Abstract: Introduction: Coronavirus 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus-2. The majority of patients have at most mild symptoms, however, a significant proportion develops respiratory failure. COVID-19 may also progress beyond the lungs. Coagulopathy and thromboembolism are prevalent in severe COVID-19 and relate to decreased survival. Coagulation is an intricate balance between clot promoting and dissolving processes in which vitamin K plays a well-known role. We hypothesized that vitamin K status is reduced in patients with severe COVID-19. Methods: Vitamin K status was assessed by measuring desphospho-uncarboxylated matrix Gla protein (dp-ucMGP; inversely related to vitamin K status) and the rate of elastin degradation by measuring desmosine. We included 123 patients who were admitted with COVID-19 and 184 controls. Results: Dp-ucMGP levels were significantly elevated in COVID-19 patients (1,673Å}1,584 pmol/L) compared to controls (536±291 pmol/L; p<0.0005). Dp-ucMGP levels were significantly higher in COVID-19 patients with unfavorable outcome compared to those with less severe disease. Furthermore, dp-ucMGP and desmosine levels were significantly associated (r=0.65; p<0.0005). Conclusions: Vitamin K status was reduced in patients with COVID-19 and related to poor prognosis. Also, low vitamin K status seems to be associated with accelerated elastin degradation. An intervention trial is now needed to assess whether vitamin K administration improves outcome in patients with COVID-19.