When I went to the doc in December, he said that the recommendation for Vitamin D is now closer to 800 units per day, double what it used to be. This is mainly for people in the higher latitudes like me and north of here (and the far south) because our days are so short in spring, summer and fall, and also the tilt of the sun through the atmosphere means that more sunlight is filtered before it gets to the surface of the earth.
I take a supplement of D and Calcium together. My uncle was recently diagnosed (good weight, very active guy) with osteoporosis and has compression fractures in his spine--he's in his 50's. NOT what I want. I'd rather take the supplement and have too much Calcium/D than end up with osteoporosis.