🧬 Family & Essentiality

🌿 Plain-Language Summary

Vitamin B12 is crucial for red blood cell formation, neurological function, and DNA synthesis. It is naturally found in animal-derived foods, and absorption requires a multi-step process involving intrinsic factor. Deficiency can lead to anaemia, neurological impairment, and irreversible damage if untreated.

⚗️ Molecular & Chemical IDs

• Cobalamin core: corrin ring with central cobalt atom
• CAS: varies by form (e.g., cyanocobalamin 68-19-9)
• Transport: Active B12 carried by transcobalamin II (holo-TC) in circulation

⚡ Functions

• Cofactor for methionine synthase (homocysteine → methionine; methylation cycle)
• Cofactor for methylmalonyl-CoA mutase (propionate metabolism → succinyl-CoA)
• Supports DNA synthesis, cell division, and normal neurological function

🍽️ Absorption & Bioavailability

At-risk: pernicious anaemia, gastric surgery, long-term metformin or PPIs, elderly, strict vegans/vegetarians.

🇦🇺 Australian NRVs (NHMRC)

• Adults: 2.4 µg/day
• Pregnancy: 2.6 µg/day
• Lactation: 2.8 µg/day

UL (Upper Level): Not established

🚨 Deficiency & Excess

Deficiency

• Megaloblastic anaemia
• Neurological: numbness, tingling, balance problems, cognitive changes
• Glossitis, fatigue, pallor
• Biochemical: ↑ methylmalonic acid (MMA), ↑ homocysteine

Clinical alert: Untreated deficiency can cause irreversible neurological damage. Prompt diagnosis and management are critical.

Excess

No adverse effects from food intake reported. Very high-dose supplementation generally well tolerated, but unnecessary in replete individuals.

🥗 Food Sources

• Animal foods: meat, fish, eggs, dairy
• Fortified plant milks and cereals (check AU labels)

🧪 Testing & Monitoring

• Total serum B12: Screening test; may be normal in early deficiency
• Holotranscobalamin (holo-TC): Active fraction; useful in borderline cases
• MMA & Homocysteine: Functional markers — elevated in deficiency
• Interpret results alongside clinical context and dietary history

🔗 Interactions

• Medications: Metformin, proton pump inhibitors, H2 blockers, nitrous oxide exposure
• GI factors: Bariatric/gastric surgery, atrophic gastritis

💊 Supplement Notes

• Hydroxocobalamin: Common injectable form in Australia (PBS listed); long-acting
• Methylcobalamin: Active coenzyme form; sometimes used for neurological focus
• Cyanocobalamin: Stable synthetic form; effective, but less preferred
• Choice of form and route (oral vs injectable) depends on clinical context and prescriber judgement

📊 Evidence Snapshot

• 🔬✅ Well-established: Prevention/treatment of deficiency; essential for haematologic and neurologic function
• 🧪⚖️ Clinical: Injections standard for deficiency due to malabsorption or IF loss
• ⚠️❌ Unproven/hype: Routine high-dose use in replete individuals