Humans have an internal lunar clock. We are accidentally destroying it
Most animals, including humans, carry an internal lunar clock, tuned to the 29.5-day rhythm of the Moon. It guides sleep, reproduction and migration of many species. But in the age of artificial light, that ancient signal is fading – washed out by the glow of cities, screens and satellites.
Just as the circadian rhythm keeps time with the 24-hour rotation of the Earth, many organisms also track the slower rhythm of the Moon. Both systems rely on light cues, and a recent study analysing women’s menstrual cycles shows that as the planet brightens from artificial light, the natural contrasts that once structured biological time are being blurred.
Plenty of research suggests the lunar cycle still influences human sleep. A 2021 study found that in Toba (also known as Qom) Indigenous communities in Argentina, people went to bed 30-80 minutes later and slept 20-90 minutes less in the three-to-five nights before the full Moon.
Similar, though weaker, patterns appeared among more than 400 Seattle students in the same study, even amid the city’s heavy light pollution. This suggests that electric light may dampen but not erase this lunar effect. [Continue reading…]