🔑 Core Function

• Serotonin synthesis: Precursor to serotonin → influences mood, appetite, and cognition.
• Sleep regulation: Serotonin → melatonin, helping regulate circadian rhythm and sleep.
• Niacin precursor: Converts to vitamin B3 via the kynurenine pathway (requires iron, B6, B2).
• Protein building block: Incorporated into structural and enzymatic proteins.

🧬 Family & Essentiality

🌿 Plain-Language Summary

Tryptophan is the “mood and sleep amino acid”. Your body uses it to make serotonin (for mood and appetite), melatonin (for sleep), and even niacin (vitamin B3). Because the body doesn’t store much of it, a steady supply from food is essential.

⚗️ Molecular & Chemical IDs

• Abbreviation: Trp / W
• Chemical formula: C₁₁H₁₂N₂O₂
• Structure: Aromatic indole side chain

⚡ Functions

• Neurotransmitters: Tryptophan → serotonin → melatonin.
• Vitamin B3 precursor: ~60 mg tryptophan ≈ 1 mg niacin (with iron, B6, B2 as cofactors).
• Kynurenine pathway: Produces metabolites with roles in immune & brain function.
• Protein role: Incorporated into enzymes, structural proteins, and hormones.

🍽️ Absorption & Bioavailability

🇦🇺 Australian NRVs (NHMRC)

• Adults (≥19 yrs) EAR: ~4 mg/kg/day
• RDI: ~6 mg/kg/day

Values based on NHMRC/FAO/WHO amino-acid requirement data, expressed per kilogram body weight.

🥗 Food Sources

• Poultry (turkey, chicken)
• Dairy (milk, yoghurt, cheese)
• Eggs
• Nuts & seeds (pumpkin, sesame, sunflower)
• Soy, legumes, oats, bananas

Myth check: Turkey isn’t uniquely high in tryptophan — many protein foods contain similar amounts.

🧪 Testing & Monitoring

• Plasma amino acid profiling (specialist use).
• Research assays measure serotonin/kynurenine metabolites.
• ❌ Not part of routine GP testing in Australia.

🔄 Interactions

• ➕ Requires vitamin B6, riboflavin (B2), and iron for serotonin & niacin synthesis.
• ⚠️ Deficiency or poor conversion → low serotonin → possible mood/sleep disturbance.
• ⚠️ Supplement caution: High-dose tryptophan/5-HTP may raise serotonin; avoid with SSRIs/antidepressants (risk: serotonin syndrome).

🚨 Deficiency & Evidence

Deficiency

Rare in varied diets; low intake or impaired metabolism may affect serotonin/melatonin balance and contribute to niacin deficiency (pellagra risk in extreme cases).

Evidence Snapshot

• ✅ Established: Precursor for serotonin, melatonin, niacin; essential for protein synthesis.
• ⚖️ Contextual: Supplement trials show modest benefits for sleep/mild mood disturbances; evidence mixed, diet adequacy remains key.