An integrated-questionnaire was administered to a total of 4142 (2137 women, 2005 men; answer rate: 94.4%) university students and medical training schools students aged 18-40 y. The survey was carried out between May and October, 2004-2013. This questionnaire consisted of assessment of diurnal type, questions on sleep habits, mental health (upset emotionally, irritated, angered by small triggers, and suppressed), frequency of watching TV at night, use of mobile phone and playing TV games between 21:00 and 03:00 h, and questions on lighting conditions during the daytime and night. Sleep length in evening-type students (E-type; Diurnal Type Scores = 7-12) was shorter than in intermediate-types (I-type; DTS = 13-16) and morning-types (M-type; DTS = 17-28) on weekdays (p<0.001), whereas sleep length in evening-types was shorter than intermediate-and morning-type students at weekends (p<0.001). Mental health index scores of the E-type students were significantly lower than those of I-type and M-type students in both sexes (p<0.001). Seventy-three percent of E-type women students watched TV after 23:00 h, significantly higher than 65.0% and 52.5% of I-type and M-type females, respectively (p<0.001), and 70.4% of E-type male students watched the TV after 23:00 h, significantly higher than 66.1% and 59.7% of I-type and M-type males, respectively (p=0.001). With regard to lighting conditions in the room in the afternoon, a slightly lower, but significantly so, percentage of the E-type students used the sunlight coming through the window than did the other types (p<0.001). The frequency of having three nutritionally rich meals (especially breakfast) -including carbohydrates, proteins, vitamins and minerals -was significantly higher in M-type than I-types and E-types (p<0.001). Premenstrual symptoms (PMS) were significantly more severe in E-type than I-type and M-type females (p=0.002). Lighting conditions throughout the 24 hours and at breakfast can act as a strong zeitgeber for students and exert a great influence on their mental and physical health, and can also affect PMS in women students.
This study evaluates the effects of milk intake for 20 days at breakfast on diurnal type (chronotype), sleep habits and soccer performance in Japanese university male athletes attending a university soccer club. Seventy three athletes were asked to take 200 ml of cows' milk at breakfast for 21 consecutive days during November and December, 2014. Twenty athletes attending the same soccer club did not drink cows' milk for the same period of time and acted a control group. An integrated questionnaire was administered twice, before the intervention period and 1 month after it to all 93 participants. The questionnaire included questions on sleep habits and diurnal type. On the 10th day and 21st days of the intervention period, a questionnaire on performance/skill was administered to all participants. The group which drank cows' milk showed higher frequency of improvement of soccer performance than did the control group did (performance-where higher values indicate less skill: milk drinking group=29.92, control group=31.9 on day 10; milk drinking group=28.21, control group=31.9 on day 21), and also judged that their soccer performance had improved more after 21 days than 10 days of the intervention. Those participants who changed diurnal type to becoming more morning-typed were more likely to judge that their soccer performance had improved than did those who showed no change in diurnal type.
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.
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