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Goodnight moon? Study links sleep quality and lunar cycles

the moon
When the moon is full, people appear to experience poorer sleep, even when they have been locked in a sleep lab for several days, shut off from moonlight or any other outside environmental cues.

If you had trouble sleeping earlier this week, then you may want to blame it on Monday’s full moon. For, according to a small but interesting study, the moon’s cycles may have an impact on human sleep behavior.

And it’s not a positive impact. The study found that when the moon is full, people appear to experience poorer sleep, even when they have been locked in a sleep lab for several days, shut off from moonlight or any other outside environmental cues.

“This is the first reliable evidence that a lunar rhythm can modulate sleep structure in humans,” the study’s authors conclude.

Multiple measurements

For the study, Christian Cajochen, a chronobiologist at the University of Basel in Switzerland, and his colleagues took a retrospective look at data collected from 33 healthy people, ranging in age from 20 to 74, who had participated in a sleep study — one unconnected with lunar cycles — between 2000 and 2003.  (Amusingly, the researchers note in their paper that they thought of doing the retrospective study “after a drink in a local bar one evening at full moon.”)

The data contained blood-sample results of the 33 participants’ hormone secretions while they were in the lab, as well as the results of EEG readings of their brain patterns and eye movements during sleep. The participants had also filled out questionnaires about their self-perceptions of the quality of their sleep during the experiments.

Objective and subjective correlations

An analysis showed a correlation between the quality of the participants’ sleep, both objectively and subjectively, and lunar cycles. When the participants were in the lab during a full moon, they took an average of five minutes longer to fall asleep and slept an average of 20 minutes less overall than when they were in the lab during a new moon (when the moon is not visible from Earth). In addition, the EEG readings showed that brain activity related to deep sleep dropped by an average of 30 percent on full-moon nights.

Blood levels of melatonin, a light-sensitive hormone that induces sleep, also declined during the full-moon sleep sessions. And the questionnaires revealed that participants perceived their sleep as being 20 percent worse on full-moon nights than they did during a new moon.

The measurements were from the second night of a three-night sleep experiment, so the participants did have any immediate exposure to moonlight. Furthermore, while in the lab, they were deprived of all outside environmental cues.

Because of these factors — and because the moon does not produce small “tides” in the human body — Cajochne and his colleagues speculate that the effect on sleep observed in this study may be the result of some as-yet unidentified endogenous biological rhythm.

Not definitive, but intriguing

The study, of course, has many limitations, and thus can’t prove that the full moon has a detrimental effect on human sleep. Most notably, it’s a very small study, and a retrospective one at that. Still, the findings are intriguing.

“Lunar rhythms are not as evident as circadian rhythms and are thus not easy to document — but they do exist,” write Cajochen and his colleagues. “Their role is mysterious, and there are probably large individual differences that underlie the contradictory evidence for their existence.”

“Some people,” they add, “may be exquisitely sensitive to moon phase.”

FYI: The next full moon will be Aug. 20.

The study appears in the Aug. 5 issue of the journal Current Biology.

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