Written by Chrystal Moulton, Staff Writer. This review shows various researches on the effect of tyrosine supplementation on stress.  

Tyrosine is a conditionally essential amino acid formed from phenylalanine, an essential amino acid required for various functions in the body. (1-3) It can be found in almost all proteins and peptides utilized by the body. However, tyrosine is most notable for its use in the formation of epinephrine, norepinephrine, and dopamine—neurotransmitters in the brain that are responsible for variation in mood and are released in response to stress. Tyrosine also serves as a precursor to thyroxine—a thyroid hormone responsible for the regulation of metabolic rate—and melanin, a skin pigment that protects our cells from the ultraviolet rays of the sun.(1,2) Under normal circumstances, tyrosine levels may vary throughout the day and can be readily absorbed from the foods we eat. However, under severe stress or dietary restrictions, tyrosine levels may become insufficient for optimal wellness. Dietary sources include dairy products, fish, eggs, poultry, oats, wheat germ, lima beans, sesame seeds, peanuts, almonds, bananas, and avocados. (1)

Therapeutically, tyrosine is especially used to ameliorate the symptoms related to phenylketonuria or PKU. Individuals with this genetic disease are naturally deficient in tyrosine due to their body’s inability to convert phenylalanine to tyrosine. Under the care of trusted healthcare providers, individuals with PKU are usually supplemented with tyrosine along with a diet restricting consumption of phenylalanine. (1,2) Tyrosine has also been shown to have some benefit for depression and stress.(1)

In a case study, a woman, who was unable to take conventional anti-depressants, was given tyrosine at 100mg/kg daily for two weeks. The study was a double-blind, placebo-controlled, crossover trial.(4) Following two weeks of tyrosine treatment, she was given placebo for one week. Researchers observed significant improvement in symptoms following tyrosine treatment (p<0.05). During the placebo, depressive symptoms returned. Another larger prospective, randomized, double-blind study with 65 patients suffering from major depression who received 100mg/kg of tyrosine showed no statistically significant improvement in symptoms related to depression. (5) Therefore, more studies are needed to determine the benefits of tyrosine for depression.

In regards to stress, however, various trials conducted by the military have shown that tyrosine is able to ameliorate deficits related to cognition, memory, and performance under high stress. (See Table 1) The most common effect in almost all trials was decreased blood pressure. In two other trials, when tyrosine was supplemented in subjects exposed to cold conditions, researchers observed fewer deficits in memory and task performance compared to placebo.(6,7) And in a more recent trial, tyrosine was noted to improve working memory especially when performing more difficult tasks.(8)

Type of StudySubjectsTreatmentProtocolResult
Double-blind, placebo controlled crossover trial (9)23 male military personnel (18-20 years old)50mg/kg tyrosine or placebo given 40min after exposure to either normal or stress conditionExposure to stress condition (58°F and 4,200m or 4700m altitude) and normal condition (71°F and 550m altitude) for 4.5 hoursReduction in headache, coldness, stress, fatigue, sleepiness, and muscle aches. (p<0.05) Improved mood/mental state and cognition noted (p<0.05)
Double-blind placebo controlled study (10)21 cadets (18-27 years old)2g tyrosine in 500mL protein rich orange juice or placebo (carb-rich orange juice) given daily for 6 daysCadets were undergoing combat training for 2 weeks. First week was used for the trialTyrosine group performed better on tracking tasks, memory tests, and had a lower systolic blood pressure (p<0.05)
Double-blind, placebo controlled crossover trial (11)20 healthy adult males ( average age=28)50mg/kg tyrosine or placebo (cellulose) 1hour before and after exposure to stressorInduced cardio stress by exposure to negative pressure on the lower body (-50mmHg)Improvement in pressure tolerance, pulse pressure, and decrease in heart rate were noted after tyrosine supplementation (p<0.05)
Double-blind placebo controlled study (12)16 healthy young adults ( average age=27)100mg/kg tyrosineExposure to auditory stress (90dB of noise in headphones while performing tasks under time constraints)Better short-term memory and decreased diastolic blood pressure compared to placebo (p<0.05)

Other proposed benefits of include improving symptoms related to attention deficit disorder (13) and Parkinson’s disease. (14,15) However, more studies are needed to confirm these benefits.

Side effects commonly attributed to tyrosine supplementation

Side effects commonly attributed to tyrosine supplementation occur at doses above 150mg/kg. Adverse effects above the typical dose include diarrhea, headache, nausea, vomiting, and insomnia.(1) Tyrosine may compete with L-dopa and therefore decrease its effectiveness. If you must take tyrosine and L-dopa make sure to place 2 hours separation between dosages.(1) Individuals taking thyroid medication should consult their healthcare provider before taking tyrosine as it is a precursor to thyroxine—a thyroid hormone which increases metabolism among other effects. Furthermore, individuals with hyperthyroidism or Grave’s disease should seek advice from a healthcare professional before taking tyrosine.(1) Tyrosine may also interact with MAOIs leading to a rapid decrease in blood pressure. (2) Individuals suffering from migraines should avoid tyrosine as it may trigger migraines and upset stomach. (2) Also, when consuming a protein rich diet, tyrosine may need to compete with other large neutral amino acids present in the diet for uptake into the brain. This could reduce any beneficial effects tyrosine has in the formation of neurotransmitters (norepinephrine and dopamine), which in turn affect mood and mental states. Therefore, it is recommended to take tyrosine on an empty stomach.

Currently, the typical daily dose of tyrosine supplementation ranges from 100-150mg/kg body weight.(1) However, daily changes in tyrosine level vary individually. It is best to seek advice from your healthcare provider in determining the dose that best suits your specific needs.

Posted February 12, 2015.

Chrystal Moulton BA, PMP, is a 2008 graduate of the University of Illinois at Chicago. She graduated with a bachelor’s in psychology with a focus on premedical studies and is a licensed project manager. She currently resides in Indianapolis, IN.

References:

  1. L-Tyrosine (monograph). Alt Med Rev (2007) 12(4): 364-368.
  2. University of Maryland Medical System. http://umm.edu/health/medical/altmed/supplement/tyrosine. Accessed February 6, 2015.
  3. Amino Acids. Medline Plus. http://www.nlm.nih.gov/medlineplus/ency/article/002222.htm. Accessed February 9, 2015.
  4. Gelenberg AJ, Wojcik JD, Growdon JH, et al. Tyrosine for the treatment of depression. Am J Psychiatry 1980;137:622-623.
  5. Gelenberg AJ, Wojcik JD, Falk WE, et al. Tyrosine for depression: a double-blind trial. J Affect Disord 1990;19:125-132
  6. Shurtleff D, Thomas JR, Schrot J, et al. Tyrosine reverses a cold-induced working memory deficit in humans. Pharmacol Biochem Behav 1994;47:935-941.
  7. Mahoney CR, Castellani J, Kramer FM, et al. Tyrosine supplementation mitigates memory decrements during cold exposure. Physiol Behav 2007 May 22.
  8. Colzato LS, et al. Working memory reloaded: tyrosine repletes updating in the N-back task. Front Behav Neurosci. 2013 Dec 16;7:200.
  9. Banderet LE, Leiberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull 1989;22:759-762
  10. Deijen JB, Wientjes CJ, Vullinghs HF, et al. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Res Bull 1999;48:203-209.
  11. Dollins AB, Krock LP, Storm WF, et al. L-tyrosine ameliorates some effects of lower body negative pressure stress. Physiol Behav 1995;57:223-230
  12. Deijen JB, Orlebeke JF. Effect of tyrosine on cognitive function and blood pressure under stress. Brain Res Bull 1994;33:319-323
  13. Reimherr FW, Wender PH, Wood DR, Ward M. An open trial of L-tyrosine in the treatment of attention deficit disorder, residual type. Am J Psychiatry 1987;144:1071-1073
  14. Growdon JH, Melamed E, Logue M, et al. Effects of oral L-tyrosine administration on CSF tyrosine and homovanillic acid levels in patients with Parkinson’s disease. Life Sci 1982;30:827-832.
  15. Lemoine P, Robelin N, Sebert P, Mouret J. L-tyrosine: a long term treatment of Parkinson’s disease. C R Acad Sci III 1989;309:43-47