Overview
Anaemia caused by vitamin B12 or folate deficiency is a form of megaloblastic anaemia, in which the body produces abnormally large and immature red blood cells due to impaired DNA synthesis. Both vitamin B12 (cobalamin) and folate (vitamin B9) are essential for red blood cell formation, neurological function, and DNA synthesis. Deficiency in either nutrient leads to reduced red cell production, ineffective erythropoiesis, and characteristic symptoms of anaemia such as fatigue, pallor, and breathlessness.
Causes
Vitamin B12 Deficiency
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Pernicious anaemia: An autoimmune condition that prevents absorption of vitamin B12 due to lack of intrinsic factor.
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Dietary deficiency: Common in strict vegans who avoid animal products, as B12 is found mainly in meat, fish, dairy, and eggs.
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Malabsorption: Conditions such as Crohn’s disease, coeliac disease, or surgical removal of the stomach/ileum reduce absorption.
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Medications: Long-term use of proton pump inhibitors (PPIs), H2 blockers, or metformin can impair absorption.
Folate Deficiency
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Poor dietary intake: Seen in diets low in green leafy vegetables, beans, and fortified cereals.
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Increased demand: Pregnancy, lactation, and conditions with rapid cell turnover (e.g., haemolysis, malignancy).
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Malabsorption: Coeliac disease, tropical sprue.
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Alcoholism: Impairs folate metabolism and absorption.
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Medications: Methotrexate, phenytoin, sulfasalazine, and trimethoprim interfere with folate metabolism.
Symptoms
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General anaemia symptoms: Fatigue, weakness, pallor, shortness of breath, palpitations, dizziness.
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Neurological symptoms (B12 deficiency only): Tingling and numbness in hands and feet (peripheral neuropathy), balance problems, memory loss, mood changes, in severe cases dementia.
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Gastrointestinal symptoms: Glossitis (inflamed, sore tongue), loss of appetite, weight loss, diarrhoea.
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Pregnancy-related effects (folate deficiency): Increased risk of neural tube defects in the developing fetus.
Diagnosis
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Blood tests: Full blood count (shows macrocytic anaemia, high mean corpuscular volume), serum B12, serum folate.
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Peripheral blood smear: Shows large, oval-shaped red cells (macro-ovalocytes) and hypersegmented neutrophils.
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Additional tests:
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Intrinsic factor antibody test (for pernicious anaemia).
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Homocysteine and methylmalonic acid levels (elevated in B12 deficiency, only homocysteine elevated in folate deficiency).
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Treatment
Vitamin B12 Deficiency
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Hydroxocobalamin injection (first-line in the UK):
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Dose: 1 mg intramuscularly, given every other day for 2 weeks, then 1 mg every 2–3 months for life if due to pernicious anaemia or irreversible causes.
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Cyanocobalamin (oral or injection):
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Dose: 50–150 mcg orally daily (only if deficiency due to diet, not malabsorption).
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Neurological symptoms may take several months to improve, and early treatment is crucial to prevent permanent damage.
Folate Deficiency
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Folic acid tablets:
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Dose: 5 mg orally once daily for at least 4 months (longer if underlying cause persists, e.g., haemolysis).
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Women planning pregnancy or in early pregnancy should take 400 mcg daily to prevent neural tube defects, increasing to 5 mg daily in high-risk women (diabetes, obesity, family history, or on anticonvulsants).
Important Note: Folate supplementation should never be started before excluding B12 deficiency, as correcting folate alone can worsen neurological complications of undiagnosed B12 deficiency.
Lifestyle and Dietary Advice
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Increase intake of foods rich in vitamin B12 (meat, fish, dairy, eggs, fortified cereals) and folate (green leafy vegetables, beans, citrus fruits, fortified bread/cereals).
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Limit alcohol consumption.
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For vegans, long-term supplementation of vitamin B12 is essential.
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In pregnancy, folic acid supplementation is routine.
Complications
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Neurological complications: Irreversible nerve damage in untreated B12 deficiency.
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Pregnancy risks: Neural tube defects in folate deficiency.
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Cardiovascular risks: High homocysteine levels increase risk of stroke and heart disease.
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Severe anaemia: Can lead to heart failure if untreated.
Prognosis
With early diagnosis and treatment, the prognosis is generally excellent. Most symptoms resolve with appropriate supplementation. However, delayed treatment of vitamin B12 deficiency may lead to permanent neurological damage
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