• Robb G. Best

Study Finds We Get Less Sleep Before a Full Moon



The moon's supposed strange impact on us has long been the stuff of legends. It's been said that on a full moon, crime rates and hospitalization go up as people take momentary leave of their senses. Even the word "lunacy" has its roots in "luna," referencing the then-common belief that as the moon shifted through its cycle, this caused temporary insanity.


A meta-analysis on 37 studies covering the so-called "lunar effect" in 1985 found that these studies frequently contained errors, contradicted each other, failed to consider the effect of other cycles (such as the days of the week), and displayed "a willingness to accept any departure from chance as evidence of a lunar effect," as the meta-analysis's abstract put it. All in all, a correlation between lunar cycles and unstable psychological behavior has not been proven.


That said, it does appear there is at least one way in which the cycles of the moon have a real effect on us: our sleep. In a recent collaboration by researchers at the University of Washington, the National University of Quilmes in Argentina and Yale University, they report that our sleep cycles seem to follow the 29.5-day lunar cycle. And in the days leading up to the full moon, people go to bed later and sleep less.


UW professor of biology Horacio de la Iglesia, the study leader, and his team observed this pattern in both Indigenous communities in northern Argentina and college students in Seattle--both rural and urban environments, in other words. Access to electricity did not get rid of these oscillations, although it did somewhat lessen them.


As part of the study, the team gave wrist monitors to 98 people across three Toba-Qom Indigenous communities in Argentina. Two of the communities were rural; one had no access to electricity, while the other had some limited electricity access. The other community was urban.


Those in the urban Toba-Qom community generally went to bed later and slept less than their rural counterparts. This wasn't a surprise. But all three communities displayed the same sleep oscillations as the moon moved through its 29.5 day cycle. While exact times varied from one group to another, during the three to five days leading up to the full moon, all three communities went to sleep later and slept for a shorter amount of time. The researchers then looked at sleep monitor data that had been collected from 464 Seattle-area college students for a different study. The oscillations persisted.


It's worth noting that on the three to five days before a full moon, the waxing moon gives off more and more natural light after dusk, which could have some impact on our alertness. (The waning moon immediately following a full moon also gives off considerable light, but due to the moon's later rising during this period, that light is later and thus less accessible.)


“We hypothesize that the patterns we observed are an innate adaptation that allowed our ancestors to take advantage of this natural source of evening light that occurred at a specific time during the lunar cycle,” said Leandro Casiraghi, lead author and a UW postdoctoral researcher in the Department of Biology.


While there has long been controversy in the science world about the moon's role--or not--in our sleep, De la Iglesia and Casiraghi point out that their use of wrist monitors instead of subjective and outdated journaling ensures cleaner results, and that following the same populations through the whole lunar cycle helps to turn down the "noise" created by outlier individuals and the habitual differences between those with electricity and those without.


“In general, there has been a lot of suspicion on the idea that the phases of the moon could affect a behavior such as sleep — even though in urban settings with high amounts of light pollution, you may not know what the moon phase is unless you go outside or look out the window,” Casiraghi said. “Future research should focus on how: Is it acting through our innate circadian clock? Or other signals that affect the timing of sleep? There is a lot to understand about this effect.”


In the meantime, the National Sleep Foundation says that healthy adults should aim for 7 to 9 hours of sleep every night. If you're having trouble getting to bed, they recommend setting in place a relaxing pre-bedtime routine, monitoring caffeine intake, and disconnecting from screens (laptops and smartphones) at least a half hour before bed. Leaving your sleep routine to chance? Maybe that's the real lunacy.

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