If you don't sleep well during a full moon, it is not because you have epigenetically become a werewolf after watching "Twilight" too many times, lunar cycles and human sleep behavior are connected, according to results of a study on endogenous rhythms of circalunar periodicity.

Prof. Christian Cajochen of the Psychiatric Hospital of the University of Basel and colleagues analyzed the sleep of over 30 volunteers in two age groups in the lab. While they were sleeping, the scientists monitored their brain patterns, eye movements and measured their hormone secretions.

The findings suggest that even today, despite the comforts of modern life, humans still responds to the geophysical rhythms of the moon. The lunar cycle modulates human sleep and melatonin rhythms, they say.

Results were that both the subjective and the objective perception of the quality of sleep changed with the lunar cycles. Around full moon, brain activity in the areas related to deep sleep dropped by 30 percent. People also took five minutes longer to fall asleep and they overall slept for 20 minutes less. The volunteers felt as though their sleep had been poorer during full moon and they showed lower levels of melatonin, a hormone that regulates sleep and wake cycles.

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"This is the first reliable evidence that lunar rhythm can modulate sleep structure in humans," Cajochen says. 

The researchers speculate that this circalunar rhythm might be a relic from past times, when the moon was responsible for synchronizing human behavior. This is well known for other animals, especially marine animals, where moon light coordinates reproduction behavior. Today, other influences of modern life, such as electric light, masked the moon's influence on us. However, the researchers say their study shows that in the controlled environment of the laboratory with a strict study protocol, the moon's hold over us can be made visible and measurable.

Christian Cajochen, Songül Altanay-Ekici, Mirjam Münch, Sylvia Frey, Vera Knoblauch, Anna Wirz-Justice, 'Evidence that the Lunar Cycle Influences Human Sleep', Current Biology, 25 July 2013