Mental health

Sleep patterns could be affected by the full moon

“Full Moon 'disturbs a good night's sleep'” reports BBC News.

This story is based on an analysis of data the researchers decided to do “after a drink in a local bar one evening at full moon”.

They looked at two nights of in depth sleep data collected in a sleep laboratory from 33 healthy volunteers in a previous study and what phase of the moon these nights fell into.

They found that on nights around the full moon, volunteers:

  • took longer to fall asleep
  • spent less time in deep sleep
  • slept for less time
  • reported having poorer sleep

So, why might a full moon have this effect on sleep? One apparently obvious explanation – moonlight shining into the rooms disrupts sleep – does not seem to hold up. Conditions in the sleep laboratory are tightly controlled to ensure that the amount of light was the same every night.

Still, there is the possibility that the patterns of moonlight the volunteers experienced in the months running up to the sleep laboratory nights could still be having an effect on their body’s sleep rhythms.

These results suggest that as well as our body clocks having a natural response to the time of day, when it comes to sleep, it may also have a response to the cycle of the moon.

However, due to the study’s small size and the limited time individuals were followed, conclusions from these results are only tentative.

Where did the story come from?

The study was carried out by researchers from the University of Basel and other research centres in Switzerland. It was funded by the Swiss National Foundation Grants and the Velux Foundation Switzerland. The Velux Foundation is a non-profit foundation that funds research into daylight and other areas. It was established by the founder of the Velux company, which makes windows.

The study was published in the peer-reviewed journal Current Biology.

The results of the study have generally been covered reasonably, albeit with some speculation.

For example, the Daily Mail focuses on possible evolutionary reasons for an effect of the moon on sleep – citing a so-called ‘inner caveman’ effect. That is, we tend to sleep less deeply during a fall moon as a survival technique. The moonlight could make us more noticeable to predators so we remain more aware during this time. However, the study itself does not explore this issue.

What kind of research was this?

This was a study looking at the effects of moonlight on the quality of sleep. The researchers say that there is evidence of an effect of the moon’s cycles on biological rhythms in some sea life. However, they report that the evidence of an effect on human biology is largely based on folklore.

Therefore, they wanted to investigate whether the cycle of the moon – how it waxes and wanes – affects sleep in humans.

Amusingly, the researchers say the idea to do this study came to them “after a drink in a local bar one evening at full moon”.

The researchers used data collected as part of previous short term sleep monitoring studies and compared sleep patterns from different participants monitored during different phases of the moon.

Ideally, researchers would follow the same people over a longer period to make sure differences seen were not being affected by the fact that different people were being compared.

What did the research involve?

The researchers used data collected on sleep over an extended period, and analysed whether people’s sleep patterns changed along with the cycle of the moon.

The data had been collected years earlier as part of earlier sleep studies. This meant volunteers and people collecting the data did not know that the effect of the moon would be investigated with the data being collected. This removes the chance that this knowledge could influence the results.

The data came from 17 healthy younger volunteers aged from 21 to 31 years old, and 16 healthy older volunteers aged 57 to 74 years old. They were non-smokers and didn’t take illegal drugs or medication. The volunteers were asked to keep very regular sleeping patterns for at least a week before the start of the study, and to attempt to sleep for at least eight hours each night. They were also asked to avoid excessive caffeine or alcohol consumption.

They had taken part in a study of sleep/wake patterns over three and a half days in a specially designed sleep laboratory. Conditions could be kept the same in the laboratory during the study (same level of light, temperature, bed position, no indicators of time in the rooms, and regular small snacks and water), and sleep closely monitored. The researchers monitored sleep patterns and brain waves during sleep using the electroencephalogram (EEG), which measures electrical activity in the brain.

They also monitored levels of the hormone melatonin, which is related to our body clocks, and the hormone cortisol, which is related to stress levels.

For this study, they used the data from two nights of recordings for each volunteer, which were at least a week apart.

The volunteers had taken part over a three and a half year period, across different seasons. The researchers worked out exactly what phase the moon had been in at the time each volunteer took part. They classified the days according to how many days away from the full moon they were, and looked at whether this was related to the sleep patterns seen.

What were the basic results?

The researchers found that compared to other parts of the moon cycle, around the full moon, volunteers:

  • took, on average, five minutes more to fall asleep
  • spent 30% less time in deep sleep
  • slept for an average of 20 minutes less than normal
  • reported having poorer sleep
  • had reduced levels of the hormone melatonin

Moon cycles did not have an effect on cortisol levels.

How did the researchers interpret the results?

The researchers concluded that this is “the first reliable evidence” that the moon’s cycle can affect sleep in humans when measured under the highly controlled conditions of a sleep laboratory.


This small study has suggested that human sleep patterns may vary with the moon’s cycle, with people taking longer to get to sleep, and sleeping for less time and less soundly around the full moon.

The obvious suggestion is that this finding relates to moonlight disrupting sleep, but the study took place in a sleep laboratory where the light and other conditions were tightly controlled. Despite this, the individuals only spent two nights in the sleep laboratory, and the patterns of moonlight they experienced in the weeks and months running up to the sleep laboratory could still be having an effect on their body’s sleep rhythms.

There were other limitations, including:

  • each individual was only assessed on two nights, rather than over a whole moon cycle (about a month)
  • all participants were healthy individuals in two specific age groups, and results may not be representative of less healthy individuals or individuals of different ages

Of course, some results in trials just happen by chance, but results like this do start people thinking of what might be causing an effect if it is true. Ideally, to confirm their findings, researchers need follow up a larger group of individuals of varying ages over a longer period to rule out a chance finding.

Even if the moon does have an adverse effect on sleep quality, the results presented in this study were relatively modest, such as taking five minutes more to fall asleep and sleeping for an average of 20 minutes less than normal around the full moon. Whether these differences have an effect on daytime functioning was not assessed

Read more about self-help techniques you can use to improve the quality of your sleep. 

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