How does treatment of vitamin D deficiency differ from treatment of vitamin D receptor resistance?

• A. Both require calcium supplementation
• B. Vitamin D deficiency responds to vitamin D supplementation; VDR resistant requires active vitamin D (calcitriol) with careful management
• C. Both require no treatment
• D. VDR resistance responds to high-dose cholecalciferol

Answer: (B)

The key idea is distinguishing a shortage of the vitamin from a failure of the body's response to it. When someone is vitamin D deficient, the problem is not enough substrate for the bones and kidneys to use, so repleting vitamin D with cholecalciferol (or ergocalciferol) raises 25(OH)D levels and restores normal signaling, with subsequent normalization of calcium, phosphate, and PTH.

If there is vitamin D receptor resistance, the tissues don’t respond properly to vitamin D even when levels are normal or high. In that scenario, simply giving more vitamin D isn’t effective because the signaling pathway is impaired at the receptor. The approach shifts to using the active form of vitamin D, calcitriol, to try to stimulate whatever functional receptor activity remains, with careful monitoring of calcium and phosphate to avoid hypercalcemia and related complications.

Thus, deficiency markedly improves with vitamin D supplementation, whereas receptor resistance typically requires the active vitamin D form and close metabolic follow-up to balance minerals. High-dose cholecalciferol would not overcome receptor resistance.