Effect of vitamin D supplementation on the immune response to respiratory tract infections and inflammatory conditions: A systematic review and meta-analysis

Context

Vitamin D acts as an immune modulator, by downregulating the production of inflammatory immune markers and upregulating the production of anti-microbial peptides and anti-inflammatory markers. Hence, vitamin D may be useful in improving the immune response against respiratory tract diseases.

Objective

A systematic review (following PRISMA guidelines) and meta-analysis were performed to study the effect of vitamin D supplementation on the immune response to respiratory tract diseases irrespective of population type.

Data sources

Electronic search engines Pubmed, Pubmed Central, Google Scholar, Clinicaltrials.gov, Clinical Trial Registry India, ScienceDirect, and Web of Science were searched for relevant articles.

Data extraction

Sixteen RCTs were eligible for inclusion. Jadad scale was used to assess the quality of studies. Methods of the selected studies were assessed using the Cochrane Risk of Bias assessment. Using the random-effects model meta-analysis was performed if at least three articles studied similar immune markers. Thus, IL-6, cathelicidin, CRP, TNF alpha, and IFN gamma, were included in the analysis. In all 16 articles were included for qualitative assessment, and 14 articles for meta-analysis.

Data analysis

There was a significant decrease in CRP levels after intervention with an overall effect of Z = 3.37 (P < 0.00). The observed increase in IL-10 levels was not significant with an overall effect of Z = 0.84 (p = 0.40). There was no significant decrease in IL6 [Z = 0.59 (P = 0.56)], and interferon-gamma levels [Z = 1.70 (p = 0.09)]. Secondary outcomes including mortality, and length of hospital stay did not show a significant difference in the intervention group.

Conclusion

Among the biomarkers studied CRP significantly decreased, with no significant changes in the others. Our findings suggest that vitamin D supplementation modestly affects the immune response. Pooling infectious and non-infectious respiratory diseases could have underestimated our findings. More RCTs are warranted to obtain substantial results.