Does phase of the moon influence our sleep? Three contradictory studies.

This is an update on a previous MindBlog posting. Vyazovskiy and Foster review three recent studies that give contradictory results on how or whether the phase of the moon influences our sleep. They note that the three studies compared data obtained from different subjects at different lunar phases and were biased and imbalanced in terms of age, gender, and many other factors. They suggest that in future research it should be mandatory to design within-subject experiments, rather than perform further retrospective studies. Here is their statement of the situation:

Whether the moon affects our sleep has intrigued our species since ancient times, but in the last decades only relatively few attempts have been made to address this issue with scientific rigor, and solid conclusions have been elusive [1]. A new cycle of research on the lunar effects on sleep was triggered by a retrospective study which carefully re-analyzed the sleep data collected under laboratory conditions in 33 subjects (age range 20–74 years) and showed clear cut effects of the lunar phase on several subjective and objective sleep parameters [2]. Specifically, EEG slow-wave activity (SWA), total sleep time and subjective sleep quality were reduced around the time of the full moon, while sleep latency and latency to REM sleep were prolonged. This study corroborated an earlier report [5], which found a significant decrease in the amount of subjective sleep around the full moon in 31 subjects (mean age of 50 years). This report triggered two further studies, published in the current issue, which either contradict or report novel effects of lunar phase 3 and 4.

One of these studies, a re-analysis of existing large data sets, could not confirm any of the findings made by Cajochen et al. [3]. By contrast, a second retrospective study [4], in which 47 young volunteers were analyzed, confirmed a decreased total sleep time around the full moon, but REM sleep latency was longer around the new moon. This contradicts the Cajochen et al. study as they found that the latency to REM was longest around the full moon [2].

References: 1. R.G. Foster, T. Roenneberg. Human responses to the geophysical daily, annual and lunar cycles. Curr. Biol., 18 (2008), pp. R784–R794 2. C. Cajochen, S. Altanay-Ekici, M. Munch, S. Frey, V. Knoblauch, A. Wirz-Justice. Evidence that the lunar cycle influences human sleep. Curr. Biol., 23 (2013), pp. 1485–1488 3. M. Cordi, S. Ackermann, F.W. Bes, F. Hartmann, B.N. Konrad, L. Genzel, M. Pawlowski, A. Steiger, H. Schulz, B. Rasch, M. Dresler. Lunar cycle effects on sleep and the file drawer problem. Curr. Biol., 24 (2014), pp. R549–R550 4. M. Smith, I. Croy, K.P. Waye. Human sleep and cortical reactivity are influenced by lunar phase. Curr. Biol., 24 (2014), pp. R551–R552 5. M. Roosli, P. Juni, C. Braun-Fahrlander, M.W. Brinkhof, N. Low, M. Egger. Sleepless night, the moon is bright: longitudinal study of lunar phase and sleep J. Sleep Res., 15 (2006), pp. 149–153