Tyrosine is a nonessential amino acid the body makes from another amino acid called phenylalanine. The amino-acid L-Tyrosine is the biochemical precursor of the catecholamines dopamine and norepinephrine. Given the right circumstances Tyrosine supplementation can enhance dopamine and Norepinephrine levels in the brain (Click here to know more).
Therefore several studies have explored whether tyrosine supplementation can have a beneficial effect on cognitive and behavioural performance that is dependent on dopaminergic function.
Tyrosine also helps produce melanin, the pigment responsible for hair and skin colour. It helps in the function of organs responsible for making and regulating hormones, including the adrenal, thyroid, and pituitary glands (Click here to know more).
Tyrosine is found in soy products, chicken, turkey, fish, peanuts, almonds, avocados, bananas, milk, cheese, yogurt, cottage cheese, lima beans, pumpkin seeds, and sesame seeds.
Plasma Tyrosine levels peak between 1 and 2h after consumption and can remain significantly elevated up to 8h. Once it has passed the blood-brain barrier (BBB) and is taken up by the appropriate brain cells, Tyrosine is converted into L-DOPA through an enzyme called tyrosine-hydroxylase (Click here to know more).
L-DOPA is converted into Dopamine, resulting in an increase in Dopamine level. In turn, Dopamine can be converted into Norepinephrine through the enzyme dopamine beta-hydroxylase. The last three compounds (Dopamine, NA, Adrenaline) are collectively referred to as ‘Catecholamines’.
L-Tyrosine can reverse a process called neurotransmitter depletion, in which increased brain activity leads to decreased Dopamine and Norepinephrine levels, with behavioural performance levels declining accordingly.
To understand this, let’s understand this example. When exposed to stress or a cognitively challenging task, catecholamine neurons become more active and their synthesis rate increases. As more neurotransmitters are synthesized to meet the situational demands, the resource from which they are synthesized, namely Tyrosine, is expended (Click here to know more).
Synthesis becomes limited once Tyrosine runs low, leading to less neurotransmitter availability and corresponding decrements in performance. In this situation Tyrosine might benefit brain function by providing the resources necessary to allow neurotransmitter synthesis to continue and maintain catecholamine levels needed to ensure optimal performance.
The World Health Organization’s daily upper requirement of Tyrosine is 14mg/kg, meaning an individual weighing 70kg needs to consume approximately 1g of Tyrosine per day for normal functioning. Doses far exceeding 1g are unlikely to confer any additional benefits (Click here to know more).
The main effects of L-tyrosine that have been reported are acute effects in preventing a decline in cognitive function in response to physical stress. The physical stressors include those of interest to the military, such as cold stress, the combination of cold stress and high-altitude stress (i.e., mild hypoxia), extended wakefulness and lower body negative pressure stress (designed to simulate some of the effects of space flight).
Patients or healthy people feeling somewhat stressed may read claims that L-tyrosine alleviates the effects of stress. They probably imagine that L-tyrosine will help them to feel less stressed in response to the psychosocial stressors of everyday life. What has been shown is that L-tyrosine prevents some of the cognitive decline in response to physical stressors, an effect of interest to almost no-one outside the military.
Tyrosine supplementation can be helpful in people going through sleep loss or episodes of sleep deprivation. The behavioural effects of tyrosine were examined during an episode of continuous night-time work involving one night’s sleep loss. Subjects performed a battery of performance tasks for approximately 13h, beginning at 1930 and ending at 0820. They remained awake throughout the day on which the experiment began and were awake for more than 24h by the end of testing. Six hours after the experiment began, one-half of the subjects received 150mg/kg tyrosine, while the other half received placebo.
Tyrosine administration was associated with a significant reduction of the usual performance decline on a psychomotor task and a significant reduction in lapse probability on a high-event-rate vigilance task. The improvements lasted on the order of 3h. Thus, tyrosine may prove useful in counteracting performance decrements during episodes of sustained work coupled with sleep loss.
In a study, the effects of tyrosine on cognitive task performance were studied on a group of 21 cadets during a demanding military combat training course. Ten subjects received five daily doses of a protein-rich drink containing 2g tyrosine, and 11 subjects received a carbohydrate rich drink with the same amount of calories.
The group supplied with the tyrosine-rich drink performed better on a memory and a tracking task than the group supplied with the carbohydrate-rich drink. In addition, the supplementation of tyrosine decreased systolic blood pressure. No effects on mood were found. These findings suggest that supplementation with tyrosine may, under operational circumstances characterized by psychosocial and physical stress, reduce the effects of stress and fatigue on cognitive task performance.
Acc. to a review study, Tyrosine does seem to effectively enhance cognitive performance, particularly in short-term stressful and/or cognitively demanding situations.
Another systematic review study found that tyrosine loading acutely counteracts decrements in working memory and information processing that are induced by demanding situational conditions such as extreme weather or cognitive load. The buffering effects of tyrosine on cognition may be explained by tyrosine’s ability to neutralize depleted brain catecholamine levels. There is evidence that tyrosine may benefit healthy individuals exposed to demanding situational conditions.
This amino acid may have protective effects on behavioural and cardiovascular parameters because it prevents the depletion of central and peripheral catecholamines caused by acute stress. Tyrosine can be expected to be beneficial only when the stress is severe.
Tyrosine supplementation by healthy men has no measurable effect on endurance, muscle strength, or anaerobic power. Similar studies have shown the ineffectiveness of tyrosine on sports.
L-tyrosine is Generally Recognized as Safe (GRAS) in the USA. When L-tyrosine is used orally and short term at a dose of ≤150 mg/kg or ≤12g per day for up to three months is generally safe .
It’s rare to be deficient in tyrosine. Low levels have been associated with low blood pressure, low body temperature, and an underactive thyroid. This does not mean, however, that taking tyrosine supplements will help any of these conditions (Click here to know more).
As a supplement, tyrosine is available as a free-form amino acid or N-acetyl L-tyrosine (NALT). NALT is more water-soluble than its free-form counterpart, but it has a low conversion rate to tyrosine in the body. This means that you would need a larger dose of NALT than tyrosine to get the same effect, making the free-form the preferred choice (Click here to know more).
For exercise performance, it is generally taken in the doses of 500-2000mg, 30-60min before exercise.