Tyrosine is a nonessential amino acid, which means that it is manufactured from other amino acids in the liver; it does not have to be obtained directly through the diet. Tyrosine is also the immediate precursor to the thyroid hormone thyroxin and melanin (which is the pigment in the skin). It is also needed for normal functioning of the pituitary and adrenal glands. Tyrosine and phenylalanine are needed to make the neurotransmitters epinephrine, dopamine, and norepinephrine, and as such has a role to play in the control of mood and depression. Tyrosine is also reported to have an antioxidant effect. Good sources are soy products, chicken, turkey, fish, peanuts, almonds, avocados, bananas, milk, cheese, yogurt, cottage cheese, lima beans, pumpkin seeds, and sesame seeds.

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Acutely stressful situations can disrupt behavior and deplete brain norepinephrine and dopamine, catecholaminergic neurotransmitters. In animals, administration of tyrosine, a food constituent and precursor of the catecholamines, reduces these behavioral and neurochemical deficits. Using a double-blind, placebo-controlled crossover design we investigated whether tyrosine (100 mg/kg) would protect humans from some of the adverse consequences of a 4.5 hour exposure to cold and hypoxia. Tyrosine significantly decreased symptoms, adverse moods, and performance impairments in subjects who exhibited average or greater responses to these environmental conditions. These results suggest that tyrosine should be evaluated in a variety of acutely stressful situations.

o      Banderet, LE, & Lieberman, HR. (1989). Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans . Brain Res Bull, 22(4), 759-62.

The catecholamine hypothesis of affective disorders postulates that depression reflects inadequate norepinephrine activity at unspecified brain centers that regulate mood. In light of experimental data showing that the oral administration of tyrosine, precursor of the catecholamine series of neurotransmitters, can increase brain norepinephrine concentrations and activity, we have conducted preliminary trials of tyrosine in depressed outpatients. Initial results are encouraging, and we are now conducting a double-blind, parallel-group trial comparing tyrosine to the tricyclic antidepressant imipramine and to placebo in non-bipolar outpatients with major depression.

o      Gelenberg, AJ, Wojcik, JD, Gibson, CJ, & Wurtman, RJ. (1982-1983). Tyrosine for depression . Journal of Psychiatric Research, 17(2), 175-80.

Tyrosine, a large neutral amino acid found in dietary proteins, has received recent attention as a potential treatment for stress. The behavioral effects of tyrosine were examined during an episode of continuous nighttime work involving one night's sleep loss. Subjects performed nine iterations of a battery of performance tasks and mood scales for approximately 13 h, beginning at 1930 and ending at 0820. They remained awake throughout the day on which the experiment began and were awake for more than 24 h by the end of testing. Six hours after the experiment began, one-half of the subjects received 150 mg.kg-1 tyrosine in a split dose while the other half received cornstarch placebo in a double-blind procedure. Tyrosine administration was associated with a significant amelioration of the usual performance decline on a psychomotor task and a significant reduction in lapse probability on a high-event-rate vigilance task. The improvements lasted on the order of 3 h. The results of this study also suggest that tyrosine is a relatively benign treatment at this dose. After further testing with other doses and timing of administration, tyrosine may prove useful in counteracting performance decrements during episodes of sustained work coupled with sleep loss.

o      Neri, DF et al. (1995). The Effects of tyrosine on cognitive performance during extended wakefulness. Aviat Space Environ Med, 66(4), 313-9.

In past conflicts battle stress casualties have caused a serious exit of troops from the frontlines. Recent research has linked stress-caused impairments of performance with depletion of brain stores of the neurotransmitter norepinephrine (NE), which functions in neural tracts responding to stress. The amino acid tyrosine (TYR) is the dietary precursor for NE, and supplementation with TYR has been demonstrated in the laboratory to alleviate declines in both neural NE and performance during stress. Thus, TYR supplementation might help to prevent and treat stress casualties in combat. Further research is called for to verify this hypothesis.

o      Salter, CA. (1989). Dietary tyrosine as an aid to stress resistance among troops. Mil Med, 154(3), 144-6.

In rats, dietary supplementation with the amino acid tyrosine (TYR) prevents depletion of central catecholamines observed during acute environmental stress. Concomitant changes in the animals' behavioral responses to stress suggest that TYR might have similar effects on central catecholamines and cognition in humans exposed to environmental stress. This study aimed to determine if severe cold exposure impairs human cognition and if dietary supplementation with TYR would ameliorate such deficits…………. When volunteers consumed TYR, correct responses increased on a Match-to-Sample memory measure (p<.05) and study time for the sample was shorter (p<.05), indicative of more rapid and accurate information processing. Finally, RT on the memory measure revealed a similar pattern across immersions for TYR and thermoneutral conditions, but not cold/placebo (p<.05). This study demonstrates cold exposure degrades cognitive performance and supplementation with TYR alleviates working memory decrements.

o      Mahoney, CR et al. (2007). Tyrosine supplementation mitigates working memory decrements during cold exposure. Physiol Behav, 92(4), 575-82.