Sleep patterns in Metropolitan and Regional areas in Japan: Before and during COVID-19 social restrictions

Sleep timing is an important output of the circadian system. The COVID-19-mandated social restrictions significantly altered commuting time and sleep duration regionally in Japan. This study aimed to elucidate sleep patterns, especially chronotype and social jetlag (SJL), due to changes in social time pressure through the social restrictions between the Metropolitan and Regional areas in Japan. As part of the Global Chrono Corona Survey 2020 (GCCS), the data were collected during social restrictions (SR), but pre-COVID-19 behaviours were also queried retrospectively. We analyzed a cohort of 729 respondents representing both the Metropolitan and the Regional areas separately for workdays and work-free days. While the areas showed no difference in SJL before SR, the differential decrease was larger in the Metropolitan area during SR, resulting in a significant difference in SJL between the areas. The outdoor light exposure before SR was 30 min longer in the Metropolitan areas than in the Regional; during SR both areas showed similarly low (below 1 h) outdoor light exposures. The variables associated with decreased SJL were the Metropolitan areas, work-from-home, a no-usage alarm clock on workdays, and chronotypes (mid-sleep time on free days corrected for sleep deficit accumulated over the workweek, MSFsc) during SR. The results suggest that relaxed social schedules, as reflected in the increased frequency of work-from-home and reduced alarm clock use, and moving towards earlier MSFsc during SR were linked to decreased SJL and were more prominent in the Metropolitan areas. This study provides insights into sleep patterns and the social time pressure markers, by comparison between residential groups in Japan.