I have found it to be true that keeping your vitamin D levels up will really help the most with cold and flu viruses. Vitamin D deficiency is actually in plague proportions in much of the world, even when people live in sub-tropics, because people avoid going in the sun. Now, I am one of those people, because I have always been one who burns easily, but taking natural vitamin D3 in high enough doses will actually help boost and maintain vitamin D levels. My vitamin D originally tested dangerously low, but I eventually got it up to low normal and have been able to steer clear of cold and flu viruses for the first time I can remember. A good place to get vitamin D3 at a high enough dose for a reasonable price can be found at this link: http://www.swansonvitamins.com/SW1030/ItemDetail?n=4294967184 It's even often on sale for less than this. The RDA of vitamin D is too low for people, especially in the winter time. Here is a list of articles talking about vitamin D and how important it is for your immune system: http://search.mercola.com/Results.aspx?q=vitamin%20D&k=vitamin%20D He talks about adults needing to take 4,000 mg of vitamin D3 everyday during the winter time, but once my vitamin D levels were up to low normal, my naturopath told me to go to 2,000 mg. Taking the 4,000 mg everyday while your vitamin D levels are too low will raise your vitamin D levels. My guess for why my naturopath had me drop down to 2,000 mg everyday is because 4,000 mg everyday will continue to raise the vitamin D levels and having too high of vitamin D levels is just as bad as having too low of vitamin D levels. It took me nearly a year to raise my vitamin D levels to low normal, though, and since most people are deficient, 4,000 mg is probably fine for most people to take. But, the key is getting the vitamin D levels tested regularly. So, one should probably start with 2,000 mg everyday, since that's the maintenance dose, then be sure to get tested as soon as possible.
I know from my own experience how important this is, and I know about the vitamin D deficiency epidemic. I also know how much more important vitamin D levels are for CFS/FMS patients and anyone else dealing with auto-immune problems. Mine was so low that the test almost couldn't even measure it. That's downright dangerous!
One has to question why all of these viruses are becoming resistant. New strains? Why isn't the CDC up-to-date on this problem?