Vitamin B12 and digestive disorders
Accurately diagnosing vitamin B12 deficiency is crucial to identifying its underlying cause. Without a precise assessment of active vitamin B12 status, diagnosis becomes challenging. Once deficiency is confirmed, appropriate treatment pathways, such as referral to a haematologist, gastroenterologist, or dietitian, can be determined.
While inadequate dietary intake of vitamin B12 is a recognised cause of deficiency, it’s not the most common reason. More frequently, gastrointestinal disorders are to blame, especially those affecting the stomach and intestines. Pernicious anaemia, for instance, occurs when the body’s immune system targets parietal cells in the stomach, hindering the production and secretion of intrinsic factor (IF)—a protein essential for B12 absorption in the ileum. Individuals with pernicious anaemia are unable to absorb vitamin B12 effectively.
Another common cause of active vitamin B12 deficiency is low stomach acid or hypo- or achlorhydria, often resulting from atrophic gastritis or prolonged use of antacid medication (PPIs or H2-blockers). Adequate stomach acid is necessary for releasing vitamin B12 from food sources. Individuals with chronic atrophic gastritis experience reduced gastric acid production due to the loss of parietal cells in the corpus mucosa, either due to autoimmune conditions (as seen in pernicious anaemia) or chronic Helicobacter pylori infection.
Several intestinal conditions can also lead to impaired B12 absorption and subsequent deficiency. These include Crohn’s disease, particularly affecting the terminal ileum, small bowel surgery, bacterial overgrowth, and cancer.
