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What is tryptophan?

Tryptophan is an essential amino acid [1]. In foods, tryptophan is incorporated into proteins.

Tryptophan abbreviation (symbol): Trp

Tryptophane Functions in the Human Body

Tryptophan is [1]:

  • A building block of proteins
  • A precursor for vitamin B3 (niacin), the neurotransmitter serotonin (which has a calming effect on mood) and the later is a precursor of the hormone melatonin (which induces sleep); to date, tryptophan from foods has not been shown to affect the serotonin and melatonin secretion by the pineal gland, though [4].
  • A glucogenic amino acid — it can be converted into glucose [15]
  • A ketogenic amino acid — it can be converted into ketones [15]
  • Necessary for normal growth in infants and  for nitrogen balance in adults

Tryptophan Rich Foods

  • ANIMAL FOODS (100-400 mg/3 oz or 85 g): pork, beef, lamb, veal, sea lion, salmon and other fish, oysters, lobsters, crabs, shrimps, dolphin, mollusks, elk meat, quail, goat, caribou, pheasant, turkey, squab, rabbit, buffalo, chicken, boar, egg whites, cheese [2]. NOTE: Turkey does not contain more tryptophan than other meats, and is not likely a culprit for Thanksgiving day sleepiness [5].
  • PLANT FOODS (10-150 mg/cup or 237 mL): spinach, watercress, turnip greens, asparagus, sesame seeds, sunflower seeds, winged beans, mung beans, kidney beans, soy products, peanuts, bananas, pineapples, plums, oat bran, spirulina [2]

Foods low in tryptophan: beans, peas, lentils, peanuts, cornmeal, potatoes, mushrooms, kale [3].

Tryptophan needs to compete with other amino acids for the entrance into the brain (through the blood-brain barrier), so a high-protein diet, which is usually lower in tryptophan than in other amino acids, may even decrease the amount of tryptophan that reaches the brain [5].

Hartnup’s Disease

Hartnup’s disease is a hereditary (autosomal recessive) disorder in which the absorption of tryptophan and certain other amino acids in the small intestine and their reabsorption in the kidneys is reduced due to a lack of a transport protein, which may lead to tryptophan deficiency and this in turn to vitamin B3 (niacin) deficiency [6].

Symptoms usually develop between the 3rd and 9th year of age (or, rarely, as soon as 10 days after birth) and may include pellagra-like rash on the sun-exposed skin, inflamed gums and tongue, neurological symptoms, such as wide-based gait and double vision, and mood changes, but often there are no symptoms [7]. Symptoms may be triggered by the exposure to the sun, febrile illness or drugs, such as sulfonamides, and may last from one week to one month and than resolve spontaneously; symptoms decrease with age. Complications may range from a mild mental retardation to death due to a brain damage.

Diagnosis is made by finding increased levels of certain amino acids in the urine.

Treatment involves a high-protein diet and vitamin B3 (nicotinamide) supplements [8]. Skin symptoms may be prevented by avoiding the sun exposure.

Tryptophan Deficiency

Rarely, a diet predominantly based on whole corn (with hulls) may result in tryptophan and vitamin B3 (niacin) deficiency and pellagra, since in the intestine these two nutrients are poorly absorbed from the whole corn; this may still be a problem in the poor parts of India, Africa and South America [9].

Tryptophan deficiency may lower mood in healthy individuals and trigger depression in individuals who receive treatment for depression [10].

L-Tryptophan Supplements

In 1991 the U.S. Food and Drug Administration (FDA) banned tryptophan supplements, since it has been found out that supplements from a single producer have caused an allergy-like disorder eosinophilia-myalgia syndrome (EMS) and several deaths. It is still not known, what exactly caused the symptoms: tryptophan itself, high dose or impurities in the supplements.

L-tryptophan in the form of oral supplements without prescription is on the internet market; their safety might not be sufficiently tested. The supplements typically contain 500-1000 mg tryptophan per capsule. Trypotophan supplements are also available by prescription.

L-tryptophan supplements are POSSIBLY EFFECTIVE in:

  • Treatment of premenstrual dysphoric disorder (PMDD) [11,16]
  • Helping quitting smoking [11]
  • Improvement of symptoms of phenylketonuria [17]

L-tryptophan supplements are POSSIBLY INEFFECTIVE in the prevention or treatment of teeth grinding and facial pain, and in improving athletic performance [11,18].

There is INSUFFICIENT EVIDENCE [11] about the effectiveness of L-tryptophan supplements in the prevention or treatment of anxiety, attention deficit hyperactivity disorder (ADHD), depression, insomnia [12], seasonal affective disorder (SAD) and reducing side effects of quinine [13].

L-Tryptophan Safety: Side Effects, Toxicity

L-tryptophan supplements are POSSIBLY UNSAFE [11].

Side effects may include heartburn, stomach pain, burping, gas, nausea, vomiting, diarrhea, loss of appetite, headache, lightheadedness, dry mouth, blurred vision, muscle weakness, and sexual problems [11].

Tryptophan supplements may cause a potentially deadly eosinophilia-myalgia syndrome (EMS), a disorder of blood and nerve tissues with fatigue, pain in the muscles and nerves, joint swelling, rash, baldness and damage of lungs, heart, and liver [11]. Symptoms may last for up to two years or longer.

Tryptophan is secreted in breast milk. The safety and effects of tryptophan supplements on unborn babies, breastfed infants and children have not been tested, so speak with a doctor before using tryptophan during pregnancy, breastfeeding, or giving it to a child [14].

L-Tryptophan-Drug Interactions

L-tryptophan may increase the effect of [14]:

  • Antidepressants: St. John’s wort, citalopram, fluoxetine, paroxetine, sertraline, amitriptyline, tranylcypromine, phenelzine
  • Sedatives, such as diazepam (Valium) or lorazepam (Ativan)
  • Anti-psychotics, such as chlorpromazine or prochlorperazine
  • Substances with a sedative effect: alcohol, pain relievers, muscle relaxants

Speak with your doctor before using tryptophan together with above mentioned substances.

  1. L-tryptophan  PubChem
  2. List of foods high and low in tryptophan  US Department of Agriculture
  3. Protein, Calories, Amino Acids In A Plant Based Diet  Savvyvegetarian.com
  4. Arendt J, 1992, Melatonin and the Mammalian Pineal Gland, p.33
  5. Tryptophan: What does it do?  Psychology Today
  6. Hartnup disease, overview  Emedicine
  7. Hartnup disease, presentation  Emedicine
  8. Hartnup disease, treatment  Emedicine
  9. Carpenter KJ, 1980, The relationship of pellagra to corn and the low availability of niacin in cereals  PubMed
  10. Bell C et al, 2001, Tryptophan depletion and its implications for psychiatry  The British Journal of Psychiatry
  11. L-tryptophan, uses, side effects  WebMD
  12. Buscemi N et al, 2005, Manifestations and Management of Chronic Insomnia in Adults  Agency for Healthcare Research and Quality
  13. Khozoie C et al, 2009, The antimalarial drug quinine disrupts Tat2p-mediated tryptophan transport and causes tryptophan starvation  PubMed
  14. L-tryptophan  Drugs.com
  15. Amino acid  ChemPep
  16. Steinberg S et al, 1999, A placebo-controlled clinical trial of L-tryptophan in premenstrual dysphoria  PubMed
  17. van Vliet D et al, 2014, Single amino acid supplementation in aminoacidopathies: a systematic review  PubMed Central
  18. Williams M, 2005, Dietary Supplements and Sports Performance: Amino Acids  PubMed Central

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