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Cholecalciferol Molecule also called vitamin D3

See 3d image of Vitamin D3 Molecule using Jmol

Cholecalciferol is a form of vitamin D, also called vitamin D3 or calciol.[1][2]

It is structurally similar to steroids such as testosterone, cholesterol, and cortisol (though vitamin D3 itself is a secosteroid). Cholecalciferol has a molecular weight of 384.64 g/mol and molecular formula of C27H44O.

Vitamin D3 has several forms:

  • Cholecalciferol, (sometimes called calciol) is an inactive, unhydroxylated form of vitamin D3)
  • Calcifediol (also called calcidiol, hydroxycholecalciferol, 25-hydroxyvitamin D3, etc. and abbreviated 25(OH)D is one of the forms measured in the blood to assess vitamin D status[3]
  • Calcitriol (also called 1,25-dihydroxyvitamin D3) is the active form of D3.

Metabolism of Vitamin D3

7-Dehydrocholesterol is the precursor of vitamin D3 and forms cholecalciferol only after isomerization due to UV radiation exposure from the sun or artificial sources of UVB light.

Cholecalciferol is then hydroxylated in the liver to become calcifediol (25-hydroxyvitamin D3).

Next, calcifediol is again hydroxylated, this time in the kidney, and becomes calcitriol (1,25-dihydroxyvitamin D3). Calcitriol is the most active hormone form of vitamin D3.


One gram of pure vitamin D3 is 40 000 000 (40x106) IU. Recommendations are: 15 micrograms (600 IU or International Units) daily for all individuals (males, female, pregnant/lactating women) under the age of 70 years-old. For all individuals older than 70 years, 20 micrograms daily (800 IU) is recommended.[4]

A growing body of researchers question whether the current recommended adequate levels are sufficient to meet physiological needs, particularly for individuals deprived of regular sun exposure or those at higher risk such as those with higher-melanin content in the skin (i.e. those whose ancestors are African, Latin American, or Asian), the obese, and those who live far from the equator.

The upper limit (UL) for vitamin D has been recommended as 4,000 IU daily. The 4,000 IU cut-off was determined by the Institute of Medicine in 2010 after reviewing the then-current medical literature, finding that toxicity had consistently occurred when doses of 40,000 IU daily were taken,[5] and that there was a single case of toxicity above 10,000 IU daily; this case of toxicity occurred under circumstances which have led other researchers to dispute it as a credible case to consider when making vitamin D intake recommendations.[5] The Institute of Medicine did not find evidence of toxicity between 4,000 IU and 10,000 IU, so the 4,000 IU number is more of an estimate than a number based on evidence of toxicity above 4,000 IU.[4] Patients with severe vitamin D deficiency will require treatment with a loading dose, its magnitude can be calculated based on the actual serum 25-hydroxy-vitamin D level and body weight.[6]

Vitamin D toxicity can result from regular excess intake of this vitamin, and may lead to hypercalcemia and excess bone loss.

The 25-hydroxy vitamin D (calcifediol) blood test is used to determine how much vitamin D is in the body. The normal range of calcifediol is 30.0 to 74.0 ng/mL.[3]



  1. "Nomenclature of Vitamin D. Recommendations 1981. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN)" reproduced at the Queen Mary, University of London website. Retrieved 21 March 2010.
  2. "cholecalciferol" at Dorland's Medical Dictionary
  3. ""25-hydroxy vitamin D test: Medline Plus". Retrieved 21 March 2010.
  4. DRIs for Calcium and Vitamin D
  5. Vieth R (May 1999). "Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety". Am. J. Clin. Nutr. 69 (5): 842-56.
  6. van Groningen L, Opdenoordt S, van Sorge A, Telting D, Giesen A, de Boer H (April 2010). "Cholecalciferol loading dose guideline for vitamin D-deficient adults". Eur. J. Endocrinol. 162 (4): 805-11. doi:10.1530/EJE-09-0932.

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