Seven Studies on Full Moon Sleep, and Where They Disagree
Lab studies, a file-drawer reanalysis, and field data from Argentina point in different directions on whether the full moon changes sleep. Here is the tally.
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In the sleep laboratories of the University of Basel’s psychiatric hospital, between 2000 and 2003, volunteers slept in windowless rooms under tightly controlled conditions. They could not see the sky. Nobody on the research team had written “lunar phase” into the protocol, because the experiments were about age and sex differences in sleep. Years later, a team led by Christian Cajochen went back through the records of 33 of those volunteers and sorted the nights by the moon.
The answer to whether the full moon changes sleep is: maybe a little, and the evidence is split. Cajochen’s reanalysis, published in Current Biology in 2013, found worse sleep around the full moon. A larger reanalysis of 1,265 volunteers, published in the same journal a year later, found nothing. Field data from Argentina and Seattle then reported a different kind of effect altogether. Most web answers cite one study and stop, so seven are laid side by side here.
What the 2013 Basel reanalysis found
The 33 volunteers fell into two groups: 17 healthy young adults (ages 18 to 31) and 16 healthy older adults (57 to 74). Their sleep had been recorded with EEG across a 3.5-day constant routine. Because neither the participants nor the investigators had lunar phase in mind when the data were collected, the setup looks like a natural experiment. It is also the study’s weak point, since the analysis was retrospective and the sample was small.
Cajochen and colleagues reported four things near the full moon, per the published summary: EEG delta activity during non-REM sleep fell by about 30 percent, sleep onset took about five minutes longer, total sleep was about 20 minutes shorter, and evening melatonin was lower. Participants also rated their own sleep as poorer on those nights.
Delta activity is the slow-wave signature of deep sleep, so a 30 percent drop would be a large change if it held up. A 20-minute loss of total sleep is the kind of change a late meal or a warm bedroom can produce, which is why replication matters here.
The file-drawer reanalysis that found nothing
In 2014, the sharpest challenge came from a group led by Cordi, in a Current Biology correspondence titled “Lunar cycle effects on sleep and the file drawer problem.” They went back to three large existing samples of sleep EEG recordings, of 470, 757 and 870 recordings, and tried to reproduce the Basel pattern. They could not. They also reported finding further mostly unpublished null results, which pointed to a publication-bias explanation: studies that find a moon effect get written up, and studies that do not get filed away. Across their material, the authors counted 1,265 volunteers and 2,097 nights.
Cajochen and colleagues published a reply in the same journal, noting that Cordi’s group had analyzed a large number of participants and found no significant effects, in contrast to the smaller Basel cohort. The disagreement is partly about which dataset is the right comparison.
A second lab result, and a split by sex
Within the same year, Michael Smith, Ilona Croy and Kerstin Persson Waye, working from Sahlgrenska Academy in Gothenburg, reported in Current Biology (2014) that human sleep and cortical reactivity were influenced by lunar phase. They also reanalyzed data from an earlier sleep study, in windowless rooms. Total sleep time fell by about 25 minutes around the full moon relative to a quarter moon, and cortical reactivity to environmental stimuli during sleep rose in both women and men. Only men had more trouble falling asleep and slept less, according to published summaries of the paper.
That sex split reappeared in a different form in a 2015 paper in the Journal of Sleep Research. Della Monica, Atzori and Dijk analyzed 205 carefully screened participants (91 men and 114 women, ages 20 to 84) who had slept in windowless labs at the Surrey Clinical Research Centre. Women showed reduced total sleep, stage 4 sleep and REM sleep close to the full moon, while men showed longer REM. The authors described the overall evidence as limited. Notice that the sex pattern is the opposite of Smith’s on the question of who slept less. Two lab reanalyses, two sexes, no agreement.
Out of the lab: Formosa and Seattle
The study that moved the question out of windowless rooms was led by Leandro Casiraghi, with Horacio de la Iglesia and colleagues at the University of Washington, Argentina’s National University of Quilmes and Yale, and published in Science Advances in January 2021. They gave wrist activity monitors to 98 people in three Toba/Qom communities in Formosa province, northern Argentina, and tracked their sleep for one to two months. The communities sat on a gradient of electric light: one town with round-the-clock access, a rural settlement with lights inside homes only, and a sparsely settled area with no electricity. For comparison, the team analyzed 464 University of Washington undergraduates.
The findings pointed at the days before the full moon. People went to bed later and slept less. De la Iglesia put it this way in the university’s announcement: “We see a clear lunar modulation of sleep, with sleep decreasing and 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.”
The paper reports average sleep duration varying across the lunar cycle by roughly 46 to 58 minutes and bedtimes shifting by about 30 minutes, with the latest bedtimes and shortest sleep three to five days before the full moon. Those are group averages, and they differ by community.
This study measured sleep at home, where people choose their own bedtimes, so a later bedtime could reflect behavior (more evening light to stay up by) as well as biology. The timing, in the days before the full moon, fits moonlit evenings: in the waxing phase the moon rises in the afternoon and shines after dark.
A 2026 follow-up that points at gravity
A paper titled “Lunar gravity predicts sleep timing,” indexed in PubMed in 2026 and first posted to bioRxiv in January of that year, reanalyzed actigraphy from the Seattle and Toba/Qom cohorts and from captive titi monkeys with limited access to natural light. Per its abstract, sleep onset was consistently delayed around periods of maximal gravitational variation. The predicted bedtimes were 24.5 minutes later around the new moon than around the full moon in Seattle, and 21.4 minutes later in the Toba/Qom communities. The authors suggested that other geophysical factors oscillating with lunisolar tides might mediate the effect.
Two caveats apply. The figures above are the preprint’s, and peer review may have changed them. The abstract’s framing (later bedtimes near the new moon, in a model of gravimetric cycles) does not map cleanly onto the 2021 observation of later bedtimes before the full moon. Whether the two papers describe the same signal in different terms is an open question.
A hormone result in children
One more piece belongs on the table. Hartstein, Wright, Akacem, Diniz Behn and LeBourgeois, publishing in the Journal of Sleep Research in 2022, looked at 46 children aged 3.0 to 5.9. After 5 to 7 days on a strict sleep schedule, each child completed an in-home dim-light assessment with saliva samples every 20 to 30 minutes until an hour past bedtime. Evening melatonin was lower in children assessed near the full moon than near the new moon. That echoes the Basel melatonin result in a very different population, though it says nothing directly about total sleep.
The studies side by side
| Study | Method | Sample | Finding | Main caveat |
|---|---|---|---|---|
| Cajochen et al., 2013, Current Biology | Retrospective reanalysis of lab data, windowless rooms | 33 adults | About 30% less delta activity, 5 min slower sleep onset, 20 min less sleep, lower melatonin near full moon | Small sample, lunar phase not planned |
| Cordi et al., 2014, Current Biology | Reanalysis of three existing EEG samples plus unpublished nulls | 1,265 volunteers, 2,097 nights | No lunar effect found | Different recording conditions from Basel’s |
| Smith, Croy and Persson Waye, 2014, Current Biology | Reanalysis of earlier lab data, Gothenburg | Earlier lab study | About 25 min less sleep, higher cortical reactivity near full moon; sleep-onset effects in men only | Retrospective reanalysis |
| Della Monica et al., 2015, Journal of Sleep Research | Lab data from two clinical trials, Surrey | 205 adults | Women: less total sleep, stage 4 and REM; men: longer REM | Authors call evidence limited |
| Casiraghi et al., 2021, Science Advances | Wrist actigraphy at home, 1 to 2 months | 98 Toba/Qom, 464 students | Later bedtimes and shorter sleep in days before full moon | Free-living behavior can confound |
| Hartstein et al., 2022, Journal of Sleep Research | Dim-light melatonin assessment at home | 46 children | Lower evening melatonin near full moon | Hormone only, small sample |
| “Lunar gravity predicts sleep timing,” 2026 | Actigraphy reanalysis (Seattle, Toba/Qom, titi monkeys) | Cohorts above plus monkeys | Bedtime about 21 to 25 min later near new moon in models | Preprint-derived figures |
Where the evidence conflicts
Three conflicts stand out. Size: Cordi et al. found nothing in over a thousand volunteers, while Basel, Gothenburg and Surrey each found something in a few dozen to a few hundred. Sex: Smith’s group saw men sleep worse, while Della Monica’s saw women lose sleep. Timing: the field study found its effect in the days before the full moon, and the 2026 paper is organized around the new moon.
A fair reading is that several teams, using different methods, keep finding shifts of 20 to 60 minutes or so, in different places, with different sex patterns, and that a large reanalysis could not reproduce the strongest laboratory claims. Publication bias remains a live explanation for part of the picture. So does a real but small effect that varies with context.
What remains unsure
Nobody has shown how it would work. Moonlight cannot explain results from windowless labs. A circalunar clock in humans is a hypothesis with some melatonin data behind it, not a demonstrated organ or gene. Tides and gravity are proposed in the 2026 abstract but not established. Behavior, such as staying up on bright evenings, probably explains some of the field result.
Effect size is the other open point. Even if the field data are right, a shift of 20 to 40 minutes in the lab data is comparable to what happens when people stay up for a late dinner. The gap between weekday and weekend bedtimes that sleep researchers call social jet lag can reach an hour or more, which puts the lunar signal in perspective. And anyone hoping to check it on their own wrist should read about what sleep trackers can and cannot measure first, since consumer devices estimate sleep from movement. If the melatonin findings hold, they tie into the broader question of how melatonin timing works and where supplements fit, though none of these studies tested supplements.
Does the full moon really affect how well you sleep?
Current research suggests the full moon may shorten sleep or delay bedtime by roughly 20 to 60 minutes in some people, but studies disagree, a large reanalysis of 1,265 volunteers found no effect, and no cause has been confirmed. The most defensible summary is a small, inconsistent effect that varies by population and method, which is a weaker claim than “the moon ruins sleep” and a stronger claim than “it is all superstition.”
Full moon sleep questions, with the numbers the table leaves out
Does the full moon affect how well you sleep?
Possibly, but only slightly. Studies that measured sleep carefully report shifts on the order of 20 to 25 minutes of total sleep around a full moon, while other large reanalyses found nothing. The effect, if real, is smaller than the difference between a Tuesday and a Saturday for most people.
Is the full moon effect caused by moonlight?
Moonlight is the obvious suspect, but the Basel and Gothenburg lab data came from windowless rooms. The field data from Argentina found the pattern in communities with electric light too, though it was stronger where there was none. A direct light explanation does not cover all the findings.
Do people sleep worse before the full moon or on the night itself?
The 2021 field study reported the shift in the days leading up to the full moon, with later bedtimes and shorter sleep. A calendar that only marks the night of the full moon can therefore miss the stretch where the effect was reported.
Can a sleep tracker show whether the moon is affecting me?
Only crudely. Wrist trackers estimate sleep from movement, and the lunar effects in published studies are under an hour. You would need several months of nightly records and a comparison against lunar phase to separate a real shift from ordinary night-to-night noise.
Why does the moon seem to matter if the evidence is mixed?
A bad night near a full moon gets remembered and blamed on the moon, while a bad night at a new moon is blamed on stress or coffee. Selective memory can keep a belief alive even if the underlying effect is zero or tiny.