It has been proposed that the activation of the vitamin D receptor (VDR) signaling pathway may generate beneficial effects in ARDS [
11] by decreasing the cytokine/chemokine storm, regulating the renin‑angiotensin system, modulating neutrophil activity and by maintaining the integrity of the pulmonary epithelial barrier, stimulating epithelial repair and tapering down the increased coagulability [
12,
13,
14,
15,
16]. Recently, two ecological studies have reported inverse correlations between national estimates of vitamin D status and the incidence and mortality of IDOC-19 in European countries [
17,
18]; lower concentrations of circulating 25 (OH) D have also been reported to be associated with susceptibility to SARS-CoV-2 infection [
19] and the severity of the evolution of COVID-19 [
20]. Vitamin D deficiency is frequent in wintertime even in Southern Spain [
21] and even more so in patients requiring ICU treatment [
22].