The relationship between human behavior and the phases of the moon has long been the stuff of legend and folklore. Werewolves aside, cultures throughout history have paid great attention—and celebration—to lunar phases. Beliefs about a connection between some of our most basic biological processes—including sleep—have also been common. But, scientific evidence showing connection between human sleep and lunar cycles? That’s not something we’ve seen.
Swiss scientists conducted a study that suggests sleep is significantly affected by lunar phases. Their results show changes to sleep throughout the moon’s 29.5-day cycle, and significant increases to sleep disruption during the time immediately surrounding the full moon.
The story of how these results came to be is almost as interesting as the findings themselves. The conditions of the experiment—which was conducted by scientists at Switzerland’s University of Basel—were well-suited to isolating a possible relationship between lunar phases and sleep. During study periods, volunteers slept in a highly controlled laboratory environment, which removed them from any direct visual contact with the moon, and controlled exposure to nighttime light. They were given no indications about time of day. Participants prepared for the study by having their sleep routines regulated before the study period even began: for a week before in-laboratory sleep sessions, volunteers maintained a strict sleep-wake schedule and pattern of exposure to light and dark. They also abstained from both caffeine and alcohol.
But perhaps the most significant control measure occurred without any planning at all. The researchers did not decide to use the study data for a lunar-sleep analysis until several years after the experiment itself had concluded. (The idea to compare their sleep lab to moon phases happened over drinks at a local bar—on the night of a full moon.) As a result, none of the people involved with the study—from the participants to the laboratory technicians to the scientists themselves—were aware that the data gathered would be used to investigate a connection between sleep and the phases of the moon. As with any scientific inquiry, knowledge about the questions being asked can have an influence on the course of the experiment, and the outcome.
To investigate possible links between our sleep and the phases within the cycle of the moon, investigators returned to their earlier experiment, which included 33 volunteers. Participants came from two different age groups: 17 men and women were between the ages 20-31, and the remaining 16 were men and women ages 57-74. All were nonsmokers in good health, without medical or psychiatric conditions. None took any medications. All participants were good sleepers, and were screened for sleep disorders and sleep quality.
Over a three-year period, volunteers spent a series of three and a half days in laboratory sleep sessions. During these laboratory sleep sessions, researchers collected information on several aspects of sleep, including:
- Sleep latency (the time it takes to fall asleep)
- Overall sleep time
- Time spent in REM sleep and slow-wave sleep
- Brain activity during slow wave sleep
- Nighttime melatonin levels
When researchers analyzed their data in relation to the phases of the moon, they found sleep changed significantly throughout the lunar cycle, with disruptions to sleep peaking during the days closest to the full moon.
- Sleep latency increased as the full moon approached. On the nights of a full moon, it took people an average of five minutes longer to fall asleep. After the full moon passed, sleep latency began to decrease.
- People spent 30% less time in slow-wave sleep—the deepest phase of sleep—at the full moon. As the full moon arrived, EEG scans showed brain activity during slow-wave sleep diminished.
- Melatonin levels dropped during the days surrounding the full moon, with nighttime melatonin levels at their lowest on full-moon nights
- Overall sleep time also dropped to their lowest levels—an average of 20 minutes less sleep—on nights with a full moon.
- Volunteers reported their lowest sleep quality during the full moon phase of the lunar cycle.
What’s behind this connection between our sleep and the cycle of the moon? That ultimately remains something of a mystery—but scientists have some ideas, based on other research linking animal physiology to lunar cycles. As researchers point out, the answer does not lie with forces of gravity. The moon’s gravitational force has effects on earth, specifically and most overtly on ocean tides. But the gravitational impact of the moon does not have an explicit effect on the human body. Researchers suggest that we may carry within us an internal biological rhythm that is linked to the moon’s cycle. Researchers liken this approximately 30-day “circalunar rhythm” to our circadian rhythms, which regulate several biological functions—including sleep—on a 24-hour cycle, in basic alignment with night and day. Other scientific research has demonstrated links between the phases of the moon and several species of marine life, indicating in these animals the presence of “circalunar clocks” that work in conjunction with their circadian clocks.
This is a fascinating and potentially important breakthrough in our understanding of the biological processes of sleep. We still have so much to learn about why we sleep, and how sleep works. Results like these point us in new and exciting directions, thanks to the curiosity of this group of scientists. Somebody buy these folks another round!
Michael J. Breus, Ph.D.