27th February 2025

Increased vitamin D

Vitamin D2 (ergocalciferol; mainly found in plants) or vitamin D3 (cholecalciferol; mainly found in fish & meat) are activated in a two-step process: hepatic hydroxylation creates 25(OH)D (calcifediol), with subsequent renal hydroxylation producing the active metabolite 1,25(OH)2D (calcitriol). Calcitriol increases serum calcium levels through actions on the small intestine and bones. Hypercalcaemia may, therefore, occur with prolonged and excessive ingestion of vitamin D supplements (hypervitaminosis D), granulomatous diseases, e.g. sarcoidosis, TB (as epithelioid histiocytes in granulomas display 1α-hydroxylase activity), or ectopic production of calcitriol in lymphoma. Steroids may be trialled where granulomas or malignancies producing 1α-hydroxylase are implicated.