I was doing some research in late January about how much vitamin C to take daily [through food and supplements], and stumbled across vitamin D as something that impacts upper respiratory tract infections.
Followed that up, and realized that most people think that they are getting more D than they actually get.
I thought that the cheese I eat a lot of had plenty of vitamin D - but there's only a minimal amount in cheese.
You'd have to drink most of a half gallon of whole milk [48 ounces] every day to get even 600 IU (RDA is around 700-800 IU).
Another issue is that many people are on a low fat diet [why I pinged BobL], and vitamin D absorption increases with fat in your meal.
About the only concentrated source of vitamin D in foods is canned tuna fish, canned sardines, fresh salmon [not ALL fish are good for this - just fatty fish], egg yolks, and D-fortified foods like cereal and some orange juices.
No soda No chips No processed food.
And I'm out and about. Have some good genes.