COVID AND THE VACCINE - TRUTH, LIES, AND MISCONCEPTIONS REVEALED, page-67259

I included mention of it -- vit d.
I know, wasn't real clear but you are correct, it is essential

That just means being outdoors most of the time and controlled amounts of direct exposure to the sun.
Those past 65 or so should take a supplement , it is safe and effective.
Ocean water for me is also very important, Big dripping deposits of the stuff in your nasal cavity which you get after a frolic in the waves.
The Japanese have done some research and many people there use a saline sniff.