The reasons for poor sleep can be multiple. Let's mention the lack of physical activity, the influence of screens, stress... but also the Moon! We would indeed tend to go to bed later and sleep less in the days preceding the full moon. In any case, this is what a new study finds.
As part of a study published in Science Advances, a team from the Universities of Washington and Yale (USA), in collaboration with the National University of Quilmes ( Argentina), sought to determine how and to what extent sleep cycles can evolve with the lunar cycle.
Using sleep monitoring devices (to be attached to the wrist), researchers studied the sleep habits of 98 people living in three Aboriginal communities Toba-Qom in Formosa, Argentina and 464 Seattle-area students . They opted for these two samples for the difference in their environment. Concretely, indigenous peoples have less access to artificial light (electricity), but more to natural light (Moon) and vice versa for Seattle students.
The researchers then found that the connection between sleep cycles and lunar cycles was indeed present in communities without access to electricity. However, even more surprisingly, it was also marked in areas with electricity.
In both groups, the monitoring devices indeed showed that the nights before the full moon were those when people went to bed the latest and slept the least. It also found that these nights showed more light in the night sky after dusk as the waxing moon grew brighter.
To explain these findings, the authors evoke a possible adaptation allowing our ancestors to benefit from this natural source of night light produced at a specific moment in the lunar cycle. This could have facilitated hunting, fishing and social activities.
While the timing and duration of sleep have continually evolved over the course of our evolution, researchers believe that nomadic groups typically fell asleep after dusk, so that the environment was becoming too dark to continue the activities started during the day. However, moonlight can be so bright to the human eye that it is entirely reasonable to imagine that this nighttime light source may also have played a role in modulating our sleep.
On the other hand, the fact that this connection was less marked among Seattle students could be explained by the social obligations that disrupt the sleep cycle.