You would think that question would have an easy answer. The best I can say though is this. The object is to get everyone to realize that Vitamin D is important and that certain levels in a human promote good health and will help reduce disease states. So we encourage everyone to have at least a level of 50ng/ml. It usually take an average weight person of 150lbs taking 5000iu a day to reach that level but this is why we encourage a test to make sure. If you have taken 5000iu for at least 8 weeks, tested and are at that level,then you really do not need to test again because taking that 5000iu a day should keep you at that level. I would suppose if you gain weight, or are female and get pregnant, you may want to test again. I have no scientific proof but if you were experiencing a stressful situation in your life be it physical or mental, you may want to take some extra vitamin d for a little while. This is my opinion.
Keep in mind if you take 5000iu and get some “summer sun” your levels will go higher than 50ng/ml.