Intrinsic factor is the most obscure—yet most important—glycoprotein in the human body. It has only one primary function that is essential for good health. Produced by the parietal cells of the stomach as well as the salivary glands, intrinsic factor has a brief, but very important life. Intrinsic factor is key for supporting energy, metabolism, and mental health by working with one nutrient—vitamin B12.
Why Is It Important?
To understand the importance of intrinsic factor, it’s necessary to understand the importance of B12. Vitamin B12 is involved in the metabolism of every cell in the human body. It plays a key role in DNA synthesis and formation, red blood cell creation, and brain function. The human body does not create vitamin B12 on its own, so it must be consumed from the diet. The human digestive tract may have B12-producing bacteria; however, dietary B12 is the best way to ensure adequate nutrition.
Sources of B12 include fish, shellfish, meat, liver, eggs, poultry, and dairy products. Batabata-cha, a Japanese fermented black tea, contains large amounts of B12 which may be bioavailable to humans.  This tea is considered to be a vegan source of vitamin B12. Kombucha is also reported to contain varying amounts of B12. Without this essential nutrient, neurologic problems result and, if left untreated, death follows. But B12 has a problem—it cannot survive the trip through the stomach due to the stomach’s high acid content. Fortunately for us, that’s where intrinsic factor comes to save the day.
How Intrinsic Factor Works
Intrinsic factor binds to B12 when it reaches the stomach following exposure to gastric juices. Bound with intrinsic factor, B12 will survive the journey through the stomach and reach the small intestine. Once there, intrinsic factor dissolves, releasing B12 to bind with another protein, transcobalamin II, for transit through the epithelial cells and into the bloodstream and on to the liver.
What Causes the Body to Stop Producing It?
Only the parietal cells of the stomach create enough intrinsic factor to supply the body with adequate B12. When these cells are damaged, intrinsic factor is not produced and B12 goes unabsorbed. Alcoholism and ulcerative gastritis can cause parietal cell death, greatly increasing the chances of developing a B12 deficiency. H. pylori infection and Zollinger-Ellison syndrome as well as gastric bypass surgery also cause similar effects. Age may also play a role in intrinsic factor production.
The absence of intrinsic factor leads to a condition called pernicious anemia, or the inability to initiate intrinsic factor and B12 absorption. In some cases, pernicious anemia can be passed down through families. This is most common in individuals of Scandinavian or Northern European descent. Certain diseases such as Grave’s disease, Addison disease, and type 1 diabetes may increase the risk of pernicious anemia. Individuals suffering from pernicious anemia may also be at an increased risk of gastric cancer. 
What to Do in Its Absence?
Anyone lacking intrinsic factor will need to supplement with B12. However, since B12 cannot be digested without intrinsic factor, it needs to be administered through regular injections. Although sublingual options exist, these may not provide adequate levels of B12. Consult with your doctor to discuss the best options for you.
- Kittaka-Katsura H1, Ebara S, Watanabe F, Nakano Y. Characterization of corrinoid compounds from a Japanese black tea (Batabata-cha) fermented by bacteria. J Agric Food Chem. 2004 Feb 25;52(4):909-11.
- Annibale B1, Lahner E, Fave GD. Diagnosis and management of pernicious anemia.Curr Gastroenterol Rep. 2011 Dec;13(6):518-24. doi: 10.1007/s11894-011-0225-5.