Vitamin D Toxicity

DEFINITION
Abnormal accumulation of vitamin D in the body, most commonly from ingesting vitamin D–containing rodenticides or other preparation or oversupplementation

PATHOPHYSIOLOGY
Cholecalciferol—fat-soluble vitamin; absorbed through chylomicrons and transported to the liver, where it is metabolized to 25-hydroxycholecalciferol, the major circulating metabolite during vitamin D excess; further metabolism occurs in the kidney, where calcitriol is produced.
Cholecalciferol and 25-hydroxycholecalciferol—limited biological activity
Calcitriol—most potent cholecalciferol metabolite in terms of enhancing calcium resorption from bone and intestinal calcium uptake
Excessive ingestion—increased intestinal absorption of calcium; stimulated bone resorption; increased renal tubular reabsorption of calcium; results in hypercalcemia (serum calcium > 12 mg/dL) and associated dystrophic calcification