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Title: Can tryptophan supplement intake at breakfast enhance melatonin secretion at night?
Authors: Nagashima, Shunsuke
Yamashita, Makoto
Tojo, Chiaki
Kondo, Masayuki
Morita, Takeshi
Wakamura, Tomoko  kyouindb  KAKEN_id  orcid (unconfirmed)
Author's alias: 長島, 俊輔
山下, 舞琴
若村, 智子
Keywords: Tryptophan
Bright light exposure
Dim light melatonin onset
Issue Date: 28-Feb-2017
Publisher: Springer Nature
Journal title: Journal of physiological anthropology
Volume: 36
Thesis number: 20
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. [Method]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). [Result] 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. [Conclusion]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. [Trial registration]UMIN Clinical Trial Registry: UMIN000024121
Rights: © The Author(s). 2017 This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.
DOI(Published Version): 10.1186/s40101-017-0135-9
PubMed ID: 28245865
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