You might’ve felt this intuitively yourself: It’s time for bed, the lights are out, and yet you’re wide awake, tossing and turning. You do eventually manage to fall asleep, but even then, it’s a very shallow, restless sort of sleep…
Well, now more research suggests you need not look further than outside your window and at the moon for the cause of this sleeplessness. However, in a surprising twist, the findings weren’t entirely what the researchers anticipated. While we know that humans are a species ruled by light (whether naturally-occurring or artificial), the “lunar phase effect” affects sleep even when artificial sources of light are accounted for.
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Rather than people staying up later and sleeping less during the full moon, it was just before the full moon that sleep was shorter and lighter.
“[It] turns out that the nights before the full moon are the ones that have most of the moonlight during the first half of the night,” said the study’s author Horacio de la Iglesia, a professor of biology at the University of Washington in The Guardian. The opposite was true just before the new moon — people tended to sleep more and go to bed earlier.
See also: This is how I fought insomnia and won.
Ninety-eight participants across three Indigenous communities in Argentina wore wrist monitors tracking sleep patterns over the course of one to two months. While one community had no access to electricity, the second community had limited access, and the third community was located in an urban setting with full access to electricity.
The study also found that this lunar phase effect on sleep also appeared to have greater impact on people the more limited their access to electricity was.
In every community, participants’ peak sleepless period occurred in the three to five days leading up to the full moon night, while the opposite was true for the new moon, the study authors found.
Related: Wellness educator Chivon John’s pro-tips for falling asleep fast.
Wanting further insight, the researchers compared their data to the results of a similar study of 464 Seattle-based students at the University of Washington. The findings proved consistent.
This research supports the notion that try as we may, we can’t ever fully get away from some forces of nature.