“What do humans, some primates, some bats, the spiny mouse, and the elephant shrew have in common? They all get periods.”
Gabriella Kountourides, who is studying for her doctorate at the University of Oxford shared fascinating facts about the female menstrual cycles.
Menstruation is a natural process that affects half of the world’s population during their lives, but it’s little understood. Here are five things you probably didn’t know about periods.
1. Moon syncing is not a thing.
The idea that menstrual cycles sync up with the cyclical waxing and waning of the moon, much like the ocean tides is such a compelling idea. The moon’s cycle is 29.5 days, but in 2019, an analysis of 7.5 million menstrual cycles from 1.5 million women around the world found no relationship at all.
2. Periods don’t sync up because people live together
Humans love to find patterns, and a certain amount of overlap is to be expected. But the actual syncing of cycles is not backed by data. The textbook idea of a 28-day cycle is a bit of a myth too as a normal cycle can be anything up to seven days longer or shorter than this.
Everyone is unique and hormones can be powerful in a good way.
3. Oestrogen
Oestrogen is an incredible hormone that we’re only just starting to understand. There’s a specific type of oestrogen that’s made in the ovaries called estradiol. This is released throughout the menstrual cycle, and it peaks just around ovulation.
Research suggests oestrogen can have some powerful effects. In 2021, neuroscientists at the University of California, Santa Barbara, for the first time tracked a woman’s hormones throughout the cycle and looked at whether these had any impact on the brain. They found an increase in connectivity throughout the brain at times when oestrogen was high. One theory is that oestrogen causes our neurons to form new connections to other neurons, which helps with learning and memory.
4. 98% of mammals don’t have periods
Lots of animals do have reproductive cycles, like cats and elephants, but they reabsorb the lining of the womb rather than shedding it as a period. So why do humans menstruate?
The truth is, this is not known. A theory by evolutionary geneticist Deena Emera is that it is a tug-of-war of energy between the mother and baby. Human embryos bury deep into the lining of the womb, which gives them more access to nutrients from the mother’s body. So the lining of the womb builds up nice and thick each month to create a shield to protect the mother. This thick lining also makes it easier to shed, so she doesn’t expend a huge amount of energy if a foetus won’t ultimately make it.
The ancient Greeks thought the womb wandered around the body. And as it floated around, they believed this wandering womb caused all sorts of diseases. Bizarre as it sounds, this idea stuck around for centuries, and so did the idea of hysteria – a kind of catch-all pseudo-medical term which was used to undermine women.
5. PMS
in 1931, a new term was coined – PMT, or premenstrual tension. This was later renamed premenstrual syndrome or PMS and refers to any symptoms experienced in the week before the start of a period. Some argue the term “syndrome” is not useful and it would be more accurate to refer to premenstrual symptoms. PMS might be linked to inflammation.
Why do women experience premenstrual symptoms? It could be down to inflammation which is the body’s way of protecting itself from infection. Just as our hormone levels change during a menstrual cycle, so do levels of inflammation. At ovulation, part of our immune system is temporarily suppressed a little. That’s so a fertilised egg if there is one, can implant itself without getting rejected. While inflammation is a sign of a strong immune system, too much inflammation is bad.
Symptoms include headaches, tiredness, and changes in appetite – sounds a bit like PMS, doesn’t it? Some have suggested it’s this rise in inflammation in the second half of the cycle that’s actually behind what we call PMS.
So that’s a quick rundown of a few facts, myths and theories about periods. And still, there’s so much unknown about something that happens to half of the world’s population at some point in their life. It means there is so much more to discover.
