Infections and COVID-19 in Children. Image Credit: YuliaFurman/Shutterstock.com

Background

Children often develop ARTI, which accounts for 20% of all pediatric fatalities. There are two subsets of ARTI: upper respiratory tract infections (URTIs) and lower respiratory tract infections (LRTIs).

Most URTIs are related to viral infection attributable to rhinovirus, SARS-associated coronavirus, enterovirus, influenza virus, and respiratory syncytial virus. Bronchiolitis and pneumonia are the 2 most typical LRIs in children.

SARS-CoV-2 infection in children has manifested a big selection of symptoms, i.e., from asymptomatic to severe infection. Although most kids with COVID-19 have been asymptomatically infected, a small number of kids developed severe types of multisystem inflammatory syndrome in children (MIS-C).

A really limited amount of evidence has been documented regarding the SARS-CoV-2 disease within the pediatric population worldwide. 

Vitamin D is an important micronutrient that’s related to immune function. It will possibly stimulate innate immunity, reduce the production of helper T lymphocytes (type 1), and improve the proliferation of type 2 and regulatory T lymphocytes.

Moreover, vitamin D helps decrease the pro-inflammatory cytokines (e.g., IL1, IL6, IL12, TNFα, and IL17) and interferon γ, and increase IL10 (anti-inflammatory cytokines) via NFkβ metabolic pathway.

In regards to the study

Although several studies have shown that children with vitamin D deficiency are more prone to ARTI, the scientific community doesn’t fully accept this statement.

This review focussed on understanding whether there may be a link between ARTIs and vitamin D supplementation. 

All relevant articles were obtained from PubMed. This review included every type of free articles published in English, comparable to clinical trials, systematic reviews, and meta-analyses.

The targeted population was children under 19 years of age. This review excluded studies with small sample sizes, i.e., lower than 100 participants, and non-peer-reviewed articles. 

This systematic review used the Patient, Intervention, Comparison, and Final result (PICO) framework.

A complete of 518 citations were obtained after the initial search; nonetheless, 27 studies fulfilled all inclusion criteria and were considered on this review.

Study findings

25(OH)D is the key circulating vitamin D form exhibiting antiviral properties through antimicrobial peptides. Monocytes and macrophages expressing CYP27B1 (1-α hydroxylase) enable the conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol.

Calcitriol is an energetic vitamin D form that’s crucial in limiting pathogenic presence. Previous studies have shown that vitamin D enhances nitric oxide production, which is linked to the antioxidative effect of 25OHD. Vitamin D receptor (VDR) and CYP27B1 have been detected in considerable amounts in cells and tissues.

Most studies indicated a strong association between VD status and the incidence of ARTIs, including COVID-19 infections. These studies revealed that vitamin D levels were inversely related to the severity of COVID-19.

A limited variety of studies contradicted this finding and reported no correlation between vitamin D deficiency (VDD) and the next prevalence of SARS-CoV-2 infection.

In contrast, one other study demonstrated VD’s prospective protective and preventative function against COVID-19. An elevation in inflammatory markers occurs when vitamin D serum concentrations decrease.

Quite a few aspects are related to VD’s ability to forestall ARTIs. For example, 25 hydroxyvitamin D enhances the synthesis of natural antibodies.

As well as, it improves immunity by promoting monocyte differentiation and stopping lymphocyte production. VD also enhances the phagocytic activity of macrophages. Subsequently, many studies have indicated that VD intake lowers the danger of severe SARS-CoV-2 infection.

A meta-analysis considered around 4786 children to find out the efficacy of vitamin D supplementation together with antibiotics to treat pneumonia. A better vitamin D concentration lowered the danger of recurring pneumonia.

One other study indicated that 25(OH)D concentration higher than 75.0 nmol/L significantly lowered the danger of acute pneumonia. A survey showed that 1/5 of kids hospitalized on account of pneumonia were VDD. Babies under three years old diagnosed with pneumonia subjected to 100,000 IU of VD3 almost eliminated the danger of reoccurrence.

In some cases, young patients with COVID-19 required hospitalization, and vitamin D was measured from this group with out a baseline measurement. This has generated conflicting interpretations about causality.

A previous study reported reverse causality with the expression CYP24A1, which increased SARS-CoV-2 infection. Subsequently, more research is required to elucidate how VD influences COVID-19. 

Conclusions

Although systematic reviews and meta-analyses have indicated that a lower level of 25(OH)D enhances the danger of developing ARTI in children, the experimental findings sometimes contradict this statement.

There was a growing consensus that serum VD needs to be maintained above 75 nmol/L to keep up overall health. To avoid VDI in all age groups, dietary VD intake and VD supplements have been beneficial.