To increase reproductive success, many species synchronize reproductive behavior with a particular phase of the lunar cycle. The human menstrual cycle has also a period close to that of the lunar cycle, and recent studies suggest a temporary synchrony between menstrual and lunar cycles. Nevertheless, lunar influence on human reproductive behavior remains controversial. Here, we analyzed long-term menstrual records of individual women from the past 24 years and compared them with records from the past century. We show that women’s menstrual cycles recorded before the introduction of light-emitting diodes in 2010 and the extensive use of smart phones significantly synchronized with the Moon, while those after 2010 coupled to the Moon mostly in January. We hypothesize that the high gravimetric forces between the Moon, Sun, and Earth every January are sufficient for this coupling, while the increasing exposure to artificial light at night impinges on synchrony at other times.
We conclude that humans are affected by the luminescence cycles and also the gravimetric cycles of the Moon, with the menstrual cycles aligning with the synodic month. Furthermore, we hypothesize that, in ancient times, human reproductive behavior was synchronous with the Moon, but that our modern lifestyle, particularly our increasing exposure to artificial light at night, has altered this relationship.
The synodic month is the monthly luminescence cycle of the moon. Basically women are more likely to ovulate as the moon fills but only when they aren't exposing themselves to modern levels of artificial light; the full moon more often than not coincides with menstruation. They also find that even if artificial light interrupts the synchrony, the synchrony resumes during winter, when the gravitational effects of the moon on earth are at their greatest.
When people say "howling at the full moon," I always imagined men howling. Now I'm not so sure.