FROM:
Alternative Medicine Review 2007 (Dec): 12 (4): 364–368 ~ FULL TEXT
Introduction
L-tyrosine is a conditionally essential amino acid because under normal conditions the body synthesizes sufficient quantities from phenylalanine. [1] For those with phenylketonuria, however, a severe deficiency in the enzyme phenylalanine hydroxylase prevents conversion of phenylalanine to tyrosine, making tyrosine an essential amino acid for this population. [2] Tyrosine is incorporated into proteins of all life forms and is a precursor for synthesis of thyroxin, melanin, and the neurotransmitters dopamine and norepinephrine. [1, 2] Food sources of tyrosine include fish, soy products, poultry, eggs, dairy products, lima beans, almonds, peanuts, sesame seeds, pumpkin seeds, wheat germ, oats, avocados, and bananas. [1, 3] Clinical conditions for which tyrosine supplementation may be of therapeutic benefit include depression, hypertension, stress, cognitive function and memory, Parkinson’s disease, phenylketonuria, and narcolepsy.