Tryptophan is an essential amino acid. This means that it
must be obtained through the diet in adequate quantities to meet the body's
Tryptophan is a precursor in the central nervous system of
the neurotransmitter serotonin. Serotonin modulates mood and sleep patterns.
Tryptophan is also converted in the body to niacin
(vitamin B-3) and picolinic acid. Giving high doses of vitamin B-6 along with
tryptophan increases its conversion to niacin and decreases its uptake into the
nervous system. One standard test for vitamin B-6 deficiency is to supplement
an individual with tryptophan and then look at the spill of xanthurenic acid in
his or her urine. High levels of xanthurenic acid in the urine are indicative
of the need for vitamin B-6. Low blood tryptophan levels have been reported in
depressed patients and are corrected with tryptophan supplementation.
Tryptophan has clinical impact on depression, particularly
endogenous (unipolar) depression. Doses of 1,000 to 3,000 mg divided throughout
the day and taken on an empty stomach have been employed.
Tryptophan has been shown in double-blind trials to also
be very helpful in treatment of insomnia when given in doses between 1,000 and
2,000 mg per day one hour before bed.
It has been found best to administer this amino acid along
with a carbohydrate source such as fruit juice because insulin, which is
secreted after the carbohydrate load, has been found to help tryptophan
absorption into the nervous system. Giving tryptophan along with other neutral
amino acids blocks its absorption and prevents therapeutic results. Generally,
tryptophan should be given away from a meal on an empty stomach along with a
carbohydrate source for optimal therapeutic results.
The metabolism of tryptophan is an interesting example of
biological control of amino acids. Tryptophan in the gut can be converted by
bacteria to indoxyl, which is then absorbed into the blood and sulfated by the
liver to produce indoxyl sulfate in the urine, sometimes called indican. This
is a substance related to amino acid malabsorption or intestinal toxicity
reactions. The primary breakdown pathway in humans is initiated by the enzyme
tryptophan-2,3-dioxygenase. This enzyme has often been studied because of its
regulation by hormone action, which is induced by glucocorticoids and the
amount of tryptophan in the diet. This enzyme also produces oxidants such as
singlet oxygen; therefore, activation of this enzyme is associated with
increased risk to free radical pathology. This is one of the concerns about
long-term, high-dose tryptophan therapy.
Tryptophan can also be converted to nicotinate
mononucleotide, which produces NAD, a high energy-carrying substance used in
energy metabolism. Also, this same pathway can manufacture nicotinic acid
vitamin B-3 (niacin). Vitamin B-3 is also used as a source of NAD in the body
and is about sixty times more efficient than tryptophan in this regard. A
high-tryptophan diet will partially overcome a deficiency in dietary niacin.
Tryptophan is also the precursor of a variety of other metabolites, including
serotonin, a neurotransmitter, and melatonin, a hormone secreted by the pineal
gland which seems to be related to sleep.
High doses of tryptophan have been shown, on occasion, to
produce intestinal discomfort and nausea. It is also known that high doses of
tryptophan which exceed the intestinal absorption efficiency can increase the
risk of toxic reactions in the intestinal tract due to bacterial action, which
produces substances such as indoxylsulfate.
Foods high in tryptophan include:
· Cottage cheese (dry) 450 mg/cup
· Cottage cheese (crmd) 336 mg/cup
· Fish & other seafoods 800-1,300 mg/lb
· Meats 1,000-1,300 mg/lb
· Poultry 600-1,200 mg/lb
· Peanuts, roasted w skin 800 mg/cup
· Sesame seeds 700 mg/cup
· Dry, whole lentils 450 mg/cup