title: A tryptophan-rich breakfast and exposure to light with low color temperature at night improve sleep and salivary melatonin level in Japanese students.
abstract: BACKGROUND
  Epidemiological studies in Japan have documented an association between morning type and a tryptophan-rich breakfast followed by exposure to sunlight in children. The association may be mediated by enhanced melatonin synthesis, which facilitates sleep at night. However, melatonin is inhibited by artificial light levels with high color-temperature common in Japanese homes at night. In this study, we investigated whether a combination of tryptophan-rich breakfast and light with low color-temperature at night could enhance melatonin secretion and encourage earlier sleep times.
  
  
  METHODS
  The intervention included having breakfast with protein- and vitamin B6 - rich foods and exposure to sunlight after breakfast plus exposure to incandescent light (low temperature light) at night (October-November, 2010). The participants were 94 members of a university soccer club, who were divided into 3 groups for the intervention (G1: no intervention; G2: asked to have protein-rich foods such as fermented soybeans and vitamin B6-rich foods such as bananas at breakfast and sunlight exposure after breakfast; G3: the same contents as G2 and incandescent light exposure at night). Salivary melatonin was measured around 11:00 p.m. on the day before the beginning, a mid-point and on the day before the last day a mid-point and on the last day of the 1 month intervention.
  
  
  RESULTS
  In G3, there was a significantly positive correlation between total hours the participants spent under incandescent light at night and the frequency of feeling sleepy during the last week (p = 0.034). The salivary melatonin concentration of G3 was significantly higher than that of G1 and G2 in combined salivary samplings at the mid-point and on the day before the last day of the 1 month intervention (p = 0.018), whereas no such significant differences were shown on the day just before the start of the intervention (p = 0.63).
  
  
  CONCLUSIONS
  The combined intervention on breakfast, morning sunlight and evening-lighting seems to be effective for students including athletes to keep higher melatonin secretion at night which seems to induce easy onset of the night sleep and higher quality of sleep.
authors.affiliation: Laboratory of Environmental Physiology, Graduate School of Integrated Arts and Sciences, Kochi University, Kochi, Japan.
authors.forename: Kai
authors.initials: K
authors.lastname: Wada
authors.affiliation: Department of Health and Physical Education, Faculty of Education, Kochi University, Kochi, Japan.
authors.forename: Shota
authors.initials: S
authors.lastname: Yata
authors.affiliation: Laboratory of Environmental Physiology, Graduate School of Integrated Arts and Sciences, Kochi University, Kochi, Japan.
authors.forename: Osami
authors.initials: O
authors.lastname: Akimitsu
authors.affiliation: Department of Health Education, Faculty of Education, University of South Bohemia, České Budějovice, Czech Republic.
authors.forename: Milada
authors.initials: M
authors.lastname: Krejci
authors.affiliation: Department of Health and Physical Education, Faculty of Education, Kochi University, Kochi, Japan.
authors.forename: Teruki
authors.initials: T
authors.lastname: Noji
authors.affiliation: Department of Nutritional Education, Tokai Gakuen University, Miyoshi, Aichi, Japan.
authors.forename: Miyo
authors.initials: M
authors.lastname: Nakade
authors.affiliation: Laboratory of Environmental Physiology, Graduate School of Integrated Arts and Sciences, Kochi University, Kochi, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Takeuchi
authors.affiliation: Laboratory of Environmental Physiology, Graduate School of Integrated Arts and Sciences, Kochi University, Kochi, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Harada
keywords: Lighting with low color temperature; Protein rich breakfast; Salivary melatonin; Sunlight exposure; Tryptophan