“What we think is that when our ancestors were hunting and gathering, it was highly adaptive to extend the end of the day,” Dr. de la Iglesia says. The extra light of a nearly full moon at dusk would grant them more time to find food before darkness fell – so, as Dr. de la Iglesia posits, why wouldn’t they evolve to stay up later on those nights? Even though we may not be as reliant on natural light now, he notes that our bodies may still be primed, evolutionarily speaking, to delay sleep before a full moon.
That likely applies even if you can’t see the moon’s light (whether it’s shrouded by clouds or light pollution or just a great blackout curtain). One hypothesis is that our bodies can sense the full moon’s greater gravitational pull, kinda like the oceans – after all, we’re mostly made up of water.
But there are a couple limitations to that theory. For starters, “the tidal effect on humans is estimated to be extraordinarily small,” says Brandon Peters, MD, a board-certified neurologist, sleep-medicine specialist, and author of The Sleep Apnea Hypothesis. And the gravitational pull of the moon is about the same during a full or new moon, so you’d expect to see similar effects in both phases, Dr. Peters adds.
Perhaps a more likely explanation involves other changes that happen alongside the shift in gravity of a full moon, Dr. de la Iglesia says, like variations in the Earth’s magnetic field, an energetic shield protecting us from solar winds and other space weather. Though experts don’t quite know how, research suggests that certain geomagnetic shifts might affect your cardiovascular system or even alter your melatonin levels, futzing with your sleep.
It’s also possible that, over time, a bunch of biological and evolutionary ties to the moon have led us to develop a circalunar rhythm – similar to a circadian rhythm, but oriented around the roughly month-long moon cycle, versus a single day. So just like you get sleepy at night and feel more awake as the morning progresses thanks to your internal 24-hour clock, experts theorize that your body might also become more active at night (or less naturally prone to sleep) around a full moon as compared to other phases throughout the month, Dr. Cajochen says.
What to do if you struggle to sleep well around a full moon
The moon’s going to keep moon-ing, but that doesn’t mean you’re doomed to restless nights whenever it’s approaching full status.
If you find yourself getting in bed only to toss and turn for a while on those days, Dr. Peters actually suggests delaying your bedtime temporarily by, say, 30 or 45 minutes (while keeping your wakeup time consistent). “By reducing your overall time in bed, you’ll build a stronger sleep drive, which will help you fall asleep more easily,” he says. Also, aim to get 15 to 30 minutes of sunlight after waking up each day, he adds, to keep your circadian rhythm bopping along as usual.
