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IUPAC name
Other names 25-Hydroxyvitamin D3
CAS number 19356-17-3 Yes check.svgY
PubChem 5283731
MeSH Calcifediol
ChemSpider ID 4938806
Molecular formula C27H44O2
Molar mass 400.64 g/mol
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Calcifediol (INN), also known as calcidiol, 25-hydroxycholecalciferol, or 25-hydroxyvitamin D (abbreviated 25(OH)D), is a prehormone which is produced by hydroxylation of vitamin D3 (cholecalciferol) in the liver. Calcidiol is then converted in the kidneys (by the enzyme 25(OH)D-1α-hydroxylase) into calcitriol (1,25-(OH)2D3), a secosteroid hormone that is the active form of vitamin D. It can also be converted into 24-hydroxycalcidiol in the kidneys via 24-hydroxylation.[1][2]

Clinical significance

In medicine, blood concentration of calcidiol is considered the best indicator of vitamin D status.[3] It is the most sensitive measure,[4] though experts have called for improved standardization and reproducibility across different laboratories.[3] The normal range varies widely depending on several factors, including age and geographic location. A broad reference range of 20–150 nmol/L has been suggested,[5] while several studies have defined levels below 80 nmol/L as indicative of vitamin D deficiency.[6]

Increasing calcidiol levels are associated with increasing fractional absorption of calcium from the gut up to levels of 80 nmol/L (32 ng/mL). Urinary calcium excretion balances intestinal calcium absorption and does not increase with calcidiol levels up to ~400 nmol/L (160 ng/mL).[7]


  1. ^ Bender, David A.; Mayes, Peter A (2006). "Micronutrients: Vitamins & Minerals". in Victor W. Rodwell; Murray, Robert F.; Harper, Harold W.; Granner, Darryl K.; Mayes, Peter A.. Harper's Illustrated Biochemistry. New York: Lange/McGraw-Hill. pp. 492–3. ISBN 0-07-146197-3.   Retrieved December 10, 2008 through Google Book Search.
  2. ^ Institute of Medicine (1997). "Vitamin D". Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, D.C: National Academy Press. pp. 254. ISBN 0-309-06403-1.  
  3. ^ a b Heaney, Robert P (Dec 2004). "Functional indices of vitamin D status and ramifications of vitamin D deficiency". American Journal of Clinical Nutrition 80 (6): 1706S-1709S.  
  4. ^ Institute of Medicine (1997), p. 259
  5. ^ Bender, David A. (2003). "Vitamin D". Nutritional biochemistry of the vitamins. Cambridge: Cambridge University Press. ISBN 0-521-80388-8.   Retrieved December 10, 2008 through Google Book Search.
  6. ^ Hollis BW (February 2005). "Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: implications for establishing a new effective dietary intake recommendation for vitamin D". J Nutr 135 (2): 317–22. PMID 15671234.  
  7. ^ Kimball et al. (2004). "Safety of vitamin D3 in adults with multiple sclerosis". J Clin Endocrinol Metab. PMID 17823429.  

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