Abstract
- Background
Vitamin D acts as an immune modulator by downregulating the production of inflammatory immune markers and upregulating the production of antimicrobial peptides and anti-inflammatory markers. Hence, vitamin D may be useful in improving the immune response against respiratory tract diseases. The objective of this systematic review (following PRISMA guidelines) and meta-analysis was to study the effect of vitamin D supplementation on the immune response to respiratory tract diseases, irrespective of population type.
- Methods
Electronic search engines (PubMed, PubMed Central, Google Scholar, ClinicalTrials.gov, Clinical Trial Registry India, ScienceDirect, and Web of Science) were searched for relevant articles. Sixteen randomized controlled trials ($\text{RCTs}$) were eligible for inclusion. The Jadad scale was used to assess study quality, and the Cochrane Risk of Bias tool was used to assess methodology. Using a random-effects model, meta-analysis was performed for immune markers evaluated in at least three articles ($\text{IL-6}$, cathelicidin, $\text{CRP}$, $\text{TNF-}\alpha$, and $\text{IFN-}\gamma$). In total, 16 articles were included for qualitative assessment and 14 for meta-analysis.
- Results
There was a significant decrease in $\text{CRP}$ levels after intervention with an overall effect of $Z = 3.37$ ($p < 0.001$). The observed increase in $\text{IL-10}$ levels was not significant ($Z = 0.84$, $p = 0.40$). There was no significant decrease in $\text{IL-6}$ ($Z = 0.59$, $p = 0.56$) or interferon-gamma ($\text{IFN-}\gamma$) levels ($Z = 1.70$, $p = 0.09$). Secondary outcomes, including mortality and length of hospital stay, did not show significant differences in the intervention group.
- Conclusions
Among the biomarkers studied, $\text{CRP}$ significantly decreased, with no significant changes in the others. Findings suggest that vitamin D supplementation modestly affects the immune response. Pooling infectious and non-infectious respiratory diseases could have underestimated the findings. More $\text{RCTs}$ are warranted to obtain substantial results.
https://www.sciencedirect.com/science/article/pii/S2666149724000343