Dietary Tryptophan Intake Research Articles

Sleep Patterns and Tryptophan Consumption among Students at Spanish Universities: The Unihcos Project.

The objective of this cross-sectional study was to explore sleep patterns and the potential relationship between sleep and tryptophan intake among Spanish university students. A total of 11,485 students self-reported their sleep and dietary patterns and habits. Tryptophan intake was calculated using a food intake matrix and results were presented as quartiles of total intake. Short sleep duration prevalence was 51.0%, with males exhibiting a significantly higher frequency. A total of 55.0% of participants presented inadequate sleep efficiency, with males again presenting a higher rate. Median tryptophan intake was 692.16 ± 246.61 mg/day, 731.84 ± 246.86 mg/day in males and 677.24 ± 244.87 mg/day in females (p = 0.001). Dietary tryptophan intake below the first quartile (<526.43 mg/day) was associated with a higher risk of short sleep duration in males (1.26; 95%CI: 1.02-1.55) and females (1.19; 95%CI: 1.05-1.34) and with the Athens Insomnia Scale insomnia in males (2.56; 95%CI: 1.36-4.82) and females (1.47; 95%CI: 1.10-2.05). Regarding academic specializations, females in the humanities field showed a higher risk of Athens Insomnia Scale insomnia due to low tryptophan intake (Q1: 3.15; 95% CI: 1.04-9.55 and Q2: 3.41; 95%CI: 1.01-11.5). In summary, lower tryptophan consumption appears to be associated with poorer sleep quality in Spanish university students; however, other social factors affecting students may also influence sleep quality. These findings have important implications for nutritional recommendations aimed at enhancing tryptophan intake to improve sleep quality.

Exploration of associations among dietary tryptophan, microbiome composition and function, and symptom severity in irritable bowel syndrome.

Imbalance of the tryptophan (TRP) pathway may influence symptoms among patients with irritable bowel syndrome (IBS). This study explored relationships among different components that contribute to TRP metabolism (dietary intake, stool metabolite levels, predicted microbiome metabolic capability) in females with IBS and healthy controls (HCs). Within the IBS group, we also investigated relationships between TRP metabolic determinants, Bifidobacterium abundance, and symptoms of IBS. Participants with IBS (Rome III) and HCs completed a 28-day diary of gastrointestinal symptoms and a 3-day food record for TRP intake. They provided a stool sample for shotgun metagenomics, 16 S rRNA analyses, and quantitative measurement of TRP by mass spectrometry. Our cohort included 115 females, 69 with IBS and 46 HCs, with a mean age of 28.5 years (SD 7.4). TRP intake (p= 0.71) and stool TRP level (p= 0.27) did not differ between IBS and HC. Bifidobacterium abundance was lower in the IBS group than in HCs (p= 0.004). Predicted TRP metabolism gene content was higher in IBS than HCs (FDR-corrected q= 0.006), whereas predicted biosynthesis gene content was lower (q= 0.045). Within the IBS group, there was no association between symptom severity and TRP intake or stool TRP, but there was a significant interaction between Bifidobacterium abundance and TRP intake (q= 0.029) in predicting stool character. Dietary TRP intake, microbiome composition, and differences in TRP metabolism constitute a complex interplay of factors that could modulate IBS symptom severity.

A Reduced Tryptophan Diet in Patients with Diarrhoea-Predominant Irritable Bowel Syndrome Improves Their Abdominal Symptoms and Their Quality of Life through Reduction of Serotonin Levels and Its Urinary Metabolites.

(1). An essential component of any treatment for patients with irritable bowel syndrome (IBS) is an adequate diet. Currently, a low FODMAP diet is recommended as a first-line therapy, but it does not relieve abdominal discomfort in all patients, and alternative nutritional treatment is required. The purpose of this study was to evaluate the effect of a tryptophan-lowering diet (TRP) on abdominal and mental symptoms in patients with irritable bowel syndrome with predominant diarrhea (IBS-D). (2). The study included 40 patients with IBS-D, and 40 healthy subjects served as a baseline for IBS-D patients, after excluding comorbidities. The TRP intake was calculated using the nutritional calculator. The severity of abdominal symptoms was assessed using the gastrointestinal symptom rating scale (GSRS-IBS). Mental state was assessed using the Hamilton anxiety rating scale (HAM-A), the Hamilton depression rating scale (HAM-D), and the insomnia severity index (ISI). The serum levels of serotonin and melatonin and the urinary excretion of their metabolites 5-hydroxyindoleacetic acid (5-HIAA) and 6-sulfatoxymelatonin (aMT6) were determined by the ELISA method. The severity of symptoms and laboratory data were analyzed before and after a 12 week diet with tryptophan restricted to a daily dose 10 mg per kilogram body weight. (3). Compared to the control group, patients with IBS-D had a higher serum level of serotonin (198.2 ± 38.1 vs. 142.3 ± 36.4 ng/mL; p < 0.001) but a similar level of melatonin (8.6 ± 1.1 vs. 9.4 ± 3.0 pg/mL; p > 0.05). The urinary excretion of 5-HIAA was also higher in patients with IBS-D patients (7.7 ± 1.5 vs. 6.0 ± 1.7 mg/24 h; p < 0.001). After nutritional treatment, both the serum serotonin level and the urinary 5-HIAA excretion significantly decreased (p < 0.001). The severity of the abdominal symptoms and anxiety also decreased, while the HAM-D score and the ISI score remained unchanged (4). Lowering the dietary intake of tryptophan may reduce abdominal complaints and does not alter the mental state of IBS-D patients.

Baseline differences may impact on relationship between dietary tryptophan and risk of obesity and type 2 diabetes.

Recently, we read with great interest an article reporting a relationship between dietary tryptophan and the risk of obesity and type 2 diabetes (T2D). However, baseline characteristics differed among tertiles of cumulative dietary tryptophan intake in that study, which may be a confounding factor for the relationship between dietary tryptophan and the risk of obesity and T2D.

A192 CONSUMPTION OF FOOD LOWER IN TRYPTOPHAN IS ASSOCIATED WITH SIGNIFICANT ANXIETY IN PATIENTS WITH CELIAC DISEASE

BackgroundTryptophan, an essential amino acid found in many protein-based foods, has been involved in the pathogenesis of mood disorders and celiac disease (CeD). However, dietary tryptophan consumption has not been investigated in CeD.AimsTo estimate 1) differences in tryptophan content in food consumed in CeD patients compared to matched healthy controls (HC), and 2) whether consumption of tryptophan is associated with the presence of anxiety and depression in patients with CeD.MethodsThis prospective observational study examined adult patients with a diagnosis of CeD, based on positive specific serology and confirmed by duodenal biopsies, enrolled in the Celiac Registry at McMaster University. A group of sex matched HC were recruited from within the community. Participants completed several questionnaires to evaluate, gastrointestinal symptoms (GSRS), Anxiety and Depression (HADS), and dietary intake of tryptophan (Modified Food Frequency Questionnaire). In addition, CeD patients were assessed for celiac disease activity (CSI), gluten-free diet (GFD) adherence (CDAT) and nutritional status. HADs >11 denoted significant anxiety or depression. Cut-off for low vs high amount of tryptophan content in food was established based on the median tryptophan food content in the HC population.ResultsA total of 443 participants were enrolled in the study; 222 with CeD and 221 controls. The majority of participants were female (74.3%) and the adherence to the GFD was very good (Median CDAT=13; IQR 11–15). The CeD patients were older than HC (Median age, yrs. CD= 40 vs HC= 35; p<0.01). Patients with CeD consumed higher amount of tryptophan compared with HC (Median tryptophan g/day CeD=4.41 vs HC=3.31; p<0.01). There were 157 active CeD patients (CSI ≧ 30). There was no difference in tryptophan consumption between patients with and without active CeD (OR=1.021; 95%CI 0.86–1.21; p=0.88). There was no association between tryptophan consumption and gastrointestinal symptoms or depression scores. Fifteen % of the overall population and 18% of the CeD population had anxiety. There was an increased risk of anxiety in the overall population that consumed low amount of tryptophan (OR=1.87; 95%CI 1.01–3.11; p=0.04), and the risk was greater in the CeD population (OR=4.57; 95%CI 1.26–16.41; p<0.01).ConclusionsConsumption of food with lower amounts of tryptophan in patients with CeD is associated with significant anxiety, which may influence disease management. Future studies should evaluate whether increasing tryptophan in the diet compared to supplements improves outcomes in CeD population, especially in those with anxiety.Funding AgenciesNone

Rapid Determination of Total Tryptophan in Yoghurt by Ultra High Performance Liquid Chromatography with Fluorescence Detection.

Tryptophan (TRP) is an essential amino acid which cannot be synthesized by humans and animals, but has to be supplied by exogenous sources, notably through the diet. The bulk of dietary TRP flows into the synthesis of body’s proteins, but the TRP metabolism also involves several biochemical reactions (i.e., serotonin and kynurenine pathways). Defects in the TRP transport mechanism or catabolism are related to a large number of clinical abnormalities. Therefore, dietary TRP intake is necessary not only for the body’s growth but also for most of the body’s metabolic functions. Among protein-based foods, milk proteins provide a relatively high amount of TRP. In this paper, a rapid chromatographic method for TRP determination in yoghurt, by ultra high performance liquid chromatography on a reversed-phase column with fluorescence detection (280 nm Ex; 360 nm Em), is provided. A linear gradient elution of acetonitrile in water allowed TRP analysis in 8.0 min. The limit of detection and limit of quantification of the method were 0.011 ng/µL and 0.029 ng/µL, respectively, using 5-methyl-l-tryptophan as the internal standard. The analytical method was successfully applied to commercial yoghurts from different animal species, and the TRP values ranged between 35.19 and 121.97 mg/100 g (goat and cow Greek type yoghurt, respectively).

Dietary tryptophan and bone health: a cross-sectional, population-based study.

Tryptophan metabolites, such as serotonin, influence bone. We sought to determine the relationship between dietary intake of tryptophan and bone health in a population-based study of men and women. Participants (1033 women and 900 men, aged 20-98years) enrolled in the Geelong Osteoporosis Study (GOS) were investigated. Dietary information was collected using a validated questionnaire. Tryptophan levels were calculated (mg/day) in accordance with Food Standards Australia and New Zealand and dichotomised according to the median. Bone mineral density (BMD; g/cm2) was measured at the spine (postero-anterior projection) and total hip using dual-energy X-ray absorptiometry. Stiffness index (SI), broadband ultrasound attenuation (BUA) and speed of sound (SOS) were derived from quantitative heel ultrasound. Linear regression models were used to test associations between dietary tryptophan and bone health, after adjustment for potential confounders. Tryptophan intakes ranged from 112 to 3796mg/day (median 1035) in men and 115-2869mg/day (median 885) in women. In men older than 45years and women, a high tryptophan intake was associated with greater hip BMD compared to participants with a low tryptophan intake (p = 0.002 and p = 0.04, respectively); however, these relationships were attenuated by age (all p > 0.05). Participants with high tryptophan intake had greater BUA and SI compared to participants with low tryptophan intake (men; BUA, p = 0.02 and SI, p = 0.02, and women; BUA, p = 0.03 and SI, p = 0.08), yet also attenuated by age (all p > 0.05). No association was found between tryptophan intake and bone health in this population, which suggests a non-critical role of superfluous tryptophan consumption on the skeleton.

Physical Activity, Nutritional Status, and Autonomic Nervous System Activity in Healthy Young Adults with Higher Levels of Depressive Symptoms and Matched Controls without Depressive Symptoms: A Cross-Sectional Study.

The aim of the present study was to comprehensively investigate physical activity (PA), nutritional status, and autonomic nervous system (ANS) activity in healthy young adults with higher levels of depressive symptoms and in sex- and age-matched controls without depressive symptoms. We recruited 35 healthy young adults with higher levels of depressive symptoms (DEP group) and 35 controls (CON group). Measurement items were daily number of steps, the duration and amount of PA ≥3 metabolic equivalents (METs), exercise habits, the consumption of tryptophan (TRP) and/or vitamin B6-rich foods, plasma levels of total TRP and vitamin B6 levels, and ANS activity. The DEP group had fewer daily steps, as well as duration and amount of PA ≥3 METs, than the CON group, while there was no difference in exercise habits. The intake frequency of TRP and/or vitamin B6-rich foods and plasma vitamin B6 levels of the DEP group were rather higher than those in the control group. Plasma TRP levels and ANS activity were comparable in the two groups. Our findings suggest that a decline in overall PA, including daily steps as well as duration and amount of moderate-to-vigorous-intensity PA, could be associated with higher levels of depressive symptoms in healthy young adults. Their dietary intake of TRP and/or vitamin B6-rich foods was adequate, and there was no ANS activity dysfunction.

Tryptophan Intake and Tryptophan Losses in Hemodialysis Patients: A Balance Study.

Tryptophan depletion is common in hemodialysis patients. The cause of this depletion remains largely unknown, but reduced nutritional tryptophan intake, losses during dialysis or an increased catabolism due to an inflammatory state are likely contributors. Currently, little is known about tryptophan homeostasis in hemodialysis patients. We assessed dietary tryptophan intake, measured plasma tryptophan during dialysis, and measured the combined urinary and dialysate excretion of tryptophan in 40 hemodialysis patients (66 ± 15 years and 68% male). Patients had low tryptophan concentrations (27 ± 9 µmol/L) before dialysis. Mean dietary tryptophan intake was 4454 ± 1149 µmol/24 h. Mean urinary tryptophan excretion was 15.0 ± 12.3 μmol/24 h, dialysate excretion was 209 ± 67 μmol/24 h and combined excretion was 219 ± 66 µmol/24 h, indicating only 5% of dietary tryptophan intake was excreted. No associations were found between plasma tryptophan concentration and tryptophan intake, plasma kynurenine/tryptophan ratio or inflammatory markers. During dialysis, mean plasma tryptophan concentration increased 16% to 31 ± 8 µmol/L. Intradialytic increase in plasma tryptophan was associated with a lower risk of mortality, independent of age, sex and dialysis vintage (HR: 0.87 [0.76–0.99]; P = 0.04). Tryptophan intake was well above the dietary recommendations and, although tryptophan was removed during dialysis, mean plasma tryptophan increased during dialysis. The cause of this phenomenon is unknown, but it appears to be protective.

Urinary Excretion of N1-Methylnicotinamide, as a Biomarker of Niacin Status, and Mortality in Renal Transplant Recipients.

Renal transplant recipients (RTR) commonly suffer from vitamin B6 deficiency and its functional consequences add to an association with poor long-term outcome. It is unknown whether niacin status is affected in RTR and, if so, whether this affects clinical outcomes, as vitamin B6 is a cofactor in nicotinamide biosynthesis. We compared 24-h urinary excretion of N1-methylnicotinamide (N1-MN) as a biomarker of niacin status in RTR with that in healthy controls, in relation to dietary intake of tryptophan and niacin as well as vitamin B6 status, and investigated whether niacin status is associated with the risk of premature all-cause mortality in RTR. In a prospective cohort of 660 stable RTR with a median follow-up of 5.4 (4.7–6.1) years and 275 healthy kidney donors, 24-h urinary excretion of N1-MN was measured with liquid chromatography-tandem mass spectrometry LC-MS/MS. Dietary intake was assessed by food frequency questionnaires. Prospective associations of N1-MN excretion with mortality were investigated by Cox regression analyses. Median N1-MN excretion was 22.0 (15.8–31.8) μmol/day in RTR, compared to 41.1 (31.6–57.2) μmol/day in healthy kidney donors (p < 0.001). This difference was independent of dietary intake of tryptophan (1059 ± 271 and 1089 ± 308 mg/day; p = 0.19), niacin (17.9 ± 5.2 and 19.2 ± 6.2 mg/day; p < 0.001), plasma vitamin B6 (29.0 (17.5–49.5), and 42.0 (29.8–60.3) nmol/L; p < 0.001), respectively. N1-MN excretion was inversely associated with the risk of all-cause mortality in RTR (HR 0.57; 95% CI 0.45–0.71; p < 0.001), independent of potential confounders. RTR excrete less N1-MN in 24-h urine than healthy controls, and our data suggest that this difference cannot be attributed to lower dietary intake of tryptophan and niacin, nor vitamin B6 status. Importantly, lower 24-h urinary excretion of N1-MN is independently associated with a higher risk of premature all-cause mortality in RTR.

Dietary intake of tryptophan tied emotion-related impulsivity in humans.

Emotion-related impulsivity, defined as the tendency to say or do things that one later regret during periods of heightened emotion, has been tied to a broad range of psychopathologies. Previous work has suggested that emotion-related impulsivity is tied to an impaired function of the serotonergic system. Central serotonin synthesis relies on the intake of the essential amino acid, tryptophan and its ability to pass through the blood brain barrier. Objective: The aim of this study was to determine the association between emotion-related impulsivity and tryptophan intake. Methods: Undergraduate participants (N=25, 16 women, 9 men) completed a self-rated measure of impulsivity (Three Factor Impulsivity Index, TFI) and daily logs of their food intake and exercise. These data were coded using the software NutriNote to evaluate intakes of tryptophan, large neutral amino acids, vitamins B6/B12, and exercise. Results: Correlational analyses indicated that higher tryptophan intake was associated with significantly lower scores on two out of three subscales of the TFI, Pervasive Influence of Feelings scores r=-.502, p<.010, and (lack-of) Follow-Through scores, r=-.407, p<.050. Conclusion: Findings provide further evidence that emotion-related impulsivity is correlated to serotonergic indices, even when considering only food habits. It also suggests the need for more research on whether tryptophan supplements might be beneficial for impulsive persons suffering from a psychological disorder.

The association between dietary tryptophan intake and migraine.

Migraineurs have been identified to have chronically decreased serotonin levels while its concentrations markedly increase during ictal periods. Regarding the importance of adequate tryptophan intake in regulating serotonin homeostasis and subsequent effect on migraine attacks, we designed the current study. The migraine group (n = 514, diagnosed according to the ICHDIII criteria) was recruited from a tertiary headache clinic. The controls consisted of 582 sex-matched healthy volunteers who were randomly selected from general population. After collecting demographic and anthropometric data, a validated 168-item semi-quantitative food frequency questionnaire (FFQ) was used for dietary intake assessments. Multiple regression models were applied to explore the relationship between migraine and tryptophan intake. The mean (SD) of the age of participants in the controls and migraine group was 44.85 (13.84) and 36.20 (9.78) years, respectively. The multiple regression models were adjusted for age (year), sex, body mass index (BMI) (kg/m2), total daily energy intake (kcal/day), dietary intakes of total carbohydrates (g/day), animal-based protein (g/day), plant-based protein (g/day), total fat (g/day), saturated fat (g/day), and cholesterol (mg/day). It was shown that there is a negative association between tryptophan intake and migraine risk ((OR in the 3rd quartile = 0.46; 95% CI = 0.25-0.85) (OR in the 4th quartile = 0.40; 95% CI = 0.16-0.98) compared with the first quartile; P for trend = 0.045). Therefore, our results showed that subjects who had a median intake of 0.84-1.06g of tryptophan per day had reduced odds of developing migraine by approximately 54-60%, relative to those consumed ≤ 0.56g/day.

Association between habitual tryptophan intake and depressive symptoms in young and middle-aged women

BackgroundThe intake of tryptophan, the precursor of serotonin, is assumed to affect serotonin availability and depression onset. Nevertheless, a definitive relationship between dietary tryptophan intake and depressive symptoms has not been established. We examined the association between tryptophan intake and depressive symptoms screened in a group of 4272 first-year female dietetic students and 3651 their mothers. MethodsDietary tryptophan intake during the preceding month was assessed with a validated, self-administered diet history questionnaire. Depressive symptoms were assessed with the Center for Epidemiologic Studies Depression Scale (CES-D) using two cutoff scores: CES-D score ≥ 16 and CES-D score ≥ 19 (the optimal cutoff score for Japanese people). The multivariate adjusted prevalence ratio (PR) and 95% confidence interval (CI) for depressive symptoms were calculated using Poisson regression analysis. ResultsThe prevalence of depressive symptoms (CES-D score ≥ 16) was 50.0% for young women and 26.5% for middle-aged women. The adjusted PR (95% CI) for depressive symptoms in the highest versus lowest quintile of tryptophan intake was 0.84 (0.75, 0.93) in young women (P for trend < 0.0001) and 0.83 (0.64, 1.01) in middle-aged women (P for trend < 0.0001). These associations were stable even when depressive symptoms were defined as a CES-D score ≥ 19. LimitationsThis is a cross-sectional study. Depressive symptoms were assessed using a self-reported questionnaire. ConclusionsThis cross-sectional study showed that a higher tryptophan intake was independently associated with a lower prevalence of depressive symptoms in young Japanese women.

Tu1801 - Dietary Tryptophan Intake and Risk of Incident Crohn's Disease and Ulcerative Colitis

Tu1801 - Dietary Tryptophan Intake and Risk of Incident Crohn's Disease and Ulcerative Colitis

The association of sleep quality and insomnia with dietary intake of tryptophan and niacin

Introduction: Dietary intake of tryptophan and niacin have been related to sleep. However, the sleep-promoting effects of these nutrients are still under investigation. The aim of the current study was to examine the relationship between daily dietary intake of tryptophan and niacin and sleep. Materials and methods: A survey on past week's dietary intake (food frequency questionnaire)was completed by N = 509 Dutch university students (20.8 years old). The SLEEP-50 questionnaire subscale on insomnia was completed, and sleep quality (0-10 score) and total sleep time (TST) were also assessed. Daily intake of tryptophan and niacin was correlated to insomnia rating, sleep quality and TST using nonparametric (Spearman) correlations. Analyses were conducted for the group as a whole, and for men (N = 143) andwomen (N = 366) separately. Results: Mean [SD] scores of insomnia (14.6 [4.3]), sleep quality (7.3 [1.2]), TST (7.7 h [0.9]), and daily dietary intake of tryptophan (0.618 g [0.3]) and niacin (15.88 mg[6.7])were within normal ranges. Insomnia scores correlated significantlywith dietary intake of tryptophan (r = -0.180, p = 0.0001) and niacin (r = -0.157, p = 0.001). When controlling for total caloric intake, the partial correlation between tryptophan intake and insomnia remained significant (r = -0.105, p = 0.029). Niacin intake also correlated significantly with sleep quality (r = .094, p = 0.045). No significant correlation was found with TST. In men, insomnia scores correlated significantly with dietary intake of tryptophan (r = -0.287, p = 0.002) or niacin (r = -0.243, p = 0.008). Sleep quality scores also correlated significantly with dietary intake of tryptophan (r = 0.205, p = 0.026) and niacin (r = -0.240, p = 0.008). In women, none of the correlations were significant. Conclusion: A modest but significant association was found between dietary intake of tryptophan and niacin and insomnia and sleep quality. The nature and causes of the observed gender differences require further investigation.

Placebo-controlled dietary intervention of stress-induced neurovegetative disorders with a specific amino acid composition: a pilot-study.

BackgroundPsychosocial stress leads to altered neuroendocrine functions, such as serotonergic dysfunction, as well as alterations of the autonomic nervous system and the hypothalamic-pituitary-adrenal (HPA)-axis activity resulting in an imbalance between inhibitory and excitatory neurotransmitters. Poor dietary intake of L-tryptophan as a precursor of serotonin increases sensitivity to stress.MethodsThis randomized, double-blind, placebo-controlled study investigated the effect of a specific amino acid composition with micronutrients on neurovegetative disorders and the cardiometabolic risk profile in psychosocially stressed patients. 32 patients (18–65 years) were eligible for protocol analysis. Points in the Psychological Neurological Questionnaire (PNF), clinical and blood parameter, in particular the serotonin level, salivary cortisol levels, and dietary intake were evaluated at baseline and 12 weeks after supplementation.ResultsThe intervention in the form of either verum or placebo resulted in both groups in a significant decrease of neurovegetative symptoms. However, patients of the placebo group achieved significantly less points in the PNF compared to the verum group. But the rate of responders (≥10 points loss in PNF) was not significantly different between the groups. The macronutrient intake did not differ between verum and placebo group. On average, the HPA-axis was not disturbed in both groups. Blood serotonin indicated in both groups no significant correlation with dietary tryptophan intake or PNF.ConclusionsDaily supplementation of a specific amino acid composition with micronutrients in psychologically stressed patients resulted in no improvement of neurovegetative disorders as measured by the PNF when compared to the placebo group.Trial registrationClinical Trials.gov (NCT01425983)Electronic supplementary materialThe online version of this article (doi:10.1186/s12937-015-0030-3) contains supplementary material, which is available to authorized users.

M1791 Dietary Intake of Tryptophan in IBS Patients

M1791 Dietary Intake of Tryptophan in IBS Patients

Dietary tryptophan intake and suicide rate in industrialized nations

Dietary tryptophan intake and suicide rate in industrialized nations

The effects of dietary tryptophan metabolism on the “vigor” and “confusion” factor of mood

Abstract Previously, we reported that tryptophan metabolites affect mood. According to research conducted using the Profile of Mood States (POMS) test, kynurenin and serotonin, which are intermediary metabolites of tryptophan, appear to be correlated with some factors of mood. The present study examined one of the tryptophan metabolites that affects mood using a nutritional method. According to the results of the POMS-test and the nutrition survey, the “vigor” and “confusion” factors of mood were correlated with the intake of tryptophan and niacin. In contrast, serum tryptophan and kynurenin were correlated resting conditions (r = 0.872). Furthermore, correlations were observed between “vigor” and serum kynurenin (r = 0.597) and between “confusion” and serum kynurenin (r = 0.681). These findings indicate a positive relationship between the intake of tryptophan and niacin and emotional state. Therefore, we investigated the relationship between intake values of tryptophan, niacin and each mood. The observed intake of tryptophan was 610 ± 134 mg/day, while the intake of niacin was 13 ± 4 mg/day. Correlations were observed between intake of tryptophan and “confusion”(r = − 0.602) and “vigor”(r = 0.727), and between the intake of niacin and “confusion” (r = − 0.786) and “vigor”(r = 0.585). These results suggest that dietary intake of tryptophan and niacin is correlated to tryptophan metabolites and mood. In particular, we suggest that the correlation between serum tryptophan, kynurenin and observed resting conditions of “vigor” and “confusion” resulted from dietary intake of tryptophan.

Dietary tryptophan intake and suicide rate in industrialized nations

Background The objective of this study was to assess the ecological association of dietary tryptophan intake and suicide rates across industrialized nations. Tryptophan, an essential amino acid, is the rate-limiting precursor of serotonin biosynthesis. The serotonergic system has been strongly implicated in the neurobiology of suicide. Methods Contemporary male and female suicide rates for the general population (42 countries) and the elderly (38 countries) were correlated with national estimates of dietary tryptophan intake. Results Measures of tryptophan intake were significantly negatively associated to national suicide rates. Controlling for national affluence, total alcohol consumption and happiness levels slightly attenuated these associations, but left all of them negative. Limitations The effect is an ecological (group-level) finding. Estimated per capita tryptophan supply is only a proxy for actual consumption. Conclusions Developed nations ranking high in dietary tryptophan intake rank low in suicide rates, independent of national wealth, alcohol intake and happiness.