A Powerful Amino Acid with Many Benefits

Although not an essential amino acid, tyrosine serves as a precursor to thyroid and adrenocortical hormones. It is similarly important for the production of the brain neurotransmitters dopamine and norepinephrine. Also, tyrosine is useful in the formation of amino-sugars, compounds which are critically important to the integrity of many tissues.

Under normal circumstances, phenylalanine is the essential amino acid which is used by the body to synthesize tyrosine in addition to the tyrosine which is consumed in the diet. Iron, Vitamin C and niacin are needed for this synthesis.

Tyrosine readily passes the blood brain barrier into the brain, where it serves as a brain nutrient. Upon entry into the brain, tyrosine is used as a precursor for the neurotransmitters epinephrine (E), norepinephrine (NE) and dopamine (DA). However, tyrosine must compete with other amino acids for entry into the brain.

Specifically, tryptophan, phenylalanine and the Branched Chain Amino Acids (BCAAs) isoleucine, leucine and valine compete with tyrosine for uptake into the brain. What's more, other nutrients must be available for this synthesis, particularly Vitamin B-6, folic acid, copper and zinc.

Although tyrosine is supplied by the diet, there is great variation in the tyrosine content in foods. In general, meats have substantially higher concentrations than do vegetables or grains. Wheat germ is an exception among grain-derived foods in that it is a good source of tyrosine.

Because tyrosine is a precursor for the excitatory neurotransmitters, it is important in conditions of stress, which tend to exhaust body stores of many important neurochemicals as well as of adrenal hormones.

In studies performed by researchers at MIT, animals given extra amounts of tyrosine were able to control stress and prevent depression. Later trials performed with soldiers undergoing intense physical training by the United States Army confirmed these results.

Tyrosine and Mood

Everyone is occasionally sad or discouraged, and such emotions are a natural response to disappointment or loss. Nevertheless, mood is often out of kilter as a result of imbalances in diet and lifestyle. Health care professionals often find that depressed patients have diets that are inadequate in terms of vitamins and minerals and, in many cases, protein.

Eating large amounts of sugars, refined carbohydrates and junk food in general affects physical health, even if it's not immediately apparent. "Anti-nutrients" may also play a role. Many studies have shown that an intake of roughly 700 mg or more caffeine per day (about five cups of coffee) is associated with depression and mood swings. Both eating right and exercising can go a long way in evening out mood swings.

An inadequate intake of dietary protein and/or an excessive intake of stimulants can lead to reduced levels of norepinephrine and related hormones and neurotransmitters for which tyrosine is an important precursor.

Likewise, chronic stress can exhaust the body's production of tyrosine-dependent compounds. For instance, individuals who suffer from depression may test positive for the presence of MHPG (3-methyl-4 hydroxy-phenylglycol), which is indicative of a lowered metabolism of tyrosine and its metabolites. Supplemental tyrosine may help under these circumstances to return the body to nutritional balance.

Tyrosine and Brain Metabolism

As we age, the production of dopamine in the brain declines. Under special circumstances usually associated with older individuals, there may be a marked dopamine deficiency in the basal ganglia portion of the brain. This results in uncoordinated movement, improper responses in reflex pathways, stiffness of gait and other motor problems.

It has been postulated that this is caused by the decrease in two key enzymes, catalase and peroxidase. Reduced amounts of catalase and peroxidase permit the accumulation of the toxic metabolite hydrogen peroxide.

Hydrogen peroxide is produced during the normal metabolism of dopamine, but an elevated level of this metabolite in the brain accelerates the destruction of the substantia nigra portion of the basal ganglia.

With aging in general, therefore, but more so under certain conditions, the brain's ability to produce and to respond to dopamine declines. Inasmuch as tyrosine is a dopamine precursor, this amino acid may provide nutritional support in increasing brain dopamine levels.

Dopamine plays other important roles. Aside from assisting in coordination and in tissue repair (some authors suggest that it improves the pituitary gland's release of growth hormone), this neurotransmitter is significant for its part in the "pleasure" response found with activities as diverse as eating and sex.

Some researchers, for example, have suggested that one source of overeating is poor production of dopamine in the brain after ingestion of normal amounts of food. According to this view, some individuals overeat because a primary brain signal is not present in sufficient quantity.

Indeed, yet another use of tyrosine, one which is closely related to food consumption, is as an anorectic agent when tyrosine is taken in conjunction with ephedrine/ma huang can be potentated - and lower doses of the stimulant used - if tyrosine is taken at the same time.

Indications of Tyrosine Deficiency

A clinical deficiency of tyrosine may produce symptoms such as edema, weakness, impaired liver function and loss of muscle or other tissues. Low protein diets may produce marginal deficiency states.

Source: Jarrow Formulas

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Scientific References

• Agharanya JC., Wurtman RJ. Effect of acute administration of large neutral and other amino acids on urinary excretion of catecholamines. Life Sci. 1982 Mar 1; 30(9): 739-46.
• Alonso R., Gibson CJ., Wurtman RJ., Agharanya JC., Prieto L. Elevation of urinary catecholamines and their metabolites following tyrosine administration in humans. Biol Psychiatry. 1982 Jul; 17(7): 781-90.
•  Galenberg AJ., Wojcik JD., Growdon JH., Sved AF., Wurtman RJ. Tyrosine for the treatment of depression. Am J Psychiatry. 1980 May; 137(5): 622-3.
• Goodnick PJ., Evans HE., Dunner DL., Fieve RR. Amino acid concentrations in cerebrospinal fluid: effects of aging, depression, and probenecid. Biol Psychiatry. 1980 Aug; 15(4): 557-63.