Touched by The Moon

People sleep fitfully during the full moon. Other things happen, too.

[Cross-posted at The Fallible Mind, my blog at Psychology Today]


Sleeping in moonlight can affect your well-being.

Folklore has clung to the idea that the Moon affects people—usually for the worse. Our language still harbors words such as “lunacy,” “lunatic,” or “moonstruck” (the latter notion turned into a film with Cher and Nicholas Cage). At the idea’s outer reaches is the lycanthrope who, rather than sleeping peacefully during the full moon, turns into a werewolf instead and wreaks havoc.

The idea of lunar influence on human affairs has never been proven. Until now the possibility had never been subjected to scientific scrutiny, so it is a welcome surprise that The Economist reports a new study in Current Biology about the Moon’s possible influence on human behavior.

Over beers with colleagues one moonful night, Dr. Christian Cajochen at the Center for Chronobiology in Basel, Switzerland pondered whether the Moon’s phases might affect sleep patterns. Years earlier his group had examined how the brain’s daily circadian clock influenced sleep. These kinds of circadian studies are difficult to conduct because subjects need to be shut away from daylight—and, by extension, moonlight—for days at a time so that the daily cycles of illumination can’t affect them.

Dr. Cajochen’s original study had nothing to do with the effects of moonlight, making his current query about the possible effects of a full Moon a perfect double–blind experiment. Neither subjects nor the researchers could be biased because the question wasn’t on anyone’s mind at the time the data were collected.

Phases of the moon do affect humans.

Examining that old data set with the Moon question in mind his team found that yes, indeed, the phase of the Moon does affect human sleep—even when the person involved cannot possibly see the Moon.

EEG recordings, which categorize the standard stages of sleep, showed that around the time of the full Moon it took 5 minutes longer for volunteers to fall asleep and that they slept 20 minutes less. Their delta brainwaves, an indication of the depth of sleep, was 30% lower during the full Moon than at other phases, the level of the sleep hormone melatonin dropped, and subjectively they said they had not slept as well as usual. Female volunteers’ menstrual cycles had no connection to these results.

Before we get too weird, Dr. Cajochen points out that he does not think these changes are directly caused by moonlight. Rather, he may have discovered “an additional hand on the body’s clock–face.” In addition to the daily circadian timekeeper that is reset every day by the sun, he suggests that there is an endogenous monthly cycle entrained to the Moon. We observe its light over long periods of time, but are not consciously aware of doing so.

Light of very low intensity can affect circadian pacemakers in plants and insects. Lunar cycles exist in other species that depend on knowing the tides, such as marine iguanas. But what importance a human lunar cycle once served or perhaps serves today is currently unknown.

An anecdote from a physicist friend at the National Science Foundation concerns a folk belief still prevalent in the Shetland Islands, which lie only 6 degrees below the Arctic Circle. Winter daylight is only a few hours long and the winter Moon is prominent in the sky. My friend’s mother repeatedly voiced the widely–held belief that moonlight should never fall on a sleeper’s face.

Unused to illumination during the long winter nights, Shetlanders noticed the unsettling effect of exposure to moonlight. My friend further suggests that the “accumulated experience that led to this folk belief could have contributed to the widespread importance accorded to the moon in prehistoric Britain” by, of course, the Druids.

Sleep tight, everyone.

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