The full moon robs you of sleep. It's not a sensation, it's not superstition: it's a biological fact documented by at least four independent studies conducted in Switzerland, Hungary, the United States, and Argentina. You sleep twenty minutes less, it takes you five minutes longer to fall asleep, your deep sleep drops by thirty percent, and your blood melatonin levels drop to a minimum. All this without you having to see the moon, without its light shining through the window. Your body knows it anyway. As if it had an internal clock calibrated to the lunar phases. Evolutionary legacy? Very likely. Uncomfortable? Definitely.
The Swiss laboratory that discovered everything
Thirty-three volunteers sleep in a laboratory of theUniversity of BaselThey don't know that their sleep will be analyzed in relation to the lunar phases. The researchers wait, record, compare. When the full moon arrives, the data changes: twenty-five minutes less sleep For everyone, thirty more minutes to reach the REM phase, reduced melatonin. Men seem to be more affected than women: they lose up to fifty minutes. But then a Hungarian study overturns the dataWomen suffer the most. Confusion? Yes. But one thing is certain: the full moon alters sleep.
Christian Cajochen, coordinator of Swiss research published on Current BiologyHe says the idea came to him in a pub. On the night of a full moon, of course. "Delta wave activity during deep sleep decreased by 30%, the time it took to fall asleep increased by 5 minutes, and total sleep duration was reduced by 20 minutes," he explains. The volunteers were completely isolated from natural light. The lab had no windows. Yet their bodies responded to the phases of the moon.
From Argentina to Seattle: Sleep Changes Everywhere
The team ofUniversity of Washington, together with researchers from Yale and National University of Quilmes in Argentina, has long since brought research outside the laboratory. The study published in Science Advances in 2021 monitored the sleep of 98 inhabitants of three Toba-Qom indigenous communities in the Argentine province of Formosa, plus 464 university students in Seattle. Argentine communities had different access to electricity: one had no access, one had limited access, one had complete access.
The result? Sleep fluctuated with the lunar cycle in all groups. In the days leading up to the full moon, people went to bed later and slept less. The overall variation in sleep ranged from 46 to 58 minutes during the lunar cycle. Bedtime varied by about 30 minutes. The effect was more pronounced in communities without electricity, but present everywhere.
“We hypothesize that the observed patterns are an innate adaptation,” he explains. Leandro Casiraghi, co-author of the study. “It allowed our ancestors to exploit this natural source of evening light.” When more moonlight was available, they stayed awake longer. They hunted, worked, socialized. The human body has adapted to this rhythm for millennia. And it hasn't forgotten.
Melatonin in free fall
Melatonin is the director of sleep. pineal gland It produces it when darkness arrives, preparing the body for rest. During the full moon, Levels drop even without direct exposure to moonlight. It's like a genetic switch that automatically turns on. The Swiss study measured a significant decrease in endogenous melatonin levels in participants during full moon nights.
The mechanism is the same that explains why checking your smartphone before bed is a bad idea. Blue light inhibits melatonin. The moon, with its increasing brightness in the days leading up to a full moon, does something similar. Only it works even if you're locked in a windowless room. The body "knows" it's a full moon. Exactly how it knows this is still being studied.
Artificial light and lunar rhythm
Horacio de la Iglesia, Professor of Biology at the University of Washington, points out a paradox. “Artificial light disrupts our innate circadian clocks, causing us to go to bed later and sleep less. But we never use artificial light to wake up earlier. These are the same patterns we observe with the phases of the moon.”
Basically, when we invented electricity, we have artificially replicated What the moon did naturally: extend the evening hours of wakefulness. The difference is that the moon did this a few days a month. We do it every night.
What to do when there's a full moon
If you find yourself tossing and turning during a full moon, here are some practical strategies. Darken your bedroom completely with heavy curtains or use an eye mask. Avoid bright screens at least an hour before bed. Create a relaxing evening routine with herbal teas or a warm bath. No caffeine after 16 p.m. And if you really can't fall asleep, get up and do something relaxing instead of staring at the ceiling.
Research continues. Future studies will clarify whether the effect is due to innate circadian rhythms or whether other factors exist. But one thing is certain: the full moon is no longer just folklore. It's biology. And your body knows it, even when you don't realize it.
