PTH and Insulin resistance: Although we acknowledge that the causes of insulin resistance are very different from those of vitamin D resistance, and high-dose insulin injections cause comparatively more side effects than high-dose vitamin D3 injections, the above analogy illustrates the principles of the Coimbra protocol: The calculation of the required vitamin D dose depends on the grade of vitamin D resistance and the stage of the particular disease and incorporates the PTH concentration in analogy to the insulin/blood glucose example.