Tonight, the UK will experience the first full moon of 2021, the so-called Full Wolf Moon.
And if you’re feeling a bit tired or groggy today, then you’re not alone.
It turns out that people go to bed later and sleep less on nights before a full moon, according to a new study.
The research indicates that the moon has a major impact on human sleep patterns.
For centuries, people have blamed the moon for their moods, accidents and even natural disasters.
But the new study, published in the journal Science Advances, suggests that our planet’s celestial companion actually has a profound impact on our sleep.
A team of American and Argentinian researchers found 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 research team, led by University of Washington Professor of biology Horacio de la Iglesia observed the 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 research team say that the proliferation of the pattern may indicate that our natural circadian rhythms are somehow synchronised with — or entrained to — the phases of the lunar cycle.
Prof de la Iglesia said: ‘We see a clear lunar modulation of sleep, with sleep decreasing and a 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.’
How the study was conducted
Using wrist monitors, the team tracked sleep patterns among 98 people living in three Toba-Qom Indigenous communities in the Argentine province of Formosa.
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 the third community was located in an urban setting and had full access to electricity.
Previous studies by Prof de la Iglesia’s team and other 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 rural participants with limited or no access to electricity.
However, participants in all three communities also showed the same sleep oscillations as the moon progressed through its 29.5-day cycle.
Depending on the community, the total amount of sleep varied across the lunar cycle by an average of 46 to 58 minutes, and bedtimes seesawed by around 30 minutes.
For all three communities, on average, people had the latest bedtimes and the shortest amount of sleep in the nights three to five days leading up to a full moon.
When they discovered the pattern among the Toba-Qom participants, the team analysed sleep-monitor data from 464 Seattle-area college students that had been collected for a separate study. They found the same oscillations.
The researchers confirmed that 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 lunar cycle
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.
Study lead author Doctor Leandro Casiraghi, a University of Washington researcher, said: ‘We hypothesise 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.’
Prof de la Iglesia believes that the lunar effects may also explain why access to electricity causes such pronounced changes to human sleep patterns.
He said: ‘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 sleep less.
‘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.’
Dr.Casiraghi said: ‘At certain times of the month, the moon is a significant source of light in the evenings, and that would have been clearly evident to our ancestors thousands of years ago.’
He added: ‘In general, there has been a lot of suspicion on the idea that the phases of the moon could affect a behaviour 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.’