Moonstruck sleep: Synchronization of human sleep with the moon cycle under field conditions
Authors: Eduardo Fern√°ndez-Duque
Kaitlyn McGlothlen
Gideon P Dunster
Claudia Valeggia
Leandro Casiraghi
Ignacio Spiousas
Horacio O de la Iglesia
Journal: Science Advances (2021)
Discipline: Multidisciplinary
Keywords: moonlight; sleep timing; lunar cycle; wrist actimetry; synchronization
Affiliations: Department of Biology, University of Washington, Seattle, WA, USA., Sensorimotor Dynamics Lab (LDSM), CONICET, Universidad Nacional de Quilmes, Bernal, Argentina., Yale University, New Haven, CT, USA.

Abstract:  Before the availability of artificial light, moonlight was the only source of light sufficient to stimulate nighttime activity; still, evidence for the modulation of sleep timing by lunar phases is controversial. Here, we use wrist actimetry to show a clear synchronization of nocturnal sleep timing with the lunar cycle in participants living in environments that range from a rural setting with and without access to electricity in indigenous Toba/Qom communities in Argentina to a highly urbanized postindustrial setting in the United States. Our results show that sleep starts later and is shorter on the nights before the full moon when moonlight is available during the hours following dusk. Our data suggest that moonlight likely stimulated nocturnal activity and inhibited sleep in preindustrial communities and that access to artificial light may emulate the ancestral effect of early-night moonlight. 

Retracted: No

PubPeer comments:
 #1 If you look closely at the single points pattern of the 1st 2nd cycle in figs 1, 2 4, you can see that the pattern of the dots is *identical*. To my eyes, this looks like duplication of the data. I would like to author to explain how they got this exact patterns. , 
 Hi Gal, Indeed the data is double plotted. This means that the data is duplicated to ease visualization. This is a common plotting technique used for visualization in chronobiology. This is clearly indicated in the methods as well as in the figure legends. , 
 #2 The data is double-plotted, as clearly indicated in the figure legends. This is a very common practice when illustrating cyclic phenomanae, as there are no correct  ends to the frame of reference (e.g. January is as close to February as to December). , 
 #3 I see. My apologies. Thank you for clarifying. , 
 Moon phase and sleep correlation is not quite a sine wave Casiraghi et al. (2021) in Science Advances (DOI: 10.1126 sciadv.abe0465) show that human sleep duration and onset depends on the phase of the moon. Their interpretation is that light availability during the night caused humans to adapt their sleep over evolutionary time. Casiraghi et al. fit a sine curve to both sleep duration and onset as functions of the day in the monthly lunar cycle, but their Figure 1 A, B for the full sample and the blue and orange curves for the rural groups in Figure 1 C, D show a statistically significant deviation from a sine function. Instead of same-sized symmetric peaks and troughs, sleep duration has two peaks with a small trough between, then a large sharp trough which falls more steeply than rises, then two peaks again. Sleep onset has a vertically reflected version of this pattern. These features are statistically significant, based on the confidence bands Casiraghi and coauthors have drawn in Figure 1. The significant departure of sleep patterns from a sine wave calls into question the interpretation that light availability over evolutionary time caused these patterns. What fits the interpretation of Casiraghi et al. is that sleep duration is shortest right before full moon, but what does not fit is that the duration is longest right after full and new moons, but shorter during a waning crescent moon between these. It would better summarise the data to use the first four terms of a Fourier series instead of just the first term. There seems little danger of overfitting, given N=69 and t 60. A questionable choice of the authors is to plot the sleep duration and onset of only the 35 best-fitting participants in Figure 2. A more honest choice yielding the same number of plots would pick every other participant in the ranking from the best fit to the worst. In the section Materials and Methods, Casiraghi et al. fitted both a 15-day and a 30-day cycle to test for the effect of the Moonu2019s gravitational pull on sleep. The 15-day component was weaker in urban communities than rural, but any effect of gravity should be the same in both. By contrast, the effect of moonlight should be weaker in urban communities, but the urban community data (Figure 1 C, D green curve) fits a simple sine curve better than rural. It seems strange that sleep in urban communities would correlate more strongly with the amount of moonlight, like Figure 1 shows. ,