Vitamin D supplementation and risk of respiratory tract infections: A meta-analysis of randomized controlled trials

Background: It is well-documented that serum levels of 25-hydroxyvitamin D (25-OHD) are inversely associated with the risk of respiratory tract infections (RTIs). However, whether or not vitamin D supplementation prevents RTIs remains inconclusive. The aim of this study was to evaluate the role of vitamin D supplementation in preventing RTIs in healthy populations by performing a meta-analysis of randomized controlled trials (RCTs). Methods: RCTs regarding the association between vitamin D supplementation and the risk of RTIs were identified by searching PubMed, Embase, and Cochrane databases through January 2013. Reference lists of retrieved articles were also reviewed. Either a fixed-effects or, in the presence of heterogeneity, a random-effects model was used to calculate the pooled preventive effects. Results: Seven RCTs involving 4827 participants were included in this meta-analysis. The pooled relative risk (RR) for subjects administered with vitamin D compared with control groups was 0.98 (95% confi dence interval 0.93-1.03, p = 0.45). Meta-regression analyses showed almost no impact on the RR of age, vitamin D dosing regimen, and length of follow-up. Omission of any single trial had little impact on the pooled risk estimates. No evidence of publication bias was observed. Conclusions: Our findings do not support the routine use of vitamin D supplementation for RTI prevention in healthy populations. Larger studies are needed to investigate the effects of vitamin D supplementation on RTI prevention in various populations and to further clarify the influences of age, vitamin D dosing regimen, baseline levels of vitamin D, and study length.