title: Can tryptophan supplement intake at breakfast enhance melatonin secretion at night?
abstract: BACKGROUND
  Tryptophan (TRP) is an essential amino acid, and it has been suggested that TRP intake at breakfast combined with daytime bright light exposure can increase nocturnal melatonin secretion. However, the mechanisms involved are not yet clear. The aim of this study was to examine the effect of TRP supplement intake at breakfast on nocturnal melatonin secretion under different daytime light intensities in humans.
  
  
  METHODS
  Twelve subjects (aged 21.3 ± 3.0 years, mean ± standard deviation) participated in a random order in experimental sessions lasting 3 days under four conditions in a laboratory setting. The four conditions were TRP*Bright, Placebo*Bright, TRP*Dim, and Placebo*Dim. A TRP capsule (1000 mg) or a placebo starch capsule (1000 mg) were taken at breakfast. In addition, during the daytime (07:00-18:00), the subjects were asked to stay under different light intensities: >5000 lx (bright) or <50 lx (dim). Saliva samples were collected for measuring the concentration of melatonin. The time courses of melatonin concentration and dim light melatonin onset (DLMO) were compared among the four conditions using repeated measurements analysis of variance (ANOVA).
  
  
  RESULTS
  Nocturnal melatonin concentrations in the bright light condition tended to be higher than in the dim light condition (main effect of light: p = .099). Moreover, in the bright light condition, the change in DLMO between baseline and after the intervention was significantly higher than that in the dim light condition (main effect of light: p <.001). However, the ANOVA results indicated no significant effect of TRP intake on melatonin secretion.
  
  
  CONCLUSIONS
  Our findings indicated that intake of 1000 mg of TRP at breakfast on 1 day did not change nocturnal melatonin secretion, even though TRP is the precursor of melatonin. In contrast, daytime bright light exposure increased nocturnal melatonin secretion and advanced the phase of melatonin onset. Therefore, TRP supplementation, unlike exposure to daytime bright light, does not acutely affect biological rhythm and sleep in humans.
  
  
  BACKGROUND
  UMIN Clinical Trial Registry: UMIN000024121.
authors.affiliation: Graduate School of Medicine, Kyoto University, Kyoto, Japan.|Japan Society for the Promotion of Science, Tokyo, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Nagashima
authors.affiliation: Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Yamashita
authors.affiliation: Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Chiaki
authors.initials: C
authors.lastname: Tojo
authors.affiliation: Comprehensive Housing R&D Institute, Sekisui House, Ltd., Kyoto, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kondo
authors.affiliation: Department of Environmental Science, Fukuoka Women's University, Fukuoka, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Morita
authors.affiliation: Graduate School of Medicine, Kyoto University, Kyoto, Japan. wakamura.tomoko.5v@kyoto-u.ac.jp.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Wakamura
mesh_terms: D000293:Adolescent; D000328:Adult; D062408:Breakfast; D003404:Creatinine / Q000652:urine; D019587:Dietary Supplements; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D012463:Saliva / Q000737:chemistry; D014364:Tryptophan / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D014364:Tryptophan; D003404:Creatinine; D008550:Melatonin
keywords: Breakfast; Bright light exposure; Dim light melatonin onset; Melatonin; Tryptophan