L-Tyrosine: Benefits, Dosage, Contraindications
Other name(s)
Acetyl-L-Tyrosine
Scientific name(s)
2-amino-3-(4-hydroxyphenyl)propanoic acid
Family or group:
Amino acids
Indications
Rating methodology
EFSA approval.
Phenylketonuria ✪✪✪✪✪
Tyrosine is used for individuals with phenylketonuria (PKU), a genetic disorder related to a deficiency in phenylalanine hydroxylase, leading to phenylalanine accumulation in the blood and brain. Tyrosine is used as a component of medical foods for people with phenylketonuria (PKU), a genetic disorder where there is an inability to metabolize phenylalanine, a precursor of tyrosine, leading to phenylalanine accumulation in the blood and brain. Current guidelines recommend that people with PKU maintain a low phenylalanine diet and incorporate tyrosine as a component of medical foods to maintain normal blood levels of tyrosine. Tyrosine supplementation is recommended only for patients with persistently low blood tyrosine levels despite using medical foods containing tyrosine. Routine free tyrosine supplementation is not recommended for most PKU patients as it may cause large fluctuations in plasma tyrosine concentrations and side effects. Medical foods provide 4 to 6 grams of tyrosine per day for most patients, or 6 to 7.6 grams per day for pregnant or breastfeeding women.
Posologie
Oral
4 - 7.6 g
Adults
Cognitive performance ✪✪✪✪✪
Tyrosine seems to effectively enhance cognition during acute stress factors (altitude and cold being the most tested). It's reliable if the acute stress factor is present, but it's unclear if this applies to chronic stress. Indeed, taking 100 to 300 mg/kg of tyrosine before acute cold stress exposure appears to enhance cognitive performance compared to placebo. Additionally, taking 100 mg/kg of tyrosine before a cognitive test seems to improve short-term memory compared to placebo, among patients tested during noise-induced stress. It's unclear if tyrosine's effects on cognitive performance depend on dosage.
Posologie
Oral
100 - 300 mg/kg
Adults
Memory ✪✪✪✪✪
Tyrosine intake seems to improve memory under stress conditions. Some clinical research shows that taking 150 to 300 mg/kg of tyrosine improves memory performance when taken before acute cold stress exposure. Additionally, taking 100 mg/kg of tyrosine before a cognitive test seems to enhance short-term memory compared to placebo, among patients tested during noise-induced stress.
Posologie
Oral
100 - 300 mg/kg
Adults
Stress ✪✪✪✪✪
The perception of stress during acute stress periods, as well as associated symptoms such as headaches, fatigue, and muscle aches, appear to be reduced following tyrosine ingestion. A dose of 100 mg/day was used.
Posologie
Oral
100 mg/kg
Adults
Dietary tyrosine suppresses the rise in plasma corticosterone following acute stress in rats.
Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans.
Dietary tyrosine benefits cognitive and psychomotor performance during body cooling.
Emotional balance ✪✪✪✪✪
Catecholamines like epinephrine, norepinephrine, and dopamine synthesized from tyrosine may become depleted during stress periods. It's believed that increasing the availability of tyrosine in the brain allows for increased catecholamine synthesis and helps mitigate the negative effects of stress.
Posologie
Oral
100 mg/kg
Adults
Dietary tyrosine suppresses the rise in plasma corticosterone following acute stress in rats.
Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans.
Dietary tyrosine benefits cognitive and psychomotor performance during body cooling.
Cognitive decline ✪✪✪✪✪
Clinical studies have shown that subjects with cognitive disorders exhibit significant levels of mitochondrial dysfunction and oxidative protein damage. In particular, tyrosine nitration is a common early indicator of cognitive deficiency, including among people whose brains show age-related cognitive decline or neurodegenerative disorders such as Alzheimer's dementia. The modification of tyrosine residues induced by oxidative stress can cause significant changes in the structure and function of proteins, which in some cases can contribute to biological aging and age-related pathologies such as neurodegeneration. No clinical research is available to determine the effects of changing tyrosine intake. The only available research showing promising results concerns whey peptides rich in tryptophan- and tyrosine-related peptides.
Posologie
Oral
100 mg/kg
Synergies
Properties
Neurological
It is believed that the brain may be unable to synthesize enough tyrosine from phenylalanine in stressful conditions. Hence, catecholamines such as epinephrine, norepinephrine, and dopamine synthesized from tyrosine may become depleted during stress periods. Increasing the availability of tyrosine in the brain is thought to allow for increased synthesis of catecholamines, helping to mitigate the negative effects of stress. Note that folate, vitamins B3, B6, B12, and C, iron, copper, and other nutrients are necessary for tyrosine metabolism into catecholamines.
Usages associés
Hormonal Metabolism
Thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3), are hormones produced in the thyroid from iodine and tyrosine. Tyrosine undergoes iodation to form monoiodotyrosine (T1), a second iodation produces diiodotyrosine (T2), and these combine to produce the active thyroid hormones known as triiodothyronine (T3) and tetraiodothyronine or thyroxine (T4). Tyrosine is also involved in the production of other compounds, such as melanin, enkephalins, and certain types of estrogens.
Cognitive Function
Increasing levels of L-tyrosine in the brain is considered a means to mitigate cognitive decline, as catecholamines are generally decreased in dementia states. Moreover, catecholamines can act as antioxidants in the brain and be neuroprotective.
Usages associés
Antidepressant
In healthy humans, acute tyrosine intake increases plasma levels of norepinephrine, epinephrine, and dopamine. Low levels of norepinephrine and dopamine may play a role in depression. In clinical research, drinking an amino acid-based beverage devoid of tyrosine and phenylalanine, which are precursors of catecholamines, led to a reduced brain response to stimuli. However, no behavioral changes were observed.
Usages associés
Safety dosage
Adult: 150 mg/kg
L-Tyrosine has been safely used, orally at doses up to 150 mg/kg or 12 g per day, for a maximum of 3 months.
Interactions
Médicaments
Levodopa: moderate interaction
There is concern that L-tyrosine may decrease the effectiveness of L-dopa. Indeed, it can limit its absorption through a competitive phenomenon at the level of the proximal duodenum. Please separate tyrosine and L-dopa doses by at least 2 hours.
Thyroid hormone-based medications: moderate interaction
There is concern that tyrosine may have additive effects with thyroid hormone-based medications. Therefore, tyrosine is a precursor of thyroid hormone and could increase their levels. Levothyroxine and liothyronine are among these medications.
Monoamine oxidase inhibitor (MAOI): weak interaction
It may interact with MAOIs and cause a hypertensive crisis.
Precautions
Pregnant woman: avoid
There is not enough reliable information on the safety of tyrosine during pregnancy.
Breastfeeding woman: avoid
There is not enough reliable information on the safety of tyrosine during pregnancy.
Contraindications
Hyperthyroidism: prohibited
Tyrosine is a precursor of thyroxine and could increase thyroid hormone levels.
