On average, participants went to bed 30 minutes later and slept 50 minutes less on nights before a full moon, said study coauthor Horacio de la Iglesia, professor at the department of biology at the University of Washington in Seattle.
Researchers outfitted each participant with a sleep monitor on their wrist to track sleep schedules over the course of one to two lunar cycles. A lunar cycle takes 29.5 days to complete.
Ninety-eight people from three different Toba Indigenous communities, also known as the Qom people, in Argentina participated in the study.
The light from the moon after sunset is bright on the days leading up to a full moon, said study coauthor Leandro Casiraghi, postdoctoral scholar at the department of biology at the University of Washington.
“We believe this modulation aims to take advantage of such moonlit nights which may be good for safe outdoor activities such as hunting or fishing, or for engaging in social interactions with other groups,” Casiraghi said via email.
One community had no access to electricity, one had some access to electricity, and one had full access to electricity. Regardless of their electricity access, there was a strong pattern that showed they all went to bed later and slept less in the days leading up to a full moon.
In the urban community, participants went to bed even later and slept less than the participants in rural communities. Casiraghi said he was surprised that the urban community was affected because he hypothesized only people in the rural communities would be affected by the lunar phases.
“The fact that this modulation was present even in communities with full access to electric light suggests that these effects are mediated by something other than moonlight itself,” Casiraghi said.
After collecting sleep data from Toba/Qom communities, researchers compared their results with sleep data that was collected from 464 Seattle students for another study and found the same sleeping pattern.
People’s biology and a community’s social patterns might also play a role in the sleep cycle found in this study, said Dr. Vsevolod “Seva” Polotsky, director of Sleep Basic Research and a professor at Johns Hopkins Medical School, who was not involved in the study.
People’s sleep is controlled by our circadian rhythm, an internal clock that regulates sleep for about a 24-hour period, but some people could have longer internal clocks, Polotsky said.
A prime example of the human body regulating itself over a longer period of time is a woman’s menstrual cycle, he said, which is roughly a month long. Other mammals have seasonal sleep schedules and hibernate for months at a time, Polotsky noted.
Social calendars might also affect someone’s sleep schedules, he said, such as going to bed later or sleeping longer on weekends.
For people who have trouble going to sleep, de la Iglesia recommended avoiding bright lights and screens during the evening hours and being especially proactive before a full…