The moon and sleep
Popular belief has it that the full moon disrupts sleep, making people more prone to insomnia. There is something attractive about the notion that the moon could influence such intimate aspects of our lives.
Someone who claimed that the full moon did indeed disrupt her sleep told Medical News Today that “there’s something romantic about being woken up by moonlight, as often as I vow to buy thicker curtains.”
But is there anything to this notion, or has it become a self-fulfilling prophecy for those people who have specific ideas on the influence of the full moon?
Once more, the evidence is not abundant and is primarily based on small-scale studies, but it does seem to suggest that the full moon can affect a person’s quality of sleep.
A study published in Sleep Medicine in 2014 assessed the sleep quality of 319 participants during different moon phases. This study found that during a full moon, participants had lower sleep efficiency. This means that they remained awake or in a state of light sleep for most of the time they spent in bed overnight.
It may be intuitive to blame sleeplessness — as our reader did — on the bright moonlight and the lack of heavy drapes, but that is not the conclusion reached by Christian Cajochen — from the University of Basel in Switzerland — and colleagues.
In 2013, Cajochen and team conducted an a posteriori analysis of data they had collected some years prior as part of an experiment conducted in laboratory conditions.
This experiment involved 17 healthy volunteers aged 20–31 and 16 healthy volunteers aged 57–74. The volunteers agreed to sleep in windowless, dark rooms over a study period of 3.5 days.
During this time, the researchers measured changes in sleep structure, brain activity during sleep, as well as in melatonin and cortisol levels.
The team got the idea to look at any correlations with moon phases only later. “We just thought of it after a drink in a local bar one evening at full moon, years after the study was completed,” they write in their paper.
The analysis the investigators then conducted suggested that immediately before and after a full moon, participants took about 5 minutes longer, on average, to fall asleep, and their sleep duration fell by about 20 minutes.
Their sleep was also lighter than usual, and melatonin levels also dropped close to the full moon, the researchers note. The researchers could not explain these changes by exposure to bright moonlight since the participants slept in fully dark, controlled environments.
“The lunar cycle seems to influence human sleep, even when one does not ‘see’ the moon and is not aware of the actual moon phase,” Cajochen told the BBC.
The moon and mental health
Another widely held notion has it that the moon influences mood and psychiatric health, and that the full moon, in particular, can make people more aggressive.
In folklore, the full moon triggers the metamorphosis from human to wolf of the werewolf, a mythical creature that reflects our ongoing fascination with the “bestial” potential of humans.
English words denoting madness or eccentricity, such as “moony,” “lunatic,” or “lunacy,” all have Old English or Latin roots meaning “moon.”
One study from 1984 suggested that the rate of criminality was likely to increase on nights with a full moon. Its authors said this might be because of “‘human tidal waves’ caused by the gravitational pull of the moon.”
And more recent research, published in 2009, suggested that psychiatric facilities admitted more people during the full moon than usual. This small study, which looked at the records of 91 patients “with violent and acute behavioral disturbance,” found that 23% of these admissions took place during the full moon.
This “was approximately double the number for other lunar phases,” the researchers write in their study paper.
However, other research has contradicted the notion that the full moon makes people more likely to harm themselves and others. A study published in the journal Psychiatry in 1998 found “no significant relationship” between any phase of the moon and a rise in violent behavior.
And, in 2019, researchers from Switzerland and the United States analysed the data of 17,966 individuals treated at 15 different psychiatric wards over 10 years. This study also found no evidence of a rise in aggression during the full moon phase.
“[Beliefs that the moon influences human behavior] seem largely impervious to the fact that a great deal of research, including the present study, has failed to support them,” the researchers warn in the study paper.
“The reasons for the persistence of such beliefs may not be found in a rational understanding but more in a primal, emotional desire to believe that we are not solely responsible for our own behaviors,” they write. They emphasize that in the future, we may all find it more helpful to look to our own biology and human context, rather than to celestial bodies, for answers.