Impact of vitamin D supplementation on the clinical outcomes of COVID-19 pneumonia patients: a single-center randomized controlled trial

Background: Vitamin D supplementation for infectious diseases has been discussed, but its role in COVID-19 is unclear. Therefore, this study examined the clinical outcomes of COVID-19 pneumonia patients who received vitamin D supplementation. Methods: This prospective, open-label, randomized controlled trial was conducted in a university hospital between July 2020 and March 2022. The inclusion criteria were patients aged ≥ 18 years with COVID-19 pneumonia patients. The patients were randomized into two groups: an intervention group receiving vitamin D supplementation (alfacalcidol, two mcg orally daily) until discharge and a control group. The clinical outcomes were pneumonia treatment duration, length of hospital stay, and change in pneumonia severity index between enrollment and discharge. Subgroup analysis was conducted for supplemental oxygen use, high-dose corticosteroid administration, evidence of lymphopenia, C-reactive protein concentration, and total serum vitamin D concentration. Adverse events were monitored. Results: Two hundred ninety-four patients were recruited (147 per group). The two groups did not differ in pneumonia treatment duration to discharge (p = 0.788) or length of hospital stay (p = 0.614). The reduction in the pneumonia severity index between enrollment and discharge was more significant in the intervention group (p = 0.007); a significant decrease was also observed among patients who had C-reactive protein > 30 mg/L (p < 0.001). No adverse reactions were recorded. Conclusions: Adding active vitamin D to standard treatment may benefit COVID-19 pneumonia patients who require supplemental oxygen or high-dose corticosteroid therapy or who have high C-reactive protein concentrations (> 30 mg/L) upon treatment initiation. Trial registration: Thai Clinical Trials Registry TCTR20210906005 (retrospectively registered, 6 September 2021).