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

People have been blaming our moon, accidents and even natural disasters for centuries. But new research indicates that our planet’s heavenly companion is affecting something else – our sleep.

In an article published on January 27 in Scientific progress, scientists at the University of Washington, the National University of Quilmes in Argentina and Yale University report that sleep cycles in humans oscillate during the 29.5-day lunar cycle: In the days to a full moon, people go to bed later in the evening and sleep for shorter periods. The research team, led by UW professor of biology Horacio de la Iglesia, observed these variations in the time of sleep and the duration of sleep in urban and rural areas – from indigenous communities in northern Argentina to university students in Seattle, ‘ a city of more than 750,000. They saw the oscillations regardless of an individual’s access to electricity, although the variations are less pronounced in individuals living in urban environments.

The ubiquity of the pattern may indicate that our natural circadian rhythms are somehow synchronized with the phases of the lunar cycle – or have been dragged along.

“We are seeing a clear lunar modulation of sleep, with sleep declining and a later onset of sleep in the days before a full moon,” said de la Iglesia. “And while the effect is more powerful in communities without access to electricity, the effect is present in communities with electricity, including undergraduate students at the University of Washington.”

Using pulse monitors, the team tracked sleep patterns among 98 individuals living in three indigenous Toba-Qom communities in the Argentine province of Formosa. The 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 – such as a single source of artificial light in homes – while a third community in an urban environment and had full access to electricity. For nearly three-quarters of the Toba-Qom participants, researchers collected sleep data for one to two full lunar cycles.

Previous studies by de la Iglesia’s team and other research groups have shown that access to electricity affects sleep, which the researchers also saw in their study: Toba-Qom in the urban community later went to sleep and slept less than participants in rural areas with limited or no access to electricity.

But study participants in all three communities also showed the same sleep changes as the moon progressed during its 29.5-day cycle. Depending on the community, the total amount of sleep during the lunar cycle ranged from 46 to 58 minutes on average, and the sleep time ranged for about 30 minutes. For all three communities, people averaged the last bedtime and the shortest amount of sleep at night three to five days before a full moon.

When they discovered this pattern among the Toba-Qom participants, the team analyzed the sleep monitor data of 464 students in Seattle in the area 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 for the last time – became more natural light available at dusk: The washing moon becomes brighter as it progresses to a full moon and rises over generally late afternoon or early evening, and place it high in the air after sunset in the evening. The last half of the full moon phase and waning moons also emit considerable light, but in the middle of the night, as the moon rises so late in the evening at those points in the lunar cycle.

“We assume that the patterns we observed are an innate adaptation that enabled our ancestors to take advantage of this natural source of evening light that occurred at a specific time during the lunar cycle,” said lead author Leandro Casiraghi , a postdoctoral researcher from the UW in the Department of Biology.

The question of whether the moon affects our sleep has been a controversial issue among scientists. Some studies suggest lunar effects that can only be contradicted by others. De la Iglesia and Casiraghi believe that this study showed, in part, a clear pattern because the team used pulse monitors to collect sleep data, as opposed to sleeping pads or other methods reported by users. More importantly, they tracked individuals across lunar cycles, which filtered out the “noise” in data that was driven by individual variations in sleep patterns and large differences in sleep patterns between people with and without access to electricity.

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

“In general, artificial light interrupts our innate circadian clocks in specific ways: it makes us sleep later in the evening; it makes us sleep less. But in general, we do not use artificial light to ‘go ahead’ in the morning. “No, at least not willingly. These are the same patterns we observed here with the phases of the moon,” said de la Iglesia.

“At certain times of the month, the moon is a significant source of light in the evenings, and it would have been clear to our ancestors thousands of years ago,” Casiraghi said.

The team also found a second, ‘crescent’ oscillation of sleep patterns in the Toba-Qom communities, modulating the main lunar rhythm with a 15-day cycle around the new and full moon phases. This crescent effect was smaller and only noticeable in the two rural Toba-Qom communities. Future studies will have to confirm this crescent effect, suggesting that these lunar rhythms are the result of effects other than light, such as the moon’s maximum gravity “tug” on Earth during the new and full moons, according to Casiraghi.

Regardless, the lunar effect the team discovered will have an impact on sleep research going forward, the researchers said.

‘In general, there has been a lot of suspicion about the idea that the phases of the moon can influence behaviors such as sleep – although in urban environments with a large amount of light pollution you do not know what the lunar phase is unless you go outside or look out the window, ‘says Casiraghi. “Future research should focus on how: does it work through our innate circadian clock? Or other signals that affect the timing of sleep? There is a lot to understand about this effect.”