According to legend, those under the curse of the werewolf tend to get restless and have trouble sleeping in the nights leading up to the full moon.
A new study suggests we’re all prone to this behaviour – going to sleep later in the evening and sleeping for shorter periods of time as the Moon gets fuller and brighter.
And while the full moon won’t trigger a murderous rampage in most of us – as seen in the movies – the researchers suggest that this full-moon restlessness dates back to early human-hood when we hunted on the plains.
The idea is that early humans would generally hunker down to sleep when the Sun went down.
But with the full moon, they could hunt for longer – and to facilitate this, their circadian rhythms were governed by the lunar cycle, and not only by the Sun.
It’s this link to the lunar cycle that modern man has inherited.
How did the scientists prove this to be true
According to a statement from the University of Washington, Seattle:
- The researchers used wrist monitors to track sleep patterns among 98 individuals living in three Toba Qom Indigenous communities in the Argentine province of Formosa
- 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, researchers collected sleep data for one to two whole lunar cycles
- Sleep cycles in the participants oscillated during the 29.5-day lunar cycle
- In the days leading up to a full moon, the participants went to sleep later in the evening and slept for shorter periods of time
- The researchers saw these oscillations regardless of an individual’s access to electricity, though the variations are less pronounced in individuals living in urban environments
- Depending on the community, the total amount of sleep varied across the lunar cycle by an average of 46 to 58 minutes, and bed times seesawed by around 30 minutes
- For all three communities, on average, people had the latest bed times and the shortest amount of sleep in the nights three to five days leading up to a full moon
- When the researchers analysed sleep-monitor data from 464 college students in Seattle (a city of 750,000 people) they found the same oscillations.
“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,” said lead author Dr Leandro Casiraghi, a University of Washington postdoctoral researcher in the Department of Biology.
The team also found a second, ‘semi-lunar’ 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 semi-lunar effect was smaller and only noticeable in the two rural TobaQom 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, according to Dr Casiraghi.