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Washington researchers find the phase of the moon affects how long we sleep

UPDATED: Fri., Feb. 26, 2021

Shawn Griffith, of South Port, Maine, watches the nearly-full "snow moon" rise in clear skies over Penobscot Bay, Friday, Feb. 26, 2021, in Camden, Maine.   (Robert F. Bukaty)
Shawn Griffith, of South Port, Maine, watches the nearly-full "snow moon" rise in clear skies over Penobscot Bay, Friday, Feb. 26, 2021, in Camden, Maine.  (Robert F. Bukaty)

University of Washington researchers are beginning to peel away at the mystery of how moon cycles affect sleep, and what they’ve found so far surprised them.

Despite the option of “extending the end of the day” with artificial lighting in highly urbanized Seattle, scientist Horacio de la Iglesia said UW students slept shorter hours in the days before a full moon, as did indigenous Argentinans with no electricity.

De la Iglesia, a UW biology professor , led the study published in Science Advances Jan. 27, which pooled efforts from scientists at UW in Seattle, the National University of Quilmes in Argentina and Yale University.

Researchers observed the sleep habits of 98 people in Toba-Qom Indigenous communities in Argentina over a period of one to two moon cycles. One group lived in a village without electricity, one was partially electrified and one was urbanized, de la Iglesia said. Then, the scientists aggregated data collected on UW students’ sleep to see if the patterns held in an American city. They did.

“We were never thinking in Seattle there would be lunar rhythms,” de la Iglesia said.

He said light pollution is so high in Seattle that it’s “always above the full moon level.” With lots of tall buildings around too, undergraduates at UW likely don’t see the moon at all and are unaware of its current phase, de la Iglesia said.

“We think that our built environments have completely isolated us from nature, but if you can see these rhythms in undergrads living in dorms in a post-industrial, highly urbanized area, that means we haven’t gotten away from our cycles,” de la Iglesia said.

Light seems to play a part, but de la Iglesia suspects it’s not the only factor affecting sleep during moon cycles.

People slept about 46 to 58 minutes less in the days before a full moon. There was a 15-minute difference in sleep durations between the electrified and non-electric villages, de la Iglesia said, meaning people with electricity were slightly less affected by moon cycles.

In all three groups, people went to bed later and slept fewer hours in the several days before the full moon but, curiously, not on the night of the full moon itself or the days after. He expected people might lose sleep in the days before and after the full moon.

The researchers then factored in moon rise times. In the nights before a full moon, when the moon is still very bright, the moon rise occurs early in the night, at times that people would still be awake. After the full moon, moon rises happen in the middle of the night, when people are already asleep, and therefore it seems to have a lesser effect on keeping people up, the researchers hypothesize.

But, because the moon’s cycle still had an effect in light-polluted Seattle, de la Iglesia suspects the moon’s shifting gravitational pull might be changing sleep schedules, though they haven’t researched that possibility yet.

“What is the usefulness of this? We think evolutionarily, for our ancestors who were nomadic hunter-gatherers, it was very advantageous to take advantage of the few added hours of light,” de la Iglesia said. “As that became an evolutionary selective pressure, maybe those traits were selected for.”

There is little research on the effects of moon cycles on sleep, and the study of Argentinans’ sleep durations was the first longitudinal study on the subject, meaning researchers followed the same participants over time rather than taking snapshots from different participants at different points in the moon cycle, de la Iglesia said.

He’s looking ahead to research that will examine the possibility that gravity is changing how we sleep. In the meantime, he hopes insomniacs can make use of the knowledge that those few days before the full moon could be some of the hardest.

Maggie Quinlan can be reached at (509) 459-5135 or at

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