Tyrosine – Amino Acid, Functions and Deficiency
Tyrosine is a conditionally essential amino acid that the body produces from phenylalanine and serves as a precursor for key neurotransmitters such as dopamine and adrenaline.
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Tyrosine is a conditionally essential amino acid that the body produces from phenylalanine and serves as a precursor for key neurotransmitters such as dopamine and adrenaline.
What is Tyrosine?
Tyrosine (also known as L-tyrosine) is an amino acid that the human body can synthesize on its own, provided that sufficient phenylalanine is available. For this reason, it is classified as a conditionally essential amino acid. Tyrosine plays numerous important roles in the body, most notably as a building block for hormones and neurotransmitters.
Biological Functions
Tyrosine is involved in the production of several vital substances:
- Neurotransmitters: Tyrosine is the direct precursor of dopamine, norepinephrine, and epinephrine – messengers that regulate mood, motivation, stress response, and concentration.
- Thyroid hormones: Tyrosine is a structural component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which control metabolism.
- Melanin: As a precursor to melanin, tyrosine is involved in the pigmentation of skin, hair, and eyes.
Dietary Sources
Tyrosine is found in many protein-rich foods, including:
- Meat and poultry
- Fish and seafood
- Dairy products (e.g., cheese, yogurt)
- Eggs
- Legumes (e.g., soybeans, lentils)
- Nuts and seeds (e.g., pumpkin seeds, almonds)
Recommended Intake
There is no specific daily intake recommendation for tyrosine alone. The WHO recommends a combined intake of phenylalanine and tyrosine of approximately 25 mg per kilogram of body weight per day. A balanced, protein-rich diet typically covers this requirement without difficulty.
Tyrosine as a Dietary Supplement
L-tyrosine is widely marketed as a dietary supplement, particularly to support concentration, mental performance, and stress resilience. Some studies suggest that additional tyrosine intake may temporarily improve cognitive performance during stressful situations or sleep deprivation.
Typical dosages in supplements range from 500 mg to 2,000 mg per day. It is ideally taken on an empty stomach or between meals, as other amino acids can compete for absorption.
Deficiency and Risk Groups
An isolated tyrosine deficiency is rare. However, individuals with the metabolic disorder phenylketonuria (PKU) are unable to convert phenylalanine into tyrosine and therefore rely on a tyrosine-rich diet or supplementation.
Possible symptoms of deficiency may include:
- Fatigue and mood fluctuations
- Difficulty concentrating
- Reduced thyroid hormone levels
- Changes in skin pigmentation
Safety and Interactions
Tyrosine is generally considered safe at supplemental doses. However, the following individuals should consult a physician before use:
- People taking MAO inhibitors (MAOIs), as the combination can dangerously raise blood pressure.
- People with hyperthyroidism (overactive thyroid), since tyrosine may stimulate thyroid hormone production.
- People with melanoma, as tyrosine can promote melanin production.
References
- World Health Organization (WHO) – Protein and Amino Acid Requirements in Human Nutrition. Report of a Joint WHO/FAO/UNU Expert Consultation, 2007.
- Jongkees B.J. et al. – Effect of tyrosine supplementation on clinical and healthy populations under stress and cognitive demands: A review. Journal of Psychiatric Research, 2015.
- Fernstrom J.D., Fernstrom M.H. – Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. Journal of Nutrition, 2007.
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