Tryptophan is involved in serotonin production via vitamin B6-dependent pathways resulting in the intermediate 5-hydroxytryptophan (5-HTP).
5-HTP is often used as a supplement for serotonin formation instead of tryptophan, which can be quickly metabolized in other pathways. Serotonin is further metabolized to melatonin via methylation. Because of these downstream conversions, therapeutic administration of 5-HTP has been shown to be effective for depression, fibromyalgia, binge eating associated with obesity, chronic headaches, and insomnia.
Tryptophan can be alternatively metabolized via the kynurenine pathway to produce various organic acids - kynurenic acid, quinolinic acid, and xanthurenic acid.
Two percent of dietary tryptophan is converted to niacin (vitamin B3) in the liver and deficiencies of vitamin B6, riboflavin, iron, and heme as essential cofactors for enzymes can slow the reaction rate.
Hartnup disease is a rare genetic disorder involving an inborn error of amino acid metabolism with symptoms developing in childhood. The intestines cannot properly absorb neutral amino acids and the kidney cannot properly resorb them. This leads to increased clearance of neutral amino acids in the urine, and normal or low levels in the plasma. Tryptophan deficiency is thought to account for the symptoms, since tryptophan converts to vitamin B3. This B3 deficiency causes dermatitis, a characteristic feature of Hartnup disease.
- Adrych K, Smoczynski M, Stojek M, et al. Decreased serum essential and aromatic amino acids in patients with chronic pancreatitis. World J Gastroenterol. 2010;16(35):4422-4427.
- Birdsall TC. 5-Hydroxytryptophan: a clinically-effective serotonin precursor. Alt Med Review. 1998;3(4):271-280.
- Gasperi V, Sibilano M, Savini I, Catani MV. Niacin in the Central Nervous System: An Update of Biological Aspects and Clinical Applications. Int J Mol Sci. 2019;20(4).
- Patel AB, Prabhu AS. Hartnup disease. Indian journal of dermatology. 2008;53(1):31-32.
- Ciecierega T, Dweikat I, Awar M, Shahrour M, Libdeh BA, Sultan M. Severe persistent unremitting dermatitis, chronic diarrhea and hypoalbuminemia in a child; Hartnup disease in setting of celiac disease. BMC Ped. 2014;14:311.
- NORD. Hartnup Disease. Rare Dis Info 2019, 2020.
- Gulati K, Anand R, Ray A. Nutraceuticals as adaptogens: their role in health and disease. In: Nutraceuticals. Elsevier; 2016:193-205.
- Wolf H, Brown RR. The effect of tryptophan load and vitamin B 6 supplementation on urinary excretion of tryptophan metabolites in human male subjects. Clin Sci. 1971;41(3):237- 248.
- Shibata K. Organ Co-Relationship in Tryptophan Metabolism and Factors That Govern the Biosynthesis of Nicotinamide from Tryptophan. J Nutr Sci Vitaminol. 2018;64(2):90-98.
- Shibata K, Shimada H, Kondo T. Effects of feeding tryptophan-limiting diets on the conversion ratio of tryptophan to niacin in rats. Biosci Biotech Biochem. 1996;60(10):1660-1666.
- Murray MF, Langan M, MacGregor RR. Increased plasma tryptophan in HIV-infected patients treated with pharmacologic doses of nicotinamide. Nutrition. 2001;17(7- 8):654-656.
- Capuron L, Ravaud A, Neveu PJ, Miller AH, Maes M, Dantzer R. Association between decreased serum tryptophan concentrations and depressive symptoms in cancer patients undergoing cytokine therapy. Molec Psych. 2002;7(5):468- 473.
- Ramos-Chavez LA, Roldan-Roldan G, Garcia-Juarez B, et al. Low Serum Tryptophan Levels as an Indicator of Global Cognitive Performance in Nondemented Women over 50 Years of Age. Ox Med Cell Longevity. 2018;2018:8604718.
Low levels of essential amino acids may indicate a poor-quality diet, or maldigestion due to deficient digestive peptidase activity or pancreatic dysfunction. Because some dietary tryptophan is converted to niacin, tryptophan-deficient diets have been associated with lower niacin production. Interestingly, niacin administration increased plasma tryptophan by 40%.
Clinically, low serum tryptophan levels have been shown to correlate with depressive symptoms and cognitive impairment.
Understand and improve your laboratory results with our health dashboard.
Upload your lab reports and get interpretation today.
Our technology helps to understand, combine, track, organize, and act on your medical lab test results.
Tryptophan is the precursor of niacin and serotonin (vasoconstrictor and neurotransmitter). Urinary wasting of tryptophan (inflammation, heavy metal toxicity, chemical exposure or inherited defects) can result in low serotonin that can be associated with disturbed sleep cycle or insomnia, anxiety or depression, aggressive behavior and low pain threshold.
Urinary tryptophan can also be associated with a form of impaired amino acid transport in the renal tubules (Hartnup Disorder). Other amino acids that are likely to be elevated in the urine with Hartnup disorder include valine, leucine, isoleucine, phenylalanine, tyrosine and alanine. Those amino acids may be low or normal in plasma.
Interpret Your Lab Results
Upload your lab report and we’ll interpret and provide you with recomendations today.Get Started
Get Started With Our Personal Plan
Are You a Health Professional?
Get started with our professional plan
Welcome to Healthmatters Pro.
Save time on interpreting lab results with the largest database of biomarkers online. In-depth research on any test at your fingertips, all stored and tracked in one place. Learn more
for health professionals
$45 per month
1-Methylhistidine, 3-Methylhistidine, Alanine, Alpha-amino-N-butyrate, Alpha-aminoadipate, Ammonia (NH4), Ammonia Level (NH4), Anserine, Arginine, Asparagine, Aspartate, Beta-alanine, Beta-aminoisobutyrate, Carnosine, Citrulline, Creatinine, Cystathionine, Cysteine, Cystine, Ethanolamine, Gamma-aminobutyrate, Glutamate, Glutamine, Glutamine/Glutamate, Glycine, Histidine, Homocystine, Hydroxyproline, Isoleucine, Leucine, Lysine, Methionine, Methionine Sulfoxide, Ornithine, Phenylalanine, Phosphoethanolamine, Phosphoserine, Proline, Sarcosine, Serine, Taurine, Threonine, Tryptophan, Tyrosine, Urea, Valine