I was prescribed 3-5000 iu daily and then I changed doctors. When I asked about continuing the vitamin the new doctors said "I won't recommend doing a test because almost everyone has low vit d levels, even with daily supplements. Just keep taking the pills. As long as its not a very high dose you should be fine".

My wife has a different doctor who does regular vitamin testing, she was prescribed 5000iu and a year and a half later her tests barely read "normal", still being on the borderline.