Human sleep sensitive to moon cycle

25 July 2013
Posted by Chris Smith.

True to their Swiss reputation for crafting exquisite timepieces, scientists in Basel have shown that the lunar calendar significantly affects human sleep patterns.

The Moon has been held in high regard by different cultures across many millenia, but despite other organisms displaying lunar-influenced behaviours, evidence of a moon-impact on the physiology of healthy humans has been lacking.

Now, Basel University reseacher Christian Cajochen and his colleagues have shown a profound relationship between the phase of the Moon and how long, and how well, subjects sleep.

A drink in a local bar on a night when there was also a full moon gave the researchers the idea, they say in their Current Biology paper, of retrospectively re-analysing data collected over 10 years ago from 33 men and women who had participated in a sleep study designed to answer a question about sleep deprivation.

In this original work, brain activity, various measures of sleep quality as well as blood hormone levels had been recorded while the participants spent several nights sleeping in a laboratory under strictly-controlled conditions. This included removing access to time cues and external light stimuli.

The team plotted when the data had been collected from each of the subjects onto a lunar calendar.

Around the time of the full moon, they found, brain-wave activity corresponding to deep sleep was 30% lower, subjects took 5 minutes longer on average to nod off at night, each subject took about 20 minutes less sleep in total and the sleep hormone melatonin was significantly lower.

These changes also coincided with subjective reports from the volunteers of lower quality sleep at this time.

It's not clear how, or why, these effects are manifest, but the researchers speculate that they might reflect the existence in the brain of an underlying "circalunar clock" which ticks at the same rate as the roughly 30 day moon cycle.

Evidence for such a clock has been uncovered in other animals including a species of Galapagos marine iguanas that keep track of tides to optimally time their feeding forays. Also, some cases of human epilepsy have shown peak rates of seizures following a full moon.

These lunar cycles "are mysterious," the Swiss team say, pointing out that the challenge now is to unravel the neurological clockwork that underpins these effects...

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