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Is Your Menstrual Cycle Really Connected to the Lunar Cycle?

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What myths and scientific publications have in common is they are both grounded in human nature. As humans, we seek understanding and explanation for the world around us, and our inquisition has resulted in different methods emerging throughout time.

Across the centuries, one of the main characters within these methods has been the moon. As a force that is both metaphorically and literally out of our world, the moon has been associated as a key agent of change, serving as an explanation for everything from the tides to varied species’ behaviors to periods of change (yes, I’m talking about werewolves!). Most often, major mythologies and works of literature associate the moon with femininity and fertility.

The celestial body’s significance in our lives have encouraged many to study it further and provide more insight into how the world around us works. For example, lunaception, popularized by Louise Lacey in the 70s and 80s, is a practice that synchronizes one’s menstrual cycle with the phases of the moon in order to predict ovulation and hormonal balance. While limited research exists to validate this, two recent studies published in January 2021 revealed that the relationship between menstruation and the moon are more intertwined than previously believed.

Does the moon affect life on earth?

It has been hypothesized that the moon affected human behavior within pre-industrial communities on the basis that moonlight modulates nocturnal in a variety of species. For example, bats decrease their activity during full moons, oysters open their shells more during new moons, and songbirds sing their morning songs earlier during full moons. Similar to how the moon is portrayed as passive within some folklore, mythologies, and literary pieces, the moon’s effects on living beings is subtle (certainly not as observable as a werewolf transformation, but still observable!). 

Image credit: Mark Tegethoff
Image credit: Mark Tegethoff

Lunar phases are shown to affect late-night human activity

In a study done by Casiraghi et al., rural indigenous Toba/Qom communities in Argentina were observed and interviewed, and results were compared to . During the researchers’ observations, it was confirmed that activity increased and sleep started later during nights leading up to the full moon, when moonlight was 

A study completed by Casiraghi et al. sought to uncover the relationship between nighttime activity and lunar phase. They observed the activity and sleeping patterns between those in highly urbanized settings in the United States and in rural indigenous Toba/Qom communities in Argentina. From their research, the data revealed that, in both settings, sleep was delayed during nights leading up to the full moon, when there was more moonlight at night. Thus, the study suggests that moonlight prompted nighttime activity and inhibited sleep within pre-industrial communities, and access to artificial light simulates early-night moonlight.

What does this mean for menstruation?

First, let’s relate this back to nature—many marine and terrestrial species’ reproductive behaviors are synchronized with particular phases of the lunar cycle in order to increase reproductive success. While a lunar influence on human reproductive behavior remains controversial, some historical accounts say otherwise. 

In Casiraghi et al.’s study, elders were interviewed in the Toba/Qom communities. They told mythological stories that associate the moon with sexual relations and the menstrual cycle, and pointed out that sexual activities were more frequent during nights with more moonlight. The researchers of this study suggest that in ancestral times, moonlight, reproductive activity, and menstrual cycles were synchronized.

However, these are accounts from one community. Does that apply to the rest of humankind? 

In a study published by Helfrich-Förster et al., the researchers analyzed documents of 22 women, who kept detailed records of their menstrual cycles for an average of 15 years. What they found was that at some moments, menstrual cycles were synchronized with the lunar cycle. When both the moon’s light and gravitational cycles cooperated, lunar and menstrual rhythms aligned the most. This proves that not only do humans respond to fast gravitational changes (do you recall the feeling you get at the top of a rollercoaster right before you drop?), but also to slow and periodical gravitational changes

This study also revealed that the probability of cycles synchronizing decreases with age. Similar to what the previous study revealed, exposure to artificial light at night simulates early-night moonlight. With light pollution in large cities, changes that come with modern lifestyles, and aging, an individual who is more exposed to artificial light is more likely to have a shortened menstrual cycle, reducing the probability of synchronization with the moon.

Image credit: ThisIsEngineering
Image credit: ThisIsEngineering

The moon’s relationship with menstruation is subtle and tells a story of preindustrial times

These studies may not hold all of the answers we are seeking, but do reveal the connection between preindustrial human behaviors and mythological stories relating the moon to the feminine divine and fertility. When the moon was our only source of nocturnal light, there was an increased chance that the 28-day lunar cycle and 28-day menstrual cycle synchronized, most likely to increase fertility during nights where activity was higher. Today, these effects are even more subtle due to exposure to artificial light, though the moon’s gravitational forces still play a hand.

All in all, myths and scientific studies both tell us that, when we are seeking to learn more about ourselves, we should first look to the past.

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