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Menstrual cycle and the moon: does the moon affect menstruation?

  • 3 min read

In many cultures throughout history, the Sun is considered masculine and the Moon is considered feminine. Maybe because of that, all-things-women have been associated with the moon phases, like mood, behaviour and periods. And since the lunar phase period is close in length to the average menstrual cycle, it is no wonder that the menstrual cycle and the moon have been thought to be tightly linked. But is that the case?

What’s up with the menstrual cycle and the moon?

Extensive research has been done on the possible connection of the menstrual cycle and the moon cycle, but the truth is there isn’t an evident one. Some women can sync up with the moon cycle, but that is considered to be just a coincidence. And the similarity between the length of the moon phase cycle and the length of the average menstrual cycle is also thought to be a coincidence. In fact, if we are going to be accurate, the lunar cycle is not even exactly 28 days long.

The moon phase cycle (or synodic period) is 29 days and 13 hours long, and its sidereal period (the time it takes to complete a turn around the Earth) is 27 days and 8 hours long. This means the moon moves around the earth just a little bit faster than it moves around itself. The menstrual cycle in humans, on the other hand, has an average length of 28 days, but it can be shorter or longer than that.

Women are not the only mammals with a menstrual cycle

Humans were thought to be the only animals to have a menstrual cycle, but it turns out that some of our close relatives, the primates, also show a menstrual cycle. A menstrual cycle was also found in some bats, one species of rodents, and in an adorable species called the elephant shrew. And these cycles have very varied lengths, from only 9 days to more than a month.

Other animals have what is called an oestrous cycle, which is similar to a menstrual period, but not quite the same. It is known as “heat”. And even the oestrous cycle length can vary greatly from species to species.

Does the moon affect life on Earth at all?

The moon affect on the Earth. Most notably the moon affects tides, but its cycle does also affect some animal and plant behaviours. What is not yet understood is if and how the moon cycle can affect human psychology, behaviour, mood or others. A lot has been speculated about the menstrual cycle and the moon, but, as we said, the connection has not been found, other than a similarity in cycle length.

However, in ancient times, the moon and its cycle were thought to influence on certain illnesses. In fact, if you look at the words “lunacy”, “lunatic” and “loony”, they come from the Latin word for moon, luna. And the moon was indeed thought to have some sort of influence in many psychological and psychiatric afflictions.

Can moon phases affect humour and behaviour?

On a sadder note, this connection between the moon and women was not just about the menstrual cycle and the moon phases; the moon has also been linked many times to erratic behaviour in women – which was an extremely sexist thing. In the past, as you know, women were seen as “less than”, and thus many medical problems and symptoms in women were disregarded as hysteria, madness, and others. The phases of the moon were blamed for women’s “mood swings” or “bursts of madness”.

However, and how you might already know, this was just a poor excuse the ignorant and sexist society of that time made up to not treat women as equals. Rather, it was much more convenient to treat women as irrational beings who could not make their own decisions and needed a patriarchal system to function.

On that note, no, there is no scientific evidence that the phases of the moon have some sort of effect on humour or behaviour in humans.

Take care. Of the planet. Of yourself. Of your vagina.

 

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