I think the urban myth that multivitamins don’t work has some validity to it because some vitamins are water soluble and others fat soluble. So one rock hard pill taken with water isn’t going to cover all the bases.
Vitamin D is a fat soluble substance hence why it’s found in egg yolks and fatty fish. So the ‘multi Vit’ tablets aren’t going to give you any. A proper vitamin D tablet will look like a small fish oil cap.
in terms of its purpose, Vitamin D is actually responsible for keeping bones and muscles healthy, however it also has other functions such as reducing inflammation, modulation of cell growth and the immune system as well as glucose metabolism.
So in terms of its importance here, it’s not a cure for covid, however - most people are vitamin D deficient as they stay indoors all day and the media has demonised red meat and eggs so they aren’t really a regular staple in people’s diets.
In terms of the links to reducing the impact of covid, the correlation is currently not very strong at the moment but then it’s early days for everything covid.
I would simply say, taking a Vit D tablet once a day isn’t going to break anyone’s bank and shouldn’t go against anyone’s morals so there is no reason not to do it. Especially the older more vulnerable sections of the population here.