Vitamin D supplementation and Covid-19 outcomes: A systematic review, meta-analysis and meta-regression

Vitamin D has many protective properties and potential role against acute lung injury. Low serum vitamin D is associated with high risk of pneumonia and development of acute respiratory distress syndrome. This study sought to analyse the efficacy of vitamin D in improving the outcomes of coronavirus disease 2019 (Covid-19) patients. Using specific keywords, we comprehensively searched the potential articles on PubMed, Europe PMC and ClinicalTrials.gov database until 8th May 2021. All published studies on Covid-19 and vitamin D were retrieved. Statistical analysis was conducted using Review Manager 5.4 software. A total of 11 studies with 22,265 Covid-19 patients were included in the meta-analysis. Our data suggested that vitamin D supplementation was associated with reduction in intensive care unit admission rate (OR 0.27; 95% CI: 0.09-0.76, p = 0.010, I-2 = 70%, random-effect modelling); reduction of the need for mechanical ventilation (OR 0.34; 95% CI: 0.16-0.72, p = 0.005, I-2 = 61%, random-effect modelling) and reduction of mortality from Covid-19 (OR 0.37; 95% CI: 0.21-0.66, p < 0.001, I-2 = 50%, random-effect modelling). Further analysis showed that the associations were influenced by age (p = 0.020). Our study suggests that vitamin D supplementation may offer beneficial effects on Covid-19 outcomes. However, more randomized clinical trials are required to confirm this conclusion.