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Tyrosine
Supplement Review
By Dr. John M Berardi, Ph.D.
First published at www.johnberardi.com, Oct 20
2003.
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Nutrient:
Tyrosine (and N-Acetyl-L-Tyrosine)
What is it?
Tyrosine is one of the non-essential amino acids (can be manufactured
by the body) and has powerful physiological effects when both administered
alone and provided in high concentrations.
What does it do?
Tyrosine is an amino acid and nutrient precursor for approximately
90% of the brain’s 3 stimulatory catecholamines (dopamine, norepinephrine,
and epinephrine). For a dietary neurotransmitter precursor to be important:
a) Blood concentrations must vary with dietary intake
b) It must cross the blood brain barrier
c) Its transport systems must be able to accommodate more precursor
than what is regularly available
d) The levels of the precursor are what limit neurotransmitter formation
Since tyrosine meets these qualifications, it’s evident that
a large increase in dietary tyrosine will lead to increases in both
brain and peripheral catecholamine concentrations. Human studies confirm
that large doses of tyrosine (33mg/kg – 3x per day) can increase
blood and urinary catecholamines by up to 25%.
By increasing brain neurotransmitter concentrations, tyrosine can help
increase attention and combat performance decrements during sustained
efforts, especially when sleep deprived. In addition to this mild stimulant
effect, tyrosine may act as an “anti-stress supplement”,
suppressing rises in cortisol and the norepinephrine depletion associated
with the stress response. Finally, tyrosine supplementation may reduce
reaction time.
Where does it come from?
Tyrosine is a basic dietary component and is present in protein-containing
foods. However, the provision of this amino acid individually can lead
to more rapid digestion and absorption as well as increased blood concentrations.
How do I use it?
For strength athletes, 3g of tyrosine taken both before and after
exercise can improve both workout intensity and recovery of the CNS.
Since tyrosine can increase catecholamine synthesis and caffeine and
green tea can increase catecholamine release, these compounds should
act synergistically to increase arousal and performance.
N-acetyl-L-tyrosine acts similarly to tyrosine. The main difference
is that acetylation (adding an acetyl group) of the nitrogen terminus
(end) of the amino acid makes it more soluble in water. Increased solubility
means better dissolution in water and potentially increased digestion
and absorption of the amino acid. Most people report the similar effects
to tyrosine at ½ the dose. Therefore 1.5g of N-acetyl-L-tyrosine
should do the trick.
Credibility Rating -- 3/4
Rating Scale:
| 4/4 |
This supplement/regimen has significant scientific backing and
can
produce significant benefits in most individuals. |
| 3/4 |
There exists a sound theoretical basis for its ergogenic effects;
may
work in certain individuals; further research is needed to elucidate
their respective effects. |
| 2/4 |
Science is equivocal, animal data and human data may be conflicting;
or mechanism of action may be unclear. |
| 1/4 |
Little or no science as well as poor theoretical foundation. |
Scientific References:
1. Agharanya J, et al. Am J Clin Nutr. Jan;34(1):82-7, 1981.
2. Melamed E. J Neural Transm. 47(4): 299-306, 1980
3. Neri D, et al. Aviat Space Environ Med 66(4): 313-9, 1995.
4. Reinstein D et al. Life Sci. 37(23): 2157-63, 1985.
5. Lieberman H, et al. Am J Clin Nutr. 42(2): 366-70, 1985.
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