Introduction to Tyrosine

Tyrosine is a neutral amino acid meaning it is a building block for proteins. It can be found in many high-protein foods such as cheese, chicken, and eggs. In the body, tyrosine is mainly used in the brain as a precursor to a class of neurotransmitters called catecholamines.

The three major catecholamines that tyrosine can become are dopamine, norepinephrine, and epinephrine. To become a catecholamine, tyrosine requires two transformative steps. First off, it must be converted into dihydroxyphenylalanine or DOPA for short. Then, an enzyme (usually some form of a decarboxylase) will turn the DOPA into one of the three catecholamines. These catecholamines are used in many different cognitive functions.

Tyrosine is a Precursor to Neurotransmitters

Tyrosine is a precursor to neurotransmitters which include dopamine, norepinephrine, and epinephrine. [R]

Elevated levels of tyrosine can increase production of these neurotransmitters during situations in which neurotransmitter synthesis is increased. [R]

However, these situations had to be sufficiently challenging to require extra release of neurotransmitters and subsequent depletion of these neurotransmitters. To maintain optimal neural performance, tyrosine supplementations were seen to prevent the neurotransmitters from depleting. [R]

1) Tyrosine Replenishes Cognitive Resources Used in Memory


Tyrosine supplements were seen to restore certain cognitive resources used to increase working memory. [R]

Working memory is responsible for the continued updating and maintenance of memory. [R]

Studies showed that tyrosine only replenishes certain cognitive resources when the resources get used up, so only challenging situations that require the use of these cognitive resources will see an enhancement of the cognitive resources. [R]

2) Tyrosine Increases Dopamine Levels in the Brain

Tyrosine supplementation increases dopamine levels in the striatum of the brain when animals are given treatments that increase dopamine demand. [R]

Tyrosine administration also increased dopamine levels in the extracellular fluid of the brain. However, this effect was short-lived as the extra levels of tyrosine were seen to activate mechanisms in the brain which slowed neuronal firing. This, in turn, brought the dopamine levels back to the original levels before tyrosine administration. [R]

3) Tyrosine Reduces Stress

Tyrosine is a precursor to norepinephrine and stress can reduce norepinephrine levels in the locus coeruleus, the hippocampus and the hypothalamus, which are regions in the brain. [R]

Rat studies showed that when rats were subjected to shock, norepinephrine levels dropped heavily, but when tyrosine was injected into the rats, the norepinephrine levels remained constant. This is most likely caused by the fact that tyrosine enhanced the rate at which norepinephrine was produced in stressful situations. [R]

The added tyrosine caused the rats to showcase no behavioral deficits while rats that did not get the tyrosine supplements did show behavioral changes resulting from stress. [R]

It is also hypothesized that tyrosine may improve physical performance only if the exercise being done produces enough cognitive stress and depletes dopamine or norepinephrine levels. [R]

4) Tyrosine may Improve Attention Deficit Disorders


Clinical trials of using tyrosine to try improving attention deficit disorder symptoms in humans showed some positive results. Of the 12 adults that volunteered for the clinical trials, eight of them showed some form of clinical improvement in two weeks. [R]

However, after six weeks, all eight of the patients were seen to develop a tolerance to the tyrosine and improvements stalled. Further investigation into how tyrosine may be used to cure attention deficit disorders needs to be done. [R]

One risk of attention deficit disorders is impaired neurotransmitter metabolism. [R]

Although this only accounts for 5-10% of the attention deficit disorder cases, it is more likely that such cases would benefit more from tyrosine supplementations. [R]

5) Tyrosine may be Used to Treat Depression


Tyrosine was found to help depression in certain patients in some clinical trials. A single case, placebo-controlled, case for a 30 year old woman suffering from depression showed marked improvement after tyrosine therapy. [R]

Placebo treatments immediately showcased a return of depression symptoms. Continued tyrosine therapy brought back a marked improvement. [R]

Further trials regarding two other patients with depression also showed improvements in symptoms. [R]

However, larger clinical trials of 65 patients did not support that tyrosine can be used as an antidepressant. [R]

This can be attributed to the fact that depression is dependent on a wide variety of factors, not simply a lack of dopamine or norepinephrine. Tyrosine as an antidepressant could possibly be used for patients in which the depression is stemming from low dopamine and norepinephrine levels. [R]

6) Tyrosine may be Used to Treat Parkinson’s


Nine patients who had Parkinson’s were treated with tyrosine and probenecid. These patients showed an increase in homovanillic acid in the cerebrospinal fluid. The presence of homovanillic acid, a product of dopamine metabolism, correlates to the fact that dopamine is being released in the brain. [R]

Because Parkinson’s is strongly linked with the degeneration of neurons that release dopamine, increased levels of homovanillic acid could be good proof that tyrosine may be used to treat the disease. [R]

7) Tyrosine Decreases Unwanted Action Tendencies

Studies have shown that when patients get tyrosine administered, they will be better at reducing unwanted tendencies. [R]

The study describes these tendencies as inhibitory control. When patients were asked to perform a stop-signal task (where the patient clicks stop when a green arrow turns red), patients with tyrosine injections were seen to do better than those with a placebo. [R]

8) Tyrosine Increases Mood

When patients were subjected to stressful conditions such as the cold or elevated altitudes, increased tyrosine levels were seen to better patient’s moods. One of the reasons for this betterment was due to lowered symptom intensities. [R]

In a long term study, patients in Antarctica were given tyrosine supplements daily over the summer and winter. However, only during stressful conditions in the winter did the tyrosine supplements work to increase mood (by 47%). [R]

Summer conditions were not harsh enough to illicit a response. [R]

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  • jon miller

    one of the best things for thyroid problems,try it,you will be glad you did,helps with depression

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