Illuminating sleep in the dark: The relationship between electric light and sleep on Tanna Island, Vanuatu

Ideal sleep duration has been a topic of debate for centuries. In industrialized nations, access to electric lighting has had impacts on our daily circadian rhythms and, consequently, our sleep. Because of this, desire to understand human “ancestral” sleep is increasing. It is hypothesized that industrialization, complete with 24h access to electric lighting, delays sleep onset and shortens sleep period. This could suggest that in industrialized societies, people may be getting insufficient sleep, which is important to overall health. Conversely, study of some non-industrialized societies without electricity has shown sleep durations that are shorter, or no different, from those in Westernized societies. To further investigate the direct effect of light exposure on sleep, actigraphy was used to measure these in individuals living traditional subsistence lifestyles, with or without access to electricity, on Tanna Island, Vanuatu. Bedtime, wake time, and rise time were similar between villages, however sleep onset was delayed in electrically lit villages, leading to shorter sleep duration. This effect was strongly influenced by mothers with infants, who were up throughout the night, and therefore exposed to more light at night in villages with electricity. Comparatively, sleep durations measured on Tanna were long relative to those reported in industrialized nations. The results support a hypothesis that exposure to artificial light after sunset can delay sleep onset and reduce sleep duration. Lifestyle differences appear to play a large role in human sleep, and continued investigation of varying levels of industrialization should uncover other industrialization-related impacts on sleep, and subsequently, health.