Research
L-Tryptophan
95 peer-reviewed studies curated from PubMed and Semantic Scholar.
Studies
Sorted by quality and recency
Suggestive Association Between Tryptophan-indole Metabolic Pathway and Total Joint Arthroplasty Early Revision for Heterogeneous Failure Modes in Patients With Primary Osteoarthritis: A Meta-analysis of Metabolomics.
Meta-analysis of metabolomics data from two osteoarthritis cohorts to identify metabolic biomarkers associated with early revision of total joint arthroplasty. Overactivation of the tryptophan-indole metabolic pathway was suggestively linked to early revision, though no metabolite reached significance after correction.
Interrelation between cycling and renal and urological health: A bibliometric and systematic review.
This systematic and bibliometric review synthesizes current knowledge of the relationship between cycling and renal and urological health. It discusses the benefits and risks associated with cycling, including improved cardiovascular health and metabolic function, but also urological symptoms and risks of erectile dysfunction. Sodium intake and L-tryptophan supplementation demonstrated positive effects on fatigue reduction and recovery.
A systematic review of the effect of L-tryptophan supplementation on mood and emotional functioning.
Systematic review of 11 RCTs examining the effects of L-tryptophan supplementation on mood in healthy adults. Four RCTs showed significant improvements in mood, suggesting TRP intake may decrease anxiety and increase positive mood. The effectiveness for aggressive feelings was not recognized.
Effects of tryptophan, serotonin, and kynurenine on ischemic heart diseases and its risk factors: a Mendelian Randomization study.
Mendelian Randomization study using genetic instruments to assess associations of tryptophan, serotonin, and kynurenine with ischemic heart disease (IHD) and its risk factors. Tryptophan and serotonin were not associated with IHD, while kynurenine showed a nominal positive association with IHD, but not after correction for multiple comparisons.
The Usefulness of the Low-FODMAP Diet with Limited Tryptophan Intake in the Treatment of Diarrhea-Predominant Irritable Bowel Syndrome.
RCT evaluating the efficacy of a low-FODMAP diet with reduced tryptophan intake in 80 IBS-D patients. Group with limited tryptophan intake showed greater improvement in gastrointestinal symptoms and psychological status compared to the standard low-FODMAP diet group.
An integrated meta-analysis of peripheral blood metabolites and biological functions in major depressive disorder.
Meta-analysis of peripheral blood metabolites in major depressive disorder (MDD) patients identified 23 differentially expressed metabolites. L-tryptophan and kynurenic acid were consistently downregulated in MDD patients, with depression rating scores negatively associated with decreased L-tryptophan levels. Altered amino acid and lipid metabolism pathways were noted.
Tryptophan supplementation and postoperative delirium--a randomized controlled trial.
RCT of 325 elderly adults undergoing major elective operations to assess the effect of postoperative tryptophan supplementation on delirium. Tryptophan did not reduce the incidence or duration of postoperative excitatory delirium or overall delirium.
Mulberry leaf extract combined with tryptophan improves sleep and post wake mood in adults with sleep complaints - A randomized cross-over study.
A randomized, crossover, double-blind, controlled trial with 42 adults evaluated a supplement containing mulberry leaf extract and tryptophan. The treatment reduced sleep onset latency, improved sleep quality, and enhanced post wake mood. It also reduced postprandial glucose response and nocturnal glucose variation.
Acute decrease in the plasma tryptophan-to-large-neutral-amino-acids ratio attenuates the effects of L-tryptophan on gut hormones and energy intake in healthy males: a randomized, cross-over, exploratory trial.
This randomized, cross-over trial explored the effects of L-tryptophan and L-leucine on gut hormones and energy intake in 12 healthy males. Tryptophan alone led to a sustained increase in plasma CCK and GLP-1 and reduced energy intake compared to control. The addition of leucine attenuated these effects, suggesting a complex interaction between tryptophan and large neutral amino acids in appetite regulation.
Effects of phototherapy on biopterin, neopterin, tryptophan, and behavioral neuroinflammatory reaction in patients with post-stroke depression.
RCT investigating the effects of phototherapy on biopterin, neopterin, tryptophan, and behavioral neuroinflammatory reactions in 100 patients with post-stroke depression. Phototherapy reduced depressive symptoms, improved neurotransmitter levels, and enhanced antioxidant capacity compared to routine treatment.
Oral tryptophan activates duodenal aryl hydrocarbon receptor in healthy subjects: a crossover randomized controlled trial.
A crossover RCT in 20 healthy volunteers assessed the effects of oral tryptophan supplementation (3 g/day) on AhR activation and tryptophan metabolism. Tryptophan increased AhR activation in duodenal contents and elevated urinary and plasma kynurenine metabolites and indoles, with no significant changes in gastrointestinal or psychological symptoms, cytokine production, or fecal microbiome profiles.
Intraduodenal calcium enhances the effects of L-tryptophan to stimulate gut hormone secretion and suppress energy intake in healthy males: a randomized, crossover, clinical trial.
This randomized, crossover clinical trial investigated the effects of intraduodenal calcium on L-tryptophan's ability to stimulate gastrointestinal hormones and suppress energy intake in 15 healthy males. The study found that calcium enhanced the effects of L-tryptophan to stimulate plasma cholecystokinin, GLP-1, and PYY, and suppress energy intake, suggesting potential for nutrient-based approaches to energy intake regulation.
Decreased Gut Microbiome Tryptophan Metabolism and Serotonergic Signaling in Patients With Persistent Mental Health and Gastrointestinal Symptoms After COVID-19.
Study of gut microbiome tryptophan metabolism and serotonergic signaling in patients with persistent mental health and gastrointestinal symptoms after COVID-19. Decreased tryptophan metabolism was associated with more severe GI and mental health symptoms. Plasma 5-HT concentration was increased in those with GI symptoms.
Effects of intraduodenal infusion of lauric acid and L-tryptophan, alone and combined, on glucoregulatory hormones, gastric emptying and glycaemia in healthy men.
RCT in 12 healthy men examining the effects of intraduodenal infusion of lauric acid and L-tryptophan, alone and combined, on glucoregulatory hormones, gastric emptying, and glycaemia. Lauric acid and the combination with L-tryptophan delayed the rise in glucose following a nutrient drink by slowing gastric emptying, likely due to stimulation of CCK and GLP-1.
Suppression of Energy Intake by Intragastric l-Tryptophan in Lean and Obese Men: Relations with Appetite Perceptions and Circulating Cholecystokinin and Tryptophan.
This study evaluated the effects of intragastric l-tryptophan on energy intake in lean and obese men. l-Tryptophan increased plasma CCK and the Trp:LNAAs ratio, suppressing energy intake in both groups, with no significant difference between them.
NAD+-Precursor Supplementation With L-Tryptophan, Nicotinic Acid, and Nicotinamide Does Not Affect Mitochondrial Function or Skeletal Muscle Function in Physically Compromised Older Adults.
A randomized, double-blind, controlled trial in 14 older adults with impaired physical function tested NAD+-precursor supplementation (L-tryptophan, nicotinic acid, and nicotinamide) on mitochondrial and skeletal muscle function. The study found no significant improvement in mitochondrial function or exercise efficiency, although NAD+ metabolism increased.
Randomised clinical trial on the effect of a single oral administration of l-tryptophan, at three dose rates, on reaction speed, plasma concentration and haemolysis in horses.
RCT on the effect of oral l-tryptophan administration on reaction speed in horses. Sixty horses received placebo or TRP at different doses. Plasma TRP concentrations increased, but there was no effect on reaction speed or signs of haemolytic anaemia. The study confirms the safety of TRP doses but not its efficacy as a calmative.
L-Tryptophan as a Novel Potential Pharmacological Treatment for Wound Healing via Aryl Hydrocarbon Receptor Activation.
The study assessed the effect of tryptophan on wound healing using an in vitro scratch wound model and a clinical trial with 51 patients with lower limb ulcers. Tryptophan increased the rate of scratch recovery in vitro and induced stronger pain relief and faster re-epithelialization in patients compared to the vehicle.
The effect of increased serotonergic neurotransmission on aggression: a critical meta-analytical review of preclinical studies.
Meta-analytical review of preclinical studies examining the effect of increased serotonergic neurotransmission on aggression. The analysis found that increased serotonin levels generally inhibit aggression, with variations based on genetic background, drug type, treatment duration, and aggression-inducing conditions.
Effects of supplemental L-tryptophan on serotonin, cortisol, intestinal integrity, and behavior in weanling piglets.
RCT investigating the effects of supplemental dietary L-tryptophan (5 g/kg) on weanling piglets. The study found increased hypothalamic serotonergic activity, reduced salivary cortisol response to mixing, improved intestinal morphology, and reduced physical activity 10 days after diet introduction. No effect on behavioral reactivity during weaning and mixing was observed.
Safety and efficacy of L-tryptophan and behavioral incentives for treatment of cocaine dependence: a randomized clinical trial.
RCT evaluating L-tryptophan and behavioral incentives for cocaine dependence treatment in 199 patients. Tryptophan did not significantly prevent relapse or reduce cocaine use, while contingent vouchers increased time to relapse and reduced cocaine use compared to non-contingent vouchers.
Tryptophan, serotonin and human social behavior.
Double-blind cross-over study with 100 healthy people testing the effects of tryptophan (1 g after each meal) versus placebo on social behaviors. Tryptophan caused a significant decrease in quarrelsome behaviors and a significant increase in dominant behaviors.
The effects of a sleep/recovery supplement: 'Night Time Recharge' on sleep parameters in young adults.
Double-blind, randomized, placebo-controlled, cross-over study of 20 young adults assessing the effects of 'Night Time Recharge' (NTR) supplement containing cherry extract on sleep parameters. NTR increased urinary 6-sulphatoxymelatonin levels and improved sleep latency, but had no significant effect on other sleep parameters. The tryptophan content is suggested as the reason for improved sleep latency.
Effects of intraduodenal administration of lauric acid and L-tryptophan, alone and combined, on gut hormones, pyloric pressures, and energy intake in healthy men.
RCT with 16 healthy, lean males receiving intraduodenal infusions of lauric acid, L-tryptophan, or their combination. The combination significantly reduced energy intake and modulated gut hormones, including increased CCK and GLP-1 and decreased ghrelin, compared to control.
Selective dietary supplementation in early postpartum is associated with high resilience against depressed mood.
Open-label study assessing a dietary supplement containing tryptophan, tyrosine, and blueberry extract on postpartum mood. The supplement group showed no increase in depressed mood following a mood induction procedure, while the control group did, suggesting the supplement reduces vulnerability to depressed mood during postpartum blues.
Effect of L-Tryptophan and L-Leucine on Gut Hormone Secretion, Appetite Feelings and Gastric Emptying Rates in Lean and Non-Diabetic Obese Participants: A Randomized, Double-Blind, Parallel-Group Trial.
Randomized, double-blind, parallel-group trial comparing effects of L-tryptophan and L-leucine on gastric emptying and gut peptide secretion in 10 lean and 10 non-diabetic obese participants. L-tryptophan at a higher dose stimulated CCK release and retarded gastric emptying, with a minor increase in GLP-1 secretion. Neither amino acid affected subjective appetite feelings or insulin/glucose concentrations.
Differential effects of L-tryptophan and L-leucine administration on brain resting state functional networks and plasma hormone levels.
RCT investigating the effects of L-tryptophan and L-leucine on brain networks and plasma hormone levels in 20 healthy subjects. L-tryptophan modified connectivity in several brain networks and influenced plasma insulin concentration, while L-leucine had lesser effects.
Time-dependent effects of L-tryptophan administration on urinary excretion of L-tryptophan metabolites.
Randomized, double-blind, placebo-controlled, crossover intervention study in 17 healthy Japanese women to assess the effects of L-tryptophan supplementation on urinary excretion of its metabolites. L-tryptophan administration increased urinary excretion of several metabolites in a dose-dependent manner on day 7, but not on days 14 and 21. No accumulation of L-tryptophan or its metabolites was observed.
Pharmacotherapy for sleep bruxism.
This meta-analysis evaluated the effectiveness and safety of pharmacological therapy for sleep bruxism, comparing drugs like amitriptyline, bromocriptine, clonidine, propranolol, levodopa, and tryptophan with placebo. The results were imprecise and showed no consistent benefit or harm. The review highlights the need for more well-designed RCTs with larger sample sizes.
Effects of intraduodenal infusion of L-tryptophan on ad libitum eating, antropyloroduodenal motility, glycemia, insulinemia, and gut peptide secretion in healthy men.
RCT in 10 healthy men testing intraduodenal infusion of L-tryptophan on gastrointestinal function and eating behavior. L-tryptophan suppressed antral pressures, stimulated pyloric pressures, increased cholecystokinin and glucagon, and reduced energy intake. Plasma L-tryptophan levels inversely correlated with energy intake.
Supplementing healthy women with up to 5.0 g/d of L-tryptophan has no adverse effects.
A randomized, double-blind, placebo-controlled, crossover intervention study in 17 healthy Japanese women assessed the no-observed-adverse-effect-level for L-tryptophan. Doses up to 5.0 g/d showed no adverse effects on food intake, body weight, or general biomarkers. Urinary excretion of L-tryptophan metabolites increased proportionally with intake, suggesting normal metabolism and identifying 3-hydroxykynurenine as a potential biomarker for excess ingestion.
Dietary L-tryptophan supplementation with reduced large neutral amino acids enhances feed efficiency and decreases stress hormone secretion in nursery pigs under social-mixing stress.
RCT evaluating the effect of L-tryptophan supplementation on nursery pigs under social-mixing stress. L-tryptophan improved feed efficiency and reduced stress hormone secretion, with effects enhanced by lowering large neutral amino acids in the diet.
Effects of tryptophan depletion and tryptophan loading on the affective response to high-dose CO2 challenge in healthy volunteers.
Randomized, double-blind placebo-controlled study on 18 healthy volunteers to investigate the effects of acute tryptophan depletion and loading on CO2-induced panic response. Tryptophan depletion resulted in lower CO2-induced subjective distress and breathlessness compared to balanced and tryptophan loading conditions.
Increased serum free tryptophan in patients with diarrhea-predominant irritable bowel syndrome.
Study on 13 d-IBS patients measuring serum free and total tryptophan and kynurenine metabolites before and after a dairy-free diet. d-IBS patients had higher free serum tryptophan and lower tryptophan oxidation compared to controls. Dairy-free diet did not alter kynurenine pathway metabolites or symptoms, suggesting inhibited tryptophan metabolism in d-IBS.
Effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behaviour in horses.
RCT investigating the effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behavior in 12 Thoroughbred horses. Plasma tryptophan increased 3-fold after dosing, but no significant behavioral changes were observed regardless of diet.
Effects of elevated plasma tryptophan on brain activation associated with the Stroop task.
Double-blind, cross-over study with eight subjects investigating the effects of acute tryptophan feeding on brain activation during the Stroop task. Tryptophan administration increased plasma-free tryptophan levels and caused distributed functional changes in brain regions, with mixed effects on reaction times and brain activation patterns.
The effect of tryptophan depletion on brain activation measured by functional magnetic resonance imaging during the Stroop test in healthy subjects.
Placebo-controlled double-blind cross-over study with 20 healthy volunteers investigating the effect of tryptophan depletion on brain activation during the Stroop test. Tryptophan depletion decreased plasma tryptophan levels by up to 90% but did not affect Stroop test performance. Increased fMRI activation was observed in the mediofrontal cortex, anterior cingulate, and left dorsolateral prefrontal cortex.
Elevated prolactin responses to L-tryptophan infusion in medication-free depressed patients.
RCT measuring hormonal responses to l-tryptophan infusion in 20 patients with MDD and 20 healthy controls. The prolactin response to l-tryptophan was significantly greater in MDD patients than in healthy controls, suggesting increased dopamine receptor sensitivity.
Effect of L-tryptophan on memory in patients with schizophrenia.
Double-blind crossover study of 21 antipsychotic-treated schizophrenic patients in remission, comparing l-tryptophan to placebo. L-tryptophan improved memory functions but had no effect on psychotic state or medication side effects.
Baseline prolactin and L-tryptophan availability predict response to antidepressant treatment in major depression.
Study of 104 patients with major depression assessing baseline prolactin and L-tryptophan availability as predictors of response to antidepressant treatment. Found significant interaction between TRP/LNAA ratio and baseline prolactin on treatment outcome.
L-Tryptophan does not influence acute ventilatory response at moderate altitude.
Randomised, double blind, placebo controlled crossover trial with 8 healthy subjects to evaluate the effect of 500 mg L-tryptophan on ventilation at moderate altitude. Blood gas analysis showed no significant changes in PaO2 and PaCO2 before and after L-tryptophan administration at altitudes of 171 m and 3,000 m.
Seasonal variation in neuroendocrine and mood responses to i.v. L-tryptophan in depressed patients and healthy subjects.
The study examined seasonal effects on neuroendocrine and mood responses to L-tryptophan in 126 drug-free depressed patients and 58 healthy subjects. Seasonal variation was observed in prolactin and tryptophan levels, with more evident effects in female patients, suggesting seasonal variability in serotonin function abnormalities in depression.
The metabolic fate of infused L-tryptophan in men: possible clinical implications of the accumulation of circulating tryptophan and tryptophan metabolites.
This study investigates the metabolic fate of infused L-tryptophan in healthy young men, focusing on the time- and dose-dependent alterations in plasma levels of tryptophan metabolites and large neutral amino acids. The study found that major tryptophan metabolites increased dose-dependently, with significant rises in N-acetyl-Trp and 5-hydroxy-Trp after infusion. Whole blood serotonin levels were largely unaffected, but a dose-dependent rise in circulating melatonin was observed.
The effect of L-tryptophan supplementation and dietary instruction on chronic myofascial pain.
RCT testing L-tryptophan supplementation and dietary manipulation on patients with chronic myofascial pain around the temporomandibular joints. No significant reduction in pain was noted compared with control groups.
Decrease in plasma tryptophan after tryptophan-free amino acid mixtures in man.
Study on the effects of tryptophan-free amino acid mixtures on plasma tryptophan levels in healthy male subjects. Ingestion of the mixture led to a rapid and significant decrease in plasma tryptophan levels, which remained reduced for 6 hours after treatment.
Effect of L-tryptophan and phenylalanine on burning pain threshold.
Double-blind RCT with 60 healthy female students testing the effects of L-tryptophan and phenylalanine on burning pain threshold. No significant difference in pain tolerance was found between the L-tryptophan, phenylalanine, and placebo groups after 14 days.
Chronic insomnia: effects of tryptophan, flurazepam, secobarbital, and placebo.
This study compared the effects of l-tryptophan, secobarbital, flurazepam, and placebo on sleep in 96 serious insomniacs over 7 nights. Flurazepam showed significant improvement in sleep measures compared to placebo, while tryptophan did not during the treatment week. However, tryptophan showed improvement in sleep latency during the post-treatment week.
Selectivity in response to L-tryptophan among insomniac subjects: a preliminary report.
RCT evaluating the hypnotic effects of l-tryptophan, secobarbital, and flurazepam compared to placebo in 54 outpatient chronic insomniacs with sleep maintenance insomnia. L-tryptophan's hypnotic effect was significantly associated with specific types of sleep maintenance complaints.
The treatment of depression in general practice: a comparison of L-tryptophan, amitriptyline, and a combination of L-tryptophan and amitriptyline with placebo.
A 12-week, double-blind RCT with 115 patients compared L-tryptophan, amitriptyline, and their combination to placebo for depression treatment. All active treatments were more effective than placebo, with more treatment failures in the placebo group. Side-effects led to more withdrawals in the amitriptyline group, though not significantly. No significant changes in plasma tryptophan levels were observed.
Prospective trial of L-tryptophan in maternity blues.
Double-blind RCT with 55 bottle-feeding, multiparous women receiving L-tryptophan 3 g daily or placebo for ten days post-delivery. L-tryptophan did not reduce 'maternity blues', but blues scores correlated with anxiety, depression, and hysteria scores from pregnancy.
Metabolism of an oral tryptophan load. II: Effect of pretreatment with the putative tryptophan pyrrolase inhibitors nicotinamide or allopurinol.
The study investigated the effect of seven days of allopurinol or nicotinamide administration on the metabolism of an oral L-tryptophan load. Neither drug altered plasma tryptophan or kynurenine levels, nor urinary excretion of related metabolites. Allopurinol increased the volume of distribution of tryptophan, but neither drug was effective as a tryptophan pyrrolase inhibitor.
Metabolism of an oral tryptophan load. I: Effects of dose and pretreatment with tryptophan.
The study investigated the metabolism of three oral doses of L-tryptophan in healthy young males. It found a linear relationship between peak and area under curve of total plasma tryptophan concentrations, while the relationship with plasma free tryptophan was hyperbolic. Long-term administration of L-tryptophan increased basal plasma tryptophan levels and affected plasma clearance rates. The study discusses implications for L-tryptophan administration in depression treatment.
A placebo controlled evaluation of L-tryptophan in depression in the elderly.
RCT of elderly patients with mild to moderate depression comparing 6 grams L-tryptophan daily to placebo for six weeks. Both groups improved, but there was no statistical difference, suggesting L-tryptophan is not an effective anti-depressant.
Symptom reduction in depression after treatment with L-tryptophan or imipramine. Item analysis of Hamilton rating scale for depression.
Double-blind trial with 58 in-patients with depression comparing 6 g L-tryptophan to 150 mg imipramine daily for 3 weeks. L-tryptophan showed significant improvement in Work and Activities for endogenously depressed patients, while imipramine showed significant improvement in Agitation and Suicide items.
Comparative trial of L-tryptophan and amitriptyline in depressive illness.
Double-blind RCT comparing L-tryptophan and amitriptyline in depressed patients over four weeks. Both groups improved steadily, with no marked differences between treatments, though tryptophan's effect tended to fade between the third and fourth weeks. Anxious patients in the tryptophan group improved least.
Xanthine oxidoreductase knockout mice with high HPRT activity were not rescued by NAD+ replenishment
The study investigated the mechanisms behind the short lifespan of xanthine oxidoreductase knockout (Xor-KO) mice with high HPRT activity. It found that NAD+ depletion due to hypoxanthine accumulation may cause renal failure in these mice. Oral supplementation with 1% L-tryptophan, an alternative precursor of NAD+, did not rescue the mice, suggesting complications from gut microbiota effects.
A controlled study of tryptophan and cortisol in violent offenders.
Case-control study comparing tryptophan, competing long amino acids, and cortisol levels in serum and CSF between 22 violent offenders and 15 healthy controls. Offenders showed significantly increased levels of S-L-tryptophan, S-free tryptophan, S-CAAs, S-cortisol, and CSF-cortisol, suggesting abnormal neurophysiological processes.
Tryptophan depletion in normal volunteers produces selective impairment in memory consolidation.
RCT with 27 healthy volunteers assessing cognitive effects of tryptophan depletion. Tryptophan depletion specifically impaired long-term memory performance, affecting delayed recall, recognition sensitivity, and reaction times, without affecting short-term memory or psychomotor functions.
A placebo controlled investigation of the effects of tryptophan or placebo on subjective and objective measures of fatigue.
RCT with six healthy volunteers testing the effects of L-tryptophan on fatigue. Tryptophan increased subjective and central fatigue compared to placebo, but also increased ergometric work output, possibly due to reduced perception of discomfort.
Testmeal responses following m-chlorophenylpiperazine and L-tryptophan in bulimics and controls.
RCT involving 26 bulimic patients and 17 controls testing the effects of m-chlorophenylpiperazine (m-CPP) and L-tryptophan (L-TRP) on food intake. m-CPP significantly decreased meal size and intake of carbohydrates, protein, and fat, while L-TRP showed trends for reducing fat intake in controls.
Postoperative pain treated by intravenous L-tryptophan: a double-blind study versus placebo in cholecystectomized patients.
Double-blind RCT on 45 female cholecystectomy patients comparing intravenous L-tryptophan to placebo for postoperative pain management. L-tryptophan significantly decreased pain compared to controls, with more lasting relief in the higher dose group.
The influence of intravenous L-tryptophan on plasma melatonin and sleep in men.
RCT measuring the effects of intravenous L-tryptophan on sleep and plasma melatonin levels in nine and five healthy men during daytime and nighttime, respectively. L-tryptophan administration significantly induced sleep and elevated plasma melatonin levels, suggesting a role for melatonin in L-tryptophan's sleep-inducing effects.
A double-blind amino acids, L-tryptophan and L-tyrosine, and placebo study with cocaine-dependent subjects in an inpatient chemical dependency treatment center.
A six-month double-blind study in an inpatient chemical dependency facility with 29 cocaine-dependent subjects tested L-tryptophan and L-tyrosine for reducing cocaine craving and withdrawal symptoms. The study found no significant reduction in most symptoms of cocaine craving and withdrawal when using these amino acids alone.
Plasma tryptophan to large neutral amino acid ratios in depressed and normal subjects.
The study measured plasma tryptophan to large neutral amino acid ratios in 16 depressed inpatients and 9 normal subjects after oral loading with L-tryptophan. Ratios were significantly lower in depressed patients compared to normal subjects, both before and after starting treatment with a tricyclic antidepressant. No significant correlation was found between plasma tryptophan ratios and severity of depression.
Effects of l-tryptophan and various diets on behavioral functions in essential hypertensives.
RCT studying the effects of tryptophan with high-carbohydrate and high-protein diets on mood, sleep, and performance in 34 hypertensive patients. Tryptophan intake tended to decrease sleep latency and increase sleep duration, and significantly improved performance in a concentration task. No significant dietary effects were observed.
The effect of L-tryptophan on daytime sleep latency in normals: correlation with blood levels.
RCT with 10 healthy volunteers testing the effects of L-tryptophan on sleep latency and sleepiness. Both doses of L-tryptophan reduced sleep latency compared to placebo, with the 2.4-g dose showing a persistent effect at 2 hours. There was a positive correlation between blood L-tryptophan levels and reduced sleep latency.
The use of benzodiazepines in the treatment of manic-depressive illness.
The paper discusses the use of clonazepam and lithium in the treatment of acute mania, with clonazepam proving more effective than lithium in controlling mania symptoms. L-tryptophan is mentioned as an adjunct in the maintenance treatment of bipolar disorder when concomitant medication is needed.
Treatment of severe chronic insomnia with L-tryptophan: results of a double-blind cross-over study.
Double-blind, cross-over study of 39 subjects with chronic insomnia treated with L-tryptophan. A significant difference in sleep improvement was observed in the subgroup taking the full L-TRP dose first compared to a very low dose, suggesting L-TRP is effective in promoting sleep.
Maternal dietary substrates and human fetal biophysical activity. I. The effects of tryptophan and glucose on fetal breathing movements.
RCT examining the effects of L-tryptophan and glucose on fetal breathing activity in 40 women with normal term pregnancies. Tryptophan and glucose increased the incidence of fetal breathing movements, with glucose having a more pronounced effect. Breathing rates increased significantly in glucose and combined tryptophan-glucose groups.
L-tryptophan administered to chronic sleep-onset insomniacs: late-appearing reduction of sleep latency.
RCT assessing the effects of 3 g L-tryptophan on sleep in 20 male chronic sleep-onset insomniacs. L-tryptophan significantly reduced sleep latency on nights 4-6 without altering sleep stages or impairing performance.
A controlled clinical trial of L-tryptophan in acute mania.
Controlled clinical trial of L-tryptophan in 24 manic patients over 2 weeks. Initial treatment with L-tryptophan showed significant reduction in manic symptoms. Patients continuing L-tryptophan maintained symptom reduction, while those switched to placebo showed a tendency for increased symptoms.
L-tryptophan: effects on daytime sleep latency and the waking EEG.
RCT studying the effects of L-tryptophan (4 g) on daytime sleep latency and waking EEG in 20 normal adults. L-Tryptophan significantly reduced sleep latency and altered EEG patterns, increasing alpha and theta time and intensity during waking, without affecting nap sleep stages.
L-tryptophan in the treatment of impaired respiration in sleep.
RCT of 15 subjects with sleep apnea treated with 2500 mg L-tryptophan at bedtime. Significant improvement in obstructive sleep apnea was observed, particularly in non-REM sleep, but not in central sleep apnea. L-tryptophan increased REM time and shortened REM latency.
l-Tryptophan in hyperactive child syndrome associated with epilepsy: a controlled study.
Double-blind cross-over study of l-tryptophan versus placebo in 11 epileptic boys with hyperactivity. Each treatment phase lasted 5 weeks with a 3-week washout period. No significant beneficial effect on behavior was observed, and seizure frequency remained unaltered.
The effect of intravenous L-tryptophan on prolactin and growth hormone and mood in healthy subjects.
Intravenous L-tryptophan was administered to ten healthy subjects to assess its effects on prolactin, growth hormone, and mood. The infusion induced robust increases in prolactin and a significant, though variable, increase in growth hormone. Subjects reported feeling more high, mellow, and drowsy compared to placebo, indicating serotonin's role in hormone secretion and mood regulation.
L-tryptophan-carbidopa trial in patients with long-standing progressive myoclonus epilepsy.
RCT involving 11 patients with progressive myoclonus epilepsy receiving L-tryptophan combined with carbidopa. The trial noted improvements in activities of daily living, decreased action myoclonus, and reduced seizure frequency in PME patients compared to controls. Plasma Trp and platelet 5-HT levels increased significantly.
Interval therapy with L-tryptophan in severe chronic insomniacs. A predictive laboratory study.
Predictive, double-blind study testing interval therapy with L-tryptophan in severe chronic insomniacs. Patients showed significant improvements in sleep parameters with no side effects, suggesting L-tryptophan is a potent treatment for chronic primary insomnia.
Effect of L-tryptophan on spasmodic torticollis.
The study investigated the effect of L-tryptophan on spasmodic torticollis in eight patients. L-Tryptophan increased plasma tryptophan levels significantly but improved symptoms in only one out of six patients. Some improvement was noted when L-tryptophan was combined with nicotinamide, though the clinical improvement was not substantial.
Efficacy and side effects of chloral hydrate and tryptophan as sleeping aids in psychogeriatric patients.
RCT comparing placebo, L-tryptophan 3 g, and chloral hydrate 500 mg on sleep in 19 nonpsychotic, mildly demented geriatric inpatients. Chloral hydrate was more effective than placebo in inducing and maintaining sleep, while L-tryptophan showed no significant effect. No significant side effects were observed for either substance.
Sleep induced by L-tryptophan. Effect of dosages within the normal dietary intake.
RCT comparing doses of 1/4 g, 1/2 g, and 1 g of L-tryptophan with placebo in 15 mild insomniacs. One gram of L-tryptophan significantly reduced sleep latency, and 1/4 g increased Stage IV sleep. Results suggest sleep-inducing effects at low doses within normal dietary intake.
L-tryptophan and sleep in healthy man.
The study investigated the effect of L-tryptophan on night-time and day-time sleep in six healthy males. While no significant effect was found on night-time sleep compared to placebo, 4 g of L-tryptophan suggested reduced awakenings and increased stage 3 and REM sleep. The evidence for L-tryptophan's hypnotic activity is limited and uncertain.
Addition of L-tryptophan to electroconvulsive treatment in endogenous depression. A double-blind study.
Double-blind study comparing ECT combined with i.v. L-tryptophan to ECT with saline in 20 patients with endogenous depression. No significant difference was found in the number of ECT sessions or reduction of depressive symptoms. Plasma and cerebrospinal fluid tryptophan levels showed no significant differences.
Failure of L-tryptophan to stimulate prolactin secretion in man.
RCT examining the effect of oral L-tryptophan on prolactin secretion in eight normal women during different phases of the menstrual cycle. Despite a significant increase in plasma free L-tryptophan levels, the prolactin response was not significantly different from placebo.
L-tryptophan in depression.
L-tryptophan was administered to 16 depressive patients in a double-blind study to assess its antidepressant efficacy. Antidepressant responses were observed in one of ten unipolar patients and in three of six bipolar patients.
Effects of L-tryptophan treatment on central indoleamine metabolism and short-lasting neurologic disturbances in multiple sclerosis.
Twelve MS patients were treated with L-tryptophan for 30 days, with or without a decarboxylase inhibitor. Tryptophan and 5-HIAA levels increased, while HVA remained constant. A slight alleviation of MS symptoms, particularly motility, bladder disturbances, and mood, was observed during treatment.
Affective disorder: studies with amine precursors.
RCT assessing the antidepressant effects of L-tryptophan alone and in combination with L-dopa in 12 patients with primary affective disorder. Preliminary results showed no antidepressant response with the combination, not supporting the catecholamine or biogenic amine hypotheses.
Amine precursors and depression.
Double-blind placebo-controlled study administering levodopa and L-tryptophan to hospitalized depressed patients. Large doses did not result in sufficient clinical improvement for discharge, with conflicting findings compared to previous studies.
Biochemical phenotyping of multiple myeloma patients at diagnosis reveals a disorder of mitochondrial complexes I and II and a Hartnup-like disturbance as underlying conditions, also influencing different stages of the disease.
The study used a biochemical quantitative phenotyping platform to identify plasma metabolic signatures in 36 multiple myeloma patients compared to 73 healthy controls. Findings included increased acylcarnitines, decreased phosphatidylcholine, lysophosphatidylcholine, and sphingomyelins, and a drop in essential amino acids, especially tryptophan, in MM patients.
Effect of l-tryptophan and its metabolites on food passage from the crop in chicks.
The study investigated the effects of l-tryptophan and its metabolites on the crop emptying rate in chicks. Oral administration of l-tryptophan, as well as intraperitoneal injection of 5-HT and melatonin, significantly reduced the crop emptying rate, suggesting an inhibitory effect on food movement in the digestive tract.
Pharmacokinetics and CNS pharmacodynamics of the 5-HT1A agonist buspirone in humans following acute L-tryptophan depletion challenge.
This study evaluated the pharmacokinetics and CNS pharmacodynamics of buspirone in 6 healthy male volunteers on an acute L-tryptophan deficient diet. The ATD diet reduced unbound plasma L-tryptophan concentrations significantly, serving as a model for depression by inducing transient symptoms. The study found that the ATD diet decreases the buspirone-induced neuroendocrine response and increases systemic exposure to buspirone.
The Newcastle chronic depression study: results of a treatment regime.
RCT of a treatment regime for treatment-resistant chronic depression using a '5HT-cocktail' of phenelzine, L-tryptophan, and lithium, with a regime to reduce vanadium concentrations. Eleven of 20 patients showed improvement in depression scores, primarily within the first 6 weeks.
Analysis, Nutrition, and Health Benefits of Tryptophan
This narrative review provides an integrated overview of tryptophan, covering its analytical methods, nutritional significance, and potential health benefits. It discusses tryptophan's role in the biosynthesis of bioactive metabolites and its potential therapeutic contributions to various human diseases. The review also addresses the safety and nutritional value of tryptophan-fortified foods and genetically engineered plants.
Epidemiology of potential association between L-tryptophan ingestion and eosinophilia-myalgia syndrome.
The article reviews the epidemiological studies on the association between L-tryptophan ingestion and eosinophilia-myalgia syndrome (EMS), highlighting methodological issues such as selection bias, information bias, and confounding in the initial case-control studies. It questions the validity of the conclusions due to these inadequacies.
L-tryptophan and 5-hydroxytryptophan in the treatment of depression. A review.
Review of trials on L-tryptophan and 5-hydroxytryptophan for depression treatment. No evidence for 5-HTP as an antidepressant. L-tryptophan alone is not well-documented as an antidepressant, but it may enhance the effect of MAOIs.
L-tryptophan: a rational hypnotic with clinical potential.
The paper reviews nine studies on the effects of L-tryptophan on sleep, showing that it reduces sleep latency in rats, normal human subjects, and subjects with mild insomnia. Unlike other hypnotics, L-tryptophan does not distort sleep physiology upon administration, long-term use, or withdrawal.