Mechanisms of intestinal calcium absorption

J Cell Biochem. 2003 Feb 1;88(2):387-93. doi: 10.1002/jcb.10330.


Calcium is absorbed in the mammalian small intestine by two general mechanisms: a transcellular active transport process, located largely in the duodenum and upper jejunum; and a paracellular, passive process that functions throughout the length of the intestine. The transcellular process involves three major steps: entry across the brush border, mediated by a molecular structure termed CaT1, intracellular diffusion, mediated largely by the cytosolic calcium-binding protein (calbindinD(9k) or CaBP); and extrusion, mediated largely by the CaATPase. Chyme travels down the intestinal lumen in approximately 3 h, spending only minutes in the duodenum, but over 2 h in the distal half of the small intestine. When calcium intake is low, transcellular calcium transport accounts for a substantial fraction of the absorbed calcium. When calcium intake is high, transcellular transport accounts for only a minor portion of the absorbed calcium, because of the short sojourn time and because CaT1 and CaBP, both rate-limiting, are downregulated when calcium intake is high. Biosynthesis of CaBP is fully and CaT1 function is approximately 90% vitamin D-dependent. At high calcium intakes CaT1 and CaBP are downregulated because 1,25(OH)(2)D(3), the active vitamin D metabolite, is downregulated.

Publication types

  • Review

MeSH terms

  • Animals
  • Biological Transport, Active / physiology
  • Calbindins
  • Calcium / metabolism*
  • Calcium / pharmacokinetics
  • Calcium-Transporting ATPases / metabolism
  • Diffusion
  • Humans
  • Intestinal Absorption / physiology*
  • S100 Calcium Binding Protein G / metabolism
  • Vitamin D / metabolism


  • Calbindins
  • S100 Calcium Binding Protein G
  • Vitamin D
  • Calcium-Transporting ATPases
  • Calcium