On nights before a full moon, people go to bed later and sleep less, study finds

For centuries, humans have blamed the moon for our moods, accidents, and even natural disasters. But new research indicates that our planet’s celestial companion has an impact on something else: our sleep.

In an article published on January 27 in Scientific advances, scientists at the University of Washington, the National University of Quilmes in Argentina and Yale University report that sleep cycles in people oscillate during the 29.5-day lunar cycle: in the days before on a full moon, people fall asleep later in the evening and sleep for shorter periods. The research team, led by UW biology professor Horacio de la Iglesia, observed these variations in both sleep onset time and sleep duration in urban and rural settings – indigenous communities in northern Argentina to students in Seattle, a city of over 750,000. They saw the oscillations regardless of an individual’s access to electricity, although the variations were less pronounced among individuals living in urban settings.

The ubiquity of the model may indicate that our natural circadian rhythms are somehow synchronized with – or driven into – the phases of the lunar cycle.

“We are seeing a clear lunar modulation of sleep, with decreased sleep and later sleep in the days leading up to the full moon,” de la Iglesia said. “And while 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.”

Using wrist monitors, the team tracked the sleep patterns of 98 people living in three indigenous Toba-Qom communities in the Argentine province of Formosa. Communities differed in their access to electricity during the study period: one rural community had no access to electricity, a second rural community had only limited access to electricity – 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 Toba-Qom participants, the researchers collected sleep data for one to two entire lunar cycles.

Previous studies by the Iglesia team and other research groups have shown that access to electricity has an impact on sleep, which the researchers also saw in their study: Toba-Qom in the urban community went to bed later and slept less than the rural participants with little or no access to electricity.

But study participants in all three communities also showed the same oscillations of sleep as the moon progressed through its 29.5-day cycle. According to the community, the total amount of sleep varied throughout the lunar cycle from 46 to 58 minutes on average, and bed times varied by around 30 minutes. For the three communities, on average, people had the last bedtime and the least sleep during the nights three to five days before the full moon.

When they discovered this pattern among Toba-Qom participants, the team analyzed sleep monitor data from 464 Seattle-area students that had been collected for a separate study. They found the same oscillations.

The team confirmed that the evenings leading up to the full moon – when participants slept the least and went to bed the latest – had more natural light available after dusk: the waxing moon grew brighter as it progresses towards a full moon, and usually rises in the late afternoon or early evening, placing it high in the sky in the evening after sunset. The second half of the full moon phase and the waning moons also emit significant light, but in the middle of the night, as the moon rises so late in the evening at these points in the lunar cycle.

“We hypothesize that the patterns we have 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 in the lunar cycle,” said the lead author Leandro Casiraghi, postdoctoral researcher at UW in the Department of Biology.

Whether the moon affects our sleep has been a controversial question among scientists. Some studies suggest lunar effects to be contradicted by others. De la Iglesia and Casiraghi believe this study showed a clear pattern in part because the team used wrist monitors to collect sleep data, as opposed to sleep logs reported by users or others. methods. More importantly, they tracked individuals through lunar cycles, which helped filter some of the “noise” in the data caused by individual variations in sleep patterns and the major differences in sleep patterns between them. people with and without access to electricity.

These lunar effects may also explain why access to electricity causes such pronounced changes in our sleep patterns, de la Iglesia added.

“In general, artificial light disrupts our innate circadian clocks in specific ways: it makes us fall asleep later in the evening; it makes us sleep less. But in general, we don’t use artificial light to ‘move’ the clock. morning, at least These are the same patterns that we observed here with the phases of the moon, ”said de la Iglesia.

“At certain times of the month, the moon is an important source of light in the evening, and this would have been clearly evident to our ancestors thousands of years ago,” Casiraghi said.

The team also found a second “semilunar” oscillation in sleep patterns in Toba-Qom communities, which appeared to modulate the main lunar rhythm with a 15-day cycle around the new and full moon phases. This semilunar effect was weaker and noticeable only in the two rural communities of Toba-Qom. Future studies should confirm this semi-lunar effect, which could suggest that these lunar rhythms are due to effects other than those of light, such as the maximum gravitational “tug” of the moon on Earth on new and full moons. , according to Casiraghi.

Either way, the lunar effect discovered by the team will impact sleep research in the future, the researchers said.

“In general, there has been a lot of suspicion that the phases of the moon might affect behavior such as sleep – although in urban settings with large amounts of light pollution, you may not know not what the moon phase is unless you step outside or look out the window, ”Casiraghi said.“ Future research should focus on how: does it act through our innate circadian clock? Or other signals that affect when you sleep? There is a lot to understand about this effect. ”