I read somewhere that vitamin D is fat soluble. If you get too much it can be toxic. I can't believe a doctor told you 3,000 I.U. a day. That is too much. The natural form of vitamin D is different. I guess 20 mins. in the sun can give you 10,000 I. U. but the natural form is ok. When you take the man-made stuff I thought they said people should get 800 I.U. a day.