This isn't something a regular person can easily decide using test results. Because vitamin D accretes over time, it's possible to overshoot. A possible scenar

This isn't something a regular person can easily decide using test results. Because vitamin D accretes over time, it's possible to overshoot. A possible scenario: you get a test, take the supplement, take another test, see no difference, take a bigger dose, and the test after that shows the effect of the first dose. Then you decide to keep the bigger dose even though it's unnecessary. The moderate dosages are safe according to most studies. However, I agree with what dragonwriter below wrote: people who think they need the bigger dosages better consult a doctor before making a decision.