As the so-called Wolf Moon approaches, you might find you’re not getting as much shut-eye as you’d like. But don’t worry, on this occasion it’s probably not because of the pandemic or work worries. You can blame the full moon.
A new study has found that in the days leading up to a full moon, people go to sleep later in the evening and sleep for shorter periods of time – regardless of whether they live in cities or the countryside. Researchers believe this may be due to increased light exposure, however other studies suggest humans are simply attuned to the moon’s cycle.
The next full moon in the UK is on Thursday January 28 and will appear for roughly three nights. This winter moon is known colloquially as Wolf Moon, it’s thought because wolves used to be heard howling at this time – whether from hunger or to bond with the pack.
But back to your sleep! What else do you need to know?
Human sleep cycles oscillate during the 29.5-day lunar cycle, the paper published in Science Advances revealed. This may indicate our natural circadian rhythms are synchronised with, or entrained to, the phases of moon.
A research team, led by Professor Horacio de la Iglesia, an expert in biology from the University of Washington, observed later bedtimes and shorter sleep periods in urban and rural settings.
Using wrist monitors, the team tracked sleep patterns among 98 people living in three Toba-Qom Indigenous communities in the Argentine province of Formosa. One rural community had no electricity access, a second rural community had only limited access, while a third community lived in an urban setting with full access to electricity (and therefore artificial light).
For nearly three-quarters of the Toba-Qom participants, researchers collected sleep data for one to two whole lunar cycles. They saw the changes in sleep patterns regardless of an individual’s access to electricity, though the variations were less pronounced in city dwellers.
“We see a clear lunar modulation of sleep, with sleep decreasing and a later onset of sleep in the days preceding a full moon,” said Prof de la Iglesia.
“And although the effect is more robust in communities without access to electricity, the effect is present in communities with electricity, including undergraduates at the University of Washington.”
Past studies by Prof de la Iglesia’s team and other research groups have shown access to electricity impacts our sleep, as also evidenced in this study. Toba-Qom in the urban community went to bed later and slept less than rural participants with limited or no access to electricity.
But participants in all three groups showed the same sleep pattern changes as the moon progressed through its 29.5-day cycle. The total amount of sleep varied across the cycle by an average of 46 to 58 minutes, while bedtimes changed by around 30 minutes. On average, the latest bedtimes and shortest amount of sleep came in the three to five nights leading up to a full moon.
The team analysed sleep-monitor data from 464 college students in Seattle that was collected for a separate study – and found a similar pattern. The evenings leading up to the full moon have more natural light available after dusk – and it might be this light that’s keeping us up, researchers suggested.
The patterns could be “an innate adaptation that allowed our ancestors to take advantage of this natural source of evening light,” said lead author Leandro Casiraghi. The brightness of the moon might also explain why electricity causes such pronounced changes to our sleep patterns, Prof de la Iglesia added.
“In general, artificial light disrupts our innate circadian clocks in specific ways: it makes us go to sleep later in the evening; it makes us sleep less. But generally we don’t use artificial light to ‘advance’ the morning, at least not willingly. Those are the same patterns we observed here with the phases of the moon.”
There’s been “a lot of suspicion” around the idea that the phases of the moon could affect sleep, acknowledged Casiraghi. “Future research should focus on how: is it acting through our innate circadian clock? Or other signals that affect the timing of sleep?” he said. “There is a lot to understand about this effect.”
Dr Andrew Bagshaw, of the Centre for Human Brain Health at the University of Birmingham, tells HuffPost UK the latest study is “interesting” – particularly the participation of different communities to understand the universality of human relationships with the lunar cycle.
“Their hypothesis that this prolonged oscillation in sleep patterns linked to the lunar cycle is driven by access and exposure to light makes sense,” he says. “We know that variation in sunlight during the 24-hour light-dark cycle is the most potent determinant of sleep patterns generally.
“The more subtle variation in light exposure over the course of the lunar cycle might also be expected to have an impact on sleep patterns, as they have found. The fact that the effect is less pronounced in urban dwellers, where there is likely to be less access to moonlight, would fit with this idea.”
He adds the caveat that moonlight contains less blue than sunlight – and blue light is thoughts to have the largest impact on circadian rhythms and therefore sleep. “It is possible, in addition to light exposure, the effect could be the result of the many molecular processes in the body that are impacted by the lunar cycle,” he says. “There are plenty of issues still to understand!”
A study from 2013, published in the journal Cell, found similar results, only with research undertaken in controlled laboratory conditions – meaning study participants weren’t kept awake by bright light in the evening. Researchers analysed sleep structure, brain activity during non-rapid-eye-movement sleep, and secretion of melatonin and cortisol in volunteers.
Around a full moon, deep sleep decreased by 30%, the time to fall asleep increased by five minutes, and sleep duration reduced by 20 minutes.