For centuries, people have attributed all kinds of abnormal behaviors to the moon. The so-called “lunar effect” has been linked to changes in women’s menstrual cycles, induction of labor, and even aggressive behavior and psychosis. (The term “lunatic” is derived from a Latin word meaning “moonstruck.”) Insomnia or a bit of extra tossing and turning around the time of a full moon is another common complaint.
And while there’s more than enough anecdotal evidence, scientists aren’t convinced that the moon’s position in the sky causes a disruption in the ability to fall and stay asleep.
Many factors influence humans’ ability to sleep, but physiologically speaking, probably none are more influential than the internal, 24-hour clock known as the circadian rhythm. The brain’s hypothalamus controls and regulates this “clock” with the help of the eyes, which take light and darkness as cues that it’s time to stay awake or go to sleep. When it’s dark enough, the body produces melatonin, a sleep-inducing hormone. When there’s light, the body suppresses melatonin production, making it harder to sleep.
Wakefulness is normal and expected when the eye is exposed to sunlight in the morning, when most people naturally wake up. But too much light at the wrong time can make it difficult to sleep. Dr. Alon Avidan, a neurology professor at the David Geffen School of Medicine at UCLA and director of the UCLA Sleep Disorders Center, says light exposure can suppress melatonin production, disrupting a person’s sleep-wake patterns. That’s why doctors often recommend avoiding blue light (a type of light wavelength often found on electronics) too close to bedtime.
“One would assume the same applies when you have a full moon, particularly for people who are already suffering from insomnia,” he says. “The light exposure from the moon is essentially sunlight that’s filtered a little bit. It can be very physiologically activating.” Avidan says that moonlight exposure in the hours before bedtime could theoretically disrupt a person’s circadian rhythm.
But some researchers have suggested there may be another internal clock at play: an evolutionarily-wired, 29.5-day cycle that correlates to lunar…