Dave, that is fair comment and a fair appraisal of Vit-D. There are some dietary sources too, oily fish and eggs. I agree that advice to take supplements is reasonable and I think that that has been the advice before 2020 for a number of years. I don’t agree that it would have been far more effective in reducing cases numbers than lockdowns. You can still go outside and get sun.
Also, other countries where the lack of winter sun isn’t an issue also had significant excess deaths.
For what it’s worth I came across a site dedicated to debunking covid myths. It’s been up since Jan 19.
“dedicated to debunking common Covid Sceptic arguments, and highlighting the track record of some of the most influential and consistently-wrong Covid Sceptics. We mostly focus on UK-based people, since most of this site’s creators are UK-based as well.”
I haven’t read through it all yet but so far it seems to be considered and well thought out.