L-Tyrosine

L-Tyrosine Clinical Report Summary

Tyrosine is effective at combating the memory and cognitive decline associated with physical and mental stress. Several placebo controlled human trials show that tyrosine can minimize debilitation brought on by noise, cold, physical strain and sleep deprivation (1, 2, 3, 4, 5, 6, 7). Research also shows that tyrosine can reduce blood pressure when it becomes elevated in stressful situations (2, 5, 6). Scientists believe tyrosine does this by helping the body regulate levels of stress-related hormones (2).    

L-Tyrosine Overview

L-Tyrosine is a nonessential amino acid found in numerous dietary proteins like cheese, chicken and nuts. Nonessential does not mean tyrosine is unimportant; it means that the body can manufacture tyrosine on its own if necessary (1). Tyrosine is a critical building block for mood regulating brain chemicals like norephinephrine, seratonin and dopamine. Research shows that these neurotransmitters become depleted when the body is under stress (1, 2). This amino acid is also utilized by the body's adrenal, pituitary and thyroid glands to make and maintain hormones that regulate temperature and blood pressure (1). Because it is important to mood and physical function, tyrosine has become a popular dietary supplement. Tyrosine supplements are primarily used to aid depression, detoxification, premenstrual syndrome and mental function when the body is under stress (1, 2).

Safe Use of L-Tyrosine

Dosages of tyrosine vary but benefits may be seen at 150 mg a day (2, 3). Results are best when tyrosine is taken with food or multivitamins. Tyrosine was well tolerated in research studies but some people should consult a doctor before taking the amino acid. Tyrosine may interact with antidepressants and other medications that effect brain chemistry (2). Researchers say more studies should be done to access long-term safety.

L-Tyrosine Clinical Reports

Several human clinical studies demonstrate that tyrosine can improve memory and cognitive function when the body is under a variety of stressors like noise, cold, physical strain and lack of sleep (1, 2, 4, 5, 6, 7). In one study, researchers from the US Navy tested tyrosine on human subjects that were kept awake all night and given a battery of tests. Midway through the night, half of the subjects were given either tyrosine or placebo. The tyrosine group performed better than the others on physical and mental tasks for 3 more hours of testing (3). Similar results were found when naval researchers tested tyrosine in male volunteers exposed to the frigid temperature of 4 degrees Celsius. Despite the cold, the subjects short-term memory returned to the abilities found at normal temperature after taking tyrosine (4). Other tests show mood and performance benefits when subjects are exposed to noise, oxygen depletion and physical strain (5, 6, 7). Many researchers found that subjects given tyrosine had decreased blood pressure when put in stressful situations (2, 5, 6).     

L-Tyrosine References

1. Complementary medicine review: Tyrosine. University if Maryland Medical Center website. 2002: www.umm.edu/altmed/articles/tyrosine-000329.htm.
2. Kelly GS. Nutritional and botanical interventions to assist with the adaptation to stress. Alt Med Rev. 1999; 4(4): 249-265.
3. Neri DF et al. The effects of tyrosine on cognitive performance during extended wakefulness. Aviat Space Environ Med. 1995; 66(4): 313-319.
4. Shurtleff D et al. Tyrosine reverses a cold-induced working memory deficit in humans. Pharmacol Biochem Behav. 1994; 47(4): 935-941.
5. Deijen JB et al. Effect of tyrosine on cognitive function and blood pressure under stress. Brain Res Bull. 1994; 33(3): 319-323.
6. Deijen JB et al. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of combat training course. Brain Res Bull. 1999; 48(2); 203-209.
7. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull. 1989; 22(4): 759-762.