Efficacy of Vitamin D Supplements in Treatment of Acute Respiratory Infection: A Meta-analysis for Randomized Controlled Trials

Background: Recent randomized controlled trials (RCTs) have reported inconsistent findings regarding the efficacy of vitamin D supplementation in the treatment of acute respiratory infections (ARIs). This study aimed to investigate the efficacy of vitamin D supplementation in the treatment of ARIs using a meta-analysis of RCTs. Methods: PubMed, EMBASE, and the Cochrane Library were searched for relevant articles in June 2021. Two of the authors independently assessed the eligibility of the trials. Results: Out of 390 articles retrieved from the databases, we included 18 RCTs, which involved 3648 participants, with 1838 in an intervention group and 1810 in a control group in the final analysis. In the meta-analysis of all the trials, vitamin D supplements had a beneficial effect in the treatment of ARIs (relative risk (RR) = 1.07; 95% confidence interval (CI), 1.01–1.13; I² = 66.9%). Publication bias was observed in the funnel plot. In the subgroup meta-analysis of high-quality RCTs, no significant efficacy of vitamin D supplements was found (RR = 1.02; 95% CI, 0.98–1.06; I² = 24.0%). Although statistically significant changes of 7% in the treatment effects were observed, they are not considered as clinically substantial ones. Conclusions: The current meta-analysis suggests that vitamin D supplements are not clinically effective in the treatment of ARIs.