Overdiagnosed and Oversupplemented: The Iatrogenic Rise of Vitamin D Toxicity

Spanish pharmacovigilance alerts have highlighted vitamin D overdosing. We retrospectively analysed adult serum 25(OH)D results from a Barcelona tertiary hospital (2020-2025), measured using a VDSCP-certified immunoassay. For results >100 ng/mL (250 nmol/L), concomitant calcium, phosphorus, albumin, alkaline phosphatase and parathyroid hormone were retrieved. Hypercalcaemia was defined as albumin-corrected calcium >10.5 mg/dL. Among 185,604 results, annual testing increased by 54.1% and median 25(OH)D rose from 25.3 to 28.6 ng/mL. Very high results more than doubled (31 [0.14%] to 108 [0.31%]; n=393). Calcium was available in 324/393 results, and hypercalcaemia occurred in 14/324 (4.3%). Calcifediol was documented in 183/201 (91.0%) hypervitaminosis D patients with available supplementation data and in 12/14 (85.7%) hypercalcaemic cases, often in short-interval dosing regimens. Rapid test growth paralleled a rightward shift and expanding high-concentration tail, supporting evidence-based requesting, clearer intermittent-dosing and supplementation instructions, and selective serum calcium surveillance when 25(OH)D is greatly elevated.