Would you struggle to believe that I took 50k IU daily for over a year with no side effects? Or that others have accidentally taken significantly more than that without issue? With vitamin D, absorption varies a lot between individuals. And the recommended doses that people frequently throw around are generally just a low-ish dose that is guaranteed not to be harmful. This misleads people into thinking that such a dose is the upper bound on the set of non-harmful doses, which is not even remotely true. Honestly I find it shocking that this woman developed hypercalcemia at 5k IU daily, the only explanation for this is that she has an unusually high absorption.