vitamin B₁₂ deficiency

References

vitamin B₁₂ deficiency

pathology

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 14, 2026

Quick Summary

Vitamin B12 deficiency, often leading to pernicious anemia, occurs when the body cannot absorb enough of this essential nutrient. Vitamin B12 is crucial for developing red blood cells and maintaining healthy nerve cells. Its absorption relies on a substance called intrinsic factor, produced by the stomach. Without sufficient intrinsic factor, vitamin B12 cannot be absorbed, impairing DNA synthesis and red blood cell maturation.12

Symptoms can include fatigue, weakness, neurological issues like numbness or instability, and gastrointestinal disturbances. Strict vegetarians may also be at risk if not supplementing. Treatment involves lifelong vitamin B12 injections, though neurological damage may not be fully reversible. Malabsorption tests can help diagnose the cause of deficiency.123

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

3 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

blood disease
Megaloblastic anemias
A deficiency of vitamin B₁₂ leads to disordered production of DNA and hence to the impaired production of red cells. Unlike other vitamins, it is formed not by higher plants but only by certain bacteria and molds and in the rumen (first stomach chamber) of sheep…
Read More
A deficiency of vitamin B₁₂ leads to disordered production of DNA and hence to the impaired production of red cells. Unlike other vitamins, it is formed not by higher plants but only by certain bacteria and molds and in the rumen (first stomach chamber) of sheep…
Read More

digestive system disease
Tropical sprue
…anemia caused by malabsorption of vitamin B₁₂ develops. Steatorrhea (excess fat in stools) is common, and glucose absorption is impaired. Prolonged treatment with antibiotics, such as tetracycline, and the replacement of vitamins, especially B₁₂ and folic acid, are successful.
Read More
…anemia caused by malabsorption of vitamin B₁₂ develops. Steatorrhea (excess fat in stools) is common, and glucose absorption is impaired. Prolonged treatment with antibiotics, such as tetracycline, and the replacement of vitamins, especially B₁₂ and folic acid, are successful.
Read More

nervous system disease
Subacute combined degeneration
…degeneration, which results from a vitamin B₁₂ deficiency, causes demyelination of the corticospinal and the dorsal columns. Much of the damage is to the large dorsal-root ganglion neurons; the peripheral nerve fibres also demyelinate, so that peripheral neuropathy also occurs. Symptoms include tingling, numbness, weakness, mental disturbances, and vision changes.…
Read More
…degeneration, which results from a vitamin B₁₂ deficiency, causes demyelination of the corticospinal and the dorsal columns. Much of the damage is to the large dorsal-root ganglion neurons; the peripheral nerve fibres also demyelinate, so that peripheral neuropathy also occurs. Symptoms include tingling, numbness, weakness, mental disturbances, and vision changes.…
Read More