Research progress on the role of vitamin D supplementation in adjuvant therapy for COVID-19

The pandemic caused by coronavirus disease of 2019 （COVID-19） has brought severe challenges to public health all over the world. Vitamin D plays an important role in immune regulation and anti-respiratory virus infection as an immune enhancer. Several studies have demonstrated that vitamin D can regulate the angiotensin-converting enzyme 2/angiotensin （1-7）/Mas receptor axis signaling pathway， inhibit the over-activation of renin-angiotensin system signal， fight against SARS-CoV-2 infection and suppress the production of inflammatory cytokine storm， thereby reducing the risk of pneumonia infection and improving acute respiratory distress syndrome， cardiogenic obstruction and thrombosis in COVID-19 patients. In this article， the mechanism of vitamin D in reducing the risk of SARS-CoV-2 infection and mitigating clinical symptoms was reviewed. It is hypothesized that vitamin D plays a critical role in the prevention or adjuvant therapy for novel coronavirus pneumonia and alleviating clinical manifestations in COVID-19 patients.