Sulphur-containing essential amino acid • Methyl donor • Antioxidant precursor. Educational profile — independent, evidence-informed overview. This content is not medical advice. Please consult your healthcare provider for personalised guidance.
🔑 Core Function
- Methylation donor: Provides methyl groups via S-adenosylmethionine (SAMe) for DNA, neurotransmitters, and phospholipids.
- ️ Antioxidant support: Precursor to cysteine → glutathione (the body’s master antioxidant).
- Collagen & connective tissue: Contributes sulphur for cartilage, skin, and nails.
- ⚡ Metabolic role: Initiator amino acid in protein synthesis (start codon = AUG).
🧬 Family & Essentiality
ClassEssential sulphur amino acid
EssentialityMust be obtained from diet
PartnershipInteracts with cysteine; requirement often expressed as Met + Cys
🌿 Plain-Language Summary
Methionine is like a molecular multitool. It starts every new protein your cells build, fuels key methylation reactions for DNA and neurotransmitters, and supplies sulphur to make glutathione, the body’s master antioxidant.
⚗️ Molecular & Chemical IDs
- Abbreviation: Met / M
- Chemical formula: C₅H₁₁NO₂S
- Structure: Sulphur-containing, non-polar side chain
⚡ Functions
- Methyl donor: Via SAMe, supports DNA methylation, neurotransmitters, phospholipids.
- ️ Antioxidant: Provides cysteine for glutathione production.
- Structural: Supplies sulphur for hair, skin, nails.
- Protein synthesis: Universal initiator amino acid in translation (start codon AUG).
🍽️ Absorption & Bioavailability
AbsorptionWell absorbed from dietary proteins
NotePlant proteins (grains/legumes) generally lower in methionine than animal proteins
🇦🇺 Australian NRVs (NHMRC)
- Adults (≥19 yrs) EAR: ~10 mg/kg/day (Met + Cys)
- RDI: ~15 mg/kg/day (Met + Cys)
Values based on NHMRC/FAO/WHO amino-acid requirement data, expressed as total sulphur amino acids (methionine + cysteine).
🥗 Food Sources
- Meat, poultry, fish
- Dairy (milk, cheese, yoghurt)
- Eggs
- Nuts, seeds, whole grains, legumes (lower amounts than animal foods)
Tip: Combining legumes + grains improves Met/Cys adequacy in plant-based diets.
🧪 Testing & Monitoring
- Plasma amino acid profiling (specialist use).
- ❌ Not a standard GP pathology test in Australia.
🔄 Interactions
- ➕ Works with folate, vitamin B12, and vitamin B6 in methylation cycles (homocysteine metabolism).
- ⚠️ Low B-vitamin status → impaired methionine metabolism → homocysteine accumulation (vascular risk marker).
- ➕ Partnered with cysteine to meet sulphur amino acid requirements.
🚨 Deficiency & Evidence
Deficiency
Uncommon with adequate protein intake; low levels may impact methylation, glutathione production, and connective tissue health.
Evidence Snapshot
- ✅ Established: Crucial for protein initiation, methylation reactions, and glutathione production.
- ⚖️ Contextual: Excess intake without adequate B-vitamin support may raise homocysteine; balanced diets mitigate this.
