Full Moon Insomnia: How the Moon Messes With Your Sleep

Last updated: October 14, 2019

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People have long noticed that it’s harder to fall asleep and stay asleep during a full moon. Even people who don’t notice any lunar effects on their sleep still occasionally report feeling sluggish and “hungover”, a sensation that isn’t noticeable on normal days.

Is this a real phenomenon or are our minds playing tricks on us? An obvious explanation is that the additional light from a full moon might be keeping people up later. But that simple explanation doesn’t make sense in modern times when we all sleep indoors with curtains covering our windows. For most people it seems hard to believe that the moon could affect our sleep. Here’s what the science says.

Full moon over a body of water
Can a full moon really cause insomnia?

Scientific studies on full moon insomnia

A report in the journal Current Biology shows that the phases of the moon absolutely do have an effect on your sleep.

The report was released in 2013, but the results were a long time coming. The initial research took place in 2000, when a team of researchers from University of Basel, the Swiss Federal Institute of Technology and the Switzerland Centre for Sleep Medicine studied 33 volunteers and studied their sleep in a lab over the course of 3 years.

The scientists obtained tons of data about the participants. They studied their melatonin levels, brain wave activity as measured by electroencephalograms (EEG), how long it took subjects to fall asleep, how long they stayed asleep, and finally their subjective reports detailing how well-rested they felt after a night of sleep.

The initial intent of this research was to study human sleep patterns in a general way. It was only later that the investigators discovered that they could use the data to study how the moon affects all of our sleep.

“The aim of exploring the influence of different lunar phases on sleep regulation was never a priori hypothesized,” they wrote in their  paper. “We just thought of it after a drink in a local bar one evening at full moon.”

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After taking a second look at the data, the researchers discovered that the full moon did in fact have an effect on human sleep patterns. The subjects in the study took an average of 5 minutes longer to fall asleep during the 3-4 days surrounding a full moon. The total amount of time the subjects slept was also affected, with participants sleeping an average of 20 fewer minutes during the days surrounding a full moon.

Remember all of that data that the scientists obtained? It turns out that on virtually every single metric, the subjects’ sleep was affected.

How does the full moon affect your sleep?

The study found that a full moon affects your sleep during the 3-4 nights surrounding sleep in the following ways:

  • It takes an average of 5 minutes longer to fall asleep
  • Average time spent asleep is 20 minutes less
  • EEG activity related to deep sleep falls by 30%
  • Melatonin levels are lower
  • Subjectively feel “less refreshed” during the following day

The subjects of the study all slept in a completely darkened room with no sight of the moon. Most importantly, since the study was intended to research general human sleep patterns, neither the subjects nor the researchers were even thinking about lunar cycles. The moon was not an experimental variable during the research and was thus not mentioned to researchers or participants.

The benefits of this are obvious: since no on involved in the study was even thinking about the moon, the study ends up being uniquely objective. There’s no way to alter the results of something that you don’t even know about.

The weaknesses of this study are also apparent. A study that is intended to research the effects of the moon on sleep should be set up to give an equal weight to every night in the lunar cycle. This study did so in a very haphazard way, which gives us less rigorous data to work with.

“The a posteriori analysis is a strength and a weakness,” said lead author Christian Cajochen, head of the University of Basel’s Centre for Chronobiology, in an e-mail he sent to TIME. “The strength is that investigators and subject expectations are not likely to influence the results, yet the weakness is that each subject was not studied across all lunar phases.”

Bottom line

The final answer is that, while it seems like the moon definitely has an effect on your sleep, we still don’t know why. This study was conducted in a dark sleep lab where participants were not able to see the moon and were not even thinking about it.

Gravity is not a good explanation either. While the moon’s gravitational pull raises tides in the ocean, it does not affect seas or lakes because they are too small. It stands to reason that a human body is also too small to be affected by the moon’s gravity.

The most likely answer is that we evolved on a specific planet that has specific astronomical cycles. We have a day and night, full moon and non-full moon, etc. Since our circadian systems evolved under these specific circumstances, it’s reasonable to assume that we adapted to accommodate them.

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If you suffer from full moon insomnia, know that you aren’t alone! This is a phenomenon that has been researched and confirmed by scientists (at least in a limited way). We still need more specific research to confirm the findings of this study, but as of right now it seems like a full moon can definitely cause insomnia.

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