Vitamin B12 deficiency is caused by several factors, primarily related to inadequate intake, impaired absorption, or certain medical conditions.
Main Causes of Vitamin B12 Deficiency
- Pernicious anemia : An autoimmune condition where the immune system attacks stomach cells that produce intrinsic factor, a protein essential for vitamin B12 absorption. Without intrinsic factor, vitamin B12 cannot be absorbed effectively.
- Dietary deficiency : Vitamin B12 is mainly found in animal products like meat, fish, eggs, and dairy. People who follow strict vegan diets without supplementation or fortified foods may develop B12 deficiency over time.
- Stomach conditions or surgeries : Conditions like atrophic gastritis, Helicobacter pylori infection, or surgical removal of part of the stomach (gastrectomy) can reduce the production of intrinsic factor or stomach acid needed for absorption.
- Intestinal disorders : Diseases such as Crohn's disease, celiac disease, or surgeries removing parts of the small intestine can impair B12 absorption at the ileum, where B12-intrinsic factor complex is absorbed.
- Medications : Certain drugs like proton pump inhibitors, metformin, and repeated exposure to nitrous oxide can reduce B12 absorption or utilization.
- Other causes : Small intestinal bacterial overgrowth or parasitic infections like fish tapeworm compete for vitamin B12, reducing availability for absorption.
Vitamin B12 stores in the body last 2 to 5 years, so deficiency symptoms may take time to appear after onset of cause.
In summary, vitamin B12 deficiency is most commonly caused by pernicious anemia, insufficient dietary intake (especially in vegans), and malabsorption conditions affecting the stomach or intestines, as well as medication effects.