Increased levels of Vitamin D important to help prevent acute respiratory distress and other problems?

I am not competent or knowledgeable enough to evaluate this, but by reputation and approach, this British doctor seems credible. Something to think about and possibly act on, on the theory that it isn't likely to be harmful and might be quite salutary. 

https://www.youtube.com/watch?v=V5g9AVqRsjo