🔑 Core Function

• Protein synthesis: Incorporated into proteins for growth and repair.
• Haemoglobin support: Required for haem formation and oxygen transport.
• Precursor to histamine: Via histidine decarboxylase; supports immune response, gastric acid secretion, and neurotransmission.
• pH buffering: Imidazole side chain helps buffer acids in blood and tissues.

🧬 Family & Essentiality

🌿 Plain-Language Summary

Histidine is one of the nine essential amino acids you need to get from food. It helps your body build proteins, make red blood cells, and produce histamine — important for immunity, digestion, and alertness.

⚗️ Molecular & Chemical IDs

• Abbreviation: His / H
• Chemical formula: C₆H₉N₃O₂
• Side chain: Imidazole group (key for acid–base buffering)

⚡ Functions

• Protein building: Incorporated into enzymes, structural proteins, and transporters.
• Blood health: Essential for haemoglobin and red cell production.
• Histamine production: Histidine → histamine (immune & gastric roles).
• Carnosine precursor: Combines with β-alanine to form carnosine (muscle antioxidant/acid buffer).

🍽️ Absorption & Bioavailability

🇦🇺 Australian NRVs (NHMRC)

• Adults (≥19 yrs) EAR: ~10 mg/kg/day
• RDI: ~14 mg/kg/day

Values reflect amino-acid requirements expressed per kilogram body weight (NHMRC/FAO/WHO frameworks).

🥗 Food Sources

• Meat, poultry, fish
• Dairy (milk, cheese, yoghurt); eggs
• Legumes, soy products, whole grains, nuts

Adequate protein diets generally supply sufficient histidine.

🧪 Testing & Monitoring

• Plasma amino-acid profiling (specialist labs) when clinically indicated.
• ❌ Not a routine clinical test.

🔄 Interactions

• Requires balance with other essential amino acids (e.g., lysine, methionine).
• Vitamin B6 (pyridoxal-5-phosphate) is a cofactor for histidine → histamine conversion.

🚨 Deficiency & Evidence

Deficiency

Rare outside severe protein–energy malnutrition; consider overall protein adequacy and clinical context.

Evidence Snapshot

• ✅ Established: Essential for protein synthesis, haemoglobin production, and histamine formation.
• ⚖️ Emerging: Carnosine (histidine-derived) studied for muscle performance and healthy ageing; evidence is developing.