What is the intrinsic factor of vitamin B12?

January 13, 2026 •

2 min read

According to the National Institutes of Health, intrinsic factor is a glycoprotein produced by parietal cells in the stomach that is necessary for the absorption of vitamin B12. This protein plays a critical role in the complex process of nutrient absorption, protecting the delicate vitamin B12 as it travels through the digestive system. Without it, the body is unable to absorb vitamin B12 efficiently, which can lead to significant health problems.

Quick Summary

Intrinsic factor is a protein made in the stomach that is vital for the absorption of vitamin B12. It binds to the vitamin, transports it through the digestive tract, and enables its uptake in the small intestine. Its absence leads to impaired B12 absorption and conditions like pernicious anemia.

Key Points

Intrinsic Factor is a Glycoprotein: It is a protein produced by parietal cells in the stomach that is crucial for the body to absorb vitamin B12.
Facilitates B12 Absorption: Its primary function is to bind to vitamin B12 and facilitate its uptake in the terminal ileum of the small intestine.
Protects Vitamin B12: By binding with B12, intrinsic factor protects the vitamin from being digested as it travels through the digestive system.
Deficiency Causes Pernicious Anemia: A lack of intrinsic factor is the most common cause of pernicious anemia, an autoimmune disease where the body attacks the cells that produce IF.
Bypasses Absorption Issues: Treatment for intrinsic factor deficiency, such as pernicious anemia, often requires injections of vitamin B12 to bypass the problematic absorption pathway in the gut.
Essential for Cellular Health: Without sufficient B12 absorption, vital processes like DNA synthesis and red blood cell maturation are impaired, leading to serious health consequences.

The Crucial Role of Intrinsic Factor in B12 Absorption

Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a specialized glycoprotein produced by the parietal cells within the lining of the stomach. Its primary and indispensable function is to facilitate the absorption of vitamin B12, or cobalamin, in the body. This process is far from simple, involving a multi-step journey through the digestive system that relies heavily on IF's protective and transport capabilities.

The B12 Absorption Journey

Release of B12: Vitamin B12 is first released from food proteins in the stomach with the help of acid and pepsin.
Binding with R-Protein: Initially, B12 binds to haptocorrin (R-protein) for protection in the stomach's acidic environment.
Transfer to Intrinsic Factor: In the small intestine, haptocorrin is digested, allowing B12 to bind with intrinsic factor, forming a B12-IF complex.
Ileal Absorption: This complex travels to the terminal ileum where it is absorbed into the bloodstream via specific receptors.
Entry into the Bloodstream: Inside the intestinal cells, B12 binds to transcobalamin II for transport throughout the body.

What Happens When Intrinsic Factor is Lacking?

Insufficient intrinsic factor production severely impairs B12 absorption, leading to deficiency. The most common cause is pernicious anemia, an autoimmune disease that destroys parietal cells. Stomach surgery can also cause IF deficiency. Symptoms of B12 deficiency due to IF issues include fatigue, neurological problems like tingling and numbness, and poor memory.

Comparison: Intrinsic Factor Deficiency vs. Other B12 Deficiencies


Feature	Intrinsic Factor Deficiency (Pernicious Anemia)	Other B12 Deficiencies (e.g., Dietary)
Cause	Autoimmune destruction of parietal cells, stomach surgery.	Poor diet (vegans), malabsorption (Crohn's), certain medications.
Mechanism	Lack of intrinsic factor hinders B12 transport and absorption.	Issues with intake, digestion, or absorption not directly related to IF production.
Treatment	Non-oral B12 administration (injections) bypasses absorption problems.	Oral B12 supplements may be effective if intestinal absorption is normal.
Diagnosis	Often involves testing for intrinsic factor antibodies.	Based on serum B12 levels, antibody testing less common unless pernicious anemia is suspected.

The Importance of Intrinsic Factor Function

B12 absorption is crucial for DNA synthesis, metabolism, and proper red blood cell formation; deficiency can cause megaloblastic anemia. B12 also protects nerve cells, and deficiency can lead to irreversible damage. Intrinsic factor's role is therefore vital for both hematopoietic and nervous system health.

Conclusion

So, what is the intrinsic factor of vitamin B12? It's a stomach-secreted glycoprotein essential for B12 absorption in the small intestine. It binds and protects B12 for uptake. Intrinsic factor deficiency, often due to pernicious anemia, leads to severe B12 deficiency. Treatment for IF deficiency requires bypassing the gut, typically with B12 injections. This process highlights the link between digestion and health. More information on B12 deficiency is available from resources like the National Institutes of Health.

Frequently Asked Questions

Intrinsic factor is a special protein known as a glycoprotein, which is produced by the parietal cells located in the lining of the stomach.

Intrinsic factor is necessary for vitamin B12 (cobalamin) because it must bind with the vitamin to protect it from being degraded by the acidic stomach environment and to enable its absorption in the small intestine.

If a person doesn't produce enough intrinsic factor, they cannot properly absorb vitamin B12, which can lead to a deficiency and, in many cases, a type of anemia called pernicious anemia.

Pernicious anemia is an autoimmune disease where the body's immune system attacks the parietal cells that produce intrinsic factor. This leads to a lack of intrinsic factor and subsequent vitamin B12 malabsorption.

Diagnosis can involve measuring serum vitamin B12 levels, and testing for anti-intrinsic factor antibodies, which are highly specific for pernicious anemia.

Since oral supplements cannot be absorbed effectively, treatment involves intramuscular injections of vitamin B12 to bypass the digestive tract and deliver the nutrient directly to the bloodstream.

No, other causes of vitamin B12 deficiency include inadequate dietary intake (especially in vegans), conditions affecting the small intestine like Crohn's disease, or long-term use of certain medications that reduce stomach acid.