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Open Access Research

A tryptophan-rich breakfast and exposure to light with low color temperature at night improve sleep and salivary melatonin level in Japanese students

Kai Wada1, Shota Yata2, Osami Akimitsu1, Milada Krejci3, Teruki Noji2, Miyo Nakade4, Hitomi Takeuchi1 and Tetsuo Harada1*

Author Affiliations

1 Laboratory of Environmental Physiology, Graduate School of Integrated Arts and Sciences, Kochi University, Kochi, Japan

2 Department of Health and Physical Education, Faculty of Education, Kochi University, Kochi, Japan

3 Department of Health Education, Faculty of Education, University of South Bohemia, České Budějovice, Czech Republic

4 Department of Nutritional Education, Tokai Gakuen University, Miyoshi, Aichi, Japan

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Journal of Circadian Rhythms 2013, 11:4  doi:10.1186/1740-3391-11-4

Published: 25 May 2013

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).

Conclusion

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.

Keywords:
Salivary melatonin; Tryptophan; Protein rich breakfast; Sunlight exposure; Lighting with low color temperature