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Where are iron and B12 absorbed in the GI tract?

Current as of 23 July 2026 · added 23 July 2026

Answer:

  • Iron is absorbed mostly in the first part of the duodenum.
  • B12 goes through several steps before final absorption in the terminal ileum:
  • B12 binds R-factor, secreted by the salivary glands.
  • The B12–R-factor complex is cleaved in the small intestine by pancreatic enzymes.
  • Intrinsic factor (IF), secreted by gastric parietal cells, then binds B12.
  • The B12–IF complex binds receptors in the ileum for absorption.

B12 references: Vitamin B12 Deficiency and Physiology, Gastric Intrinsic Factor (StatPearls).

Source: Iron Absorption: Molecular and Pathophysiological Aspects