Tyrosine is a nonessential protein amino acid that is critical for the structural integrity of nearly all proteins found in the body. It is synthesized from the essential amino acid phenylalanine, and may be conditionally essential in times of prolonged stress or severe conditions. Tyrosine is a direct precursor to the catecholamines epinephrine, norepinephrine, dopamine, and serotonin. These neurotransmitters are vital in processes relating to the regulation of mood, stress response, and mental functioning. 
Tyrosine also aids in the function and maintenance of organs responsible for the production of specialized hormones. The adrenal, thyroid, and pituitary glands are all dependant upon sufficient levels of tyrosine to create hormones that regulate various metabolic and neurological processes within the body.  Tyrosine is also required to form melanin, the dark pigment responsible for hair and skin color. This pigment is critical as it also provides protection from the harmful effects of ultraviolet light (UV exposure).
This unique nonessential amino acid may also afford the body with mild antioxidant properties. Tyrosine binds many unstable molecules that may potentially cause damage to certain cellular and tissue structures (free radicals). Supplemental tyrosine, consequently, may be beneficial for individuals suffering from the exposure to toxic chemicals often found in the pollution resulting from smoking and radiation.
Tyrosine is principally derived from animal and vegetable proteins. The highest concentrations of this nonessential amino are found in dairy products, meats, fish, almonds, avocados, and bananas. Fermented foods such as yogurt and miso also contain higher percentages of tyrosine. Serving sizes below are based upon 100 grams of a given food source and are expressed in milligrams, representing the amount of tyrosine contained.
|Vegetables and Vegetable Products|
|2584||Seaweed, spirulina, dried|
|1579||Leavening agents, yeast, baker’s, active dry|
|Nut and Seed Products|
|2100||Seeds, sesame flour, low-fat|
|1796||Seeds, cottonseed flour|
|1689||Seeds, sesame flour, partially defatted|
|Legumes and Legume Products|
|3222||Soy protein isolate|
|2301||Soy protein concentrate|
|2122||Peanut flour, defatted|
|1778||Soy flour, defatted|
|1760||Soy flour, low-fat|
|1700||Soy meal, defatted, raw|
|1604||Tofu, dried-frozen (koyadofu)|
|1497||Soybeans, mature seeds, dry roasted|
|1457||Winged beans, mature seeds, raw|
|Finfish and Shellfish Products|
|2121||Fish, cod, Atlantic, dried and salted|
|1518||Mollusks, whelk, unspecified, cooked, moist heat|
|Dairy and Egg Products|
|3153||Egg, white, dried|
|3089||Egg, white, dried, flakes, glucose reduced|
|2328||Cheese, parmesan, grated|
|2319||Cheese, parmesan, shredded|
|1995||Cheese, parmesan, hard|
|1932||Egg, whole, dried|
|1746||Milk, dry, nonfat, regular, without added vitamin A|
|1656||Milk, buttermilk, dried|
|1523||Egg, yolk, dried|
Clinical studies have suggested that tyrosine may be effective in the treatment of various cognitive disorders. Tyrosine is believed to be an adaptogen, assisting the body in coping with the effects of both psychological and physical stressors. The two main stress-related hormones, norepinephrine and epinephrine, are created by tyrosine. Supplemental tyrosine may be useful in minimizing many bodily reactions and symptoms resulting from elevated stress. [4, 5]
Tyrosine levels are often low in moderately depressed individuals. Studies have proved encouraging, regarding tyrosine supplementation and its ability to ease symptoms associated with moderate depression. Tyrosine in combination with 5-hydroxytryptophan (5-HTP) yielded even greater results in diminishing depressant activity than tyrosine administered alone.  Depression caused by Parkinson’s and Alzheimer's disease, has also been reduced with supplemental tyrosine. [7, 8] Although these results are promising, more research is needed to accurately assess tyrosine and its continued benefit in persons suffering from mild to moderate depression.
Due to tyrosine’s ability to enhance the production of the neurotransmitter dopamine, it has been used in the detoxification of certain highly addictive drugs. Tyrosine has been used in union with conventional treatments for cocaine abuse and withdrawal. Cocaine is a drug which rapidly depletes the body of natural dopamine. Cocaine and methamphetamines create an addiction to dopamine which is delivered through an increased usage of the drug. Tyrosine may assist these individuals by synthesizing more dopamine rather than relying on these harmful substances.  Successful withdrawals of caffeine and nicotine have also been attributed to tyrosine supplementation.
In addition, tyrosine may assist in the condition Vitiligo. Vitiligo is characterized by an irregular depigmentation of skin. It has been proposed that because tyrosine is a critical component in the formation of melanin, it may be an effective treatment for vitiligo sufferers. Phenylalanine, the essential amino acid from which tyrosine is derived, has been used successfully in the treatment of this disorder.  In combination with ultraviolet radiation, supplemental phenylalanine was effective in darkening the white patches, or depigmented areas, in those suffering this condition.
A Recommended Dietary Allowance (RDA) has not been established for tyrosine. Several research studies conducted upon various conditions have estimated the supplemental dosage of tyrosine being 100 milligrams per 2.2 pounds of bodyweight. This equates to approximately 7 grams per day for the average sized person. It is suggested that supplemental tyrosine be taken at least 30 minutes prior to meals so that it does not compete with the absorption of other amino acids. Vitamin B6, Vitamin B9, and copper assist tyrosine’s conversion into critical compounds in the brain.
The U.S. National Academy of Sciences recommends that healthy people achieve .36 grams of highly bioavailable protein for each pound of bodyweight - equaling 0.8 grams of protein, per kilogram of bodyweight. Listed below are the Recommended Daily Allowances (RDAs) for the majority of amino acids. Tyrosine is an aromatic amino acid, and its approximate daily dosage is listed below.
|Requirement - mg. per kg. of body weight|
|Amino acid||Infant 3 - 6 mo.||Child 10 - 12 yr.||Adults|
|Histidine||33||not known||not known|
|S-containing amino acids||45||22||10|
|Aromatic amino acids||132||22||16|
Deficiencies of tyrosine are often seen in persons suffering from the inborn error PKU, or Phenylketonuria. (See Phenylalanine) This rare condition occurs in people who lack the ability to metabolize the amino acid phenylalanine. Tyrosine is synthesized from phenylalanine. The restriction of phenylalanine from diet often times leads to a paralleled deficiency of tyrosine. Findings are mixed, but studies show that many experts recommend and advocate the supplementation of tyrosine-enriched proteins in persons suffering from this disease. 
Ordinarily, symptoms of tyrosine deficiency may manifest as nervousness, impaired thought patterns, emotional agitation, behavioral changes such as depression and impaired alertness, bloodshot eyes, cataracts, as well as loss of memory and sexual interest. Impacts in the production of skin melanin and insulin production have also been studied.
Lower levels of this amino acid have also been associated with the lowering of systolic blood pressure, body temperature, and impairment in the production of thyroid hormones.
It remains unclear whether prolonged usage of tyrosine in large amounts (> 1000 milligrams per day) is safe. There have been no reported side effects associated with these excessive dosages. However, It is theorized that dosages over this amount may lead to an increase in blood pressure, emotional agitation, insomnia, and frequent headaches. More research regarding tyrosine toxicity is needed.
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