It’s widely held that some people become disturbed when the Moon is full, or even just getting brighter – and a new study suggests that men are affected more than women.
Researchers from Uppsala University in Sweden found that men’s sleep is more “powerfully influenced” by the lunar cycle: They stay awake longer and enjoy less sleep “efficiency” than women when the Moon is in its waxing phase.
During the waning phase, when the Moon rises during the day, the disturbances weren’t demonstrated.
The new study
In the new study, the researchers used one-night, at-home sleep recordings from 492 women and 360 men.
They found that men whose sleep was recorded during nights in the waxing period of the lunar cycle – during which the Moon becomes brighter and the time at which it is highest in the sky moves from noon to midnight – “exhibited lower sleep efficiency and increased time awake after sleep onset compared to men whose sleep was measured during nights in the waning period”.
In contrast, the sleep of women “remained largely unaffected by the lunar cycle”.
“Our results were robust to adjustment for chronic sleep problems and obstructive sleep apnea severity,” said Christian Benedict, Associate Professor at Uppsala University’s Department of Neuroscience, and corresponding author of the study.
The researchers concede that previous studies “have produced somewhat conflicting results on the association between the lunar cycle and sleep, with some reporting an association whereas others did not”.
There are several possible explanations for these discrepant findings, including that some of the results “were chance findings”.
The researchers are confident of their findings because “many past studies investigating the association of the lunar cycle with human sleep did not control their analyses for confounders known to impact human sleep, such as obstructive sleep apnea and insomnia”.
During the waxing period, the Moon’s illumination increases and the moment that the Moon crosses a location’s meridian gradually shifts to late evening hours.
In contrast, during the waning period, the Moon’s illumination decreases and the moment that the Moon crosses a location’s meridian gradually shifts to daytime hours.
One mechanism through which the Moon may affect sleep is sunlight reflected by the Moon around times when people usually go to bed.
“Our study, of course, cannot disentangle whether the association of sleep with the lunar cycle was causal or just correlative,” Dr Benedict said.
But why men?
In speculating why men are more sleep-disturbed than women during the waxing period, the authors cite a range of studies.
One study reported that blood concentrations of melatonin were lower during the full moon that during the new moon among 20 male subjects.
Another suggested that men are more sensitive to ambient light than women.
In a small study of men this year, blood concentrations of the male hormone testosterone were lower, while those of the stress hormone cortisol were higher, during the full moon compared with the new moon.
Low testosterone and elevated cortisol have been linked with disturbed sleep.
In January, The New Daily reported on a study that found both men and women go to sleep later in the evening and sleep for shorter periods of time as the Moon gets fuller and brighter (in the waxing phase).
The researchers, from the University of Washington, Seattle, suggested that ancient people were essentially programmed to stay awake during the fuller moon, so they could hunt at night.
If that was true, then it might make sense that men – the hunters – be more susceptible to these sleep disturbances.