Can't sleep? Blame it on the Moon! Scientists have found evidence that human sleep patterns are timed to the phases of the Moon, and that people sleep 20 minutes less on average during a full Moon.
Many people complain about poor sleep around the full Moon and the study offers some of the first convincing scientific evidence to suggest that this really is true.
The findings add to evidence that humans - despite the comforts of our civilised world - still respond to the geophysical rhythms of the moon, driven by a circa-lunar clock.
"The lunar cycle seems to influence human sleep, even when one does not 'see' the Moon and is not aware of the actual Moon phase," said Christian Cajochen of the Psychiatric Hospital of the University of Basel.
In the new study, the researchers studied 33 volunteers in two age groups in the lab while they slept. Their brain patterns were monitored while sleeping, along with eye movements and hormone secretions.
The data show that around the full Moon, brain activity related to deep sleep dropped by 30 per cent. People also took five minutes longer to fall asleep, and they slept for twenty minutes less time overall.
Study participants felt as though their sleep was poorer when the Moon was full, and they showed diminished levels of melatonin, a hormone known to regulate sleep and wake cycles.
"This is the first reliable evidence that a lunar rhythm can modulate sleep structure in humans when measured under the highly controlled conditions of a circadian laboratory study protocol without time cues," the researchers said.
Cajochen said that this circalunar rhythm might be a relic from a past in which the Moon could have synchronised human behaviours for reproductive or other purposes, much as it does in other animals.
Today, the Moon's hold over us is usually masked by the influence of electrical lighting and other aspects of modern life, researchers said.
They said it would be interesting to look more deeply into the anatomical location of the circalunar clock and its molecular and neuronal underpinnings. It could turn out that the Moon has power over other aspects of our behaviour as well, such as our cognitive performance and our moods.
The study was published in Current Biology.