Colecalciferol
Vitamins
Vitamins
Vitamin D3, the form the skin makes in sunlight. Liver and kidney turn it into the hormone that lets the gut absorb calcium.
Also called: cholecalciferol, vitamin D3
Quick facts
- Group
- Vitamins
- Target
- Vitamin D receptor (VDR), a nuclear receptor
- Used for
- Prevention and treatment
- Key effects
- Usually none at normal amounts · With excess
- Monitor
- Signs of hypercalcaemia
- ATC
- A11CC05
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows calcitriol, the active hormone made from colecalciferol in the liver and kidney, bound to the ligand-binding domain of the human vitamin D receptor.
Colecalciferol is a prohormone. The liver adds a hydroxyl group (25-hydroxyvitamin D, the form measured in blood) and the kidney adds a second one, making calcitriol. Calcitriol binds the vitamin D receptor and switches on genes that increase calcium and phosphate absorption in the gut, help mineralise bone and restrain parathyroid hormone.
- Skin (sunlight) or diet supplies vitamin D3
- Liver: 25-hydroxylation; kidney: 1α-hydroxylation to calcitriol
- Calcitriol binds the vitamin D receptor
- More calcium and phosphate absorbed; bone mineralises
Indications
- Prevention and treatment of vitamin D deficiency, including rickets and osteomalacia Rickets and osteomalacia →
- Vitamin D deficiency in people with, or at risk of, osteoporosis Osteoporosis →
Adverse effects
Common
- Usually none at normal amounts
- With excess: nausea, vomiting, weakness, loss of appetite, constipation
Contraindications
- Hypercalcaemia
- Vitamin D toxicity (hypervitaminosis D)
Key interactions
- Mineral oil
- Reduces absorption of vitamin D and other fat-soluble vitamins
- Thiazide diuretics
- Can cause hypercalcaemia, especially in hypoparathyroidism
- Other vitamin D products, fortified foods and calcium supplements
- Total intake adds up; risk of toxicity
What is monitored
- Blood calcium when high amounts are used or kidney function is reduced
- Signs of hypercalcaemia
Pregnancy and breastfeeding
Needed in pregnancy; amounts above the recommended intake are avoided unless prescribed, because excess vitamin D harmed the fetus in animal studies.
Nursing care
- Ask about all sources of vitamin D: fortified foods, multivitamins and prescriptions.
- Teach the signs of too much vitamin D: thirst, frequent urination, nausea, constipation, weakness, confusion.
- Identify people at risk of deficiency: little sun exposure, darker skin, malabsorption, older age.
Pharmacokinetics
- Absorption
- Fat-soluble; absorbed from the gut with dietary fat; mineral oil reduces absorption
- Metabolism
- Activated in two steps, first in the liver, then in the kidney
- Onset and duration
- Delayed, because the active hormone must first be made
Test yourself
Think of the answer, then tap the question to see it.
Where is colecalciferol activated?
First in the liver (25-hydroxylation), then in the kidney (1α-hydroxylation) to calcitriol.
Which bone diseases follow vitamin D deficiency in children and adults?
Rickets in children, osteomalacia in adults.
What lab abnormality explains the symptoms of vitamin D toxicity?
Hypercalcaemia.
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Vitamin D: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - ERGOCALCIFEROL capsule (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); RCSB PDB - 1DB1: CRYSTAL STRUCTURE OF THE NUCLEAR RECEPTOR FOR VITAMIN D COMPLEXED TO VITAMIN D (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.