The link between blood levels of vitamin D and the strength of the immune system is much debated. A recent Israeli study examined the link between low vitamin D levels and the severity of COVID-19. In line with laboratory data, clinical studies have found an association between low 25-hydroxyvitamin D (25(OH)D) levels and an increased risk of flu and respiratory viruses. As with other respiratory infections, there is an emerging link between low blood levels of vitamin D and COVID-19 infection in COVID-19 infections. Low serum 25(OH)D levels in hospitalized COVID-19 patients were also associated with increased disease severity and worse clinical outcomes in this study. In addition, it was shown that the hospitalized COVID-19 patients studied had lower mean vitamin D levels than the general population and outpatient COVID-19 patients.

PLOS ONE | https://doi.org/10.1371/journal.pone.0263069 February 3, 2022 1 / 18Covid-19-PatientenPre-infection 25-hydroxyvitamin D3 levels and association with severity of COVID-19 illness

Amiel A. DrorID1,2*, Nicole MorozovID3, Amani Daoud1,2, Yoav Namir2, Orly Yakir4, Yair Shachar1, Mark Lifshitz5, Ella Segal1,2, Lior Fisher1,2, Matti Mizrachi1,2, Netanel Eisenbach1,2, Doaa Rayan1,2, Maayan Gruber1,2, Amir Bashkin2,6,
Edward Kaykov2,7, Masad Barhoum8, Michael Edelstein2, Eyal Sela1,2 

You can access the article here.