hormone
Calcitriol
Calcitriol is the active hormonal form of vitamin D produced mainly through a final conversion in the kidney.
It binds the vitamin-D receptor and helps coordinate calcium and phosphate absorption and handling; it is distinct from vitamin D as a nutrient and from 25(OH)D as a blood marker.
The active vitamin-D hormone
Vitamin D precursors are converted in the liver and then hydroxylated in the kidney to form calcitriol. Calcitriol acts through the vitamin-D receptor to regulate gene expression, including genes involved in intestinal calcium and phosphate transport.
Related topics
Parathyroid hormone (PTH) stimulates renal production of Calcitriol
PTH increases renal 1-alpha-hydroxylase activity, which produces calcitriol.
Calcitriol helps regulate intestinal absorption of Calcium
Calcitriol helps regulate calcium and phosphate transport, including intestinal calcium absorption.
Worth knowing
It is not the usual blood test. 25(OH)D is the main marker used to assess vitamin-D status; calcitriol is the active hormone and is regulated differently.
A closer look
PTH is one upstream regulator
PTH can stimulate renal calcitriol production. The relationship is part of calcium homeostasis and does not imply that more dietary vitamin D automatically means more calcitriol.
It is not a dietary form
Vitamin D intake and calcitriol concentration are separate because activation is regulated through liver and kidney steps rather than determined by intake alone.
References
Source-checked local draft.
Human editorial review pending.
- NIH National Library of MedicinePhysiology, ParathyroidChecked 2026-09-05
- NIH Office of Dietary SupplementsVitamin D: Fact Sheet for Health ProfessionalsChecked 2026-09-05