Vitamin B12 (Cobalamin)
Vitamin B12 is essential for DNA synthesis, red blood cell formation and nerve function. Deficiency causes macrocytic anaemia and neurological symptoms.
What it measures
Vitamin B12 comes from animal foods (meat, fish, dairy, eggs) and is absorbed in the terminal ileum with help from intrinsic factor secreted by the stomach. Liver stores hold years of B12, so deficiency develops slowly and can present without obvious dietary cause. Serum B12 is the standard screening test, but it can be normal in early deficiency — methylmalonic acid (more specific) and homocysteine (less specific) help confirm borderline cases.
What a high value can mean
- Recent supplementation or B12 injections — almost always the cause.
- Liver disease — released B12 stores.
- Myeloproliferative neoplasms, certain leukaemias — rarely.
- High values are usually not actionable; the value matters when low.
What a low value can mean
- Vegan / strict vegetarian diet — without supplementation, depletion is essentially inevitable.
- Pernicious anaemia — autoimmune destruction of gastric parietal cells, classic cause in older adults.
- Metformin — long-term use lowers B12 by 5–10% on average; check yearly in treated diabetics.
- Gastric surgery, ileal disease (Crohn's), proton pump inhibitors, atrophic gastritis.
- Older age — declining absorption is common.
When to discuss with a doctor
Symptoms of B12 deficiency (fatigue, paraesthesias, balance problems, glossitis) with a borderline-low value warrant follow-up with methylmalonic acid and a clinician visit. Neurological symptoms can be irreversible if deficiency is left untreated — see a doctor promptly. Mediora.AI flags borderline B12 alongside MCV (macrocytosis) in your report.