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Vitamin B12 Deficiency

Vitamin B12 deficiency develops when the body cannot absorb enough B12, leading to anemia, fatigue, numbness, and memory problems. Early treatment with supplements or injections prevents permanent nerve damage.

Hematology
Vitamin B12 is essential for making red blood cells, maintaining nerves, and building DNA. Because the liver stores several years' worth, vitamin B12 deficiency develops slowly and quietly — and it is common, especially in older adults, affecting a meaningful share of people over 60. Caught early, it is completely correctable; left untreated, it can cause nerve damage that becomes permanent. Unlike many vitamin deficiencies, B12 deficiency is usually caused by absorption problems rather than by poor diet alone. Causes and Risk Factors: B12 absorption is a multi-step process involving stomach acid and a protein called intrinsic factor, so problems anywhere along the way can cause deficiency — and more than one factor is often present in the same person, particularly in older adults:
  • Pernicious anemia: An autoimmune condition that destroys the stomach cells making intrinsic factor, preventing B12 absorption.
  • Atrophic gastritis: Chronic thinning of the stomach lining, often age-related or following long-standing gastritis, reduces the acid needed to free B12 from food.
  • Medications: Long-term metformin use and long-term acid-suppressing medicines (proton pump inhibitors and H2 blockers) lower B12 levels.
  • Digestive disease or surgery: Celiac disease, Crohn's disease involving the small intestine, and gastric or ileal surgery impair absorption.
  • Vegan or vegetarian diets: B12 occurs naturally only in animal foods, so strict plant-based diets require supplementation.
Symptoms: Deficiency affects the blood, the nervous system, and the mind — and nerve symptoms can occur even before anemia appears:
  • Fatigue, weakness, and pallor: Signs of the large-cell (megaloblastic) anemia that B12 deficiency causes.
  • A sore, smooth tongue and mouth ulcers: Classic but often overlooked.
  • Numbness and tingling: Typically starting in the feet and hands as nerves lose their insulation.
  • Balance problems and unsteady walking: From involvement of the spinal cord's position-sense pathways.
  • Memory difficulty, irritability, and depressed mood: B12 deficiency is a reversible contributor to cognitive symptoms, particularly in older adults.
  • Shortness of breath with exertion: A less common sign reflecting more significant anemia.
Diagnosis: A complete blood count may show anemia with enlarged red blood cells, and a serum vitamin B12 level confirms the deficiency. When the B12 level is borderline, a methylmalonic acid level helps clarify the picture, since it rises when cells are truly short of B12. Testing for intrinsic factor antibodies identifies pernicious anemia, which requires lifelong treatment. Folate deficiency can look identical on a blood count, so both vitamins are usually checked together; treating with folate alone can mask B12 deficiency while nerve damage quietly continues. Treatment: Treatment replaces B12 and addresses the reason it was low:
  • B12 injections: The standard approach when absorption is the problem, given frequently at first and then monthly for maintenance.
  • High-dose oral B12: Effective for many people, including some with absorption problems, because a small fraction is absorbed without intrinsic factor.
  • Treating the cause: Adjusting contributing medications when appropriate, treating digestive disease, and supplementing during strict plant-based diets.
  • Follow-up: Blood counts recover within weeks; nerve symptoms improve more slowly, which is why early treatment matters most.
Complications: Most effects of B12 deficiency reverse with treatment, but the nervous system is far less forgiving than the blood:
  • Lasting nerve and spinal cord injury: Long-standing deficiency damages the insulating sheath around nerve fibers, a pattern called subacute combined degeneration that can leave permanent numbness, weakness, or unsteady walking.
  • Falls and injury: Loss of position sense in the feet makes older adults more likely to fall, especially in the dark or on uneven ground.
  • Strain from severe anemia: Deep anemia forces the heart to work harder and can worsen chest pain or breathlessness in someone with coronary artery disease.
  • Stomach changes with pernicious anemia: The autoimmune stomach inflammation behind pernicious anemia carries a modestly increased long-term risk of stomach cancer, so persistent new digestive symptoms should be evaluated rather than assumed benign.
If you have unexplained fatigue, numbness, or memory changes, a simple blood test can rule this treatable condition in or out. The internal-medicine team at Zimmer Medical Group screens for B12 deficiency when symptoms or risk factors suggest it — schedule an appointment to be evaluated.

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