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Clinical Studies
References
Tyrosine is a non-essential amino acid that the body synthesizes from phenylalanine. Tyrosine is a precursor of thyroxine and melanin; it is also a precursor for the synthesis of catecholamines, norepinephrine, epinephrine and dopamine.
There is interest in tyrosine for preventing the negative effects related to stress. The brain may not be able to synthesize enough tyrosine from phenylalanine under stressful conditions. Catecholamines like epinephrine, norepinephrine and dopamine, that are synthesized from tyrosine, can become depleted during stress. Increasing the availability of tyrosine to the brain may allow increased catecholamine synthesis and avoidance of the negative effects of stress. There is some evidence in animals and humans that supplemental tyrosine might improve performance, memory and learning under extreme environmental conditions, intense exercise, or psychological stress.
For people with phenylketonuria (PKU) who cannot synthesize tyrosine from phenylalanine, tyrosine is an essential amino acid. Tyrosine is used for depression, phenylketonuria (PKU) and improving alertness following sleep deprivation. It is also used for stress, premenstrual syndrome (PMS), Parkinson's disease, chronic fatigue syndrome (CFS), narcolepsy, alcohol and cocaine withdrawal, Alzheimer's disease, cardiovascular disease, impotence, loss of libido, schizophrenia, and as a suntan agent and appetite suppressant. Taking tyrosine orally seems to improve alertness following sleep depravation.
Published Clinical Studiesclin
The effects of tyrosine on cognitive performance during extended wakefulness.1
Neri DF, Wiegmann D, Stanny RR, Shappell SA, McCardie A, McKay DL.
Naval Aerospace Medical Research Laboratory, Pensacola, FL, USA.
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.
Publication Types:
PMID: 7794222 [PubMed - indexed for MEDLINE]
Nutrition, brain function and cognitive performance.2
Lieberman HR.
Military Nutrition Division, US Army Research Institute of Environmental Medicine (USARIEM), Natick, MA 01760-5007, USA. harris.lieberman@na.amedd.army.mil
Military interest in the effects of nutritional factors on cognitive function has stimulated considerable research on a variety of food constituents. This paper will review the research on the amino acids tryptophan and tyrosine, caffeine and carbohydrate. It will focus on research that addresses the potential utility of these compounds in military applications, particularly the acute, as opposed to chronic, effects of these substances on cognitive functions such as alertness, vigilance and resistance to stress. Caffeine, the most intensively studied food constituent, has unequivocal beneficial effects on vigilance, and in sleep deprived individuals it enhances other cognitive functions as well. Tryptophan, although it clearly has sedative-like properties, has not been extensively studied by military laboratories for use as a hypnotic, due to safety concerns. Tyrosine has been examined in animal models and human studies, and appears to prevent the substantial decline in various aspects of cognitive performance and mood associated with many kinds of acute stress. Carbohydrate supplementation appears to enhance cognitive performance in soldiers engaged in sustained, intense physical activities that expend high levels of energy.
Publication Types:
PMID: 12798782 [PubMed - indexed for MEDLINE]
Tyrosine improves appetite, cognition, and exercise tolerance in activity anorexia.3
Avraham Y, Hao S, Mendelson S, Berry EM.
Department of Human Nutrition and Metabolism, Hebrew University-Hadassah Medical School, Jerusalem, Israel 91120.
PURPOSE: We have modified for mice the activity wheel model of Routtenberg to study the effects of tyrosine on exercise tolerance, behavior, and brain neurochemistry. METHODS: Mice were fed for 2 h.d(-1) over a 2-wk period. During the second week, each group was injected daily with either saline or tyrosine (100 mg.kg(-1).d(-1)) and exercised on a running wheel. Controls were in cages with inactivated wheels and received the same treatment and feeding protocols as the experimental groups. Food consumption and cognitive function (eight-arm maze) were evaluated for 1 wk. Brains were then assayed for adrenergic and serotonergic metabolites. RESULTS: Activity together with a restricted diet caused extreme weight loss (27%) (P < 0.001) together with decreased food consumption (22%) (P < 0.001). Tyrosine restored food consumption to that of the controls (P < 0.001) with no effect on weight, since there was a 22% increase in activity (P < 0.001). Saline injections caused an 18% decrease in activity (P < 0.001). Both activity and tyrosine improved maze performance (P < 0.05). In the hypothalamus, activity caused a significant increase in 5-hydroxytryptamine (5-HT) (P < 0.001), 5-hydroxyindoleacetic acid (5-HIAA) (P < 0.01), and dopamine (P < 0.05); tyrosine prevented the increase in 5-HT (P < 0.05) and increased 5-HIAA in the controls (P < 0.01). With regard to hippocampal 5-HT, there was a significant increase in 5-HIAA following activity (P < 0.05), whereas tyrosine caused significant increase in 5-HIAA in the controls (P < 0.01). Activity significantly decreased the level of hippocampal 3,4-dihydroxyphenylacetic acid (DOPAC), whereas tyrosine decreased its level only in the controls (both at P < 0.0001). The level of tyrosine hydroxylase increased with activity (P < 0.05), and tyrosine decreased it significantly (P < 0.05). CONCLUSION: Activity anorexia is associated with increased hypothalamic 5-HT concentrations. Tyrosine administration reverses this, and significantly improves food consumption, cognitive behavior, and activity performance. Such nutritional modulations may have implications for the treatment of eating disorders and, in normal circumstances, tyrosine may improve exercise tolerance and delay fatigue.
PMID: 11740306 [PubMed - indexed for MEDLINE]
Nutrient control of brain neurotransmitter synthesis and function.4
Anderson GH, Johnston JL.
Dietary fluctuations in nutrient availability are factors in the regulation of brain function. Until recently the prevailing view was that brain biochemistry and function were influenced by diet only when biochemical and clinical evidence of nutrient deficiency was present. It is now clear, however, that the brain is sensitive and responsive to diet composition. Preliminary data show that variation in vitamin and mineral nutrient intakes over ranges that are considered to maintain normal nutritional status may impact on brain biochemistry, owing to their many coenzyme roles. Furthermore, the synthesis of at least five brain neurotransmitters, namely serotonin, the catecholamines, acetylcholine, histamine, and glycine responds to dietary fluctuations in availability of their nutrient precursors, tryptophan, tyrosine, choline, histidine, and threonine, respectively. Not only are these biochemical events altered by normal variations in diet composition, but considerable evidence now exists to show that the brain uses this information to regulate many functions. Future studies can be expected to continue to elucidate the links between diet, brain neurotransmission, and brain function, and to exploit the application of these links in understanding the function of the brain under normal and disease conditions.
PMID: 6132676 [PubMed - indexed for MEDLINE]
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