Moon time. The name says it all. Or not? Scientists haven’t yet been able to prove the connection between the lunar cycle and the menstrual cycle with hard evidence. So, does your menstrual cycle sync with the moon cycle? Recent research shows that the moon may play a small supporting role after all.
But let’s start at the beginning. The word menstruation is derived from mensis, the Latin word for month. This actually means lunar month. Menses or moon time became synonyms for menstruation. The average time between two periods is 28-29 days. That’s approximately the same length as a synodic month, or the time between two consecutive new moons: 29 days and 12 hours. It’s therefore not surprising that the moon has been associated with the menstrual cycle since the beginning of time.
Changing tides
In ancient times, when the sun and moon were the only sources of light and there were no contraceptive pills, all women menstruated at the same time. At least that’s how the story goes. Their cycles aligned neatly with those of the moon. Charles Darwin hypothesised that this was a remnant from the time when all life on Earth was in or around the sea. In many marine animals and some land animals, the urge to reproduce coincides with a certain moon phase, usually a full or new moon. Or better said: with a certain tide. The tides on Earth – ebb and flow – are a result of the gravitational pull of the moon.
Do the math
The modern 24-hour economy would have eliminated this basic biological principle. Again, that’s how the story goes. In fact, very few people have a 29 day cycle and anything between 21 and 35 days is considered normal. The duration of each period can also vary considerably: anything between 2 and 8 days is seen as standard. From a mathematical point of view it’s therefore unlikely that women actually menstruate at the rhythm of the moon. For the same reason, there goes the assumption that women who live in the same house will sync up over time.
Throughout history, there have been numerous studies into a possible lunar connection, but no hard evidence has been found. Exceptions confirm the rule. If a connection is discovered, it often involves small-scale research. Conclusion of the largest analysis done until recently – which compared 7.5 million cycles from 1.5 million users of a popular menstrual app: there is no connection. You can’t set your alarm clock to the relationship between the moon and menstruation. But maybe you can set your biological clock?
Our circadian rhythm
A recent meta-study by French and American researchers, in which 26,912 cycles of 2303 European women and 4786 cycles of 721 North American women were compared to the lunar cycles, shows that it’s more likely that the cycle is driven by our internal biological clock (our circadian rhythm) than by an external factor such as the moon. Although… the study still found a weak but statistically significant relationship between menstrual and lunar cycles. The menstruation of North American women more often begins with the full moon and that of European women more often with the waxing moon.
The researchers could not explain why this geographical difference occured. Lifestyle could have an influence. When the moon has an actual impact, it’s more in the role of a co-driver. The biological clock, which spans just over 24 hours, is still the main driver. This is super stable (although there are individual differences) and seems to be hardly affected by exposure to sunlight or moonlight. Although you can temporarily throw this out of balance – as anyone who has ever had jet lag knows.
Rituals in a red tent
Hard evidence or not: many people believe in the alleged alliance with the moon. On all continents, women come together around the full or new moon in a moon hut, moon circle or red tent. The moon simply has a magical and mysterious appeal. The fact that you can divide the lunar cycle into four phases, just like the menstrual cycle, is of course intriguing too.
The shrinking moon symbolises the premenstrual phase; a creative period in which you’re likely to be less social and tend to withdraw. The new moon, with dark nights, is the time when you menstruate; an ideal time for contemplation, (self) reflection and meditation. Waxing moon is the period between menstruation and ovulation; a dynamic phase in which you get things done more easily. The full moon symbolises ovulation: this is the perfect time for fertility rituals and moon festivals.
