Individual Traits and Environmental Factors Influencing Sleep Timing: A Study of 225 Japanese Couples

Abstract

Behavioral and physiological processes, such as sleep-wakefulness, thermoregulation, and hormone secretion, exhibit 24-h rhythms in most organisms. These biological rhythms are driven by the circadian clock system and are entrained by the external environment, which in the case of humans includes social time schedules. Couples might be ideal experimental subjects to discriminate between individual traits and environmental factors, as they share lifestyle habits but not genetic backgrounds. In this study, sleep timing was compared between married Japanese couples (n = 225) who had lived together for 1 yr or more (mean 17 yrs). Additionally, the authors evaluated the influence of individual traits and environmental factors on an individual's sleep timing per each couple. The results reveal that the sleep timings of a couple are mainly associated with the chronotypes of the husband and wife, whereas the sleep timings are significantly influenced by certain environmental factors. The findings suggest that chronotype remains one of the major determinants of an individual's sleep onset and wake times. Understanding an individual's chronotype may help improve the quality of life issues surrounding sleep. (Author correspondence: [email protected])

Keywords:

• Chronotype
• Circadian rhythms
• Lifestyle habit
• Society
• Spouse

ACKNOWLEDGMENTS

We thank Dr. Shin Yamazaki for his comments on the manuscript. This study was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, and Technology of Japan and from the Ministry of Health, Labour, and Welfare of Japan. This study was partly supported by a Grant-in-Aid for the Strategic Research Program for Brain Sciences from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Understanding of molecular and environmental bases for brain health). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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