Does the phase of the Moon affect human sleep patterns?

Question

From The Economist - "Lunacy? People do not sleep easy on nights when there is a full Moon":

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.

The referenced study doesn't meet my needs because I don't believe the data supports the conclusion attributed to it by the Economist.

Is it true that the phase of the Moon affects human sleep patterns?

Answer 1

There are several very good reasons to doubt the results in the study you quoted.

First: It is a very small study. Only about 30 people took part, two nights per person. So the result was evaluated from only 64 datapoints. Even if the participants could not see the moon during the night, the author of the study himself says, he cannot be sure that they had not known about the fact, that the moon was full. Such knowledge can influence the result, when only one or two of the participants were expecting to sleep not very well, because they believe in these myths.

Second: There exist much larger studies in the same manner, that do not find any effects at all. As these studies are statistically much more significant, this is a very stron argument against the small study of Cajochen. There is for example the study of Klösch and Zeitlhofer evaluating more than 5000 nights (between 1997 and 2002) of about 400 participants. Not the least lunar effect was found in these data. It is highly unrealistic to assume, that the small study of Cajochen found an effect, that would not also have been significant in the larger study as larger studies have much better statistics than small ones.

Third: The result of the Cajochen study is by no means, what myths tell us about sleepless nights at full moon. Hey, the participants slept 5 minutes less. Who would even notice that in real life? Even if you believe the study has measured a real effect (what we can savely doubt, see above), your sleep quality is still much more depending on other effects. When you are troubled, this may keep you awake for much more than 5 minutes.