As for Vitamin D (Sun),
An estimated one billion people worldwide are either vitamin D insufficient or deficient
Blood pressure pills (ACE inhibitors) may be making people die from Coronavirus

Several observational studies, which track participants over time without assigning a specific treatment, have associated low vitamin D levels with greater susceptibility to acute respiratory infections.
https://news.harvard.edu/gazette/story/2017/02/study-confirms-vitamin-d-protects-against-cold-and-flu/