absorption (calcium)

Last reviewed 01/2018

Dietary calcium is absorbed in the duodenum and upper jejunum. The main stimulus is active vitamin D as 1,25-dihydrocholecalciferol. This promotes the synthesis of three key products within the mucosal cells which in turn causes absorption:

  • calcium ATPase
  • calcium binding protein
  • alkaline phosphatase

Growth hormone increases absorption with less potency than vitamin D. Glucocorticoids have an antagonistic effect.

Calcium must be in an ionized form for absorption and as such, absorption is retarded in the presence of:

  • increased duodenal alkalinity e.g. after vagotomy
  • the presence of chelating agents within the lumen e.g.:
    • phytates
    • phosphates
    • oxalates