Full Moon Bad Sleep Link Revealed

The moon has been blamed for many things - triggering aggression, violence and suicide - but now there's a new charge to lay at its door: bad sleep.

Unlike the other conditions however, there is scientific evidence that the lunar cycle really does influence sleep.

Just as the myth says, when the full moon is high it is harder to slumber soundly, a study has shown. But the bad night has nothing to do with the moon's eerie glow, or its gravitational influence.

Rather, scientists believe an internal clock that follows the cycles of the moon may be hardwired into our genes.

It ticks away even on the darkest of cloudy nights, when the moon cannot be seen.

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"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 psychiatrist Dr Christian Cajochen, from the University of Basel, Switzerland.

His team studied 33 young and old volunteers whose brain waves, eye movements and hormone secretions were monitored as they slept.

Around the time of the full moon, brain activity related to deep sleep dropped by 30%, the researchers found.

Participants took five minutes longer than normal to fall asleep, and slept for 20 minutes less time on average during the night.

They also showed reduced levels of melatonin, the "body clock" hormone that regulates sleep and wake cycles.

Questioned by the scientists, the volunteers said they felt their sleep was poorer when the moon was full.

The findings are published today in the journal Current Biology.

A biological "circalunar clock" synchronised to the moon phases and tides is the most likely explanation, said the scientists.

Thought to exist in many animals, it is believed to work in conjunction with the light-regulated "circadian clock" that ties many body functions to the constant rhythm of day and night.

Recently, molecular evidence of the "circalunar clock" was discovered in a marine midge.

The lunar clock was also thought to aid the survival of marine iguanas in the Galapagos islands during times of food shortage.

In humans, sensitivity to the phases of the moon may be a relic from the past when it synchronised behaviour for reproductive or other purposes, said the researchers. Today, it's effect was largely masked by electric lighting and other aspects of modern life.

The scientists wrote: "Lunar rhythms are not as evident as circadian rhythms and are thus not easy to document - but they exist.

"Their role is mysterious, and there are probably large individual differences that underlie the contradictory evidence for their existence. Some people may be exquisitely sensitive to moon phase.

"It remains challenging to unravel the neuronal underpinnings of such a putative lunar clock in humans."

They pointed out that although the moon's gravity influenced tides, it had no impact on smaller bodies of water such as lakes and could not explain the sleep effect.

The clock may provide a scientific basis for other beliefs associated with the moon - for instance its influence on mood and mental state.