Thanks for this. I remembered you posted this the other day, and I was looking for it for a while yesterday but couldn't find it (didn't check this thread). Going to be taking a look at some supplements and such
Yeah. It's really saved my butt. I did have a blood test done that showed my vitamin d levels were low, so it's good to get tested. A complete metabolic panel is a good idea too since it will show things like calcium, potassium and sodium levels.
Zinc also seems to be an important element for immunity. You can get enough through diet if you believe that the daily value figures that are published are accurate. But it's still not easy and personally I have my doubts about that anyway. There's a lot of agreement among certain specialists that the D3 DV is probably only good for avoiding gross deficiency symptoms and I think that's probably how most of those number are set - not for optimal health.
Here is one short article and one longer but detailed one on vitamin D. They talk about the importance of D3 not just for immunity but for a host of other health issues from proper cardiovascular function to neurochemistry.
http://www.businessinsider.com/am-i-getting-enough-vitamin-d-2014-11
https://www.sciencenews.org/article/power-d - from 2011 but still a lot of good information.
Of course since D like vitamin A is fat soluble, it can build up over time so you never want to take megadoses. It can be very toxic if you do that. But up to a couple thousand IUs per day should be ok.
As long as I'm on a roll here I should also mention magnesium. This is really difficult to get enough of even with a good diet so it's worth looking into chelated supplement. Always buy from a reputable vendor like Solgar though since supplements aren't FDA regulated.
Hope you feel good and when all else fails - chicken soup and warm blankets. Cheers!!!