The phenomenon of menstrual synchronisation was described in the literature. And there was a scandal

‘I have always menstruated at the same time as two of my female colleagues at work. Due to working remotely, I don’t know anything about their cycle’, Marta says as we discuss the pros and cons of not going to the office. This change is obviously a downside.

Many of us have experienced synchronised periods, with our best friend, for instance. Is this a coincidence, or does science have an explanation for it? I ask a gynaecologist, Anna Fuchs, MD, PhD. ‘I have patients in my office who spend a lot of time together: student friends, sisters or mums and daughters. I have heard a lot of statements that their periods had synchronised. This is a very common belief among women. Patients say, for example, “We’re about to start exam season and we’re all going to get our periods right then”. But during our studies and later during our specialisation, no one discussed such a phenomenon with us’, says Dr Fuchs.

Pheromones and miscalculations

I’m scrolling through the @drannafuchs Instagram account, while the doctor is checking the date of the first scientific publication on menstrual synchronisation. ‘It was 1971’, she says. ‘Psychologist Dr Martha McClintock conducted a study among female students living in a dorm. She demonstrated that the timing of menstruation was similar among female friends and room-mates. Her publication appeared in the prestigious journal Nature. Since then, the phenomenon of menstrual synchronisation has been called the McClintock effect in the literature. The researcher hypothesised that it involves the action of pheromones, volatile substances secreted by the body. She explained that women who spent a lot of time together influenced each other, synchronising the functioning of the reproductive system. In subsequent years, publications have appeared that contradict this effect. Some also accused McClintock of statistical error. And that means her research wasn’t reliable’, Dr Fuchs concludes.

Then there’s the issue of pheromones themselves – scientists dispute whether they even exist. Some people refer to them as ‘love drugs’ and explain that they are what make us feel attracted to someone. Others believe that these are just stories to make perfumes sell better.

But the topic of menstrual synchronisation doesn’t end on the criticism of McClintock’s research. ‘I read about a study done in China that confirmed this phenomenon. These researchers looked for an explanation in the effects of the Moon’s phases on the female body’, says Dr Fuchs.

Gynaecologists don’t like the full moon

‘Talking about the Moon in the context of health makes many people feel that it is not science. But gynaecologists don’t like being on-call during a full moon’, Dr Fuchs reveals. ‘When I started working on-call, I thought it was superstition, and I laughed that my older colleagues check the phases of the moon when planning their schedules. With time, I found out for myself that during a full moon the number of births and the number of women reporting after the loss of amniotic fluid are the highest. That is, the gynaecology department is busiest during a full moon.’

Last year in the Science Advances journal, researchers argued that the moon affects our sleep and menstrual cycles. They recalled research showing that babies are more likely to be born on nights with a full moon and a new moon (a new moon is the phase in which the moon is between the Sun and the Earth, so the side that’s visible from the Earth is in shadow). They also wrote about studies showing that women whose menstrual cycles are synchronised with the lunar cycle are more likely to become pregnant.

New research shows that lunar cycles affect menstruation. Researchers analysed the long-term menstrual cycle records of 22 women. They found that they were most likely to adjust their menstrual cycle to a synodic month lasting on average 29.53 days, which is the average time between new moons. Bleeding most often appeared on the night of the new moon or just before it. But in some of the subjects, the moment of menstruation occurred during a full moon.

The Moon’s influence on the menstrual cycle was stronger during the winter months. The youngest women were affected most strongly by the Moon. Its influence was disrupted by artificial light. In women who worked at night or went to bed late, the natural synchronisation of the monthly cycle weakened.

We go through it together

So maybe some of us have not so much a shared menstrual bond with a friend as a shared menstrual bond with the Moon? You can then rejoice that you have a circadian rhythm undisturbed by civilisation.

But what about the mutual influence of loved ones? A 2017 study by researchers at Oxford University and the makers of the menstrual cycle monitoring app Clue found that period syncing is a myth.

‘Many publications indicate that menstrual synchronisation may be pure chance or impression’, Dr Fuchs says. And she explains where this impression comes from, ‘Each person’s period is different, and a cycle can last 27, 28, or 25 days. Some women always menstruate the same way, even the exact time their periods appear is always the same. In others, the cycle is sometimes 27 days and sometimes 30 days. So, if you have two or three women living together and each has a slightly different cycle, eventually they will still get their periods at the same time because the cycles overlap. One woman will be on day three of her cycle when another will start hers. They will remember that they were menstruating at the same time. Talking about the symptoms of PMS, or premenstrual syndrome, also fosters this impression. For some women, abdominal pain or lowered mood occurs a few days before menstruation; for others, it occurs with menstruation. When we share such an experience with a loved one and she responds that she feels the same way now, we remember that we are at the same point in our menstrual cycles.’

Anna Fuchs, MD, PhD, is in the process of pursuing her habilitation. She is conducting research and reading scholarly articles. I ask if it bothers her that women talk about their periods being synchronised, even though science does not support this phenomenon.

‘We have various mutually exclusive theories about menstrual synchronisation. That means there’s still a lot to learn about how the body works and about fertility’, she answers. ‘We are still learning about the importance of lifestyle, nutrition, sleep and exercise. While these issues used to be downplayed, their importance is now crucial. I ask patients about their daily habits because it can be important for effective treatment. I will probably continue hearing about synchronised periods for some time to come.’

Author: Katarzyna Staszak

Photo: unsplash.com

The text was published on wysokie obcasy.pl on 22 January 2022