Can the moon really influence our health? In this Spotlight feature, we consider the evidence.
"The moon had been observing the earth close-up longer than anyone. It must have witnessed all of the phenomena occurring — and all of the acts carried out — on this earth," writes Haruki Murakami in 1Q84.
The earth's natural satellite has always fascinated human minds. Throughout the ages, humans have worshipped the moon, studied it, and referred to it to predict the direction of their lives... and their state of health.
The moon influences life on Earth and natural mechanisms in a way that must have seemed natural hundreds and thousands of years ago. At full moon, corals release eggs and gametes in a reproductive frenzy.
And the gravitational attraction between the moon and the Earth causes sea tides — the rising and falling of the sea.
Since the moon influences such mechanisms of life on Earth, people have also believed that it can affect various aspects of physical and mental health.
But is this true, and to what extent? In this Spotlight feature, we aim to find out.
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The moon and menstrual cycles
Some people still refer to menstrual cycles as "moon cycles," and many remain convinced that there is a form of synchronicity between the phases of the moon and female menses.
Researchers still disagree on whether or not the moon is likely to influence menstrual cycles in any way.
A myriad of webpages and smartphone apps purport to help you track your moon cycle or to achieve full synchronization between your menses and the phases of the moon.
Some even advise readers on how to maximize their chances of becoming pregnant by taking moon phases into account.
But is it true that the phase of the moon can influence fertility windows? This question is far from settled.
The notion that the menstrual cycle and the phases of the moon are somehow linked derives from the concept that, on average, a menstrual cycle lasts 28 days, which is about as long as a moon cycle. The moon takes 27 days, 7 hours, and 43 minutes to complete one revolution around the Earth, and 29.5 days for a moon phase cycle.
In the '70s, '80s, and '90s, various small-scale studies suggested that females' periods and ovulation phases coincided with the "light" phase (in the leading to full moon), and the "dark" phase (in the leading to new moon) of the moon cycle, respectively.
Some of these studies also found correlations between moon phases, changes in the levels of melatonin — a hormone that helps regulate sleep-wake cycles — and the phase of the menstrual cycle.
As recently as 2005, one study working with a small cohort from Nepal, indicated that women whose ovulation phase coincided with the full moon, and who got pregnant during the full moon, were more likely to give birth to male babies. Those who conceived before the full moon were more likely to give birth to female babies.
However, most periods are unlikely to "synch" with particular moon phases, except by coincidence. Menstrual cycles can last anywhere between 21–35 days, and their length can also change with age and due to hormonal factors.
A more recent 1-year-long retrospective study of 74 females of reproductive age contradicted the idea that the moon had a say in menstrual cycles. The study found no correlation whatsoever between menses, fertility, and the phases of the moon.
The moon and sleep
Research seems to suggest that a full moon can disrupt sleep, though the evidence is still limited.
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.
Recent evidence disproves the notion that certain moon phases could 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 analyzed 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.