What is the intrinsic factor secreted by parietal cells helps in?

January 6, 2026 •

2 min read

Millions of people worldwide suffer from vitamin B12 deficiency, a condition often linked to the malfunctioning of a critical protein called intrinsic factor secreted by parietal cells. Without this vital substance, the body cannot absorb this essential nutrient, leading to severe health consequences that develop over time.

Quick Summary

Intrinsic factor is a glycoprotein produced by parietal cells in the stomach, essential for vitamin B12 absorption. A deficiency of intrinsic factor results in malabsorption of B12 and can cause pernicious anemia and neurological issues.

Key Points

Facilitates Vitamin B12 Absorption: The intrinsic factor (IF) is the glycoprotein secreted by parietal cells that binds to and protects vitamin B12, allowing for its absorption in the small intestine.
Prevents Pernicious Anemia: A lack of intrinsic factor leads to a B12 deficiency that causes pernicious anemia, a condition characterized by abnormally large and immature red blood cells.
Protects B12 from Degradation: Intrinsic factor binds with vitamin B12 in the stomach, forming a complex that prevents the vitamin from being digested by enzymes before it can be absorbed.
Enables Absorption in the Ileum: The vitamin B12-IF complex is specifically recognized by receptors in the terminal ileum, where it is taken up into the intestinal cells.
Failure Has Severe Consequences: Without functioning intrinsic factor, B12 deficiency can result in serious neurological damage, cognitive decline, and other severe symptoms over time.

The Role of Intrinsic Factor in Vitamin B12 Absorption

Intrinsic factor (IF) is a glycoprotein produced by parietal cells in the stomach lining. Its primary function is to facilitate the absorption of vitamin B12 (cobalamin) in the small intestine. Intrinsic factor's secretion by the stomach is essential for the effective absorption of dietary vitamin B12.

The Complex Journey of Vitamin B12 Absorption

Absorbing vitamin B12 involves several steps:

Vitamin B12 is released from food proteins in the stomach by acid and enzymes.
It then binds to haptocorrin, protecting it in the stomach's acidic environment.
In the small intestine, haptocorrin is broken down, allowing B12 to bind to intrinsic factor.
The B12-intrinsic factor complex travels to the terminal ileum, where it is absorbed into intestinal cells via specific receptors.
Inside the cells, B12 is released from IF and binds to transcobalamin II for transport throughout the body.

Consequences of Intrinsic Factor Deficiency

Inadequate intrinsic factor production prevents vitamin B12 absorption, leading to pernicious anemia. This often stems from autoimmune destruction of parietal cells or intrinsic factor itself. B12 deficiency symptoms develop gradually but can be severe, affecting multiple systems.

Symptoms may include:

Neurological issues like numbness, tingling, memory loss, and difficulty walking, potentially leading to permanent nerve damage.
Hematological problems such as megaloblastic anemia, causing fatigue and paleness.
Gastrointestinal symptoms like a sore tongue, diarrhea, or constipation.
Psychological effects including irritability and depression.

Conditions Affecting Intrinsic Factor Production

Several factors can impair intrinsic factor production or function:

Pernicious Anemia: An autoimmune condition targeting parietal cells or intrinsic factor.
Gastrectomy: Surgical removal of the stomach.
Atrophic Gastritis: Chronic inflammation damaging the stomach lining and parietal cells.
Bariatric Surgery: Procedures that alter the digestive tract.
Medications: Some drugs, like PPIs, can indirectly affect B12 absorption by reducing stomach acid.

Intrinsic Factor Deficiency vs. Dietary B12 Deficiency

Both lead to B12 deficiency but have different causes and treatments.


Feature	Intrinsic Factor Deficiency (Pernicious Anemia)	Dietary Vitamin B12 Deficiency
Cause	Autoimmune issues or gastric surgery.	Insufficient B12 intake, common in vegans.
Absorption Mechanism	Impaired IF-dependent pathway.	Normal IF-dependent pathway but low B12 supply.
Treatment	Bypassing normal absorption, typically with injections or high-dose oral supplements.	Increasing dietary intake or using standard oral supplements.
Associated Risks	Increased gastric cancer risk.	Lower risk if treated early.

Conclusion

Intrinsic factor, produced by stomach parietal cells, is vital for vitamin B12 absorption. It binds to and protects B12, enabling its uptake in the small intestine. A deficiency, often due to pernicious anemia, prevents B12 utilization, leading to serious neurological and hematological issues. Effective treatment typically involves bypassing the impaired absorption pathway with B12 injections or high-dose oral supplements.

To learn more, consult resources like the National Institutes of Health.

Frequently Asked Questions

The intrinsic factor is a protein secreted by the parietal cells of the stomach that helps in the intestinal absorption of vitamin B12 (cobalamin). It binds to the vitamin, protecting it and enabling its uptake in the terminal ileum.

Parietal cells are epithelial cells in the stomach lining that have two main functions: they secrete hydrochloric acid and they produce intrinsic factor. Both secretions play a crucial role in proper digestion and nutrient absorption.

If a person lacks intrinsic factor, their body cannot absorb vitamin B12 from food. This leads to a severe vitamin B12 deficiency, most commonly manifesting as pernicious anemia and potentially causing long-term nerve damage.

Pernicious anemia is an autoimmune disease where the body's immune system attacks and destroys the parietal cells in the stomach. This prevents the production of intrinsic factor, causing vitamin B12 malabsorption and resulting in anemia.

Symptoms often develop slowly and can include fatigue, weakness, a sore tongue, numbness or tingling in the hands and feet, trouble walking, and memory problems. Untreated deficiency can lead to severe nerve damage.

Diagnosis typically involves blood tests to check vitamin B12 levels. Further tests, such as checking for anti-intrinsic factor antibodies or parietal cell antibodies, may be conducted to confirm the presence of pernicious anemia.

Since oral supplements are often ineffective due to the absorption issue, treatment for intrinsic factor deficiency usually involves intramuscular injections of vitamin B12. High-dose oral supplements may also be used in some cases, bypassing the need for intrinsic factor absorption.