Effect of Birth Season on Circadian Typology Appearing in Japanese Young Children Aged 2 to 12 Years Disappears in Older Students Aged 18 to 25 Years

Abstract

Several studies suggest that season of birth differentially affects the physiological characteristics of humans. Those living at relatively high latitude, such as Canada, Spain, and Italy (44°N–45°N), and born in the fall tended to be “morning-type” persons in comparison to those born in other seasons. There are relatively little data on the affect of season of birth on people residing at low latitude. Here the authors show that at low latitude, Kochi, Japan (33°N), the effect of season of birth on the morningness chronotype is confined to young children aged 1–12 yrs, disappearing in elderly persons. Only female participants aged 2–12 yrs born in the fall, especially in November, were significantly morning-typed (p < .001) in comparison to those born in the other seasons, whereas there were no such significant season-of-birth differences in morningness-eveningness preference among male participants. Moreover, both female and male participants aged 13–25 yrs showed no significant seasonal differences in morningness-eveningness preference. The small effects detected in this study might be due to smaller seasonal change in day length at the relatively lower latitude of Kochi. (Author correspondence: [email protected])

Keywords:

• Adolescents
• Birth season
• Circadian typology
• Infants
• Older students

ACKNOWLEDGMENTS

We would like to sincerely thank all participants and all staffs who have supported the epidemiological study. This study was financially supported by Academic Supporting Foundation by President of Kochi University (2009–2011), Academic Supporting Foundation by Dean of Faculty of Education, Kochi University (2008–2009), and Foundation from Japan Society for the Promotion of Science (Foundation No. 22370089) (2010–2014).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.