A full moon can make a good night’s sleep difficult, say scientists.
Researchers found that volunteers took longer to get to sleep and suffered from poorer quality sleep, when the moon was at its fullest, despite being shut in a darkened room.
Scientific publication, Current Biology, reported that in the study of 33 volunteers, there was also a dip in levels melatonin, a hormone that is linked to natural-body clock cycles.
Being exposed to bright lights in the evening or too little light during the day can disrupt the body's normal melatonin cycles.
But the boffins at Basel University in Switzerland, suggests the moon's effects may be unrelated to its brightness.
Around the full moon, brain activity related to deep sleep dropped by nearly a third. Melatonin levels also dipped.
The volunteers also took five minutes longer to fall asleep and slept for 20 minutes less when there was a full moon.
Prof Christian Cajochen, who is leading the study said: "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."
UK sleep expert Dr Neil Stanley said the small study appeared to have significant findings.
He said: “It's one of these folk things that you would suspect has a germ of truth.
"It's up to science now to find out what's the cause of why we might sleep differently when there's a full moon."