Tyrosine | Supplementopedia

Overview

Tyrosine (L‑tyrosine) is a non‑essential, aromatic amino acid that serves as a building block for proteins and a precursor to several biologically active compounds. These include:

The neurotransmitters dopamine, norepinephrine, and epinephrine
Thyroid hormones
Melanin

In humans, tyrosine is synthesized from phenylalanine or obtained directly from the diet. It supports neuro‑chemical and metabolic processes critical for:

Cognition
Stress response
Pigmentation

Benefits

Cognitive performance under stress: Randomized trials show that 2 g of L‑tyrosine improves working memory and mental flexibility during sleep deprivation or acute stress (e.g., military training, cold‑stress tests).
Mood and stress resilience: Supplementation (100–200 mg kg⁻¹) attenuates the decline in mood and reduces perceived stress in demanding tasks.
Physical performance: Small‑scale studies suggest 150–200 mg kg⁻¹ before prolonged exercise can reduce perceived exertion, likely via catecholamine support.
Thyroid support: As a substrate for thyroxine (T4) synthesis, tyrosine may aid individuals with sub‑optimal thyroid hormone production, though data are limited.
Phenylketonuria (PKU) management: In PKU patients, supplemental tyrosine improves growth and neuro‑developmental outcomes when dietary intake is insufficient.

How It Works

L‑Tyrosine enters cells via neutral amino‑acid transporters (LAT1/2).
Once inside, it is phosphorylated by tyrosine hydroxylase to L‑DOPA, the rate‑limiting step for catecholamine synthesis.
The resulting dopamine can be further converted to norepinephrine and epinephrine, augmenting sympathetic tone and cognition under stress.
Tyrosine also undergoes transamination to p‑hydroxyphenylpyruvate, entering the melanin pathway via dopa‑quinone, influencing skin and hair pigmentation.
In the thyroid gland, tyrosine residues on thyroglobulin are iodinated by thyroid peroxidase, forming T3/T4 after coupling.
By replenishing the intracellular pool, tyrosine sustains these pathways, especially when catecholamine turnover is high (e.g., acute stress, sleep deprivation), thereby stabilizing neurotransmission and hormonal output.

Dosage

General cognitive/ stress support: 500 mg–2 g per day, divided into 2–3 doses; the most studied acute dose is 2 g taken 30–60 min before a stressor or demanding task.
Exercise performance: 150–200 mg kg⁻¹ (≈10–15 g for a 70 kg adult) 30 min pre‑exercise; split dosing may reduce gastrointestinal discomfort.
Thyroid support / PKU: 50–150 mg kg⁻¹ per day, divided, under medical supervision.
Timing: On an empty stomach for faster absorption; food can reduce peak plasma concentrations.
Special considerations: Lower doses (250 mg) are advisable for beginners or those sensitive to stimulant‑like effects.

Safety & Side Effects

L‑Tyrosine is well tolerated at ≤5 g day⁻¹ for most adults. Common mild side‑effects include:

Nausea
Heartburn
Headache

Contraindications include:

(1) hyperthyroidism (excessive catecholamine/thyroid hormone synthesis may exacerbate symptoms)
(2) MAO‑inhibitor therapy (risk of hypertensive crisis due to elevated catecholamines)

Interactions:

levodopa (competition for transporters)
thyroid hormone replacement (possible dose‑adjustment needed)

Pregnant or lactating women, children, and individuals with phenylketonuria (due to phenylalanine conversion) should use only under clinical guidance. High doses (>10 g day⁻¹) may cause insomnia or anxiety.

Chemistry

IUPAC name: (2S)-2‑amino‑3‑(4‑hydroxyphenyl)propanoic acid.
Molecular formula: C₉H₁₁NO₃; Molar mass: 181.19 g mol⁻¹.
Structure: An α‑amino acid with a phenolic (‑OH) substituent at the para position of the aromatic ring, giving it both hydrophilic (carboxyl, amino) and aromatic characteristics. The p‑hydroxy group confers antioxidant activity and serves as the site for iodination in thyroid hormone synthesis. It is a zwitterion at physiological pH, with a pKa₁ ≈ 2.2 (carboxyl) and pKa₂ ≈ 9.1 (amino). Solubility: ~0.45 g L⁻¹ in water at 20 °C; soluble in dilute acid and alkaline solutions.

Sources & Quality

Dietary sources include high‑protein foods:

Dairy (cheese, yogurt)
Meat
Fish
Eggs
Soy products
Legumes
Nuts
Seeds

Commercial supplements are produced either by:

fermentation of genetically engineered Escherichia coli
chemical synthesis from phenylacetate

Both methods yield high‑purity L‑tyrosine (>98 %). Extraction from natural protein hydrolysates is also used but may contain mixed amino‑acids. Quality considerations:

certificate of analysis (COA) confirming enantiomeric purity (L‑form)
absence of heavy metals
compliance with USP/NF or EFSA standards

For clinical use, GMP‑certified production and third‑party testing (e.g., USP, NSF) are recommended to ensure purity and minimize contaminants.