Although werewolves are creatures of fiction, many people report having sleep issues whenever a full moon rises. These complaints may not be as crazy at you think, given that new research from the University of Basel, Switzerland, shows human sleep patterns do change during the lunar cycle.

"The lunar cycle seems to influence human sleep, even when one does not 'see' the moon and is not aware of the actual moon phase," said lead author Dr. Christian Cajochen of the Psychiatric Hospital of the University of Basel.

Over the course of three years, 33 people intermittently participated in a sleep experiment, with each session lasting 3.5 days.

At the time, the researchers were simply investigating circadian rhythms, but years later while sitting under a full moon at a bar, they decided to reanalyze the data to check for a lunar pattern.

Brain activity during the non-rapid-eye movement (NREM) sleep is often used as an indication of deep sleep.

A 30-percent drop in NREM-related brain waves was witnessed during the full moon, suggesting that deep sleep was affected by the lunar cycle. It also took about five minutes longer for the subjects to fall asleep when the moon was full, even though they were housed in a room that wasn't exposed to outdoor lighting.

Theses findings add to evidence that humans — despite the comforts of our civilized world — still respond to the geophysical rhythms of the moon, driven by a circalunar clock. Credit: Current Biology, Cajochen et al.

The volunteers reported that their sleep was less satisfying during the full moon, and their levels of melatonin — a hormone that regulates sleep/wake cycles — dropped during this time.

"This is the first reliable evidence that a lunar rhythm can modulate sleep structure in humans when measured under the highly controlled conditions of a circadian laboratory study protocol without time cues," concluded the researchers.

It's hard to say why this might be happening. The moon is known to regulate tides, and consequently the behaviors of marine life, but that shouldn't really bother terrestial species like us.

The authors mention that this human pattern might be the remnants of our days without electricity, when the only light at night was provided by the moon and the stars. Full moons could have made humans easier to see by predators, so perhaps we adapted ways to remain alert while sleeping.

The Swiss team plans to investigate whether there is a cellular or genetic explanation for this wakefulness in future studies.

Source: Cajochen C, Altanay-Ekici S, Münch M, Frey S, Knoblauch V, Wirz-Justice A. Evidence that the Lunar Cycle Influences Human Sleep. Current Biology. 2013.