Same thing happened to me. I was in the single digits for Vitamin D, and my doc had me taking 10000 a day (or week) I think. Within a month, I started to feel way more energy in the afternoon (I used to feel dead by 1pm). I also mysteriously kept getting sick with small colds that winter before supplementing, and those also went away.
USDA experiments have shown that exposing certain mushrooms to UV light converts cholesterols in the mushrooms to vitamin D. Since sunlight contains UV, an easy solution would be to leave some portabella mushrooms out in the noonday sun for a while. So far I can't find any articles that give a precise number for how long the mushrooms were exposed, though.
How is it taken in the rest of the world? In Norway, it's traditionally done by drinking cod liver oil daily during the winter months. At least that's what I do.
It doesn't really say that: it just repeats the standard advice that 4000 IU is the safe upper limit. The real answer is to get yourself tested regularly if you supplement large amounts of D3. (I'd advise taking K2 with it too, but do your own research.)
