When the intrinsic factor is not being produced your intestinal bacteria eat up the bulk of the vitamin B12 that is ingested. The rest is simply excreted. So if you aren’t producing the intrinsic factor it doesn’t matter if you are getting enough vitamin B12. The B12 needs to get to the right place in your body.
There are a few things that can cause the intrinsic factor to stop producing. In some cases your body will attack the cells and lead to an intrinsic factor deficiency. This is a type of autoimmune disease. Another way it can happen is if you have atrophic, or other forms of, gastritis. Gastritis can damage the parietal cells of the stomach walls, which can cause intrinsic factor deficiency. Problems with the pancreas can cause the vitamin B12 to not bind to protein properly in the small intestine, which can also result in lack of intrinsic factor.
People who have stomach surgeries, like bariatric surgery, are known to be high risk for pernicious anemia. Stomach tumors, gastric ulcers, alcoholism and taking medication for acid reflux or heartburn also are risk factors for problems with proper production of intrinsic factor.
When you are not producing enough intrinsic factor you become intrinsic factor deficient. When you are intrinsic factor deficient, a low dose of oral vitamin B12 will not help. Your body won’t absorb it through the wall in the small intestine.
The most common treatment is a subcutaneous or intramuscular injection of vitamin B12. By administering the B12 in this way you bypass the digestive tract and allow the B12 to be absorbed. More recent studies are finding that mega doses of B12 given sublingually works just as well. These are the two most common forms of treatment no matter how you developed vitamin B12 deficiency. As always, discuss your options with your doctor.