Vitamin B12 deficiency causes both anemia and neurological symptoms, with neurological damage potentially irreversible if treatment is delayed. The signs of b12 deficiency can be subtle and develop gradually. This guide covers symptoms, causes, and who needs testing. Always discuss with your healthcare provider.
Common symptoms
Hematologic (from megaloblastic anemia):
- Fatigue, weakness
- Pale skin
- Shortness of breath
- Rapid heartbeat
Neurological (often more concerning):
- Numbness or tingling in hands and feet (peripheral neuropathy)
- Balance problems
- Memory issues, cognitive decline
- Mood changes
- Glossitis (smooth, sore tongue)
- Severe deficiency: subacute combined degeneration (spinal cord problems)
Neurological symptoms can occur without anemia, particularly in early or moderate deficiency.
Causes
- Pernicious anemia (autoimmune destruction of intrinsic factor)
- Atrophic gastritis (especially in elderly)
- Gastric bypass surgery
- Crohn’s disease, ileal resection
- Vegan diet without supplementation
- Long-term metformin use
- Long-term proton pump inhibitor use
- Long-term H2 blocker use
Diagnosis
Initial: serum B12 level. Borderline values may need confirmation with methylmalonic acid (MMA), which is elevated in B12 deficiency. See our B12 test guide.
Treatment
- Oral B12 (1000-2000 mcg daily): effective for most including pernicious anemia
- IM injection: 1000 mcg daily for a week, then weekly for a month, then monthly
- Sublingual or nasal preparations also available
The NIH Office of Dietary Supplements provides detailed guidance.
Frequently Asked Questions
Can B12 deficiency cause permanent damage?
Yes. Severe or longstanding deficiency can cause permanent neurological damage if untreated.
Why are vegans at risk?
B12 is found in animal products. Vegans need supplementation or fortified foods.
How quickly do symptoms improve with treatment?
Anemia resolves in weeks. Neurological symptoms may take months and may not fully reverse.
Should I take B12 just to be safe?
Low risk of toxicity. Reasonable supplementation for at-risk groups.
Can metformin cause B12 deficiency?
Yes, long-term use is associated with deficiency. Periodic testing recommended.
The bottom line on B12 deficiency
B12 deficiency causes both anemia and potentially irreversible neurological damage. Multiple risk factors. Treatment with oral or IM B12 is effective. Discuss testing with your healthcare provider.