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. 2021 Apr 20;11(4):255. doi: 10.3390/metabo11040255

Table 6.

Chemical structure and pharmacokinetic characteristics of vitamin D compounds and activated forms.

Ergocalciferol Cholecalciferol Calcifediol
(or Calcidiol)
Calcitriol
Chemical Structure graphic file with name metabolites-11-00255-i001.jpg graphic file with name metabolites-11-00255-i002.jpg graphic file with name metabolites-11-00255-i003.jpg graphic file with name metabolites-11-00255-i004.jpg
Absorption Intestine (bile required) Intestine (bile required) Intestine, readily absorbed * Intestine, readily absorbed *
DBP dissociation constant 10−7 10−7 10−9 10−7
Volume of distribution very limited in plasma compartment; rapidly stored in fat tissue very limited in plasma compartment; rapidly stored in fat tissue larger than plasma volume plasma compartment
Tissue distribution for long-term adipose tissue, muscle adipose tissue, muscle blood, adipose tissue, muscle blood and tissues
Circulating half-life 2 days 2 days 3 weeks 4–8 h
Functional half-life 2–3 months ≤2 months 2–3 months 4–8 h

* Faster absorption than ergocalciferol and cholecalciferol. DBP: vitamin D binding protein.