Excess vitamin D supplementation can cause hypercalcemia.
However, vitamin D toxicity is extremely rare and generally occurs only after ingestion of large doses of vitamin D (>10,000 IU/d) for prolonged periods in patients with normal gut absorption or in patients who may be concurrently ingesting generous if not excessive amounts of calcium (1).
A 25(OH)D level of 80 ng/mL is the lowest reported level associated with toxicity in patients without primary hyperparathyroidism with normal renal function
Most patients with vitamin D toxicity have levels greater than 150 ng/mL.
It has been reported that vitamin D supplementation with 1600 IU/d or 50,000 IU monthly was not associated with any laboratory parameters of toxicity [eg, 25(OH)D, PTH, bone alkaline phosphatase, and 24-hour urine calcium] and even failed to increase total 25(OH)D levels above 30 ng/mL in 19% of participants.
One year of D2 or D3 dosing (1,600 IU daily or 50,000 IU monthly) does not produce toxicity, and 25(OH)D levels of less than 30 ng/ml persist in approximately 20% of individuals (2).
Notes:
Vitamin D toxicity should not be diagnosed solely on the basis of an elevated 25(OH)D level; instead, it should be recognized as a clinical syndrome of both hypervitaminosis D and hypercalcemia, in which hyperphosphatemia and hypercalciuria also commonly (although not always) occur (1)
patients with vitamin D toxicity could present with clinical symptoms and signs of hypercalcemia (eg, nausea, dehydration, and constipation) and hypercalciuria (eg, polyuria and kidney stones)
hypervitaminosis D in the absence of hypercalcemia may prompt further investigation to evaluate the aetiology of increased vitamin D levels
but unlike hypercalcemia, it is not a medical emergency (1)
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