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J Biol Rhythms. 2015 Aug;30(4):342-50. doi: 10.1177/0748730415590702. Epub 2015 Jun 18.

Access to Electric Light Is Associated with Shorter Sleep Duration in a Traditionally Hunter-Gatherer Community.

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Department of Biology, University of Washington, Seattle, Washington, USA
Department of Anthropology, Yale University, New Haven, Connecticut, USA Centro de Ecología Aplicada del Litoral, CONICET, Argentina Facultad de Recursos Naturales, Universidad Nacional de Formosa, Argentina.
Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes/CONICET, Buenos Aires, Argentina.
Instituto de Investigaciones Geohistóricas, CONICET, Argentina.
Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, and Division of Sleep Medicine, Harvard Medical School, Boston, Massachusetts, USA.
Department of Anthropology, Yale University, New Haven, Connecticut, USA


Access to electric light might have shifted the ancestral timing and duration of human sleep. To test this hypothesis, we studied two communities of the historically hunter-gatherer indigenous Toba/Qom in the Argentinean Chaco. These communities share the same ethnic and sociocultural background, but one has free access to electricity while the other relies exclusively on natural light. We fitted participants in each community with wrist activity data loggers to assess their sleep-wake cycles during one week in the summer and one week in the winter. During the summer, participants with access to electricity had a tendency to a shorter daily sleep bout (43 ± 21 min) than those living under natural light conditions. This difference was due to a later daily bedtime and sleep onset in the community with electricity, but a similar sleep offset and rise time in both communities. In the winter, participants without access to electricity slept longer (56 ± 17 min) than those with access to electricity, and this was also related to earlier bedtimes and sleep onsets than participants in the community with electricity. In both communities, daily sleep duration was longer during the winter than during the summer. Our field study supports the notion that access to inexpensive sources of artificial light and the ability to create artificially lit environments must have been key factors in reducing sleep in industrialized human societies.


South American indigenous communities; artificial light-dark cycle; natural light-dark cycle; sleep timing

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