hormone
Calcitriol
Calcitriol is the active hormonal form of vitamin D produced mainly through a final conversion in the kidney.
Educational draft · Human scientific and editorial review pending. About review status
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.
How it works
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.
Evidence: Established · Source checked 2026-09-05 · Sources: NIH National Library of Medicine: Physiology, Parathyroid
Calcitriol helps regulate intestinal absorption of Calcium
Calcitriol helps regulate calcium and phosphate transport, including intestinal calcium absorption.
Evidence: Established · Source checked 2026-09-05 · Sources: NIH National Library of Medicine: Physiology, Parathyroid
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.