In modern times, much research has focused on how artificial light sources interfere with our sleep and health, due to the unnatural effects of lighting after sunset.
But how unnatural is night light anyway? After all, humans have always been exposed to varying levels of light at night, due to the reflections of sunlight from the rising and falling moon – and this changing brightness stimulates us in ways we are not fully aware of, we suggest. research.
“Moonlight is so bright to the human eye that it is completely reasonable to imagine that, in the absence of other light sources, this night light source could have played a role in modulating nocturnal activity and human sleep,” said a team of researchers. , led by lead author and neurobiologist Horacio de la Iglesia of the University of Washington, explains in a new study.
“However, whether the moon’s cycle can modulate nocturnal activity and human sleep remains a matter of controversy.”
To investigate the mystery, the researchers equipped more than 500 participants with activity monitors on the wrist to track their sleep patterns and performed the experiment in very different locations.
First, they involved 98 participants from the Toba-Qom people, an indigenous community living in the Argentine province of Formosa. Some of these rural participants in the experiment did not have access to electricity, others had limited access to their homes, while a final contingent lived in an urban setting with full access to electricity.
In a separate experiment, the researchers looked at the sleep of 464 students living in the Seattle area – a major, modernized city with all the electrified traps of post-industrial society.
By monitoring participants’ sleep activity during the monthly cycle, the researchers found that the same type of pattern could be seen in sleep and wakefulness, regardless of where the volunteers lived.
“We see a clear monthly modulation of sleep, with sleep decreasing and a subsequent onset of sleep in the days leading up to the full moon,” says de la Iglesia.
“Although the effect is more robust in communities without access to electricity, the effect is present in communities with electricity, including students at the University of Washington.”
Although there was some difference between the results, in general, the data showed that sleep tends to start later and generally lasts a shorter period of time on nights leading up to a full moon, when the moonlight provided by the moon which is exceeded is brighter in the hours after dusk.
Although the sample size studied here is not particularly large – and there is certainly more research that could be done here to extend these results – the same pattern was observed in two distinct populations living in separate countries with such varying levels. access to electricity among all volunteers, tells us some important things, says the team.
“Together, these results strongly suggest that human sleep is synchronized with the monthly phases, regardless of ethnic and sociocultural background and level of urbanization,” the researchers write in their paper.
In terms of what gives rise to these effects, the researchers argue that the extensive nocturnal activity stimulated by moonlight could be an evolutionary adaptation taken from the time of pre-industrial human societies – with the ability to stay high and do more than a month full of brilliance benefiting from all kinds of traditional customs enjoyed even today by peoples without electricity.
“At certain times of the month, the Moon is a significant source of light in the evening and this would have been obvious to our ancestors thousands of years ago,” says the first author and sleep biologist, Leandro Casiraghi.
According to interviews with Toba / Qom individuals, moonlit nights are still known for high hunting and fishing, enhanced social events and enhanced sex between men and women.
“Although the true adaptive value of human activity during moonlit nights remains to be determined, our data seem to show that people – in a variety of environments – are more active and sleep less when moonlight is available in the early hours of the day. at night ”. the researchers explain.
“This finding, in turn, suggests that the effect of electric light on modern humans could have achieved an ancestral role in regulating moonlight on sleep.”
The findings are reported in Scientific advances.