Vitamin B12 Deficiency

About Vitamin B12 Deficiency

Vitamin B12 cobalamin deficiency affects approximately 6 percent of adults under 60 and approximately 20 percent over 60. B12 is essential for DNA synthesis, red blood cell formation, and neurological function. Causes include pernicious anemia autoimmune destruction of gastric parietal cells producing intrinsic factor, affecting approximately 1 to 2 percent of adults, dietary insufficiency strict vegans and vegetarians, malabsorption celiac disease, Crohns disease, gastric bypass surgery, H pylori infection, atrophic gastritis, certain medications metformin, proton pump inhibitors, H2 blockers, and genetic disorders. Symptoms develop insidiously and include fatigue, weakness, pallor, shortness of breath, dizziness, and jaundice from ineffective erythropoiesis megaloblastic anemia. Neurological symptoms are distinctive and may precede anemia: peripheral neuropathy with numbness and tingling in hands and feet, subacute combined degeneration of the spinal cord with loss of proprioception and vibration sense, cognitive changes including memory problems and dementia, mood changes including depression and irritability, and glossitis sore, beefy red tongue. If untreated, neurological damage becomes irreversible. Diagnosis involves serum B12 below 200 pg mL, with 200 to 300 being borderline. Elevated methylmalonic acid MMA and homocysteine confirm deficiency. Anti intrinsic factor and anti parietal cell antibodies identify pernicious anemia. Complete blood count may show macrocytic anemia MCV over 100 fL with hypersegmented neutrophils. Treatment is B12 replacement, either by intramuscular injection hydroxocobalamin or cyanocobalamin or by high dose oral tablets, with the regimen set by a clinician. Injections are traditionally used in pernicious anemia and severe malabsorption, although high dose oral B12 can also be effective for many people because a small fraction is absorbed by passive diffusion.