What does it do?
L-tyrosine is a nonessential amino acid (protein
building block) that the body synthesizes from
phenylalanine, another amino acid. Tyrosine is important to the structure of almost all
proteins in the body. It is also the precursor of several neurotransmitters, including L-dopa,
dopamine, norepinephrine, and epinephrine.
L-tyrosine, through its effect on neurotransmitters, may affect several health conditions,
including Parkinson’s disease, depression, and other mood disorders. Studies have suggested
that tyrosine may help people with depression.1 Preliminary findings indicate a
beneficial effect of tyrosine, along with other amino acids, in people affected by dementia,
including Alzheimer’s disease.2 Due
to its role as a precursor to norepinephrine and epinephrine (two of the body’s main
stress-related hormones) tyrosine may also ease the adverse effects of environmental,
psychosocial, and physical stress.3 4 5 6
7 8 9
L-tyrosine is converted by skin cells into melanin, the dark pigment that protects against
the harmful effects of ultraviolet light. Thyroid
hormones, which have a role in almost every process in the body, also contain tyrosine as
part of their structure.
People born with the genetic condition
phenylketonuria (PKU) are unable to metabolize the amino acid phenylalanine. Mental retardation and other severe
disabilities can result. While dietary phenylalanine restriction prevents these problems, it
also leads to low tyrosine levels in many (but not all) people with PKU. Tyrosine
supplementation may be beneficial in some people with PKU, though the evidence is
conflicting.10
L-tyrosine has been used
in connection with the following conditions (refer to the individual
health concern for complete information):
Who is likely to be deficient?
Some people affected by PKU are deficient in
tyrosine. Tyrosine levels are occasionally low in
depressed people.11 Any person losing large amounts of protein, such as those
with some kidney diseases, may be deficient in several amino
acids, including tyrosine.12
How much is usually taken?
Most people should not supplement with L-tyrosine. Some human research with people
suffering from a variety of conditions used 100 mg per 2.2 pounds of body weight, equivalent
to about 7 grams per day for an average-sized person. The appropriate amount to use in people
with PKU is not known, therefore, the monitoring
of blood levels by a physician is recommended.
Are there any side effects or interactions?
L-tyrosine has not been reported to cause any serious side effects. However, it is not
known whether long-term use of L-tyrosine, particularly in large amounts (such as more than
1,000 mg per day) is safe. For that reason, long-term use of L-tyrosine should be monitored by
a doctor.
Vitamin B6, folic
acid, and copper are necessary for conversion of
L-tyrosine into neurotransmitters.
Are there any drug
interactions?
Certain medicines may interact with L-tyrosine. Refer to drug interactions for a list of those medicines.
References
1. Gelenberg AJ, Gibson CJ, Wojcik JD. Neurotransmitter precursors for
the treatment of depression. Psychopharmacol Bull 1982;18:7–18.
2. Meyer JS, Welch KMA, Deshmuckh VD, et al. Neurotransmitter precursor
amino acids in the treatment of multi-infarct dementia and Alzheimer’s disease. J Am
Geriatr Soc 1977;7:289–98.
3. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter
precursor, reduces environmental stress in humans. Brain Res Bull
1989;22:759–62.
4. Salter CA. Dietary tyrosine as an aid to stress resistance among
troops. Mil Med 1989;154:144–6.
5. Neri DF, Wiegmann D, Stanny RR, et al. The effects of tyrosine on
cognitive performance during extended wakefulness. Aviat Space Environ Med
1995;66:313–9.
6. 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;48:203–9.
7. Shurtleff D, Thomas JR, Schrot J, et al. Tyrosine reverses a
cold-induced working memory deficit in humans. Pharmacol Biochem Behav
1994;47:935–41.
8. Deijen JB, Orlebeke JF. Effect of tyrosine on cognitive function and
blood pressure under stress. Brain Res Bull 1994;33:319–23.
9. Dollins AB, Krock LP, Storm WF, et al. L-tyrosine ameliorates some
effects of lower body negative pressure stress. Physiol Behav
1995;57:223–30.
10. Koch R. Tyrosine supplementation for phenylketonuria treatment.
Am J Clin Nutr 1996;64:974–5.
11. Chiaroni P, Azorin JM, Bovier P, et al. A multivariate analysis of
red blood cell membrane transports and plasma levels of L-tyrosine and L-tryptophan in
depressed patients before treatment and after clinical improvement.
Neuropsychobiology 1990;23:1–7.
12. Alvestrand A, Ahlberg M, Forst P, Bergstrom J. Clinical results of
long-term treatment with a low protein diet and a new amino acid preparation in patients with
chronic uremia. Clin Nephrol 1983;19:67–73.
Copyright © 2004 Healthnotes, Inc. All rights reserved.
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The information presented in Healthnotes is for informational
purposes only. It is based on scientific studies (human, animal, or in vitro),
clinical experience, or traditional usage as cited in each article. The results reported may
not necessarily occur in all individuals. For many of the conditions discussed, treatment with
prescription or over-the-counter medication is also available. Consult your doctor,
practitioner, and/or pharmacist for any health problem and before using any supplements or
before making any changes in prescribed medications. Information expires March 2005.
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Reliable and relatively consistent scientific data showing a substantial health benefit.
