According to folklore, the moon influences our sleep. With the first of this summer’s three “supermoons” taking place on Saturday, it would be useful to know whether there is any truth in this belief. The international research community has been divided on this question for a long time, but now the second of two independent, highly controlled studies has found evidence to support the ancient theory.
Led by Michael Smith at the University of Gothenburg in Sweden, the laboratory-based study saw its participants wake up more often and sleep 25 minutes less during the full moon than during the other moon phases.
“The rooms in our sleep laboratories do not have any windows,” Smith clarifies. “So the effect we found cannot be attributable to increased nocturnal light during a full moon.”
The 25-minute difference in overall time spent asleep is almost identical to the findings made in a similar Swiss study last year. Broken down by gender, the data shows that the men in Smith’s study were most affected by the full moon, sleeping on average 51 minutes less than the women during this part of the lunar cycle.
Brain scans of both the male and the female participants revealed an increased susceptibility to external disturbances when the moon was full, leading the researchers to attribute the changes in sleep pattern to this enhanced responsiveness.
“The purpose of our original study was to examine the way that noise disturbs sleep,” Smith explains. “Re-analysis of our data showed that sensitivity, measured as reactivity of the cerebral cortex, is greatest during the full moon.”
Researchers from the Max Planck Institute have also responded to the increased interest in lunar effects on sleep by re-analysing the data from three large groups of test subjects, including the Swiss study mentioned earlier. They found no evidence for an influence of lunar phase on any sleep parameters, and suggest that the conflicting results seen in the academic press could be down to the tendency to leave null results unpublished, known as “the file drawer problem”.
Smith and his team are aware of these issues, but are not prepared to dismiss the results of their study. They believe there could be a strong underlying explanation for a connection between the moon’s cycle and our night’s sleep, as an increased alertness during a full moon could have been beneficial in our species’ past. Predators with limited nocturnal vision make use of the opportunity created by the light of the full moon to extend their time on the prowl, so a heightened vigilance during these times protects anyone who is at risk of becoming their prey. There is evidence that marine worms have a “circalunar” clock, and Smith speculates that a similar system might be in place in humans.
“There may be a built-in biological clock that is affected by the moon, similar to the one that regulates the circadian rhythm. But all this is mere speculation – additionally, more highly controlled studies that target these mechanisms are needed before more definitive conclusions can be drawn.”
Whilst the scientists battle it out with their various findings, watch out for the "supermoons" on 12 July, 10 August, and 9 September to see whether any bumps in the night wake you up more easily than usual.