COVID-19 Mortality Risk Correlates Inversely with Vitamin D3 Status AND Vitamin D is a main regulator of those cells. A low level of the vitamin means a greater risk for a cytokine storm.

https://www.lifesitenews.com/opinion/thousands-of-americans-might-not-have-died-from-covid-if-govt-had-promoted-vitamin-d/

A main cause of a severe reaction from COVID results from a “cytokine storm.”

This refers to the body’s immune system releasing too many toxic cytokines as part of the inflammatory response to the virus.

Vitamin D is a main regulator of those cells.

A low level of the vitamin means a greater risk for a cytokine storm.

This is especially pertinent for lung problems from COVID.
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https://www.mdpi.com/2072-6643/13/10/3596/htm

COVID-19 Mortality Risk Correlates Inversely with Vitamin D3 Status, and a Mortality Rate Close to Zero Could Theoretically Be Achieved at 50 ng/mL 25(OH)D3: Results of a Systematic Review and Meta-Analysis