On nights before a full moon, people go to bed later and sleep less, a new study shows. Researchers report that sleep cycles in people oscillate during the 29.5-day lunar cycle: In the days leading up to a full moon, people go to sleep later in the evening and sleep for shorter periods of time.
The researchers observed these variations in both the time of sleep onset and the duration of sleep in urban and rural settings—from indigenous communities in northern Argentina to college students in Seattle, a city of more than 750,000. They saw the oscillations regardless of an individual’s access to electricity, though the variations are less pronounced in individuals living in urban environments.
The pattern’s ubiquity may indicate that our natural circadian rhythms are somehow synchronized with the phases of the lunar cycle. “We see a clear lunar modulation of sleep, with sleep decreasing and a later onset of sleep in the days preceding a full moon,” said Horacio de la Iglesia, a professor of biology at the University of Washington. Using wrist monitors, the team tracked sleep patterns among 98 individuals. Depending on the community, the total amount of sleep varied across the lunar cycle by an average of 46 to 58 minutes, and bedtimes see-sawed for around 30 minutes.
Whether the moon affects our sleep has been a controversial issue among scientists. Some studies hint at lunar effects only to be contradicted by others.
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The research was funded by the National Science Foundation and the Leakey Foundation.
