Vitamin B12 deficiency

Vitamin B12 deficiency refers to insufficient levels of cobalamin needed for nerve function and red blood cell production. Below are common signs, typical causes, diagnostic approaches and guidance on which medical specialties can help. This is general information; a clinician can determine diagnosis and next steps.

What does vitamin B12 do?

Vitamin B12 (cobalamin) supports DNA synthesis, the formation and maintenance of nerve cells, and red blood cell production. Dietary sources are mainly animal-based; problems with absorption in the stomach or small intestine can cause deficiency even with normal intake.

Signs and symptoms to notice

Early deficiency can be subtle. Typical findings include fatigue, pallor, shortness of breath on exertion, heart palpitations, tingling or numbness in hands and feet, balance or walking difficulties, and problems with memory or concentration. Some people report a sore or smooth tongue and reduced appetite. Neurological symptoms should be evaluated promptly.

Common causes and risk factors

Frequent causes include low dietary intake (for example strict vegetarian or vegan diets), gastric surgery or disorders that reduce intrinsic factor, chronic intestinal disease that impairs absorption, certain long-term medications, and older age. Pernicious anemia—an autoimmune loss of intrinsic factor—is a known cause of impaired B12 absorption.

How B12 deficiency is evaluated

Initial tests often include a complete blood count (CBC) to check for anemia and mean corpuscular volume (MCV), plus serum B12 measurement. If results are unclear, methylmalonic acid (MMA) and homocysteine levels can provide more sensitive evidence of deficiency. When autoimmune causes are suspected, tests for intrinsic factor or parietal cell antibodies and gastroenterology assessment may be arranged.

Specialist referrals and next steps

Start with your primary care clinician for initial assessment and basic tests. Hematology may be involved for significant anemia, neurology for prominent neurological symptoms, and gastroenterology if an absorption problem or prior surgery is suspected. A specialist will advise on further testing and monitoring.

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