Vitamin D related causes of hypocalcemia
• Vitamin D deficiency: associated with inadequate exposure to ultraviolet light, poor dietary intake, or malabsorption. Also, vitamin D deficiency may occur in patients with nephrotic syndrome as a result of losses of vitamin D–binding protein in the urine.
• Abnormalities of vitamin D metabolism: either reduced hydroxylation of vitamin D to 25-hydroxyvitamin D (25D) in chronic liver diseases or reduced hydroxylation of 25D to 1,25D in kidney failure or vitamin D–dependent rickets type I (deficiency of 1α-hydroxylase).
• Resistance to the actions of vitamin D: vitamin D–dependent rickets type II (molecular defects in the vitamin D receptor).
