Hi...I realize this thread was started a while ago...I just found it. Wanted to put my 2 cents in.

I'm on prescription vitamin D, which has virtually done away with my S.A.D. I recently found this: Soy foods increase the body’s requirement for vitamin D. Taken from: http://www.frot.co.nz/dietnet/basics/soy.htm

Very interesting to me, since I don't eat meat and eat a bit more soy than the average bear. I'm rethinking my position on meat now.