Sleep duration and sleep quality among men is less than among women in the days before the full moon. A researcher says that there could be many reasons for this, but no firm conclusions can be drawn.
Many people probably agree that they sleep worse during a full moon than at other phases of the 30-day lunar cycle.
For centuries, scientists and laypeople have been fascinated by whether the moon might affect our sleep, and now a new study shows that this may be true.
Researchers examined the duration and quality of sleep from the day after the new moon until the day of the full moon (the waxing period) and from the day after the full moon until the day of the new moon (the waning period). The results show – perhaps surprisingly for many – that the lunar cycle actually appears to affect men more strongly than women.
The results have been published in Science of the Total Environment.
“Many factors affect sleep, including age, sex, illness, children, family status, exercise, medication and the environment. Based on this study, we can also say that the lunar cycle affects the duration and quality of sleep and that this effect is more pronounced among men,” explains a researcher behind the study, Christian Benedict, Associate Professor and Principal Investigator, Department of Neuroscience, Uppsala University, Sweden.
Investigated two lunar periods
Christian Benedict and colleagues did not examine whether people slept better or worse during a full moon. Instead, they investigated any differences in sleep quality between the waxing and waning periods in the lunar cycle.
Christian Benedict explains that examining these two periods might be interesting because even though the light intensity is the same on equivalent days of the waxing and waning periods, the illumination occurs at different times of the night.
Illumination during the waxing period shifts to later hours of the day and early night hours. Conversely, during the waning period, illumination shifts from early night-time to daytime hours.
“If we assume that changes in sleep quality may be associated with this illumination, the effect might depend on the time of day or night a person is exposed to the light,” says Christian Benedict.
Examined very comprehensive data
To illuminate this matter, Christian Benedict studied very detailed sleep measurements a colleague recorded from 2001 to 2019.
Some sleep researchers use wrist accelerometry to measure people’s activity during sleep, but this study measured sleep much more comprehensively by using polysomnography electrodes attached to the head and face of the participants.
The data were obtained in connection with research to map sleep apnoea. The 850 participants were 20–80 years old, with slightly more men than women.
“These comprehensive data also provided knowledge on the participants’ sleep apnoea, which may affect sleep quality. We can thus screen the data for this factor and obtain an even stronger result,” explains Christian Benedict.
Men sleep less well than women
The duration and quality of sleep differed between the waxing and waning periods, and the lunar cycle is associated much more strongly with these differences among men.
- Men were awake 20 minutes longer at night during the moon’s waxing period than during the waning period. Women did not differ.
- Men’s sleep efficiency was 3.5% lower during the waxing period.
- Women slept 12 minutes less during the waning period versus 21 minutes for men.
“It is also interesting that these data were collected in connection with research which the participants did not know would be used many years later to investigate how the quality of sleep is associated with the lunar cycle. This could otherwise have affected the outcome, but it did not,” says Christian Benedict.
Many possible explanations
According to Christian Benedict, the facts that the two lunar phases can affect sleep differently and that the effects may differ between men and women may be explained in several ways.
- Some studies have shown that light affects men’s brains and circadian rhythm more strongly than those of women. The intensity of lunar illumination at different times of the night may therefore affect men more than women.
- Another possibility is that hormones play a role. Some studies have shown that blood concentrations of melatonin and testosterone are lower in the days before a full moon. This effect may be more pronounced for testosterone among men than among women, since men have higher concentrations of testosterone in the body.
- A third possibility is that the moon’s gravity can affect our sleep differentially up to and after a full moon. In the waxing period, the moon’s gravitational pull is greater earlier in the day than in the waning period. Nevertheless, other scientists have compared the moon’s gravitational pull on a human as being equivalent to a fly landing on a person’s arm.
- A fourth possibility is that the moon affects the Earth’s geomagnetic field, and studies have shown that geomagnetic activity can influence how much melatonin people produce. Again, it depends on when this effect occurs during the night.
- Finally, completely different effects may be involved, such as domestic, farm or wild animals reacting to light in the evening and in the morning. This can affect sleep in some locations if animals make more noise or wake up earlier.
“All these possibilities are speculative and none may be correct. But at least the lunar cycle seems to affect sleep, and this effect appears to be more pronounced among men. However, this does not necessarily mean that the lunar cycle is the main cause of the association,” concludes Christian Benedict.