Effects of Cow Milk Intake at Breakfast on the Circadian Typology and Mental Health of Japanese Infants Aged 1 - 6 Years

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 ?kerstedt (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 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.