Poor sleep stems from many factors—lack of exercise, screen time, stress—and surprisingly, the Moon. Research shows we tend to hit the hay later and sleep less in the nights leading up to a full moon.
Published in Science Advances, a study by researchers from the Universities of Washington and Yale (USA), alongside the National University of Quilmes (Argentina), examined how lunar cycles influence sleep patterns.
Using wrist-worn sleep trackers, the team analyzed habits among 98 individuals from three Toba-Qom Indigenous communities in Formosa, Argentina, and 464 students near Seattle. These groups were chosen for contrasting environments: Indigenous participants had limited artificial light but greater exposure to natural moonlight, while urban students experienced the opposite.
Results revealed a clear lunar-sleep connection in both low-electricity Indigenous communities and electrified urban settings.
In both cohorts, devices recorded later bedtimes and shorter sleep durations on pre-full moon nights, coinciding with brighter post-dusk moonlight during the waxing phase.
The authors suggest this pattern reflects an ancestral adaptation, leveraging moonlight—a reliable nighttime illuminant—for activities like hunting, fishing, and socializing.
Throughout human evolution, sleep timing has shifted, but nomadic ancestors likely retired after dusk when daylight faded. Moonlight, bright enough for human eyes, plausibly extended wakefulness and activities.
The weaker effect among Seattle students may stem from modern social schedules overriding natural rhythms.
