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
Scoring methodology
EFSA approval.
Phenylketonuria ✪✪✪✪✪
Tyrosine is used for people with phenylketonuria (PKU), a genetic disorder related to a deficiency of phenylalanine hydroxylase, causing accumulation of phenylalanine in the blood and brain. Tyrosine is used as a component of medical foods for people with phenylketonuria (PKU), a genetic disorder in which there is an inability to metabolize phenylalanine, a precursor of tyrosine, resulting in accumulation of phenylalanine in the blood and brain. Current guidelines recommend that people with PKU maintain a phenylalanine-restricted diet and incorporate tyrosine as a component of medical foods to maintain normal blood tyrosine levels. Tyrosine supplementation is recommended only for patients with persistently low blood tyrosine levels despite the use of medical foods containing tyrosine. Routine supplementation with free tyrosine is not recommended for most patients with PKU because it can lead to large fluctuations in plasma tyrosine concentrations and adverse 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 appears to effectively improve cognition during acute stressors (altitude and cold being the most studied). This seems reliable if the acute stressor is present, but it is not certain that this applies to chronic stress.nnIndeed, taking tyrosine at 100 to 300 mg/kg before acute cold-induced stress exposure appears to improve cognitive performance compared with placebo. In addition, taking tyrosine at 100 mg/kg before a cognitive test appears to improve short-term memory compared with placebo in patients tested during noise-induced stress.nnIt is not clear whether the effects of tyrosine on cognitive performance are dose-dependent.nn
Posologie
Oral
100 - 300 mg/kg
Adults
Memory ✪✪✪✪✪
Taking tyrosine appears to improve memory under stressful conditions. Some clinical research shows that taking tyrosine at 150 to 300 mg/kg improves memory performance when taken before acute cold-induced stress exposure. In addition, taking tyrosine at 100 mg/kg before a cognitive test appears to improve short-term memory compared with placebo in patients tested during noise-induced stress.nn
Posologie
Oral
100 - 300 mg/kg
Adults
Stress ✪✪✪✪✪
Perception of stress during periods of acute stress, as well as associated symptoms such as headaches, fatigue, and muscle pain, appear to be reduced following ingestion of tyrosine. 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 such as epinephrine, norepinephrine, and dopamine synthesized from tyrosine can become depleted during periods of stress. It is thought that increasing the availability of tyrosine in the brain allows increased synthesis of catecholamines and helps prevent 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 marker of cognitive impairment, including in people whose brains show age-related cognitive decline or neurodegenerative disorders such as Alzheimer's dementia. Oxidative stress–induced modification of tyrosine residues can cause major changes in protein structure and function that, in some cases, may contribute to biological aging and age-related pathologies such as neurodegeneration. No clinical research is available to determine the effects of modifying tyrosine intake. The only available research with promising results concerns whey peptides rich in tryptophan- and tyrosine-related peptides.
Posologie
By mouth
100 mg/kg
Synergies
Properties
Neurological
It is believed that the brain is unable to synthesize sufficient tyrosine from phenylalanine under stressful conditions. Thus, catecholamines such as epinephrine, norepinephrine, and dopamine synthesized from tyrosine can be depleted during periods of stress. It is believed that increasing the availability of tyrosine in the brain allows for increased synthesis of catecholamines and helps prevent the negative effects of stress. Note that folate, vitamins B3, B6, B12 and C, iron, copper, and other nutrients are required for the metabolism of tyrosine into catecholamines.
Usages associés
Hormonal metabolism
Thyroid hormones, that is thyroxine (T4) and triiodothyronine (T3), are hormones produced in the thyroid from iodine and tyrosine. Tyrosine undergoes iodination to form monoiodotyrosine (T1); a second iodination 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 are considered a way to mitigate cognitive decline, because catecholamines are generally decreased in states of dementia. In addition, catecholamines may act as antioxidants in the brain and be neuroprotective.
Usages associés
Antidepressant
In healthy humans, an acute intake of tyrosine increases plasma levels of norepinephrine, epinephrine, and dopamine. Low levels of norepinephrine and dopamine may play a role in depression. In clinical research, consumption of an amino acid-based drink lacking tyrosine and phenylalanine, which are precursors of catecholamines, led to a reduced brain response to stimuli. However, no change in behavior was observed.
Usages associés
Safe dosage
Adult: 150 mg/kg
L-tyrosine has been used safely, orally, at doses up to 150 mg/kg or 12 g per day for up to 3 months.
Interactions
Médicaments
Levodopa: moderate interaction
There is concern that L-tyrosine may reduce the effectiveness of L-dopa. Indeed, it may limit its absorption through a competitive mechanism in the proximal duodenum. Please separate doses of tyrosine and L-dopa by at least 2 hours.
Thyroid hormone medications: moderate interaction
There is concern that tyrosine may have additive effects with thyroid hormone medications. It is a precursor to thyroid hormone and could increase their levels. Levothyroxine and liothyronine are examples of such medications.
Monoamine oxidase inhibitor (MAOI): weak interaction
It can interact with MAOIs and cause a hypertensive crisis.
Precautions
Pregnant women: avoid
There is not enough reliable information on the safety of tyrosine during pregnancy.
Breastfeeding women: avoid
There is not enough reliable information on the safety of tyrosine during pregnancy.
Contraindications
Hyperthyroidism: contraindicated
Tyrosine is a precursor of thyroxine and could increase thyroid hormone levels.
