In a new study, scientists from the University of Washington, in collaboration with the National University of Quilmes in Argentina and Yale University, indicates that our planet’s celestial companion impacts our sleep. They reported that the 29.5-day lunar cycle oscillates the sleep cycle in people—29.5-day lunar cycle.
Scientists observed these variations in both the time of sleep onset and sleep duration in urban and rural settings — from Indigenous communities in northern Argentina to college students in Seattle. They saw the oscillations regardless of their electricity access, though the variations are less pronounced in individuals living in urban environments.
The pattern’s ubiquity indicates that our biological clock is somehow synchronized with the lunar cycle phases.
UW professor of biology Horacio de la Iglesia said, “We see a clear lunar modulation of sleep, with sleep decreasing and later onset of sleep in the days preceding a full moon. And although the effect is more robust in communities without access to electricity, the effect is present in communities with electricity, including undergraduates at the University of Washington.”
For the study, scientists tracked the sleeping patterns among 98 individuals living in three Toba-Qom Indigenous communities in the Argentine province of Formosa. They used wrist monitors to track sleep patterns.
The communities differed in their access to electricity during the study period: One rural community had no electricity access, a second rural community had only limited access to electricity — such as a single source of artificial light in dwellings — while a third community was located in an urban setting and had full access to electricity. For nearly three-quarters of the Toba-Qom participants, sleep data were collected for one to two whole lunar cycles.
Participants from all three communities showed the same sleep oscillations as the moon progressed through its 29.5-day cycle.
Contingent upon the local area, the total amount of sleep differed across the lunar cycle by an average of 46 to 58 minutes, and bedtimes seesawed by around 30 minutes. On average, for all three communities, people had the latest bedtimes and the shortest amount of sleep in the nights three to five days leading up to a full moon.
Scientists confirmed, “the evenings leading up to the full moon — when participants slept the least and went to bed the latest — have more natural light available after dusk: The waxing moon is increasingly brighter as it progresses toward a full moon, and generally rises in the late afternoon or early evening, placing it high in the sky during the evening after sunset. The latter half of the full moon phase and waning moons also give off significant light, but in the middle of the night, since the moon rises so late in the evening at those points in the lunar cycle.”
Lead author Leandro Casiraghi, a UW postdoctoral researcher in the Department of Biology, said, “We hypothesize that the patterns we observed are an innate adaptation that allowed our ancestors to take advantage of this natural source of evening light that occurred at a specific time during the lunar cycle.”
Regardless of whether the moon affects our sleep has been a dubious issue among scientists. A few examinations indicate lunar impacts just to be contradicted by others. De la Iglesia and Casiraghi believe that this study demonstrated a clear pattern to some degree because the team utilized wrist monitors to gather sleep data instead of user-reported sleep diaries or different strategies. All the more significantly, they followed people across lunar cycles, which assisted some of the “noise” in data caused by individual variations in sleep patterns and significant differences in sleep patterns between people with and without access to electricity.
de la Iglesia said, “These lunar effects may also explain why access to electricity causes such pronounced changes to our sleep patterns.”
“In general, artificial light disrupts our innate circadian clocks in specific ways: It makes us go to sleep later in the evening; it makes us sleepless. But generally, we don’t use artificial light to ‘advance’ the morning, at least not willingly. Those are the same patterns we observed here with the phases of the moon.”
Casiraghi said, “At certain times of the month, the moon is a significant source of light in the evenings, and that would have been evident to our ancestors thousands of years ago.”
“The team also found a second, “semilunar” oscillation of sleep patterns in the Toba-Qom communities, which seemed to modulate the main lunar rhythm with a 15-day cycle around the new and full moon phases. This semilunar effect was smaller and only noticeable in the two rural Toba-Qom communities. Future studies would have to confirm this semilunar effect, which may suggest that these lunar rhythms are due to effects other than from light, such as the moon’s maximal gravitational “tug” on the Earth at the new and full moons.”
Scientists noted, “Regardless, the lunar effect the team discovered will impact sleep research moving forward.”
Casiraghi said, “In general, there has been a lot of suspicion on the idea that the phases of the moon could affect a behavior such as sleep — even though in urban settings with high amounts of light pollution, you may not know what the moon phase is unless you go outside or look out the window.”
“Future research should focus on how: Is it acting through our innate circadian clock? Or other signals that affect the timing of sleep? There is a lot to understand about this effect.”
- Leandro Casiraghi et al. Moonstruck sleep: Synchronization of human sleep with the moon cycle under field conditions. DOI: 10.1126/sciadv.abe0465