SUN-780 - When Supplements Go Too Far: Severe Hypercalcemia and Encephalopathy from Excessive over-the-Counter Vitamin D Use

Vitamin D toxicity is an uncommon but important cause of non–parathyroid hormone (PTH)–mediated hypercalcemia. Older adults are particularly vulnerable due to polypharmacy, dehydration, and unsupervised supplement use.

A 91-year-old woman with a history of hypertension and hyperlipidemia presented with one week of progressive generalized weakness, lethargy, decreased oral intake, and confusion. Initial laboratory evaluation revealed severe hypercalcemia with total calcium 13.3 mg/dL (ref: 8.4–10.3) and suppressed PTH 10.7 pg/mL (ref: 9–73). Phosphorus was 2.8 mg/dL(ref: 2.3–4.7). 25-hydroxyvitamin D was markedly elevated at >311.8 ng/mL (laboratory-defined sufficiency: 30–50). 1,25-dihydroxyvitamin D₃ was 50 pg/mL, with 1,25-dihydroxyvitamin D₂ < 8 pg/mL, consistent with vitamin D toxicity rather than granulomatous disease. Evaluation for alternative causes of non–PTH-mediated hypercalcemia showed low PTH-related protein at 10 pg/mL (ref: 11–20), normal thyroid-stimulating hormone at 3.01 mcIU/mL (ref: 0.35–4.94), normal angiotensin-converting enzyme level (26), and serum protein electrophoresis without monoclonal gammopathy. Neuroimaging, including CT head and CT angiography of the head and neck, demonstrated no acute intracranial pathology. Further history revealed ingestion of excessive amounts of over-the-counter vitamin D supplements labeled as “vitamin D 50,” later confirmed to be 50,000 IU tablets. Management included discontinuation of vitamin D and calcium supplements, cessation of hydrochlorothiazide, intravenous hydration, and a single dose of pamidronate 60 mg IV. Serum calcium improved to 10.2 mg/dL, with a brief rebound associated with dehydration, before stabilizing at 9.3 mg/dL off intravenous fluids, accompanied by resolution of encephalopathy.

This case highlights severe vitamin D toxicity from over-the-counter supplementation as an uncommon but clinically significant cause of hypercalcemia and encephalopathy and underscores the importance of routinely reviewing supplement use and monitoring vitamin D levels to prevent avoidable toxicity.

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