There are many myths and legends surrounding the full moon. It’s a time of magic, of strangeness, of werewolves, witches, and fairies. It is also, apparently, a time of disturbed sleep.
But is this just a story like all the others? The word ‘lunacy’ does comes from the Latin word ‘luna’, showing that the moon has been linked with mental imbalance for thousands of years. Could there be a grain of truth in all the myths? Does the lunar cycle truly have an effect on our sleep cycles?
The truth is more nuanced, yet more fascinating than you might think.
How the moon affects sleep: separating science from myth
Shockingly, most large population studies suggest that, yes, the moon does have an impact on our sleep patterns. Across the world, people seem to get less sleep, and less high quality, restorative sleep, when the moon is full. However, this impact isn’t due to any supernatural influence. Rather, it seems to be the result of increased light.
Light stimulates us. It keeps our bodies wakeful and our minds racing. The increased light given off by a full moon reduces the amount of melatonin – the hormone that helps us relax – our brains produce, therefore delaying our internal clock.
It doesn’t have a huge effect. Most studies suggest that people only lose between 15 minutes and half an hour’s sleep on the night of a bright full moon, but it is nonetheless a measurable effect which is particularly noticeable in rural areas with fewer sources of artificial light.
The link between the moon and mental health
All those old tales of werewolves and lunacy seem to suggest that the full moon has some transformative, even sinister effect on our psyche. If the moon does affect our sleep, does it also affect our mental health?
The answer is… not in the way you might think.
Even modest sleep disruption is detrimental to mental health. In those without an underlying condition, it can cause brain fog, irritability, and weakened resolve. In the vulnerable – such as people with depression, schizophrenia, teenagers who require more sleep, and pregnant people – the effect can be more pronounced. By disrupting sleep, the moon doesn’t cause mental illness, but it may exacerbate it.
There have been studies which examined whether the gravitational, tidal pull of the moon impacted mental health, but the results have been either inconclusive or negligible. Humans may be 70% water, but that doesn’t mean the moon has the power to cause any physical imbalance.
Insufficient sleep caused by increased light exposure is by far the most likely explanation for why the moon has been associated with poor mental health for millennia.
Why does the myth persist?
There are a lot of good stories about the supposed effects of the full moon on humans, from the anthropomorphic gods of antiquity to the werewolves of modern horror cinema. But aside from love of a good yarn, why do so many people insist the moon has some magic hold over the human psyche, despite the lack of scientific evidence?
It may an example of what psychologists call illusory correlation. When you can’t sleep, what is the first thing you see, and therefore blame? The big silver ball in the sky. Other sleep disruptors, such as caffeine, stress, or an overexposure of blue light from your phone before bed, are less noticeable or memorable, and therefore less easy to focus on. We also tend to remember the sleepless nights that coincide with a full moon more than the ones that don’t.
So, if you find yourself tossing and turning during a full moon, the solution isn’t a silver bullet or a witch’s brew, but thicker curtains.
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