Chronotype-specific changes in subjective sleep quality: Differential responses to the relaxation of social time pressure in Japan

Modern societal factors frequently impede the attainment of good sleep quality by many healthy adults. We investigated the chronotype-specific predictors of changes in subjective sleep quality following the relaxation of social time pressure during COVID-19 pandemic social restrictions in Japan. One thousand two hundred and fifty-two Japanese participants were surveyed during the initial COVID-19 social restrictions. Logistic regression analyses were used to assess changes under modified social time pressure in sleep quality by chronotype group (early, intermediate, or late) from changes in patterns of daily behaviors. During social restrictions, subjective sleep quality deteriorated with delays in sleep timing across all chronotypes. Early and intermediate chronotypes' reduction in sleep quality was associated with decreased sleep duration, whereas improved subjective sleep quality was associated with increased sleep duration and minimal sleep timing delay in the early and intermediate chronotypes. In late chronotypes, improved sleep quality was also associated with longer outdoor light exposure. These findings indicate that the determinants of changes in subjective sleep quality under modified social time pressure are at least partially chronotype-specific. Maintaining sleep timing may universally enhance subjective sleep quality during perturbations of social schedules. Moreover, in late chronotypes, the exposure to daylight may improve sleep quality, regardless of changes in sleep behaviors. These insights may contribute to the development of effective strategies for promoting better sleep quality in modern societies where insufficient sleep is becoming increasingly widespread.