:Tyrosine:
Function: Antidepressant
Tyrosine is an essential amino acid that readily passes the blood-brain
barrier. Once in the brain, it is a precursor for the neurotransmitters
dopamine, norepinephrine and epinephrine,
better known as adrenalin. These neurotransmitters are an important
part of the body's sympathetic nervous system, and
their concentrations in the body and brain are directly dependent
upon dietary tyrosine.
Tyrosine is not found in large concentrations throughout the body,
probably because it is rapidly metabolized. Folic acid, copper and
vitamin C are cofactor nutrients of these reactions. Tyrosine is also
the precursor for hormones, thyroid,
catecholestrogens and the major human pigment, melanin.
Tyrosine is an important amino acid in many proteins, peptides and
even enkephalins, the body's natural pain reliever.
Valine and other branched amino acids, and possibly tryptophan and
phenylalanine may reduce tyrosine absorption.
A number of genetic errors of tyrosine metabolism occur. Most common
is the increased amount of tyrosine in the blood of premature infants,
which is marked by decreased motor activity, lethargy and poor feeding.
Infection and intellectual deficits may occur. Vitamin C supplements
reverse the disease. Some adults also develop elevated tyrosine in
their blood. This indicates a need for more vitamin C.
Tyrosine therapy is very useful in a variety of clinical situations.
An average human equivalent dose of 2 to 6 g intravenously can raise
the blood pressure in hemorrhagic shock (extreme blood loss) in experimental
animals. An average human dose equivalent of 500 mg of tyrosine given
intravenously reduces susceptibility to life-threatening ventricular
fibrillation in experimental animals.
More tyrosine is needed under stress, and tyrosine
supplements prevent the stress-induced depletion of norepinephrine
and can cure biochemical depression. However, tyrosine may not be
good for psychosis. Many antipsychotic medications apparently function
by inhibiting tyrosine metabolism.
L-dopa, which is directly used in Parkinson's, is
made from tyrosine. Tyrosine, the nutrient, can be used as an adjunct
in the treatment of Parkinson's. Peripheral metabolism of tyrosine
necessitates large doses of tyrosine, however, compared to L-dopa.
When combined with the drug Sinemet, tyrosine's effectiveness is increased.
Yohimbine, which prolongs the effects of tyrosine products, is an
aphrodisiac. Tyrosine supplements in large doses may stimulate sex
drive by raising blood pressure and catecholamine levels.
Tyrosine, like amphetamines, in large doses reduces appetite,
but in low doses stimulates appetite. Tyrosine therapy
may be useful in drug addiction; temporarily replacing
codeine and amphetamines as methadone
does for heroin addicts.
Physicians at Harvard Medical School have pioneered the use of 1
to 6 grams of tyrosine for the effective treatment of medication-resistant
depression. Many antidepressants work by prolonging the action of
tyrosine metabolites. Tyrosine is safer, although the results may
be less dramatic in the short term than the antidepressants. As little
as 1000 to 2000 mg can be effective in humans and
animals. The minimum daily requirement for adults of tyrosine and
its precursor, phenylalanine, is 16 mg/kg a day or about 1000 mg total.
Hence, 6 g is at least six times the minimum daily requirement.
Tyrosine can be used as a safe and lasting therapy, useful in a variety
of clinical situations:
Tyrosine, like the branched chain
amino acids, fights all kinds of stress because it is the precursor
of adrenalin, which is used up during stress.
