What causes low iron and low B12 levels?

Causes of Low Iron and Low B12 Levels

Low iron and low B12 levels are most commonly caused by malabsorption, inadequate dietary intake, blood loss, or increased requirements, with specific medical conditions often underlying these deficiencies. 1

Common Causes of Iron Deficiency

• Blood loss: Sources of blood loss should be investigated and excluded in individuals who present with iron deficiency anemia 1
• Malabsorption: Conditions affecting the gastrointestinal tract such as celiac disease, inflammatory bowel disease, or bariatric surgery 1
• Inadequate dietary intake: Particularly in strict vegetarians who consume no animal products 2
• Increased requirements: Pregnancy, rapid growth periods, or hemorrhage 1, 2
• Chronic inflammation: Inflammatory conditions can affect iron metabolism and lead to functional iron deficiency 1

Common Causes of Vitamin B12 Deficiency

• Pernicious anemia: Autoimmune condition affecting intrinsic factor production 2, 3
• Malabsorption syndromes: Including:
  • Celiac disease 1, 4
  • Inflammatory bowel disease 1, 4
  • Small intestinal bacterial overgrowth 2, 4
  • Pancreatic insufficiency 4
• Gastrointestinal surgery: Including:
  • Bariatric surgery 1
  • Gastrectomy (total or partial) 2, 5
  • Small bowel resection 5
• Inadequate dietary intake: Particularly in vegans and strict vegetarians 6, 2
• Medications: Some medications can affect B12 absorption, including anticonvulsants, methotrexate, and proton pump inhibitors 1, 4

Conditions That Can Cause Both Iron and B12 Deficiency

• Autoimmune atrophic gastritis: Leads to both intrinsic factor deficiency (affecting B12 absorption) and impaired iron absorption due to increased gastric pH 3
• Celiac disease: Affects absorption of multiple nutrients in the small intestine 1, 4
• Bariatric surgery: Reduces absorption capacity for multiple nutrients 1
• Inflammatory bowel disease: Particularly when affecting the terminal ileum (site of B12 absorption) 1, 4
• Strict vegetarian/vegan diet: Without proper supplementation 6, 2

Diagnostic Approach

• For iron deficiency: Evaluate serum iron, ferritin, total iron binding capacity (TIBC), and transferrin saturation 1

  • In the absence of inflammation, serum ferritin <30 mcg/L or transferrin saturation <16% define iron deficiency 1
  • In the presence of inflammation, serum ferritin <100 mcg/L with transferrin saturation <16% suggests iron deficiency 1

• For B12 deficiency: Measure serum B12 levels, methylmalonic acid, and homocysteine 6, 7

  • Macrocytic anemia (MCV >100 fL) may indicate B12 or folate deficiency 1
  • Neurological symptoms may be present even without anemia 6, 7

Special Considerations

• Combined deficiencies: Iron deficiency is found in approximately 75% of patients with pernicious anemia 3
• Masking effect: Folic acid supplementation can mask B12 deficiency symptoms while allowing neurological damage to progress 1, 6
• Reticulocyte count: A key follow-up test to distinguish between production, destruction, and loss of red blood cells 1

Treatment Considerations

• B12 deficiency treatment: Hydroxocobalamin 1 mg intramuscularly three times a week for 2 weeks, followed by maintenance treatment with 1 mg intramuscularly every 2-3 months for life 1
• Iron deficiency treatment: Oral or intravenous iron supplementation based on severity and underlying cause 1, 3
• Address underlying causes: Surgical correction of anatomic lesions, dietary changes, or treatment of underlying conditions when possible 2

Remember that both deficiencies can significantly impact quality of life and lead to serious complications if left untreated, including irreversible neurological damage in the case of B12 deficiency 6, 2.