Vitamin B12 Deficiency: Symptoms, Who Is at Risk, and How to Treat It

Vitamin B12 Deficiency: Symptoms, Causes, and Treatment

Vitamin B12 is essential for red blood cell formation, neurological function, and DNA synthesis. Deficiency is common — affecting up to 6% of adults under 60 and 20% of those over 60 — and can cause serious, sometimes irreversible neurological damage if untreated.

Why B12 Deficiency Develops Slowly

The liver stores 2-5 years' worth of B12. This means deficiency develops gradually, often without symptoms for years. By the time symptoms appear, deficiency may be severe.

Symptoms of B12 Deficiency

Hematological (from megaloblastic anemia):

• Fatigue and weakness
• Pale or jaundiced skin
• Shortness of breath
• Rapid heartbeat

Neurological (most serious — can be irreversible):

• Numbness or tingling in hands and feet (peripheral neuropathy)
• Difficulty walking and balance problems
• Weakness
• Vision changes
• Memory problems and cognitive decline
• Depression and mood changes

Other:

• Sore, red, smooth tongue (glossitis)
• Mouth ulcers
• Nausea and loss of appetite

Who Is at Risk

Vegans and strict vegetarians: B12 is found almost exclusively in animal products. Vegans must supplement.

Older adults: Gastric acid production decreases with age, impairing B12 absorption. Atrophic gastritis affects 10-30% of older adults.

People taking metformin: Metformin reduces B12 absorption; annual B12 monitoring recommended.

People taking PPIs long-term: Proton pump inhibitors reduce gastric acid needed for B12 absorption.

Pernicious anemia: Autoimmune condition destroying intrinsic factor (needed for B12 absorption). Most common cause of severe B12 deficiency.

Gastrointestinal surgery: Gastric bypass, ileal resection reduce absorption.

Celiac and Crohn's disease: Malabsorption syndromes.

Diagnosis

• Serum B12: < 200 pg/mL is deficient; 200-300 pg/mL is borderline
• Methylmalonic acid (MMA): More sensitive marker; elevated in B12 deficiency
• Homocysteine: Elevated in B12 and folate deficiency
• CBC: Shows macrocytic anemia (large red blood cells)

Treatment

Intramuscular injections (B12/cyanocobalamin or hydroxocobalamin):

• Bypasses absorption issues; used for pernicious anemia and severe deficiency
• Typically 1,000 mcg daily for 1 week, then weekly for 1 month, then monthly

High-dose oral B12:

• 1,000-2,000 mcg/day is effective even in pernicious anemia (passive absorption bypasses intrinsic factor)
• Preferred by many patients over injections

Sublingual B12:

• Absorbed under the tongue; similar efficacy to oral

Dietary sources:

• Beef liver (highest), clams, fish, meat, poultry, eggs, dairy
• Fortified cereals and plant milks for vegans

Medical Disclaimer

B12 deficiency with neurological symptoms requires urgent medical evaluation and treatment. Do not delay treatment if neurological symptoms are present.