L-tyrosine is a so-called semi-essential amino acid. Amino acids are important active substances in the body, because they are the basic building blocks for the vital proteins. Thus they fulfil important tasks in the building of cells, tissue and bones. They are also involved in hormone and enzyme formation, among other things, and contribute to the function of the cardiovascular system and the immune system. In addition, each amino acid has specific properties that are important for certain physical or mental functions.
Semi-essential means that the body can normally produce the amino acid itself. In certain life situations, however, it may be necessary to supply them from the outside. That is, they must be taken through food or supplements. Tyrosine, or L-tyrosine, is made in the body from the essential amino acid phenylalanine. It helps in the production of several very importantsubstances. These include:
- Dopamine: This neurotransmitter is important for regulating the reward center in the brain, but also plays a role in motor function and memory processes.
- Adrenaline / noradrenaline: The two neurotransmitters are the body's neurochemical response to stressful situations and prepare it for possible stress reactions ("fight" or "flight").
- Melanin: The body's own pigment is responsible for the pigmentation of eyes, skin and hair.
- Thyroid hormones: Hormones produced by the thyroid gland are important for regulating metabolic processes.
It is believed that the intake of L-tyrosine can increase the amount of these substances in the body and thus achieve positive effects on the body and psyche.
What are the effects of L-tyrosine?
Various effects are attributed to L-tyrosine, some of which are based on reports from experience and some of which have been investigated in scientific studies:
Improvement of performance in stress situations
L-tyrosine is often taken as a dietary supplement before exams or other mentally demanding situations in the form of L-tyrosine capsules, as it is said to improve performance in the short term, especially in stressful situations.
Stress can have very different causes and can be a physical or mental strain. One example is demanding cognitive tasks. Here, tyrosine was able to achieve positive effects in a study: Of the 22 participants who took either L-tyrosine capsules or a placebo, the tyrosine group showed significantly better results in a demanding task that required cognitive flexibility than the placebo group . Tyrosine also appears to have a positive effect on performance when sleep deprivation is a stressor, studies have shown. Here, with tyrosine ingestion, subjects showed a significant improvement in performance, which is usually significantly worse with sleep deprivation [2, 3].
Cold is an environmental factor that has been used as a stressor in many studies for decades. In an early U.S. study, scientists examined the effect of tyrosine on the performance of Army members. It showed that the soldiers who had to perform various tasks at lower temperatures while receiving tyrosine capsules showed significantly fewer symptoms of fatigue than the placebo group. They also showed better results in the tasks themselves . Later studies using higher doses of tyrosine confirmed the findings and also found that the negative side effects of cold (e.g., stress symptoms, memory problems) could be reduced with the use of tyrosine capsules [5, 6, 7].
Two recent review papers from the Netherlands also conclude that tyrosine capsules have a positive effect on performance in stressful situations [8, 9].
Improvement of mood
In addition, L-tyrosine, as a precursor to the "feel good" neurotransmitter dopamine, is thought to improve mood and thus may have antidepressant effects. There was early evidence that taking L-tyrosine can improve the mood of some depressed patients, but only if the depression was caused by a dopamine deficiency .
In addition, there are numerous other causes of depression, some of which are very complex and have not yet been definitively investigated. This could be one reason for the different findings in the individual studies. In a study with 65 depressed patients, the participants received either a conventional antidepressant or L-tyrosine capsules or a placebo. There was no evidence of an antidepressant effect of tyrosine .
At this point in time, it can be summarized that the findings on the effect of L-tyrosine on depression are mixed  and that further research is necessary in order to make a reliable statement.
How does L-tyrosine affect the thyroid gland?
Tyrosine is used to produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Among other things, they have important metabolic functions and regulate the metabolism depending on the current need. They also play an important role in cell and body growth. A deficiency of these thyroid hormones can result in various undesirable side effects such as fatigue, poor concentration and performance, hair loss, constipation, weight gain and depressive moods.
In order for them to perform their function well, the level of thyroid hormones must therefore be neither too high nor too low. Taking L-tyrosine - for example via tyrosine capsules - can cause the body to produce a greater amount of these hormones. Therefore, accurate dosing of L-tyrosine is very important.
Should you take L-tyrosine capsules if you have hyperthyroidism? The increased production of thyroid hormones by L-Tyrosine can lead to excessive hormone levels in individuals with an already overactive thyroid gland, which has undesirable side effects. The same is true for people taking thyroid medication. Therefore, you should always consult your doctor before taking L-Tyrosine if you have an existing hyperthyroidism and/or are taking thyroid hormones with medication.
Tyrosine in food - Which ones are they exactly?
L-tyrosine is not only available as a dietary supplement, but is found in a variety of foods. Discovered for the first time, the amino acid L tyrosine in food was found in cheese, from which it was named: "tyros" is the Greek word for cheese . In fact, the tyrosine content in cheese is particularly high, especially in Parmesan, Gouda, Edam and Camembert.
However, there are other protein-rich L-tyrosine foods. Particularly high amounts of the amino acid L-tyrosine are found in:
- Legumes such as soybeans, peas, white beans and lentils.
- fish, especially in tuna, skate, salmon and cod
- Meat, especially in cooked ham, pork, beef, and veal
- Sesame seeds
What is the optimal L-tyrosine dosage?
This depends, among other things, on the form in which L-tyrosine is taken. One form is the so-called N-acetyl L-tyrosine, which dissolves better in water, but cannot be converted as well in the body and is therefore excreted again in a larger proportion . Therefore, the dose must be higher to achieve the same effect. With the alternative, simple L-tyrosine, smaller doses are sufficient.
In principle, however, the effect of L-tyrosine is not only dose-dependent, but also varies greatly from individual to individual. Therefore, it is difficult to make general statements about the optimal dosage. As a rule, however, the dosages from studies with which the effectiveness of L-tyrosine was examined can serve as a rough guide. However, these vary greatly in this case and range from 500 mg to 12 g per day.
However, dosages should be based on body weight. In studies, even high dosages of up to 150 mg of tyrosine per kilogram of body weight taken over a period of several weeks have been shown to be safe . For a 70 kg person, that would be 10,500 mg, or more than 10 g. It is possible that high doses may lead to undesirable side effects in individual cases, such as headache, palpitations, anxiety or insomnia. The latter can be partially avoided if the intake takes place in the morning. Gastrointestinal problems are also possible, but these can also be partially avoided if the daily dose is not taken in full, but in smaller doses throughout the day.
Therefore, the World Health Organization (WHO) recommends a maximum daily dose for all aromatic amino acids of 25 mg per kilogram of body weight . For a 70 kg person, this corresponds to a daily dose of up to 1,750 mg. However, this daily dose refers to the sum of all aromatic amino acids, which, in addition to L-tyrosine, also includes phenylalanine (the precursor of tyrosine), tryptophan and histidine. Typical for these amino acids is a peculiarity in their chemical structure.
Too high a dose (of much more than 1 g) would be unlikely to provide any additional benefit. This is because once natural satiety is reached, the excess L-tyrosine would probably be metabolized and excreted rather than used to produce other substances .
As a dietary supplement, L-tyrosine is usually available in capsule form. This has the advantage that L-tyrosine capsules are easy to dose. There are usually 400-500 mg of L-tyrosine in one capsule. In any case, you should always follow the manufacturer's instructions and never exceed the recommended dose for L-tyrosine capsules. The maximum daily dose is usually 800-1000 mg, i.e. 2 L-tyrosine capsules.
Pregnant and breastfeeding women and people with pre-existing conditions should always consult their doctor before taking L-tyrosine. Since there are still too few studies on the effectiveness of L-tyrosine in children, they should refrain from taking it.
[ 16] http://apps.who.int/iris/bitstream/handle/10665/43411/WHO_TRS_935_eng.pdf?sequence=1