Endogenous rhythms of circalunar periodicity (∼29.5 days) and their underlying molecular and genetic basis have been demonstrated in a number of marine species []. In contrast, there is a great deal of folklore but no consistent association of moon cycles with human physiology and behavior []. Here we show that subjective and objective measures of sleep vary according to lunar phase and thus may reflect circalunar rhythmicity in humans. To exclude confounders such as increased light at night or the potential bias in perception regarding a lunar influence on sleep, we retrospectively analyzed sleep structure, electroencephalographic activity during non-rapid-eye-movement (NREM) sleep, and secretion of the hormones melatonin and cortisol found under stringently controlled laboratory conditions in a cross-sectional setting. At no point during and after the study were volunteers or investigators aware of the a posteriori analysis relative to lunar phase. We found that around full moon, electroencephalogram (EEG) delta activity during NREM sleep, an indicator of deep sleep, decreased by 30%, time to fall asleep increased by 5 min, and EEG-assessed total sleep duration was reduced by 20 min. These changes were associated with a decrease in subjective sleep quality and diminished endogenous melatonin levels. This is the first reliable evidence that a lunar rhythm can modulate sleep structure in humans when measured under the highly controlled conditions of a circadian laboratory study protocol without time cues.

Results and Discussion

We attempted to exclude confounders such as increased light at night, potential bias in perception regarding a lunar influence on sleep, and temporal information about the 24 hr day by retrospectively analyzing sleep structure, non-rapid-eye-movement (NREM) sleep electroencephalogram (EEG) activity, melatonin, and cortisol secretion measured in prior studies carried out under stringently controlled laboratory conditions, which allowed “unmasking” of circadian and potential lunar influences.

4 Röösli M.

Jüni P.

Braun-Fahrländer C.

Brinkhof M.W.G.

Low N.

Egger M. Sleepless night, the moon is bright: longitudinal study of lunar phase and sleep. Figure 1 Time to Fall Asleep and Lunar Phase Show full caption Each data point (total of 64 nights double plotted) represents EEG-defined sleep-onset time (i.e., sleep latency: time between lights off and the first EEG occurrence of stage 2 sleep in minutes). The different color-coded symbols depict the different gender and age groups: pink for young women, blue for young men, white for older women, and gray for older men. Note: a lunar-phase (pictures upper abscissa)-dependent distribution could be fitted with a sinusoid function [f = y0 + a ⋅ sin(2 ⋅ pi ⋅ x / b + c); goodness of fit, r = 0.46]. The colored boxes delineate the moon classes 1, 2, and 3, with moon class 1 comprising nights that occurred −4 and + 4 days around full moon, moon class 2 comprising nights that occurred 5 to 9 days before and after full moon, and moon class 2 comprising nights that occurred 10 to 14 days before and after full moon. Figure 2 Sleep EEG Power Density and Lunar Phase Show full caption EEG power density between 0.5 and 25 Hz during NREM sleep for moon class 1 (around full moon) and moon class 3 (10 to 14 days distant from the next full moon), expressed as percentage of the average of moon class 1, 2, and 3. Mean values ±SEM in the occipital derivation (Oz) are shown. Symbols near the abscissa indicate frequency bins for which a significant effect for the factors “lunar class,” “age,” and “gender” was found (PROC MIXED; open triangles facing down illustrate the factor “gender,” filled triangles facing up mark the factor “age,” and the open circles with a central dot delineate the significant effect of “lunar class”). See also Figure S2 Table 1 Sleep and Endocrine Variables and Lunar Phase Variable Lunar Class 1 Lunar Class 2 Lunar Class 3 Significance for Lunar Class Mean SE Mean SE Mean SE Bedtime 23.2 0.2 23.5 0.2 23.5 0.2 Rise time 7.2 0.2 7.5 0.2 7.5 0.2 Sleep quality 51.2 3.7 58.6 3.5 56.4 3.5 ∗ TST 409.0 7.9 433.2 6.8 424.8 11.0 ∗ WASO 13.9 2.1 8.3 1.7 10.6 2.9 SL2 16.3 1.9 10.9 1.6 12.1 1.3 ∗ RL 89.3 8.0 58.9 5.2 76.5 7.4 ∗ MT 2.9 0.4 2.0 0.2 2.7 0.3 Stage 1 14.0 1.2 14.7 1.5 12.7 1.2 Stage 2 57.6 2.3 54.8 2.2 54.2 2.1 Stage 3 8.7 1.1 8.0 0.9 9.2 1.2 Stage 4 2.4 0.6 4.2 1.3 6.1 1.5 ∗ SWS 11.1 1.6 12.1 2.0 15.2 2.0 NREM 78.1 2.2 75.6 2.5 74.5 2.5 REM 17.2 1.2 18.3 1.2 17.5 1.3 Melatonin 3.9 0.6 7.5 2.2 8.2 1.9 ∗ Cortisol 2.1 0.7 1.0 0.1 1.2 0.2 Subjective sleep quality, sleep parameters of the second baseline night (always on a Tuesday to Wednesday) based on visual scoring for all lunar classes 1–3, and melatonin levels 2 hr prior bedtime. Except for two, each volunteer contributed with two baseline nights. If both nights of a volunteer occurred in the same lunar class, the nights were averaged per subject, this resulted in n = 21 for lunar class 1, n = 17 for lunar class 2, and n = 15 for lunar class 3. TST, total sleep time; WASO, wake after sleep onset (in percent of TST); SL2, sleep latency to stage 2; RL, REM latency; MT, movement time after sleep onset (in percent of TST); Stage 1–Stage 4, sleep stages 1–4 (in percent of TST); SWS, slow-wave sleep (sum of stages 3 and 4 in percent of TST); NREM, non-REM sleep (sum of sleep stages 2–4 in percent of TST); REM, REM sleep in percent of TST. Asterisks indicate variables that yielded significance for lunar class. Figure 3 The Influence of Lunar Phase on Sleep Variables and Melatonin Show full caption From top to bottom: subjective sleep quality as assessed on the Leeds Sleep Evaluation Questionnaire (LSEQ) in the morning on waking, objective total sleep time and sleep latency in minutes from PSG recordings, stage 4 sleep and occipital EEG delta activity (0.5–1.25 Hz) as a percentage of the value at −9/+9 day around full moon, and salivary melatonin levels in the evening before lights off (average of 2 hr before lights off). Mean values ±SEM (total n = 64) are shown. Data are plotted according to lunar classes: 0–4, 5–9, and 10–14 days distant from the nearest full moon phase. See also Figure S1 and Table S1 The distribution of sleep latencies (i.e., the time span between lights off and the first occurrence of stage 2 sleep in the EEG) yielded a distinct modulation by lunar phase that could be fitted by a sinusoidal function with peak sleep latencies around full moon ( Figure 1 ). For further analysis, the data were binned into three lunar classes (see the Experimental Procedures ). As expected, we found significant effects for the factors age and/or gender in the following sleep variables: subjective sleep quality, total sleep time (TST), REM sleep latency (RL), deep slow-wave sleep (i.e., stage 4), and sleep EEG delta activity (0.5–1.25 Hz, Figure 2 ; see Tables S1 and S2 available online for descriptive and PROC MIXED statistics). Surprisingly, the factor lunar class also yielded significance for all the above mentioned sleep variables, as well as for sleep latency (SL) and evening melatonin levels ( Table 1 and Table S1 ), while cortisol levels did not attain significance. We found lower sleep quality and TST, less deep slow-wave sleep and sleep EEG delta activity, longer SL and RL, and lower evening melatonin levels 0–4 days around the full moon compared to the other lunar classes ( Figure 3 and the related Figure S1 ). Thus, we have evidence that the distance to the nearest full-moon phase significantly influences human sleep and evening melatonin levels when measured under strictly controlled laboratory conditions, where factors such as light and personal moon perception can be excluded. While lunar cycles have been much celebrated in different cultures, and despite the persistent belief that our sleep is affected by the phases of the moon, so far there has been no reliable quantitative evidence that the moon can influence cortical activity during sleep. Thus, to our knowledge, this is the first report of a lunar influence on objective sleep parameters such as EEG activity during NREM sleep and a hormonal marker of the circadian timing system (melatonin) in humans, when putative external masking factors have been diminished. In a prospective field study using daily sleep logs in 31 people over 6 weeks, Röösli et al. [] found that people slept a mean of 19 min less on nights with a full moon compared with a new moon. These 19 min are a rather good match with the 20 min reduction in EEG-assessed total sleep time in our study.

5 Rüegg S.

Hunziker P.

Marsch S.

Schindler C. Association of environmental factors with the onset of status epilepticus. 6 Quigg M.

Fowler K.M.

Herzog A.G. NIH Progesterone Trial Study Group

Circalunar and ultralunar periodicities in women with partial seizures. 7 Cain S.W.

Dennison C.F.

Zeitzer J.M.

Guzik A.M.

Khalsa S.B.

Santhi N.

Schoen M.W.

Czeisler C.A.

Duffy J.F. Sex differences in phase angle of entrainment and melatonin amplitude in humans. 8 Birchler-Pedross A.

Schröder C.M.

Münch M.

Knoblauch V.

Blatter K.

Schnitzler-Sack C.

Wirz-Justice A.

Cajochen C. Subjective well-being is modulated by circadian phase, sleep pressure, age, and gender. A lunar influence on human brain electrophysiological properties has so far only been reported in patients suffering from epilepsy, such that the onset of the status epilepticus peaked 3 to 4 days after new moon [] and the periodicity of partial seizures displayed a predominant circalunar rhythm in women []. While the latter findings can still be explained by a potential disturbing effect of nighttime light on sleep that may eventually result in overt seizure activity or by a “menstrual clock” and thus by hormonal changes in women with partial seizures, these factors cannot account for the lunar modulation in sleep and melatonin observed in our study carried out in the dark and screened from the environment. Although we carefully controlled that the study volunteers kept a very regular sleep-wake rhythm and light-dark pattern for at least 1 week prior to study begin (see the Experimental Procedures ), we cannot completely rule out potential confounds of priming or entrainment to external synchronizers (i.e., photophases of the lunar rhythm) prior to entering the lab. Thus, the observed lower evening melatonin levels around full moon may ( Figure S2 ) be indicative of more evening light prior to entering the lab. The significant three-way interaction between age, gender, and lunar class for the evening melatonin levels hints to a complex interrelation between these factors, which is difficult to interpret. It is well known that with age, melatonin levels decrease, and more recently our and others’ data indicate that premenopausal women have higher melatonin amplitudes than young men [], older men, and postmenopausal women [], which may have biased our findings related to lunar class.