Moon & Sleep — Does the Lunar Cycle Affect Sleep?

For millennia, humans have attributed changes in mood, sleep, and behaviour to the lunar cycle — but is there scientific evidence? Two landmark studies from the 2010s and 2020s suggest the answer is a qualified yes.

The most-cited study, published in Current Biology in 2013 by Christian Cajochen and colleagues at the University of Basel, analysed polysomnography recordings of 33 healthy volunteers in a controlled laboratory environment. The participants had no access to windows or clocks, eliminating any psychological expectation about the moon. Results showed that around the full moon, participants took an average of 5 minutes longer to fall asleep, slept 20 minutes less overall, and showed a striking 30% reduction in deep (slow-wave) sleep compared to the new moon phase.

A 2021 study published by University of Washington researchers, analysing sleep data from indigenous communities in Argentina with no artificial lighting as well as urban participants in the US and Argentina, found a consistent pattern: people went to sleep later and slept for shorter durations in the nights before a full moon. This cross-cultural consistency suggests the effect is biological rather than cultural.

The leading hypothesis is that humans evolved with moonlight as a key environmental signal. The bright full moon provided illumination for nocturnal activity, so our circadian rhythms may have adapted to produce lighter, more fragmented sleep during high-illumination phases — even when that moonlight is blocked by modern windows.

The lunar effect is real but modest — a 20-minute reduction in sleep is noticeable but not catastrophic. For most people, good sleep hygiene practices during full moon nights are sufficient to compensate.

Block the light. The most direct intervention is blackout curtains or a sleep mask. Even if your evolutionary circadian response to moonlight operates partly independent of direct light perception, eliminating physical moonlight through windows removes one obvious contributing factor.

Move your bedtime earlier. Since sleep onset tends to be delayed around the full moon, scheduling an earlier bedtime by 20–30 minutes can compensate for the disruption and preserve your total sleep duration.

Prioritise magnesium. Magnesium glycinate (200–400mg before bed) has well-documented effects on sleep depth and sleep onset. Some practitioners specifically recommend magnesium supplementation around full moon periods, though direct lunar-specific evidence is limited.