Tomorrow is Halloween, which leads to thoughts of ghosts, witches, vampires and scary pumpkin faces. But year round, many people believe a full moon is linked with other spooky stuff. Crime rates, psychiatric hospital admissions, emergency room visits, dog bites, sporting injuries and hyperactivity in kids are all said to increase during a full moon. Is there any truth to the rumours?

Do strange things happen when there’s a full moon? Image by cocoparisienne from Pixabay

Bad moon rising

Also known as the Transylvania Effect, the idea that people behave erratically during a full moon is not a new one. Aristotle and Pliny the Elder both suggested that because the human brain is so moist, it responds to the same pull of the moon that drives our tides (which we now know not to be true). In psychiatrist Arnold Lieber’s 1978 bestseller, How the Moon Affects You, he also argued that because our bodies are mostly water, the moon has a strong influence on us. How strong an influence? The story goes that in 19th Century England, lawyers could invoke the defence ‘not guilty by reason of the full moon’. I doubt any lawyers argued their clients had metamorphosed into drooling werewolves, but the argument is clear: under a full moon, people are no longer in control of their behaviour. And we can thank the Roman goddess of the moon, Luna, for the words lunatic and lunacy.

Sounds far-fetched, doesn’t it? But belief in the Transylvania Effect is alive and well. One survey found 43% of US college students believed people were more likely to behave strangely on a full moon night. The same study found mental health professionals were more likely to believe this than people working in other areas. In another survey, 80% of emergency department nurses and 64% of emergency department doctors believed the moon affected behaviour. Ninety-two percent of the nurses said they found working on the night of a full moon was more stressful, and they should be paid more for working those shifts.

The moon made me do it

In 2007, police in the UK employed more staff to be on patrol on full moon nights claiming ‘Research carried out by us has shown a correlation between violent incidents and full moons’. There are thousands of published research papers exploring the link between the phase of the moon and a huge variety of events and behaviours. The most striking thing about all this research is the almost complete lack of evidence for the moon having any effect on us.

Despite the fact many people believe the time of the full moon is the worst for undergoing surgery, there is no evidence a full moon affects the outcomes of heart surgery, the rate of surgical complications, levels of post-operation nausea and vomiting or post-operative pain. Professional soccer players are no more likely to be injured when playing or training during a full moon. There is no evidence for increased crisis centre calls during full moons and no link between moon phase and frequency of epileptic seizures. Research shows no increase in emergency department admissions or calls for ambulances during a full moon, nor do more people see doctors for anxiety or depression. There is also no relationship between moon phase and birth rates.

Research has found no link between the phase of the moon and psychiatric hospital admissions. A full moon doesn’t lead to increased violence in psychiatric settings, nor is there evidence for a link between moon phase and suicides or suicide attempts. No link has been found between full moons and traffic accidents, and dog bites requiring hospitalisation occur no more often during a full moon than at any other time. Kids aren’t more hyperactive at the full moon, and there are no more murders or other crimes when the moon is full.

The full (moon) truth

If nothing else, research over the past 50 years has provided us with a detailed list of all the human behaviours not influenced by the phase of the moon. Given the lack of evidence, why does the myth persist? It may simply be the result of illusory correlation – if something unusual happens on the night of a full moon, we are more likely to take note and remember it than when nothing unusual happens under a full moon. Confirmation bias probably also plays a role: if you already believe in the Transylvania Effect, you’ll pay particular attention to any information that supports your belief.

But there’s another intriguing possibility. We have some evidence people sleep a little less on full moon nights. One study found people slept an average of 19 minutes less during a full moon; another study recorded a decrease of 25 minutes of sleep on these nights. Study volunteers took longer to fall asleep and slept less deeply at the time of the full moon, even when they couldn’t see the moon and didn’t know the moon was full. They also complained of feeling less rested on waking after a full moon.  A 2-year study of nearly 6000 children living on five continents found kids also slept a little less on nights with a full moon.

Perhaps this is the source of the myth. In times gone by, before our body clocks were under the influence of electric lights and screen time, a full moon may have been very disruptive to sleep. Researchers have suggested the Transylvania Effect may have its root in the fact someone suffering bipolar or a seizure disorder may be highly susceptible to mania at times of sleep deprivation.

Seems plausible but fortunately I don’t think we’ll be hearing the defence ‘not guilty by reason of not having had quite enough sleep last night’ anytime soon.

Links and stuff

• Monday’s medical myth – hospitals get busier on full moons
• Why do we still believe in ‘Lunacy’ during a full moon?
• The Economist: Sleep and the phases of the moon