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Intrinsic factor

Intrinsic factor is a protein that helps your intestines absorb vitamin B12. It is made by cells in the stomach lining.

Information

Intrinsic factor binds to vitamin B12 in the stomach. After attaching, intrinsic factor and B12 travel to the intestines to be absorbed into the bloodstream. Vitamin B12 is needed for red blood cells to form and grow. Vitamin B12 also has effects on nerve development and DNA synthesis.

Some people do not make enough intrinsic factor or have a condition that destroys it. If your body does not make enough intrinsic factor, you can develop a type of vitamin B12 deficiency called pernicious anemia.

Surgical removal or bypass of the stomach and certain other health conditions can also cause you to stop making intrinsic factor.

References

Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 40.

Chen E, Suzuki H, Kaunitz JD. Gastric secretion. In: Chung RT, Rubin DT, Wilcox CM, et al, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 12th ed. Philadelphia, PA: Elsevier; 2026:chap 53.

Means Jr. RT. Approach to the anemias. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 144.

Review Date 1/10/2026

Updated by: Frank D. Brodkey, MD, FCCM, Associate Professor, Section of Pulmonary and Critical Care Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.