Tryptophan intake at breakfast has been known to be effective on promoting better mental health and morning-typed life through serotonin and melatonin synthesis. For Japanese children, milk seems to be important resource for taking tryptophan at breakfast because of limited meal time in the morning. This study tries to show the effects of milk intake at breakfast on circadian typology and mental health of Japanese infants aged 1 -6 years. An integrated questionnaire was administrated to 1100 infants aged 1 -6 years attending nursery schools or kindergarten in June 2012. Seven hundred and forty participants (67.3%, 360 females and 380 males, mean age: 3.5 ± 1.4) answered the questionnaire. The questionnaire included questions on sleep habits, the diurnal type scale by Torsvall and Åkerstedt (1980), questions on mental health (anger and depression), and meals contents and time. Infants who took milk at breakfast showed 21.2 (±3.4, n = 537) of the diurnal type scale scores on average which tended to be higher (more morning-typed) than 20.7 (±3.5, n = 142) (p = 0.085) shown by those who did not take milk. Infants who took carbohydrate (or carbohydrate and protein resource) plus milk at breakfast were significantly morning-typed than those who took only carbohydrate (or carbohydrate and protein resource) (p < 0.001). Infants who took milk at breakfast tended to be less frequently depressed than those who did not (p = 0.098). Taking milk at breakfast might be effective to promote serotonin synthesis in the morning which could improve mental health directly and become "inner" zeitgeber for circadian clocks in infants.

Obesity is a serious problem that is growing in developed countries and many children as short-sleepers have been reported to be obese. However, no studies have been conducted on the relationship between BMI shown by mothers of children aged 1-6 years and their own circadian typology. This study aims to clarify this relationship in Japanese mothers. An integrated questionnaire on diurnal rhythms (including the Diurnal Type Scale constructed by Torsval & Åkerstedt), sleep habits, meal habits, lighting conditions at night, weight and height was administered to mothers and their children aged 1-6 years. Sixty-two percent of 863 mothers answered the questionnaire for themselves and their children. All the obese mothers (BMI of 28 or more) had MEQ scores of less than 18 and were more evening-typed than non-obese mothers (BMI of less than 28) (p=0.02). A higher ratio of obese mothers watched TV after 11:00 p.m. (p=0.049) and used fluorescent lights while watching TV after 11:00 p.m. (p=0.023) compared to non-obese mothers. Obese mothers showed a higher frequency of depression (p=0.044) and tended to have higher frequency of becoming irritated (p=0.09) than non-obese mothers. The children of obese mothers were significantly more evening-typed (Mean±SD=18.5±3.6) than those of the other mothers (21.1±3.2) (p=0.018). Evening-typed life of mothers with watching mid-night TV would be related to obesity of mothers and children. This study concludes that obese mothers of children aged 1-6 years are evening-typed and the children of obese mothers are also more evening-typed than those of non-obese mothers Keywords: Japanese young children, circadian typology, body mass index of mothers, TV watching at night, obesity

This study explores whether morning-typed persons are aware that they are maladapted for shift-work. An integrated questionnaire was administrated to 637 students aged 18-35 yrs attending university or physical therapy training school in May, June and October, 2012. A total of 617 participants (97%) answered the questionnaire that included questions on sleep habits such as bedtime, the diurnal type scale by Torsvall and Åkerstedt (1980), questions on mental health (irritation, anger, feeling out of control, depression) and meals content and timing, and questions on experience with and attitude towards shift work, including the question, "Would you be able to mentally and physically withstand doing shift work for one year, if given the chance?" Participants that answered "Absolutely never" to this question (DIFFICULT Group) showed significantly higher scores on the diurnal-type scale (more morning-typed) (p=0.005) and subjectively evaluated themselves as "more morning-typed persons" (p<0.001) than those that chose other answers (EASIER Group). The DIFFICULT Group showed significantly earlier bedtimes (p=0.017) and earlier sleep onset times (p=0.016), and tended to show earlier wake-up times (p=0.119) than the EASIER Group. The DIFFICULT Group had breakfast (p<0.001) and dinner (p=0.047) at more regular times than the EASIER Group and had nutritionally well balanced breakfast with higher frequency than the EASIER Group (p=0.023). These results may support the hypothesis that persons with a negative attitude to rotating shift work are more morning-typed than those without such a negative attitude towards shift work.