Association of Vitamin D with severity and outcome of COVID-19: Clinical and Experimental Evidence oleh Georgios Renieris, Spyros Foutadakis, Theano Andriopoulou, Victoria-Marina Spanou, Dionysia-Eirini Droggiti, Dionysios Kafousopoulos, Theologia Gkavogianni, Georgia Damoraki, Giannis Vatsellas, Evangelos J. Giamarellos-Bourboulis