The COVID-19 pandemic  resulted in many countries imposing a lockdown, which in turn reduces sunlight exposure and alters daily social schedules. Since these are the main entrainment factors for biological rhythms , we hypothesized that the lockdown may have affected sleep and circadian rhythms. We indeed show that participants slept longer and later during lockdown weekdays, and exhibited lower levels of social jetlag. While this may seem to be an overall improvement of sleep conditions, chronotype was also delayed under the lockdown. This signature of a weaker light-dark cycle should be monitored attentively since it may progressively cause disruptive effects on sleep and circadian rhythms, affecting human performance and health .
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