Mardani, R., et al. “Association of vitamin D with the modulation of the disease severity in COVID-19.” Virus Research (2020): 198148.
This is now the 20th study (and here’s a list of the other 19) confirming that higher blood levels of Vitamin D reduce Covid-19 risks. In this study, those testing negative for Covid-19 had average blood levels of Vitamin D of 30.19 ng/ml; those testing positive had an average at 19.25 ng/ml (which is insufficiency), and those who DIED from Covid-19 had a level of 8.175 ng/ml on average (which is deficiency). The conclusion is that Vitamin D deficiency makes persons more likely to have a severe case and more likely to die from Covid-19, and that normal levels of vitamin D, 30 ng/ml and over, are protective: you are less likely to get Covid-19, less likely to have a severe case, and less likely to die. And 19 other studies back up this result.
Grant, William B., et al. “Evidence that vitamin D supplementation could reduce risk of influenza and COVID-19 infections and deaths.” Nutrients 12.4 (2020): 988.
— “To reduce the risk of infection, it is recommended that people at risk of influenza and/or COVID-19 consider taking 10,000 IU/d of vitamin D3 for a few weeks to rapidly raise 25(OH)D concentrations, followed by 5000 IU/d…. For treatment of people who become infected with COVID-19, higher vitamin D3 doses might be useful.”
Ronald L Conte Jr
I am not a physician or healthcare professional.