SEATTLE, Wash. — Does it feel like strange things always happen when there’s a full moon? You may be right, but the reason isn’t in the stars, it may be in your bedroom. A new study finds the moon cycles can have a major impact of human sleep patterns.
Researchers from the United States and Argentina say people go to bed later and sleep less on nights before a full moon. For centuries, people have blamed the moon for accidents, natural disasters, and even their moods. When it comes to people at least, the study suggests being cranky during a full moon may have more to do with how much rest someone is getting.
Study authors from the University of Washington discovered that sleep cycles in people oscillate during the 29.5-day lunar cycle. In the days leading up to a full moon, people generally go to bed later at night and then sleep for fewer hours.
Professor of biology Horacio de la Iglesia observed the changes in both bedtimes and the duration of sleep in urban and rural settings; from Indigenous communities in northern Argentina to college students living in Seattle. The major U.S. city in the Pacific Northwest has a population of more than 700,000.
No matter where you live, the moon affects you
Study authors discovered that the moon phases caused oscillations regardless of an individual’s access to electricity. The variations are less pronounced, however, in individuals living in urban environments like a busy city. The research team adds that the increase in the patterns may indicate that human circadian rhythms are somehow synchronized with the phases of the lunar cycle.
“We see a clear lunar modulation of sleep, with sleep decreasing and a later onset of sleep in the days preceding a full moon,” Prof. de la Iglesia says in a university release. “And although 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.”
Using wrist monitors, the team examined the sleep patterns of 98 people living in three Toba-Qom Indigenous communities in the Argentine province of Formosa.
One of the communities did not have electricity, while another only had limited access to electricity – such as a single light fixture in the house. Unlike those rural areas, the third community was located in an urban setting with full access to electricity.
Previous studies by Prof. de la Iglesia’s team and other groups revealed access to electricity can have an impact on sleep. Those results appeared again in this study, as Toba-Qom in the urban community went to bed later and slept less than rural participants.
However, residents in all three communities also showed the same sleep changes when the moon completed its monthly cycle. Depending on the location, the total amount of sleep varied throughout the lunar cycle by between 46 and 58 minutes. In addition, bedtimes changed by around a half-hour.
Feeling the full moon a week early
Researchers say the impact of a full moon starts to take hold nearly a week in advance. In all three communities, people started going to bed later and having the shortest amount of sleep three to five days before a full moon.
When they uncovered this pattern in Toba-Qom participants, study authors analyzed sleep-monitor data from 464 college students in the Seattle area. These students had been part of separate study however, their results revealed the same oscillations.
Researchers confirmed that the evenings leading up to a full moon provide more natural light after dusk than the rest of the month. The waxing moon grows increasingly brighter as it reaches its peak each month; generally rising in the late afternoon or early evening. This places it high in the sky during the evening after sunset.
Following a full moon, the waning moons also give off significant light, but in the middle of the night. This is because the moon rises so late in the evening during those points in the lunar cycle.
“We hypothesize that the patterns we observed are an innate adaptation that allowed our ancestors to take advantage of this natural source of evening light that occurred at a specific time during the lunar cycle,” says study lead author Leandro Casiraghi from the University of Washington.
Moonlight’s connection to your own lights
Prof. de la Iglesia believes that the lunar effects may also explain why access to electricity causes such pronounced changes to human sleep patterns.
“In general, artificial light disrupts our innate circadian clocks in specific ways: It makes us go to sleep later in the evening; it makes us sleep less,” the professor explains. “But generally we don’t use artificial light to ‘advance’ the morning, at least not willingly. Those are the same patterns we observed here with the phases of the moon.”
“At certain times of the month, the moon is a significant source of light in the evenings, and that would have been clearly evident to our ancestors thousands of years ago,” Casiraghi adds.
“In general, there has been a lot of suspicion on the idea that the phases of the moon could affect a behavior such as sleep – even though in urban settings with high amounts of light pollution, you may not know what the moon phase is unless you go outside or look out the window. Future research should focus on how: is it acting through our innate circadian clock? Or other signals that affect the timing of sleep? There is a lot to understand about this effect.”
The findings appear in the journal Science Advances.
SWNS writer Stephen Beech contributed to this report.