Vitamin B12 deficiency
Linked to Vitamin B12 (Cobalamin)
A shortage of B12 harms red blood cells and nerves, causing anaemia and neurological signs.
Where it shows on the body
Rotate the figure and click a red marker to see the affected area. Internal organs open a 3D organ model.
Causes
- Vegan/vegetarian diet without fortification
- Pernicious anaemia (poor absorption)
- Older age
- Some medications
Symptoms
- Fatigue
- Tingling or numbness in hands and feet
- Memory and mood changes
- Sore, red tongue
- Pale or jaundiced skin
- Balance problems
What happens if untreated
- Irreversible nerve damage if untreated
- Megaloblastic anaemia
- Cognitive decline
Who is most at risk
- Vegans and vegetarians
- Older adults
- People with digestive disorders
Prevention & sources
- B12-rich or fortified foods
- Injections or high-dose supplements where absorption is poor
Correcting it: foods, amounts & timing
Foods that help & safe amounts
- Meat, fish, eggs and dairy — a serving most days
- Fortified plant milks and cereals if vegetarian or vegan
- Supplement or injections where absorption is poor (as prescribed)
Energy can lift within a couple of weeks; nerve symptoms improve over 3–6 months, and long-standing nerve damage may be permanent.
Sources & references
Symptoms overlap — testing matters
Most deficiency symptoms (fatigue, poor concentration, skin and hair changes) are shared across several nutrients and many unrelated conditions. A symptom on this page is a reason to investigate, not a diagnosis.
A GP can confirm or rule out a deficiency with a blood test and check for underlying causes such as absorption problems. Do not start high-dose supplements on suspicion alone — some nutrients are harmful in excess, and supplementing before testing can mask the underlying result.