There is also a good thread on Vitamin D in the vitamin forum.

also I remember an article where they did a test on people in Hawaii (sunny all the time right) and there was a good proportion that had low vitamin D.

So there are people that either do not absorbe well through the sun or dont convert well was what I think it said.

My Vit D was low and I have been supplementing with 1000 iu a day and it has definitely helped with muscle pain and fatigue.