A few of us were discussing this on teamspeak a while back and it turned out we were all taking between 5000-10000iu per day, as were some in the politics forum.
There is a correlation between vitamin d status and coronavirus severity. If you've been locked up in your house and not getting any sun for months it might be a good idea to get some. This is not a cure all, but it might help. Generally the further north you live, the greater the chance that you will be deficient.
https://vitamind4all.org/letter.html
This site discusses the science and makes recommendations. It has a list of prominent signatories from around the world.