Copyright © 2005, Advanced Orthomolecular Research

What Are The Therapeutic Uses For Tyrosine?
According to research, the most prevalent usage for supplemental tyrosine appears to be the enhancement of cognitive function and alertness under conditions of environmental stress, such as sleep deprivation, multi-tasking, and functioning at high altitudes and/or cold temperatures. It is more than noteworthy to mention that a significantly high percentage of the clinical studies of tyrosine are conducted by the military, specifically that of the United States. Clinical trials with tyrosine have also been conducted with respect to attention deficit disorder (ADD).

Multi-tasking
In the modern workplace, multi-tasking refers to the number of competing tasks and responsibilities that simultaneously require an employee's attention. The proper execution of a diverse battery of tasks requires optimal cognitive flexibility. Typing, researching, memorizing, calculating, and providing and/or accepting oral instruction, all require the coordinated utilization of different (and cognitively competing) spheres of the brain. Neurotransmitters have to send messages from one neuron to another at sufficient speed in order to ensure an effective operation. The fact that tyrosine naturally enhances the numbers and activity of such neurons is what led researchers to test it for its effectiveness within a stressful, multi-tasking office environment.

In an exceptionally thorough office trial, 20 healthy subjects (10 males and 10 females) underwent four standardized tests on a computer screen simultaneously; these consisted of a memory test, an arithmetic test, a visual monitoring test, and an auditory monitoring test. The results of the study revealed that the tyrosine group displayed significantly enhanced accuracy and working memory scores over the control group that received a placebo.

Sleep Deprivation
Military life is one of the few areas of employment in modern society where the work is meant to be as physically and as psychologically taxing on its employees as possible. Soldiers are meant to function under conditions that are often unnaturally stressful, and none more so than those imposed on the pilots of the United States Marine Corps. In a study conducted at the U.S. Naval Aerospace Medical Research Laboratory in Pensacola, Florida, 20 such marine aviators (all males, aged 21-27) volunteered to help determine if tyrosine can improve alertness during periods of sleep deprivation. After being deprived of sleep for 24 hours, the marines taking tyrosine scored markedly higher and made significantly fewer errors in their standardized tests which measured their hand-eye coordination, memory capacity, and comprehensive skills.

High Altitudes and Cold Weather
Hypoxia is the condition whereupon the body's tissues are deprived of oxygen. This can take place in high altitudes (due to thin air) and extremely cold temperatures (due to constricting arteries). High altitude exposure causes hypobaric hypoxia, and additional exposure to extremely cold temperatures can further exacerbate this cognitive impairment. The bottom biological line is that acutely stressful situations (such as, but not limited to - hypoxia) can deplete brain norepinephrine and dopamine levels, thus disrupting behaviour and performance.

Extensive animal studies have revealed some very interesting revelations about tyrosine. In a series of trials, laboratory rats that were pre-treated with tyrosine were subjected to the Porsolt swim test, which is when the rats are placed in an escape-proof tank filled with freezing water. The amount of time that the rats were immobilized by the freezing water was then measured. It was found that the rats that were pre-treated with tyrosine had their immobility time reduced significantly, so much so in fact that the performance levels of these animals matched those that were not exposed to cold-induced stress. Another type of test called the Morris water maze tested spatial learning and memory in laboratory rats exposed to a simulated height of 19,500 feet for 8 hours. The decrements in performance among the tyrosine-treated animals were only marginal, where as the non-treated animals' decline in performance was considerable.

Human studies with tyrosine have been equally impressive. A series of clinical trials were conducted by the U.S. Army Research Institute of Environmental Medicine in Natick, Montana among soldiers operating at mountainous altitudes of 15,300 feet. They revealed that "tyrosine significantly mitigated many of the decrements in symptoms, mood, and performance induced by [hypobaric hypoxia], including functions believed to be regulated by catecholaminergic neurons such as vigilance, alertness, and anxiety." The United States Air Force, for its part, commissioned a study investigating the effectiveness of tyrosine on acute cardiovascular stress. Using a method designed to simulate gravitational stress (orthostasis), subjects who were given tyrosine experienced stabilized pulse pressures and increased central nervous system activity.

ADD
ADD or Attention Deficit Disorder (sometimes referred to as attention deficit hyperactivity disorder, or ADHD) can be defined as a persistent pattern of inattention, hyperactivity, and impulsivity, occurring more frequently and severely than is typical in individuals at a comparable level of development. As expected, many diagnoses occur among schoolchildren, and there appears to be some connection between this disorder and the maintenance of adequate levels of certain amino acids, especially phenylalanine, tyrosine, tryptophan, histidine, and isoleucine. In fact, recent data suggest that children with phenylketonuria (PKU) may have an increased prevalence of attentional dysfunction. The results from studies conducted with tyrosine with specific regard to ADD have been mixed, with their beneficial role being limited to a temporary one. In one noted clinical trial, 12 adults with ADD supplemented with tyrosine for 8 weeks. After 2 weeks, 8 of these subjects showed "marked to moderate" improvements, but after 6 weeks these particular subjects developed tolerance against tyrosine supplementation. The temporary improvements experienced by these subjects, however, leaves open the potential usage of tyrosine in cases of ADD that are of a transient type.

Dosage and Safety
Most of the successful human trials with tyrosine, especially those conducted by the U.S. military, used doses of 100-150 milligrams for every kilogram of bodyweight. This would equate to 8-12 grams of tyrosine for a 175 pound subject, and no discernibly adverse side effects were noted.

Trying to obtain the benefits of tyrosine from the diet is not an option, since the foods that are the richest sources of tyrosine, namely turkey and wild foul, are also the richest sources of the amino acid tryptophan, which is notorious for its ability to induce lethargy and sleep.

References

Thomas JR, Lockwood AP, Singh S and Deuster PA. "Tyrosine Improves Working Memory in a Multitasking Environment." Pharmacology Biochemistry and Behavior, Vol. 64, No. 3, pp 495-500, Feb 1999

Neri DF, et al. The Effects of Tyrosine on Cognitive Performance during Extended Wakefulness. Aviat Space Environ Med 66: 313-319, 1995

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

Lieberman HR. "Tyrosine and Stress: Human and Animal Studies" Food Components to Enhance Performance, 1994:Pg 277-299. Washington D.C.; National Academy Press

Bornstein RA, Baker GB, Carroll A, King A, Wong JT, Douglass AB. "Plasma amino acids in attention deficit disorder." Psychiatry Res. 1990 Sep;33(3):301-6.

Reimherr FW, et al. "An open trial of L-tyrosine in the treatment of attention deficit disorder, residual type." Am J Psychiatry. 1987 Aug;144(8):1071-3.

Copyright © 2005, Advanced Orthomolecular Research

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. Volunteers (N=19) completed three test sessions on different days (35 degrees C control/placebo, approximately 10 degrees C/placebo, approximately 10 degrees C/TYR) using a double-blind, within subjects design. During each session, volunteers completed two 90-minute water immersions and consumed a food bar (150 mg/kg TYR or placebo) before each immersion (total TYR 300 mg/kg). Cognitive performance, mood, and salivary cortisol were assessed. Cortisol was elevated in the cold (p<.01). Volunteers made fewer correct responses on a Match-to-Sample memory measure (p<.05) and reaction time (RT) and errors increased on a choice RT test (p<.01) in the cold. Self-reported tension (p<.01), depression (p<.05) and confusion (p<.01) also increased in the cold. 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.

Dietary tyrosine benefits cognitive and psychomotor performance during body cooling.
Physiol Behav. 2007 Feb 28;90(2-3):301-7. Epub 2006 Oct 31.
O'Brien C, Mahoney C, Tharion WJ, Sils IV, Castellani JW.

Supplemental tyrosine is effective at limiting cold-induced decreases in working memory, presumably by augmenting brain catecholamine levels, since tyrosine is a precursor for catecholamine synthesis. The effectiveness of tyrosine for preventing cold-induced decreases in physical performance has not been examined. This study evaluated the effect of tyrosine supplementation on cognitive, psychomotor, and physical performance following a cold water immersion protocol that lowered body core temperature. Fifteen subjects completed a control trial (CON) in warm (35 degrees C) water and two cold water trials, each spaced a week apart. Subjects ingested an energy bar during each trial; on one cold trial (TYR) the bar contained tyrosine (300 mg/kg body weight), and on the other cold trial (PLB) and on CON the bar contained no tyrosine. Following each water immersion, subjects completed a battery of performance tasks in a cold air (10 degrees C) chamber. Core temperature was lower (p=0.0001) on PLB and TYR (both 35.5+/-0.6 degrees C) than CON (37.1+/-0.3 degrees C). On PLB, performance on a Match-to-Sample task decreased 18% (p=0.02) and marksmanship performance decreased 14% (p=0.002), compared to CON, but there was no difference between TYR and CON. Step test performance decreased by 11% (p=0.0001) on both cold trials, compared to CON. These data support previous findings that dietary tyrosine supplementation is effective for mitigating cold-induced cognitive performance such as working memory, even with reduced core temperature, and extends those findings to include the psychomotor task of marksmanship.

Copyright © 2005, Advanced Orthomolecular Research