What is the role of Vitamin B12 in the body?

Role of Vitamin B12 in the Body

Vitamin B12 (cobalamin) is an essential water-soluble vitamin that functions as a crucial cofactor for two key enzymes: methionine synthase and methylmalonyl-CoA mutase, which are vital for DNA synthesis, methylation processes, neurological function, and red blood cell formation. 1

Core Functions of Vitamin B12

• DNA Synthesis and Cell Reproduction:

  • Acts as a cofactor for enzymes involved in nucleotide synthesis 2
  • Essential for cell division and growth 1
  • Helps maintain DNA stability and prevents damage 2

• Neurological Function:

  • Critical for myelin synthesis and maintenance of the myelin sheath around neurons 3
  • Supports neurotransmitter synthesis 3
  • Deficiency leads to demyelination in the central and peripheral nervous systems 3
  • Prevents neurological damage when administered promptly 4

• Hematopoiesis:

  • Essential for red blood cell formation 4
  • Prevents megaloblastic anemia 4
  • Works interdependently with folate in one-carbon metabolism 3

• Metabolic Processes:

  • Functions in the methylation cycle with methionine synthase to convert homocysteine to methionine 3
  • Works with methylmalonyl-CoA mutase to synthesize succinyl-CoA for the citric acid cycle 3
  • Supports mitochondrial metabolism 3

Absorption and Storage

• Vitamin B12 is absorbed through a complex process:

  • Released from food proteins by gastric acid and pepsin 3
  • Binds to intrinsic factor in the stomach 3
  • Absorbed in the terminal ileum via receptor-mediated endocytosis 3
  • Transported in blood by specific binding proteins (transcobalamin I and II) 4

• The liver is the main storage site for vitamin B12 3, 4

  • Average adult stores approximately 2500 μg 3
  • Can last 12-36 months without sufficient intake 3

Clinical Implications of Deficiency

• Neurological manifestations:

  • Peripheral neuropathy with numbness and tingling 1
  • Impaired coordination and balance 1
  • Subacute combined degeneration of the spinal cord 3, 4
  • Cognitive difficulties that may mimic dementia 1

• Hematological effects:

  • Macrocytic or megaloblastic anemia 1
  • Abnormal blood count findings including macrocytosis 1

• Other symptoms:

  • Fatigue and weakness 1
  • Visual disturbances 1
  • Glossitis 1
  • Increased risk of depression and anxiety 1

Risk Factors for Deficiency

• Advanced age (particularly those over 75) 1
• Vegan or vegetarian diets 1, 4
• Malabsorption conditions (atrophic gastritis, celiac disease) 1
• Medications (metformin, proton pump inhibitors, H2 blockers) 1
• Bariatric surgery 1

Monitoring and Prevention

• Neurological symptoms may precede hematological changes 1
• Serum B12 levels may be normal despite tissue deficiency 1
• Additional testing with methylmalonic acid and homocysteine may be required 1
• Early diagnosis and treatment are crucial to prevent irreversible neurological damage 1

Clinical Relevance

• Vitamin B12 deficiency is common in elderly populations (10-40%) 1
• Deficiency is associated with increased risk of frailty in older adults 5
• Low B12 levels correlate with processing speed impairment and white matter changes on MRI 6
• B12 possesses antioxidant properties that help protect against reactive oxygen species 2, 7

Vitamin B12's multifaceted role in the body underscores its importance for overall health, particularly for neurological function and hematopoiesis. Maintaining adequate levels is essential to prevent potentially irreversible neurological damage and hematological disorders.