• breakfast;
  • intervention;
  • morningness-eveningness;
  • natto and banana;
  • sunlight exposure;
  • university soccer team


This study aims to clarify whether a combined intervention of the consumption of Tryptophan and Vitamin B6 at breakfast plus sunlight exposure after breakfast could effectively increase morningness in the participants of Japanese University sport club members. The students were divided evenly into three groups with equal numbers of the different chrono-types to eliminate bias. Participants in Group 1 (G1) received no intervention. Participants in Group 2 (G2) were asked to eat protein resources such as fermented soybeans and Vitamin B6 resources such as bananas at breakfast and were also asked to record their breakfast. Participants in Group 3 (G3) were asked to do the same as G2 plus expose themselves to sunlight after breakfast and record the duration of exposure. Evening-typed participants who occupied 50% of all participants before the intervention in G2 and G3 significantly shifted to more morning-typed participants. For the evening-typed participants who occupied 50% of all participants in G2 and G3, a significant and positive correlation was shown between the change in Trp amount consumed at breakfast and the change in M-E score (more Trp consumption and shifting to morning-type) before and after intervention. Based on the correlation analysis, the consumption of Trp at breakfast might be hypothesized to cause a shift in circadian typology of university students to be more morning-typed.