IT SOUNDS like an idea dreamed up over a few beers in the pub one evening. And that, those involved freely admi...

IT SOUNDS like an idea dreamed up over a few beers in the pub one evening. And that, those involved freely admit, is exactly what it was. As Christian Cajochen and his colleagues put it in their paper on the matter in Current Biology, _We just thought of it after a drink in a local bar one evening at full Moon._

_It_ was a way of testing the persistent but unproven idea that the full Moon affects human behaviour, generally for the worse. In prescientific days this was expressed in terms like _moonstruck_ and _lunatic_. And it found even more sinister manifestation in the form of the lycanthrope, who did not sleep when the Moon was full, but turned into a wolf instead. Though few now believe in werewolves some modern thinkers still suspect the Moon_s phase affects sleep patterns_and on that particular moonlit night Dr Cajochen and his buddies realised they already had the data needed to find out.

Those data came from a study on body clocks and sleep patterns they had conducted a decade earlier at the Centre for Chronobiology at the University of Basel, where they work. Between 2000 and 2003 they had looked at the effect of the daily body clock on the sleep patterns of 33 volunteers. The protocol they had used was perfect. Volunteers were shut away from daylight (and therefore also from moonlight) for days at a time, so their sleep patterns could not be affected by the illumination a full Moon brings. And it was also the ultimate in double-blind experiments. Neither the participants nor the organisers could possibly have been biased by knowing the experiment was intended to look at the effect of the full Moon, since at the time it was conducted it wasn_t.

A few days_ number-crunching gave Dr Cajochen and his team what they were looking for. And the answer was _yes_, the phase of the Moon does affect human sleep patterns, even when the human involved cannot possibly see the Moon. Electroencephalography showed that the volunteers slept, on average, 20 minutes less around the time of the full Moon. It also took them five minutes longer to get to sleep, their delta activity (a measure of how deeply they were sleeping) was 30% lower than at other times, their level of melatonin, a sleep-related hormone, was reduced, and they reported, subjectively, that they had not slept as well as usual. Nor was any of this connected, in female volunteers, with their menstrual cycles.

Lest any astrologer reading this result get cocky, Dr Cajochen does not believe that what he has found is directly influenced by the Moon through, say, some tidal effect. What he thinks he has discovered is an additional hand on the body_s clock-face. Besides the well-known endogenous daily cycle which the experiment originally studied, there is also an endogenous monthly cycle entrained to the Moon (as the daily one is to the sun) by unconscious observation over a long period of the light from the heavenly bodies concerned.

Lunar cycles exist in other species so this is not, as it were, a lunatic idea. But those species that have been studied are animals like marine iguanas, for whom knowing the tides is important. What use an ingrained lunar calendar is (or once was) to a human being remains to be determined. Perhaps sleeping lightly on moonlit nights was a defence mechanism against predators. Wolves, for example.

The Economist

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