What causes vitamin B12 and vitamin B6 deficiencies?

Causes of Vitamin B12 and Vitamin B6 Deficiency

The most common causes of vitamin B12 deficiency are food-bound malabsorption due to atrophic gastritis (affecting up to 20% of older adults), widespread use of proton pump inhibitor drugs, and low dietary intake of animal-source foods, while vitamin B6 deficiency is primarily caused by inadequate dietary intake. 1

Vitamin B12 Deficiency Causes

Malabsorption-Related Causes

• Gastric Issues:

  • Atrophic gastritis (affects up to 20% of older adults) 1
  • Proton pump inhibitor medication use 1, 2
  • Helicobacter pylori infection 3
  • Gastrectomies 4
  • Food-bound cobalamin malabsorption in the elderly 3

• Intestinal Issues:

  • Ileal disease or resection (>20 cm of distal ileum) 2
  • Inflammatory bowel disease, particularly with ileal involvement 2, 4
  • Bacterial overgrowth 4
  • Pancreatic insufficiency 4
  • Parasitic infestations 4
  • Celiac disease 4
  • Tropical sprue 4
  • Short bowel syndrome 4
  • Chronic radiation enteritis of the distal ileum 4

• Autoimmune Conditions:

  • Pernicious anemia (autoimmune destruction of intrinsic factor) 5, 4
  • Addison's pernicious anemia 4

Medication-Related Causes

• Metformin (long-term use) 2
• Most antibiotics (can interfere with B12 absorption) 5
• Colchicine 5
• Para-aminosalicylic acid 5

Dietary Causes

• Strict vegetarian/vegan diet (B12 is not present in plant foods) 5, 3
• Low intake of animal-source foods (meat, dairy, eggs) 3

Genetic Factors

• Gene polymorphisms in transcobalamins 3
• Inherited disorders (Intrinsic factor deficiency, Imerslund-Gräsbeck disease) 4

Other Causes

• Heavy alcohol consumption for longer than 2 weeks 5, 3
• Obesity 4
• Bariatric surgery 2, 4
• Increased requirements during pregnancy and lactation 5

Vitamin B6 Deficiency Causes

Primary Causes

• Low dietary intake 1
• Aging (altered requirements) 1

Dietary Factors

• Inadequate consumption of lean meat (good source of B6) 1
• Insufficient intake of milk and dairy foods 1
• Limited consumption of fortified breakfast cereals 1

Associated Conditions

• Inflammatory bowel disease 1
• Malabsorption syndromes 1
• Celiac disease 1

Clinical Implications and Monitoring

High-Risk Populations

• Older adults (>75 years) 2
• Patients with ileal disease or resection 2
• Vegetarians and vegans 2, 3
• Patients on long-term metformin therapy 2
• Patients with inflammatory bowel disease 1
• Pregnant and lactating women 5

Consequences of Deficiency

• If B12 deficiency progresses for longer than 3 months, it may produce permanent degenerative lesions of the spinal cord 5
• B12 deficiency is associated with megaloblastic anemia, neurological symptoms, and cognitive impairment 6
• B6 deficiency is associated with increased risk of depression and anxiety 1
• Both deficiencies can contribute to elevated homocysteine levels, increasing cardiovascular risk 2

Prevention Strategies

• Regular consumption of animal-source foods (meat, dairy, eggs) for B12 3
• Include lean meat, milk, dairy foods for vitamin B6 1
• Consider fortified breakfast cereals as sources of both vitamins 1
• For high-risk individuals, supplementation may be necessary 2
• Regular monitoring of B12 levels in patients with risk factors 2

Understanding these causes is essential for proper diagnosis and management of vitamin B12 and B6 deficiencies, particularly in high-risk populations where early intervention can prevent irreversible neurological damage.