This study by several Iranian research institutes investigated the connection between vitamin D levels and the severity of COVID-19 infections. 123 people participated in this study, including 63 COVID-19 patients and 60 healthy participants. The study showed that COVID-19 patients had significantly lower vitamin D levels and a significantly higher number of ACE receptors, the virus receptors for entering the cell. The researchers concluded that a sufficient amount of vitamin D can benefit patients with COVID-19 infections. More details can be found in the study.
Mardani et al.