From what I have read on FR and elsewhere - it is all over the place. Most folks (and doctors) think the recommended dose is too low (don’t recall what it is - 1200 units a day?)
I try to remember to take 1000 in the morning and 1000 at night. I seem to recall others are in the 5000+ range per day? A doc can do a test, but I think it is fairly expensive. I also recall folks going to the doc, getting a 30,000+ dose and then followed by typical doses.
I’m sure I’m fuzzy on my actual numbers, but they are all over the place!
Here’s a thread on Vitamin D:
http://www.freerepublic.com/focus/news/2423344/posts?page=13
Here’s an interesting link from post 43 (thanks aruanan!):