evidence: We found that the associated reduction in COVID-19 infection risk was inversely proportional to vitamin D serum levels (0–19 ng/ml: HR = 0.70, [95% CI 0.64, 0.76] versus 20–39 ng/ml: HR = 0.81, [95% CI 0.77, 0.85] versus 40 + ng/ml: HR = 0.86, [95% CI 0.80, 0.92]); see Table 3. The overall treatment by vitamin D serum level interaction was significant (HR = 1.12, [95% CI 1.06, 1.18]) reflecting a 12% increase in the hazard ratio (smaller treatment related effect) with each increase in serum level category. [...] Chiodini, I. et al. Vitamin D status and SARS-CoV-2 infection and COVID-19 clinical outcomes. Front. Public Health.9, 736665. https://doi.org/10.3389/fpubh.2021.736665 (2021). [...] Stroehlein, J. K. et al. Vitamin D supplementation for the treatment of COVID-19: A living systematic review. Cochrane Database Syst. Rev.5, CD015043. https://doi.org/10.1002/14651858.CD015043 (2021).