This article, which is still in preprint form, shows a possible role in vitamin D suppressing C-reactive protein (CRP), which is a marker of cytokine storm. Cytokine storm is a mechanism by which an inflammatory response can become overwhelming and deleterious for the body. It is a feature of severe influenza and Covid-19
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Daneshkhah, Ali, Vasundhara Agrawal, Adam Eshein, Hariharan Subramanian, Hemant Kumar Roy, Vadim Backman. “The Possible Role of Vitamin D in Suppressing Cytokine Storm and Associated Mortality in COVID-19 Patients." medRxiv (2020): 2020.04.08.20058578. doi: https://doi.org/10.1101/2020.04.08.20058578