Fig. 3.

Schematic interaction of vitamin D and dietary protein on renal 1,25(OH)D production and thereby on intestinal Ca absorption. The transfer of dietary Ca from the intestinal lumen to the blood is stimulated by 1,25(OH)D, the renal production of which depends on its substrate, 25OHD, and IGF-I. The mechanism of intestinal Ca translocation depends of the presence of the vitamin D receptor (VDR), which in turn influences the transcription of several factors that are implicated in the transport of Ca across either the luminal or basolateral membranes or through the intracellular compartment of the enterocyte. CYP27B1: 25 hydroxyvitamin D-1α hydroxylase, TRPV6 = transient receptor potential cation channel, subfamily V, member 6, Calbindins = Ca binding proteins, PMCA1b = plasma membrane Ca ATPase 1b (Color figure available online.)