Current opinion on the role of vitamin D supplementation in respiratory infections and asthma/COPD exacerbations: A need to establish publication guidelines for overcoming the unpublished data.

BACKGROUND & AIMS: The role of prophylactic vitamin D supplementation in prevention and treatment of respiratory infections and other related pathologies has been extensively explored with conflicting results. The aim of this systematic review and meta-analysis was to evaluate the prophylactic and therapeutic effects of vitamin D administration on respiratory infections. METHODS: A systematic search was performed and randomized controlled trials (RCTs) of vitamin D supplementation and a total of 65 RCTs involving 50,554 participants were included. RESULTS: The overall incidence of respiratory infections in terms of count data (OR: 0.87; 95%CI [0.80-0.95]; p = 0.0028; I2 = 43%) and event rate (IRR: 0.81; 95%CI [0.70-0.95]; p = 0.010; I2 = 79%) was significantly reduced in the intervention group. However, no effect of vitamin D on duration or upper respiratory tract infection severity was observed following the overall analysis. Subgroup analyses revealed more details regarding the protective effect of particular dose ranges, administration frequencies and trial durations on different disease types. CONCLUSIONS: Despite between-study heterogeneity was high for most outcomes and publication bias may have led to an effect size overestimation of incidence count data, vitamin D supplementation could be beneficial in improving resistance to overall respiratory infections, particularly when administered on a daily basis.