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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 just 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 waxing and waning Moon – and this changing radiation energizes us in ways we are not fully aware of. conscious, suggests new research.
“Moonlight is so bright to the human eye that it is quite reasonable to imagine that in the absence of other light sources, this nocturnal light source could have played a role in the modulation. of human nocturnal activity and sleep, ”a team of researchers, led by senior author and neurobiologist Horacio de la Iglesia at the University of Washington, explains in a new study.
“However, the question of whether the lunar cycle can modulate human nighttime activity and sleep remains a subject of controversy.”
To investigate the mystery, the researchers fitted more than 500 participants with wrist-based activity monitors to track their sleep patterns, and conducted the experiment in very different locations.
First, they involved 98 participants from the Toba-Qom people, an indigenous community living in the province of Formosa in Argentina. Some of these rural participants in the experiment did not have access to electricity, others had limited access at home, while a final contingent lived in an urban setting with full access to electricity.
In a separate experiment, researchers tracked the sleep of 464 college students living in the Seattle area – a major, modernized city with all of the electrified attributes of post-industrial society.
By tracking participants’ sleep activity during the lunar month cycle, the researchers found that the same type of pattern could be observed in their sleep and awakening, regardless of where the volunteers lived.
“We are seeing a clear lunar modulation of sleep, with decreased sleep and later sleep in the days leading up to the full moon,” says de la Iglesia.
“While the effect is more robust in communities without access to electricity, the effect is present in communities with electricity, including undergraduates at the University of Washington.”
While there was some variance between the results, in general, the data showed that sleep tends to start later and lasts overall less on the nights leading up to a full moon, when the moonlight provided by the waxing moon is brighter in the hours after dusk.
While 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 separate populations living in separate countries, and with such varying levels of access the electricity between all the volunteers, tells us important things, the team says.
“Taken together, these results strongly suggest that human sleep is synchronized with lunar phases regardless of ethnicity and socio-cultural background and level of urbanization,” the researchers write in their paper.
As to what gives rise to these effects, the researchers say the prolonged nighttime activity stimulated by moonlight could be an evolutionary adaptation carried over from the days of pre-industrial human societies – with the ability to stand and do more. under a bright full moon. benefiting from all kinds of traditional customs that people still enjoy today without electricity.
“At certain times of the month, the Moon is an important source of light in the evening, and this would have been clearly evident to our ancestors thousands of years ago,” says leading author and sleep biologist Leandro Casiraghi.
According to interviews with Toba / Qom individuals, moonlit nights are always known for their intense hunting and fishing activity, increased social events and intensified sexual relations between men and women.
“Although the true fitness of human activity during full moon nights remains to be determined, our data seems to show that humans – in a variety of environments – are more active and sleep less when moonlight is available. in the early hours of the night, “explain the researchers.
“This discovery, in turn, suggests that the effect of electric light on modern humans may have exploited an ancestral regulating role of moonlight on sleep.”
The results are reported in Scientific advances.
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