Before the availability of artificial light, moonlight was the only source to stimulate nocturnal activity, and for many centuries people believed that this celestial body had a direct effect on human behavior, and the Greek philosopher Aristotle believed that the moon causes insanity and epilepsy.
In the modern era, scientists tried to search for scientific evidence proving that there are direct effects of the moon on human behavior, but the evidence for adjusting sleep timing according to the lunar phases was varied and controversial.
But according to a scientific study published in the journal Science Advances on January 7, researchers have proven that our ability to sleep is clearly affected by the lunar cycle, even when taking industrial sources of light into account.
The same pattern
There is some recent scientific evidence that indicates that the moon affects the sleep pattern of some people, by varying the days of the lunar cycle or the lunar phase, and according to the amount of light that changes throughout the month, as the moon becomes full every 29.5 days and a new crescent appears 14.8 days after Its completion.
In the new study, the researchers used wrist monitors to measure wrist activity, and to track the sleep patterns of individuals living in 3 different and diverse societies, the first being rural without electricity, and the second being rural with limited electricity, in Tuba / Qom communities where one of the largest population groups lives. The indigenous people are in Argentina, and the third is an urban environment that has integrated electricity in the United States.
Study participants in the three societies showed the same pattern of sleep oscillations as the moon advanced through a 29.5-day cycle, with sleep duration changing between 20 and more than 90 minutes, and sleep times varying from 30 to 80 minutes.
The researchers found that all study participants delayed sleep from 3 to 5 days before the full moon, and the opposite happened in the nights before the new moon appeared.
An analysis of the data showed that sleep starts later and is shorter on the nights leading up to a full moon when moonlight is available during the hours after dusk.
The data indicate that moonlight is likely to stimulate nocturnal activity and dampen sleep in pre-industrial rural communities, and the results showed that the “effect of the lunar phase” on sleep appears stronger the more access to electricity is limited.
Horacio de la Iglesia, study author and professor of biology at the University of Washington, said in a university press release that the data was somewhat surprising, because the initial prediction was lack of sleep and increased activity on full moon nights. But it turns out that the nights before a full moon are the nights when most of the moon’s light is during the first half of the night.
The researchers compared their results with data collected from 464 students studying at the University of Washington, in Seattle, Washington, and found the same fluctuations in sleep patterns.
Synchronization with the phases of the moon
The researchers write in their paper that these results “strongly indicate that a person’s sleep coincides with the phases of the moon regardless of ethnic, social, cultural and level of urbanization background.”
De la Iglesia added, “We humans tend to think that we have somehow managed to control nature, and the use of artificial light is a great example of this, but it turns out that there are some forces of nature that we cannot dismiss.”
Regarding what leads to these effects, the researchers assert that the extended nocturnal activity stimulated by moonlight could be an evolutionary adaptation carried over from the era of pre-industrial human societies, with the ability to stay awake and do more under the bright full moon.
According to interviews with Tuba / Qom individuals, moonlit nights are still known with activity of hunting and fishing, increased social events, and increased sexual relationships between men and women.
“At certain times of the month, the moon is an important source of light in the evening, and that could have been evident to our ancestors thousands of years ago,” says first author Leandro Casiraghi, a sleep biologist in the Department of Biology at the University of Washington.