Sex-specific association of the lunar cycle with sleep

Using one-night sleep recordings from 852 subjects all living in Uppsala, Sweden, the present study represents one of the largest polysomnography investigations into the association of the 29.53-day long lunar cycle with sleep among men and women and across a wide age range (22-81 years). Following the day after the new moon until the day of the full moon (also named the waxing period), the moon's illumination increases, and the timing of the meridian of the moon is gradually shifted from noontime toward midnight. In contrast, from the day after the full moon until the day of the new moon (also named the waning period), the moon's illumination decreases, and the timing of the meridian of the moon is gradually shifted from early night hours toward noontime. Thus, we focused on the contrast between the waxing and waning periods. Sleep duration was shorter on nights during the waxing period as compared to waning period (P < 0.001). In addition, a significant interaction effect of participants' sex with the lunar period on sleep was noted (P < 0.05). Men, but not women, exhibited lower sleep efficiency (P < 0.001 and P = 0.748, respectively) and were longer awake after sleep onset (P = 0.010 and P = 0.890, respectively) on nights during the waxing period. All associations were robust to adjustment for confounders (including regular sleep disturbances). Our findings suggest that the effects of the lunar cycle on human sleep are more pronounced among men. Based on the cross-sectional design of the study, no firm conclusions can be drawn on the causality of the relations.