Struggling to sleep? The phase of the moon may be to blame, study finds

The study – which was carried out by scientists from the University of Washington, Yale, and the National University of Quilmes in Argentina – says that in the days leading up to a full moon, people tend to get to sleep later and sleep for shorter periods.

Researchers used wrist monitors to track the sleep patterns of 98 participants living in three Toba-Qom indigenous communities in the province of Formosa, Argentina.

Each community differed in the amount of access it had to electricity during the study, with one rural area having no access at all, another rural group having limited access, and a community in an urban environment, which had full access.

For nearly three-quarters of the Toba/Qom participants, researchers collected sleep data for one to two whole lunar cycles.

Toba/Qom in the urban community went to bed later and slept less than rural participants with limited or no access to electricity.

But study participants in all three communities also showed the same sleep oscillations as the moon progressed through its 29.5-day cycle.

Depending on the community, the total amount of sleep varied across the lunar cycle by an average of 46 to 58 minutes, and bedtimes seesawed by around 30 minutes.

For all three communities, on average, people had the latest bedtimes and the shortest amount of sleep in the nights three to five days leading up to a full moon.

When they discovered this pattern among the Toba/Qom participants, the researchers analyzed sleep-monitor data from 464 Seattle-area college students that had been collected for a separate study. They found the same oscillations.

“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,” said first author Dr. Leandro Casiraghi, a postdoctoral researcher in the Department of Biology at the University of Washington, Seattle.

The team also found a second, semilunar oscillation of sleep patterns in the Toba/Qom communities, which seemed to modulate the main lunar rhythm with a 15-day cycle around the new and full moon phases.

This semilunar effect was smaller and only noticeable in the two rural communities.

“Future studies would have to confirm this semilunar effect, which may suggest that these lunar rhythms are due to effects other than from light, such as the moon’s maximal gravitational tug on the Earth at the new and full moons,” Dr. Casiraghi said.