It is looking like Vitamin D may have a big effect on Covid-19 progression and mortality. Recent studies have been done that looked previously done Vitamin D research on blood levels of D and compared this info with Covid-19 mortality rates yielded some interesting information.
Vitamin D is naturally produced in the skin as a result of UVB sunlight exposure. It goes from the skin to the liver where it is changed into an active hormone that help calcium uptake which leads to strong bones and fights osteoporosis.
It is also good for the immune system and is active in pathways that can help fight the SARS-CoV-2 virus. In countries that have the highest level if Vitamin D supplementation, typically where sunlight is low and the population must supplement and thereby have high D levels, the relationship between D levels and death is looking statistically significant. This is proposed to be because Vitamin D helps the immune system by working to suppress the cytokine inflammatory response. The cytokine response is what kicks the Coviid illness into high gear by causing respiratory distress, often leading to ventilation and sadly, often times death. There are currently governments discussing raising minimum Vitamin D supplementation recommendations as a result of these findings.
The current recommended daily amount of vitamin D is 400 international units (IU) for children up to age 12 months, 600 IU for ages 1 to 70 years, and 800 IU for people over 70 years or approximately 10-20 micrograms. Personally, During this world event, I have been taking up to 250 micrograms per day.
Please be careful and do not overdo taking vitamin d. It is an oil based vitamin and is not flushed out with water like vitamin C etc. Too much vitamin D can also cause heart irregularities in rhythm. Please be mindful of this symptom.
UPDATE: May 16, 2020: Here is a link to a a related article:
Update: June 4, 2020 on vitamin D: https://www.ctvnews.ca/health/coronavirus/alberta-researchers-part-of-rush-to-learn-vitamin-d-s-role-in-covid-19-prevention-1.4949729#_gus&_gucid=&_gup=Facebook&_gsc=c2wpSXb
Update: 06/14/20: https://www.cnet.com/health/vitamin-d-how-to-get-enough/