Original ArticleAssociation between lunar phase and sleep characteristics
Introduction
Human culture has been fascinated by the cycles of the moon [1]. Beliefs in lunar effects on sleep date back to ancient times. The passage from full to crescent moon provided the basis for the earliest calendars of most civilizations and can be linked to Assyrian and Babylonian mythology. Nevertheless, evidence for the supposed influence of the moon on human behavior has been particularly elusive. Surveys of workers in the mental health professions, however, show a persistent belief that the full moon may influence behavior [2], [3].
The observations made by Galileo Galilei on the phases of the moon cycle remain correct in today's astronomical understanding. There are eight phases of the moon cycle, which succeed each other with a periodicity of 3.69 days: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent. The synodic cycle is the interval between two successive new moons. This is the time it takes the moon to complete an orbit around the earth (29.53 days), corrected for the Earth's orbit around the Sun. Most studies associated with the influence of the moon on human behavior focus mainly on the full moon within the synodic cycle [4].
Several published reports suggest an association of the lunar cycle with women's menstrual cycle [5], [6]. The lunar cycle also has been suggested to have an impact on fertility and births [7], [8], [9]. However, no significant effect of the lunar cycle on the number of deliveries was found in Austrian [10] and in American studies [11], [12]. Several papers reported associations between the lunar cycle and the frequency of hospital admissions due to various causes such as cardiovascular disease [13], acute coronary events [14], gastrointestinal hemorrhage [15], and infectious diarrhea [16]. Lunar phases were also associated with the number of requests for appointment at a thyroid outpatient clinic [17]. On the other hand, a number of studies showed insufficient evidence or no association between various health-related events and the synodic lunar cycle [18], [19], [20], [21], [22], [23], [24]. Studies also showed that lunar periodicity may be associated with traffic accidents [25], crime [26], suicides, aggravated assaults, and psychiatric emergency room visits [7]. Little is known, however, about the association between the lunar cycle and sleep patterns.
Röösli et al. studied 31 volunteers and showed an association between lunar cycle and sleep characteristics. Subjective sleep duration was shortened and fatigue was increased at full moon. In contrast, sleep latency, wake-up events, level of distress, mood, and well-being were not associated with the lunar cycle [27]. A study monitoring wrist-activity showed no association between sleep duration and moon phase [28]. Lastly, the moon cycle had no effect on human daily rhythm, wake-up, and to-sleep times in four volunteers [29]. An analysis of diaries kept by 196 participants showed no association between full moon and dream recall [30]. However, a recent study involving 33 participants found that electroencephalogram (EEG) delta activity during non-rapid eye movement (NREM) sleep, an indicator of deep sleep, decreased by 30%, time to fall asleep increased by 5 min, and EEG-assessed total sleep duration decreased by 20 min around full moon [31].
In the present work, we analyzed the relationship of synodic lunar phases with subjective and objective sleep characteristics. Specifically, we wanted to test the hypothesis that full moon is associated with lower sleep efficiency and deep sleep. We also wanted to quantify the association of full moon and sleep latency. There is a strong link between sex and sleep both in the structure of sleep and in the incidence of various sleep disorders [32], [33]. Accordingly, we sought to determine whether the association between the lunar cycle and sleep was different between the sexes.
Section snippets
Sample of patients and data collection
This retrospective, cross-sectional study was performed at the 1st Department of Internal Medicine, Semmelweis University, Budapest, Hungary. Data obtained from 319 consecutive patients, referred to the sleep laboratory for sleep studies, were analyzed between January 2007 and November 2009. Exclusion criteria included technical limitations, moderate and severe obstructive sleep apnea (OSA) [apnea–hypopnea index (AHI) ≥ 15/h], and sleep efficiency of <20%.
The ethics committee of the Semmelweis
Results
Five hundred and twenty-two consecutive patients' data were enrolled: two patients had sleep efficiency <20%, four recordings were excluded due to technical limitations, and 197 patients had mild/severe OSA. Thus, 319 patients were included in the final analysis.
The participant characteristics are presented in Table 1. The mean ± SD age of the study participants was 45 ± 14 years for men and 52 ± 12 years for women. The mean BMI was 28.2 ± 5.4 kg/m2. Twenty-three individuals used sleeping
Discussion
In this cohort of patients undergoing diagnostic polysomnography, full moon was associated with less deep sleep, lower sleep efficiency, and longer REM latency. This association seemed to be more pronounced in women than in men. Our study enrolled patients referred to a sleep clinic, thereby extending previous observations regarding the association between lunar cycle and sleep variables to a clinical population with potential sleep disorders.
A few earlier studies offered support for an
Conclusion
The main result of this cross-sectional study is that there is an association of moon phases with both subjective and objective sleep parameters. Full moon was associated with significantly reduced sleep efficiency and other sleep parameters; therefore, we propose that lunar phases may contribute to the complex regulation of sleep, especially in women. Accordingly, poor sleep, the consequent emotional lability, and reduced daytime functioning may be partially related to the full moon.
Conflict of interest
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2014.06.020.
Acknowledgments
The authors thank the patients and the staff of 1st Department of Internal Medicine, Sleep Laboratory, Semmelweis University, in Budapest, Hungary, for their assistance in this survey. Special thanks to Zsolt Turányi for his essential help in sensitivity analysis.
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