![]() ![]() While recent studies have shown that electric lighting can influence sleep timing, its impact on sleep duration is controversial 11, 12, 13, 14, 15, 16. Social jetlag is associated with several health issues, including depressed mood, obesity, and cardio-metabolic risk 7, 8, 9, 10. This weekly structure of alternating short-early and long-late sleep is called social jetlag 6 and is calculated as the difference between the respective mid-sleeps on work-free and workdays. People therefore routinely use alarm clocks on workdays and thereby accumulate a sleep debt, which they compensate for on weekends. As a result of this drastically reduced zeitgeber strength, the circadian clocks of most people delay 5, while work schedules remain similar. In industrialised societies, the majority of people spend most of their time indoors, thereby being exposed to relatively dim light during the day and lack of darkness after sunset (due to the use of artificial light). It depends both on how an individual’s clock responds to a zeitgeber and on how strong the zeitgeber is. This ‘phase of entrainment’ is reflected in all aspects of physiology and behaviour (e.g., body temperature, metabolism, activity/rest, wake/sleep) 4. The entrainment process results in a stable phase relationship between the internal, circadian time and the external light-dark-cycle time. Light and darkness are therefore the predominant entraining agent (so-called zeitgeber) that biological clocks use for entrainment 1, 2, 3. They secure this by actively entraining to light signals, which are the source of all rhythmic changes (temperature, resources, predators, etc.). These temporal programmes need to run in synchrony with their cyclic environment. Practically all organisms have therefore developed biological clocks. The strategies that help organisms to cope with cyclic environments (daily or seasonal) include anticipating their regular changes. To understand the consequences of these changes for health, further studies are warranted. Our results and those of others show that use of electricity and modern lifestyles have changed sleep behaviour. ![]() ![]() People living without electricity and those, who acquired it only very recently on average sleep earlier than those in more urbanised communities (mid-sleep about 1 hour earlier) sleep duration tends to be longer. Light exposure, phase of activity, sleep timing and duration differ across communities with various levels of urbanisation and histories of access to electricity. Seven communities ( MCTQ: N = 213/ actimetry: N = 125) were compared in this study. We investigated daily rest-activity-rhythms and sleep-patterns in the Quilombolas’ by both wrist actimetry and the Munich ChronoType Questionnaire (MCTQ the results of these two instruments correlated highly). In a comparative approach, we aimed to understand whether and how human sleep changes with the introduction of artificial light. Due to individual histories, Quilombos nowadays exhibit different states of industrialisation, making them ideal for studying the influence of electrification on daily behaviour. Quilombos are settlements originally founded by Africans and African descendants (Quilombolas) in remote parts of Brazil to escape slavery. ![]()
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