title: Tryptophan Intake in the US Adult Population Is Not Related to Liver or Kidney Function but Is Associated with Depression and Sleep Outcomes.
abstract: BACKGROUND
  Tryptophan is an indispensable amino acid and is a precursor of the neurotransmitter serotonin. Tryptophan metabolites, such as serotonin and melatonin, are thought to participate in the regulation of mood and sleep and tryptophan is used to treat insomnia, sleep apnea, and depression.
  
  
  OBJECTIVE
  This study examined the intake of tryptophan and its associations with biochemical, behavioral, sleep, and health and safety outcomes in adults in a secondary analysis of a large, publicly available database of the US population.
  
  
  METHODS
  Data from the NHANES 2001-2012 (n = 29,687) were used to determine daily intakes of tryptophan and its associations with biochemical markers of health- and safety-related outcomes, self-reported depression, and sleep-related variables. Data were adjusted for demographic factors and protein intake. Linear trends were computed across deciles of intake for each outcome variable, and P-trends were determined.
  
  
  RESULTS
  The usual tryptophan intake by US adults was 826 mg/d, severalfold higher than the Estimated Average Requirement for adults of 4 mg/(kg ⋅ d) (∼280 mg/d for a 70-kg adult). Most health- and safety-related biochemical markers of liver function, kidney function, and carbohydrate metabolism were not significantly (P-trend > 0.05) associated with deciles of tryptophan intake and were well within normal ranges, even for individuals in the 99th percentile of intake. Usual intake deciles of tryptophan were inversely associated with self-reported depression measured by the Patient Health Questionnaire raw score (0-27; P-trend < 0.01) and calculated level (1 = no depression, 5 = severe depression; P-trend < 0.01) and were positively associated with self-reported sleep duration (P-trend = 0.02).
  
  
  CONCLUSIONS
  Tryptophan intake was not related to most markers of liver function, kidney function or carbohydrate metabolism. Levels of tryptophan intake in the US population appear to be safe as shown by the absence of abnormal laboratory findings. Tryptophan intake was inversely associated with self-reported level of depression and positively associated with sleep duration.
authors.affiliation: Military Nutrition Division, US Army Research Institute of Environmental Medicine, Natick, MA; harris.r.lieberman.civ@mail.mil.
authors.forename: Harris R
authors.initials: HR
authors.lastname: Lieberman
authors.affiliation: Oak Ridge Institute for Science and Education, Belcamp, MD; and.
authors.forename: Sanjiv
authors.initials: S
authors.lastname: Agarwal
authors.affiliation: Oak Ridge Institute for Science and Education, Belcamp, MD; and.|Henry M Jackson Foundation, Bethesda, MD.
authors.forename: Victor L
authors.initials: VL
authors.lastname: Fulgoni
mesh_terms: D000328:Adult; D015415:Biomarkers; D003863:Depression / Q000453:epidemiology / Q000517:prevention & control*; D005260:Female; D005504:Food Analysis; D006801:Humans; D007668:Kidney / Q000187:drug effects* / Q000502:physiology; D008099:Liver / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009749:Nutrition Surveys; D012890:Sleep / Q000187:drug effects*; D014364:Tryptophan / Q000008:administration & dosage* / Q000494:pharmacology; D014481:United States / Q000453:epidemiology
chemical_list: D015415:Biomarkers; D014364:Tryptophan
keywords: Patient Health Questionnaire (PHQ-9); glucose; insulin; kidney function markers; liver function markers; mood; serotonin