One of our readers wondered if bipolar people are more sensitive to lunar cycles. I could not find any evidence for that, but I did run across a recent research report suggesting that everyone (bipolar or not) may have a sleep cycle that corresponds to the phase of the moon.
Researchers at the University of Basel studied 33 people and measured various measures of sleep quality, as well as levels of the hormone melatonin that is involved in regulating sleep.
The study was well controlled and blinded, but it was a retrospective analysis (the original purpose of the study was not to test the hypothesis that sleep was linked to the lunar cycle, the researchers noticed an apparent correlation and then re-analyzed the data to see if there was a statistically significant association between sleep and the phase of the moon).
The researchers found a significant effect.
Around the time of the full moon it took longer to fall asleep. The quality of the sleep was poorer, melatonin levels in the blood were lower and the amount of time in deep sleep was 30% less.
Not surprisingly, people reported feeling more tired.
The effect was not related to exposure to moonlight (the subjects were indoors throughout the study).
The authors speculated that the effect was related to an endogenous (internal) circalunar clock (a biological clock that cycles along with the lunar cycle, that might be “reset” when exposed to moonlight but that keeps on cycling even when not exposed to moonlight).
This is how the internal circadian clocks work. For more information about the circadian clocks go here.
To read a longer article about the study in Time Magazine go here.
“Evidence that the Lunar Cycle Inﬂuences Human Sleep.” Christian Cajochen, Songul Altanay-Ekici, Mirjam Munch, Sylvia Frey, Vera Knoblauch, and Anna Wirz-Justice. Current Biology 23, 1485–1488, August 5, 2013