Check the videos on Dr John Campbell's (PhD nurse educator in the UK) web site. The UK national health service has good medical records that can be cross-refer

Check the videos on Dr John Campbell's (PhD nurse educator in the UK) web site. The UK national health service has good medical records that can be cross-referenced and cross-linked every which way. Someone examined the historical records, found a reasonably large number of persons who had vitamin D levels checked before the pandemic, and checked those statistics vs the Covid-19 experience of the same people. (Imagine living in a country where that could happen.) IIRC, this did find some benefits wrt COVID-19 of not having a very low vitamin D level.