Jolliffe DA, Camargo CA, Sluyter JD, et al. - By conducting this updated meta-analysis, researchers assessed the association between vitamin D supplementation and prevention of acute respiratory infections (ARIs). Relevant studies were identified from MEDLINE, Embase, the Cochrane Central Register of Controlled Trials, Web of Science, and the ClinicalTrials.gov registry. Eligible double-blind randomized controlled trials of vitamin D ₃ , vitamin D ₂ , or 25-hydroxyvitamin D supplementation for any length of time, with a placebo or low-dose vitamin D control, were included. Although significant heterogeneity was evident across trials, findings demonstrated the safety of vitamin D supplementation as well as an overall decrease in the risk of ARI resulting from this intervention vs placebo, although the risk reduction was small. Use of daily doses of 400–1000 IU for up to 12 months and age at enrolment of 1.00–15.99 years were both were correlated with protection. The relevance of these observations to COVID-19 is unknown.