Moonstruck: Lunar cycle has a marked effect on sleep

January 29, 2021

Scientists have long understood that human activity is affected by light—be it sunlight, moonlight, or artificial light. So it should be no surprise that  a new international study suggests that our ability to sleep is significantly affected by the lunar cycle, even when taking into account artificial sources of light.

The study was conducted by researchers at the University of Washington-Seattle, the Universidad Nacional de Quilmes-Bernal, Argentina, and Yale University-New Haven; and was published on January 27 in Science Advances.

Using wrist monitors, the researchers tracked sleep patterns in 98 individuals living in three indigenous communities in Argentina over the course of one to two months, The Guardian reports.

One rural community had no electricity access; a second rural community had limited access to electricity, while a third community was located in an urban setting and had full access to electricity.

Participants in all three communities showed the same pattern of sleep oscillations as the moon progressed through its 29.5-day cycle, with sleep duration changing by between 20 minutes and 90-plus minutes, and bedtimes varying by 30 minutes to 80 minutes.

In each community, the peak of participants sleeping less and staying up later occurred in the three-to-five-day period leading up to full moon nights; and the opposite occurred on the nights that preceded the new moon, the authors found.

The data were somewhat unexpected, because the researchers thought there would be less sleep and more activity on the full moon nights, said the study’s author Horacio de la Iglesia, a professor of biology at the University of Washington. “But 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.”

The data that showed the “lunar phase effect” on sleep appeared to be stronger the more limited access to electricity was.

In an attempt to corroborate their findings, the researchers compared their results to similarly collected data from 464 Seattle-based students studying at the University of Washington. They found the same oscillations in sleep patterns, The Guardian says.

“Together, these results strongly suggest that human sleep is synchronised with lunar phases regardless of ethnic and socio-cultural background and of the level of urbanization,” the researchers wrote in the journal Science Advances.

Research contact: @GuardianUS

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