I take vitamin D everyday (doctor's orders actually), and my son's neurologist is actually baselining my son for vitamin deficiency at his appt in a few weeks. There are lots of studies which show children with autism have a serious vitamin D deficiency. Interesting to see what my son's testing comes back as.
About a year ago, I went to the doc complaining of nonstop fever blisters and cold sores. Real PITA when you're a brass player.
He said, "Hmmm, sounds like your immune system isn't what it should be. We'll draw some blood and get an idea of what your Vitamin D levels are."
Sure enough, he read them and said, "Jesus, dood, your D levels SUCK." (Verbatim, that's what he said.)
I started out by taking 15,000 units a day for about a month, then scaled back to about 5,000 which is what I do today.
Since the time I started taking Vitamin D, NOT ONE fever blister.
I'm sold. That stuff works.