In the days close to a full moon, people take longer to doze off, sleep less deeply and sleep for a shorter time, even if the moon isn’t shining in their window, a new study has found.

“A lot of people are going to say, ‘Yeah, I knew this already. I never sleep well during a full moon.’ But this is the first data that really confirms it,” says biologist Christian Cajochen of the University of Basel in Switzerland, lead author of the new study. “There had been numerous studies before, but many were very inconclusive.”

Anecdotal evidence has long suggested that people’s sleep patterns and moods are linked to moon cycles. But past studies of lunar effects have been marred by statistical weaknesses, biases or inconsistent methods, Cajochen says.

Between 2000 and 2003, he and his colleagues had collected data on the sleep patterns of 33 healthy volunteers for an unrelated study. Using electroencephalograms, which measure brain activity, they recorded how deep and how long each participant’s nightly sleep was in a controlled, laboratory setting.

Years after the initial experiment, the scientists reexamined the data for correlations with moon cycles. Their findings showed a striking association between poor sleep and lunar cycles.


In the few days before and after a full moon, for example, people took an average of five extra minutes to fall asleep, slept 20 minutes less per night and had 30 percent less deep sleep. Moreover, around the time of the full moon, the volunteers recorded poorer sleep, the scientists reported last week in the journal Current Biology.

“This paper showed that it’s possible to detect a correlation between the human sleep cycle and lunar phases,” said neuroscientist Kristin Tessmar-Raible of the Max F. Perutz Laboratories in Vienna, who was not involved in the new work “And the question now is: What is the mechanism behind this?”

Because the study participants hadn’t been able to see the moon, increased light levels didn’t cause the effect, at least not entirely. More likely, the effect is influenced only slightly by light or other external factors and is maintained internally, Cajochen speculates.

— ScienceNOW, the daily online news service of the journal Science