Vitamin D and Calcium Absorption: Toward a New Model

  • Robert P. HeaneyEmail author


The standard model for regulation of calcium absorption identifies ­calcitriol as the vitamin D metabolite responsible for active transport of calcium across the intestinal mucosa, with 25-hydroxy vitamin D [25(OH)D] functioning as the substrate for renal synthesis of calcitriol. However, as experience with measurement of calcium absorption has accumulated, it has become evident that (1) calcitriol is sometimes ineffective in elevating calcium absorption and (2) 25(OH)D is sometimes effective, apparently in its own right. Additionally, supplemental administration of vitamin D or 25(OH)D sometimes increases calcium absorption, and sometimes does not. A new model that integrates the growing number of seemingly contradictory observations is needed. Missing in the current model is the fact of calcium need, which helps to explain many of the discrepancies. Finally, the apparent cooperation of 25(OH)D and 1,25(OH)2D may be explainable by sequential binding of both metabolites to different pockets of the vitamin D receptor.


Vitamin D Calcitriol 25(OH)D PTH Vitamin D receptor Calcium absorption 


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Copyright information

© Springer-Verlag London 2013

Authors and Affiliations

  1. 1.Creighton UniversityOmahaUSA

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