Vitamin B12, or cobalamin, is a vital nutrient necessary for red blood cell formation, nerve function, and DNA synthesis. Unlike other vitamins, B12 is stored in the liver for several years, so a deficiency can take a long time to manifest. The causes are typically divided into issues of intake, absorption, and utilization.
Dietary Factors
Inadequate dietary intake is a straightforward cause of low B12, but it primarily affects specific groups. Since vitamin B12 is found almost exclusively in animal products, those who follow strict vegan or vegetarian diets are at high risk. The body stores of B12 can last for several years, so it may take time for a deficiency to develop after a significant change in diet.
Populations at Risk from Diet
- Vegans: As they consume no animal products, they must rely on fortified foods or supplements to meet their B12 needs.
- Vegetarians: Though they may consume eggs and dairy, they can still be at risk if their intake is insufficient.
- Breastfed Infants: Infants born to mothers with a severe B12 deficiency, especially those on a vegan diet without supplementation, are at risk.
Malabsorption Issues
This is the most common cause of B12 deficiency. The process of absorbing B12 from food is complex. First, stomach acid releases the vitamin from its food protein. It then binds to intrinsic factor (IF), a protein produced in the stomach, before being absorbed in the small intestine. Any disruption to this process can cause a deficiency.
Pernicious Anemia
Pernicious anemia is an autoimmune disease where the immune system attacks the parietal cells in the stomach, which produce intrinsic factor. Without intrinsic factor, B12 cannot be absorbed in the intestine, leading to a deficiency regardless of dietary intake. It is a leading cause of B12 deficiency, particularly in older adults.
Gastrointestinal Conditions and Surgery
Several medical conditions and procedures can impair B12 absorption:
- Atrophic Gastritis: Inflammation of the stomach lining, common in older adults, can reduce the production of stomach acid necessary to release B12 from food.
- H. Pylori Infection: This bacterial infection can cause atrophic gastritis and reduce B12 absorption.
- Crohn's and Celiac Disease: These inflammatory bowel diseases can damage the terminal ileum, the section of the small intestine responsible for absorbing the B12-intrinsic factor complex.
- Gastrointestinal Surgery: Procedures like gastric bypass or the surgical removal of parts of the stomach or small intestine can decrease the number of intrinsic factor-producing cells or reduce the absorption area.
Medications and Other Causes
Medication Side Effects
Chronic use of certain medications can interfere with B12 absorption:
- Metformin: The primary medication for diabetes, long-term use can reduce B12 absorption.
- Proton Pump Inhibitors (PPIs) and H2 Blockers: Used for acid reflux, these drugs decrease stomach acid needed to release B12 from food.
- Other Medications: Some antiseizure drugs, antibiotics (chloramphenicol), and colchicine may also affect B12 levels.
Genetic Disorders
Rare genetic conditions can disrupt the normal metabolism and transport of B12:
- Transcobalamin II Deficiency: A genetic disorder impairing the transport of B12 throughout the body.
- Imerslund-Gräsbeck Syndrome: A hereditary condition causing selective B12 malabsorption.
Alcohol Use Disorder
Excessive and long-term alcohol consumption can damage the digestive system and interfere with nutrient absorption, including B12.
Comparison of Common Causes for Low B12
| Cause Category | Examples | Primary Mechanism | Affected Populations |
|---|---|---|---|
| Inadequate Intake | Veganism, vegetarianism | Lack of B12 in diet (found mainly in animal products) | Vegans, vegetarians, infants of deficient mothers |
| Malabsorption | Pernicious Anemia, Atrophic Gastritis | Reduced intrinsic factor or stomach acid, damaging the absorption pathway | Older adults, people with autoimmune conditions |
| Intestinal Disorders | Crohn's Disease, Celiac Disease, SIBO | Damage to the part of the intestine where absorption occurs | Individuals with inflammatory bowel disease or certain gut bacteria issues |
| Medications | Metformin, PPIs, H2 Blockers | Interference with stomach acid or the absorption process | Diabetics, those with chronic acid reflux |
Conclusion
Low B12 levels are not always a matter of simple diet and can arise from a complex interplay of genetic, digestive, and lifestyle factors. While dietary intake is a key consideration, especially for those on plant-based diets, medical conditions affecting absorption, such as pernicious anemia, atrophic gastritis, and intestinal disorders, are often the root cause. Additionally, certain medications and chronic alcohol use can significantly contribute to deficiency. Because of the wide range of potential causes and the risk of irreversible nerve damage if left untreated, it is crucial to consult a healthcare provider for proper diagnosis and a personalized treatment plan. Regular monitoring is especially important for at-risk individuals, including older adults, those with autoimmune diseases, and long-term medication users.
For more information on the B12 absorption process and its complications, consult resources from reputable health organizations such as the National Institutes of Health.
