The full moon drives people crazy: True/False?

Many people, even some working at the coal face of mental health, believe that we behave less rationally around the time of the full moon. But it turns out that they are the ones not thinking straight. The moon may lie at the root of the word lunatic, but that is as far as the association goes.

Our bodies and minds do have both daily and yearly cycles which are locked to the passage of the sun through the sky and the earth around the sun. Many animals do have behaviour that is tied to the phases of the moon, like the palolo worms of the tropical Pacific which swarm during the moon’s last quarter in October and November each year.

But we humans don’t have any detectable lunar cycle. It is true that for women the menstrual cycle has about the same length as the lunar cycle, but it isn’t very exact and every woman’s cycle starts at a different time. Women don’t all get their periods in lock-step with the moon (a blessing for which we should probably all give quiet thanks).

Over the years people have linked many disorders of body and mind to the moon, from suicide to heart attacks. On closer investigation, though, these have all turned out to be what statisticians, bless their cold, numerical hearts, call Type I errors. False positives to you and me.

The myth of mental problems around the full moon probably arises from selective memory coupled with the human fondness for seeing patterns where there are none. It is perhaps possible that in the dim dark past, before artificial light was freely available, that the full moon led to disrupted sleep. Disrupted sleep in turn is known to induce mania in people with bipolar disorder and increase the likelihood of seizures in some epileptics. So maybe it was true in the past. These days, when opportunities for sleep deprivation are available all month long, the moon has lost its power over us.

In short, unless you’re a werewolf, the full moon won’t change your behaviour at all.

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