Vitamin d toxicity

[Tariq Zaki]

Usually, vitamin D toxicity results from taking excessive amounts. In vitamin D toxicity, resorption of bone and intestinal absorption of calcium is increased, resulting in hypercalcemia. Marked hypercalcemia commonly causes symptoms. Diagnosis is typically based on elevated blood levels of 25(OH)D. Treatment consists of stopping vitamin D, restricting dietary calcium, restoring intravascular volume deficits, and, if toxicity is severe, giving corticosteroids or bisphosphonates.
Because synthesis of 1,25-dihydroxyvitamin D (the most active metabolite of vitamin D) is tightly regulated, vitamin D toxicity usually occurs only if excessive doses (prescription or megavitamin) are taken. Vitamin D 1000 mcg (40,000 units)/day causes toxicity within 1 to 4 months in infants. In adults, taking 1250 mcg (50,000 units)/day for several months can cause toxicity. Vitamin D toxicity can occur iatrogenically when hypoparathyroidism is treated too aggressively.