🔑 Core Function

• Neurotransmitter precursor: Converts to tyrosine → dopamine, norepinephrine, epinephrine.
• Pigment formation: Needed for melanin synthesis (skin, hair, eyes).
• Protein synthesis: Incorporated into structural and functional proteins.
• Mood & cognition: Via neurotransmitters, influences alertness and mental health.

🧬 Family & Essentiality

🌿 Plain-Language Summary

Phenylalanine is a neurochemical gateway. It is used to make tyrosine, the building block for key brain chemicals like dopamine and adrenaline. It also helps form melanin pigment and supports normal protein production.

⚗️ Molecular & Chemical IDs

• Abbreviation: Phe / F
• Chemical formula: C₉H₁₁NO₂
• Structure: Aromatic side chain (benzyl group)

⚡ Functions

• Brain chemistry: Precursor for dopamine, norepinephrine, epinephrine.
• Pigmentation: Converted to melanin in skin, eyes, hair.
• Protein role: Incorporated into enzymes, structural proteins, hormones.
• Metabolic conversion: → Tyrosine → catecholamines + thyroid hormones.

🍽️ Absorption & Bioavailability

🇦🇺 Australian NRVs (NHMRC)

• Adults (≥19 yrs) EAR: ~16 mg/kg/day (Phe + Tyr)
• RDI: ~22 mg/kg/day (Phe + Tyr)

Values reflect combined requirements for phenylalanine + tyrosine (NHMRC/FAO/WHO frameworks).

🥗 Food Sources

• Meat, poultry, fish
• Dairy (milk, yoghurt, cheese)
• Eggs
• Soy, legumes, nuts, seeds, whole grains

Aspartame (artificial sweetener) contains phenylalanine and must be avoided in PKU.

🧪 Testing & Monitoring

• Plasma amino acid profiling (specialist labs).
• Newborn screening (heel prick): Detects phenylketonuria (PKU) — inability to metabolise phenylalanine.
• ❌ Not a routine adult pathology test unless PKU or metabolic disease is suspected.

🔄 Interactions

• ⚠️ PKU: Deficiency of phenylalanine hydroxylase → toxic buildup. Requires lifelong phenylalanine restriction.
• ➕ Requires vitamin B6, folate, and iron for neurotransmitter synthesis.
• ⚖️ Competes with other amino acids for brain transport.

🚨 Deficiency & Evidence

Deficiency

Rare with adequate protein intake; clinical issues mainly relate to PKU or severe malnutrition.

Evidence Snapshot

• ✅ Established: Essential for protein synthesis; precursor to tyrosine and neurotransmitters.
• ⚖️ Contextual: Supplementation studied for mood, ADHD, and vitiligo — evidence mixed; not standard therapy.