Nov. 1, 2021 — A popular urban legend is that accidents and other strange things happen more often during a full moon. While the evidence doesn’t bear that out, it’s possible people might sleep differently during different phases of the moon, a new study suggests.

As the moon’s brightness increases daily from a new moon to a full moon, the time that it reaches its highest point in the sky also shifts from midday to near midnight. The reverse happens after a full moon, with brightness decreasing each night. A group of researchers from Uppsala University in Sweden examined people’s sleeping habits during these changing phases of the moon.

They analyzed sleep pattern information for 852 people from three previous, unrelated studies that assessed adult participants during one night of sleep.

The researchers found that study participants slept a little less on nights when the moon was waxing, or brightening, compared with waning.

The men, all from the same study conducted during 2016-2018, seemed more sensitive to the moon. They slept about 21 minutes less on waxing nights, whereas the women in the other two studies slept 12 minutes less. Men also tended to sleep less well on waxing nights and spent 14 extra minutes awake in the night after first falling asleep. Women experienced neither effect.

Although the researchers accounted for participant age and the season that they underwent their sleep tests, it’s important to note that the analysis is still based on a single night of sleep from each participant, with monitoring done at home. Also, the three studies took place at different times, from 2001 to 2004 and 2013 to 2015 for women and 2016 to 2018 for men. Much has changed during these years in terms of technology and social media use.

But the findings still hint that the moon could have subtle effects on human sleep. Moonlight is a reflection of sunlight, which affects levels of melatonin, a hormone that signals nighttime and sleep time. Previous studies have found lower melatonin and men’s testosterone levels during full moons and higher levels of the stress hormone cortisol during full moons.