What the Moon Really Does
SCIENCE Sleep around the full moon
In 2013 Christian Cajochen's team in Basel went back to sleep-lab data from volunteers who had slept in a windowless room, with no clocks and no view of the sky, and who never knew the study would be about the moon. Around full moon, brain activity linked to deep sleep was about 30% lower, people took around five minutes longer to fall asleep, and they slept about 20 minutes less.
A lab is one thing; real life is another. In 2021 Leandro Casiraghi and colleagues tracked sleep with wrist monitors in Toba/Qom communities in Argentina, from villages without electricity to a town with it, and in Seattle students. Everywhere, people went to bed later and slept less on the nights before a full moon, when there's bright moonlight in the evening.
SCIENCE The moon and the menstrual cycle
Charlotte Helfrich-Förster's group analysed long-term cycle diaries kept by women for up to 32 years. They found that cycles longer than 27 days were intermittently in step with the moon — synchronised for stretches of time, then drifting — and that the link weakened with more exposure to artificial light at night.
KEEP IT IN PROPORTION
The moon effects that hold up are real but modest: minutes of sleep, intermittent synchrony. They are not proof of everything said about the moon. The honest version is still a good story: our bodies seem to carry a faint memory of a night sky that used to be the brightest light after dark.
On the Dance Floor
Keep a moon diary for one month: each morning, note how you slept and how you felt, and look up the moon phase only at the end. Patterns you find after the fact are more honest than patterns you went looking for.
DONE WHEN...
You can describe what the 2013 and 2021 sleep studies found, and why the menstrual-cycle finding is described as "intermittent".
References & Resources
Cajochen, C., Altanay-Ekici, S., Münch, M., Frey, S., Knoblauch, V. & Wirz-Justice, A. (2013). Evidence that the lunar cycle influences human sleep. Current Biology, 23(15), 1485–1488.
Casiraghi, L., Spiousas, I., Dunster, G. P., McGlothlen, K., Fernández-Duque, E., Valeggia, C. & de la Iglesia, H. O. (2021). Moonstruck sleep: Synchronization of human sleep with the moon cycle under field conditions. Science Advances, 7(5), eabe0465.
Helfrich-Förster, C., Monecke, S., Spiousas, I., Hovestadt, T., Mitesser, O. & Wehr, T. A. (2021). Women temporarily synchronize their menstrual cycles with the luminance and gravimetric cycles of the Moon. Science Advances, 7(5), eabe1358.