Tyrosine is a non-essential amino acid, one of the 22 overall chemical compounds required to synthesise proteins. Its name comes from the Greek word meaning cheese, as it is one of the primary derivatives of the protein, casein, found in cheese and dairy products. Casein, together with another similar amino acid, phenylalanine, occurs naturally in breast milk, which also produces tyrosine.
Good dietary sources of tyrosine include most high-protein foods such as milk and dairy products, meat, poultry, fish, some seeds, nuts and legumes, bananas and avocados.
Tyrosine is metabolised in the brain by a related enzyme involved in the production of the neurotransmitter, dopamine. Dopamine is then converted into the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) which instigate the human fight-or-flight response.
These neurotransmitters play an important role during conditions of stress, such as prolonged periods of work, fatigue, sleep deprivation, and cold. In animal trials, researchers have found tyrosine reduces stress hormone levels and weight loss induced by stress, while in humans they found it improved physical and cognitive performance, especially working memory when multi-tasking.
Tyrosine is also closely involved in supplying the thyroid hormones which govern almost all of the body's physiological processes.