Bump for later.
I was deficient in sunny socal when I got the H1N1 flu virus as a fairly young mom of 3 kids. By day 3 I had pneumonia in both lungs and by day 4 I was having problems exhaling and inhaling, after never having had any lung problems in my life. IV antibiotics saved me.
I learned about vitamin d3 then and started supplementing, going back and forth for blood tests every couple months to titrate the dose and get it therapeutic. Ive never gotten the flu again and I dont get bad cases of anything. I take 5000 IU every day unless I was half naked in the sun for a few hours. I take a full vitamin K supplement with it.
You might still get any number of sicknesses while supplementing vitamin d to a good level. BUT YOU WILL NEVER GET THE WORST CASES.
Being deficient in vitamin D is the easiest way to get the worst cases of any illness, from a cold to cancer.