Vitamin B12 Deficiency

A large proportion of the global population is B12 deficient, often subclinically, without knowing the root cause. Serum B12 below 200 pg/mL is often used as a diagnostic threshold, but laboratory variation and threshold debate make interpretation uncertain. Focusing only on dietary insufficiency as a cause of B12 deficiency misses the majority of cases. Consuming adequate B12 does not guarantee sufficiency if absorption is impaired, since B12 is absorbed in the distal ileum and inflammation anywhere along that pathway can block uptake. B12 is critical for DNA synthesis, making deficiency a systemic problem. Vitamin B12 is involved in DNA synthesis, metabolism, red blood cell development, growth, and nervous system maintenance. Common causes of B12 malabsorption include low stomach acid, H. pylori infection, gastric bypass surgery, and bowel conditions such as IBS, Crohn's, and diverticulitis. Liver damage impairs B12 storage and metabolism, contributing to deficiency regardless of its underlying cause. B12 deficiency causes numbness, tingling, paresthesia, and progressive neurodegeneration. Untreated vitamin B12 deficiency can cause serious hematologic, neurologic, and neuropsych…