Vitamin B12 Deficiency
Low B12 causing macrocytic anaemia and potentially irreversible neurological damage.
Overview
Vitamin B12 deficiency is common, especially in older adults, vegans and people on long-term metformin or proton pump inhibitors. Neurological symptoms can occur without anaemia and become irreversible if treatment is delayed.
Symptoms
- • Fatigue, breathlessness, palpitations
- • Glossitis (sore, red tongue), mouth ulcers
- • Paraesthesia, numbness, ataxia
- • Cognitive change, depression, irritability
- • Pale or mildly jaundiced skin
Risk factors
- • Age >60
- • Vegan diet without supplementation
- • Gastric surgery, autoimmune disease
- • Long-term metformin or PPI use
Causes
- • Pernicious anaemia (autoimmune loss of intrinsic factor)
- • Dietary deficiency (vegan/vegetarian, food insecurity)
- • Malabsorption: coeliac, Crohn's, ileal resection, bacterial overgrowth
- • Drugs: metformin, PPIs, H2 blockers, nitrous oxide misuse
🚨 Red flags — seek urgent care
- • Subacute combined degeneration: progressive weakness, ataxia, sensory loss
- • New cognitive decline in older adult
- • Severe pancytopenia
When to seek care
- • Unexplained fatigue with macrocytic anaemia
- • Neurological symptoms in someone at risk
- • Tongue soreness or recurrent ulcers
Diagnosis
- • Serum B12 — low <148 pmol/L; borderline 148–258 pmol/L (check MMA / homocysteine)
- • FBC: macrocytosis, hypersegmented neutrophils; co-existing iron/folate deficiency may mask
- • Anti-intrinsic factor and anti-parietal cell antibodies for pernicious anaemia
- • Coeliac screen if malabsorption suspected
Treatment
- • Pernicious anaemia / neurological involvement: IM hydroxocobalamin 1 mg alternate days until improvement, then every 2–3 months for life
- • Dietary deficiency: oral cyanocobalamin 50–150 µg daily and address diet
- • Treat coexisting folate / iron deficiency — give B12 first to avoid worsening neurology
- • Stop or replace contributing drugs where possible
Prevention
- • Vegans and vegetarians: regular B12-fortified foods or supplements
- • Monitor B12 in long-term metformin or PPI users
- • Screen at-risk groups (gastric surgery, autoimmune disease)
Complications
- • Irreversible neurological damage
- • Heart failure from severe anaemia
- • Gastric cancer (pernicious anaemia — 2–3× risk)
- • Infertility, glossitis
Prognosis
Haematological response within weeks. Early neurological symptoms recover; longstanding deficits may persist.
Education & self-care
B12 deficiency is easily missed and easily treated. If you're at risk (vegan, on metformin or a PPI, history of gastric surgery), ask for a level.
Frequently asked questions
Can I take B12 tablets instead of injections?
High-dose oral B12 works for dietary deficiency; pernicious anaemia and neurological cases need injections.
Will my numbness fully recover?
Recent symptoms often resolve. Longstanding numbness or ataxia may improve only partly — early treatment matters.
Are injections better than tablets?
Injections are essential for pernicious anaemia or significant absorption problems. High-dose oral B12 (1,000–2,000 mcg daily) is effective for dietary deficiency and many mild cases.
Can the nerve damage be reversed?
Symptoms that have been present less than 6 months usually resolve fully with replacement. Long-standing damage can leave permanent neurological deficit, so early treatment matters.
Who is at risk?
Vegans and strict vegetarians, older adults, people on long-term metformin or PPIs, those with coeliac or Crohn's disease, and post-gastric/bariatric surgery.