Open Access

Giulia Zerbini

• Sleep is essential for health and performance and its timing and consolidation are regulated by the biological clock. There is a rich variety in sleep timing (chronotype) that is often disregarded by society when imposing uniform school/working starting times. This leads to a phenomenon called social jetlag, the mismatch between biological and social clocks. The main objectives of this thesis were to describe the consequences that arise from social jetlag, to explore possible solutions to reduce it, and to better understand entrainment (the process that keeps the biological clock synchronized with the external light-dark cycle). We found that the impact of chronotype on school grades (late chronotypes usually obtain lower grades) was stronger in the early morning and for scientific subjects. Late chronotypes were more often absent from class, which, in turn, was associated with lower grades. We tested simple protocols to decrease social jetlag involving room light and blue lightSleep is essential for health and performance and its timing and consolidation are regulated by the biological clock. There is a rich variety in sleep timing (chronotype) that is often disregarded by society when imposing uniform school/working starting times. This leads to a phenomenon called social jetlag, the mismatch between biological and social clocks. The main objectives of this thesis were to describe the consequences that arise from social jetlag, to explore possible solutions to reduce it, and to better understand entrainment (the process that keeps the biological clock synchronized with the external light-dark cycle). We found that the impact of chronotype on school grades (late chronotypes usually obtain lower grades) was stronger in the early morning and for scientific subjects. Late chronotypes were more often absent from class, which, in turn, was associated with lower grades. We tested simple protocols to decrease social jetlag involving room light and blue light blocking glasses. Although social jetlag was not reduced, our findings show that simple ‘in-home’ light interventions are potentially effective in modifying the phase of entrainment and sleep timing. Finally, we have shown that season can influence school attendance and school performance, and that the weekly structure (workdays vs work-free days) has an impact on the sleep-wake cycle and on the melatonin rhythm, especially in late chronotypes. The findings of this thesis have potential applications for society. Suggestions to improve school policies and practical solutions to delayed sleep phase derive from this work.…