WOMEN'S PERIOD: Some have argued that women's menstrual cycles begin to synchronize when living together but evidence is spotty.
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It's a classic girl-bonding scenario: While moaning to your roommate about uterine cramps, premenstrual syndrome or some other such periodic inconvenience you realize that she, unlucky girl, is having her period, too. Momentarily distracted, you take a collective step back to marvel at the wonders of human biology that have allowed your ovulation cycles to synchronize.
Though widely accepted as a fact of female life, many psychologists and anthropologists doubt the existence of such menstrual synchrony. Nearly half of the papers published on the topic find no evidence that close co-habitation draws menstrual cycles closer together. What's more, studies that do find an effect have been dogged by harsh criticisms of poor design and naive statistical analyses.
Menstrual synchrony was first demonstrated in a 1971 paper published in Nature by Martha McClintock. The University of Chicago psychologist had observed during her undergraduate days in an all-female dorm that close friends tended to get their periods at the same time.
To test the idea formally, she asked 135 college girls living in dorms to recall their period start dates at three times throughout the academic year. She found that close-friend groups had periods significantly closer together in April (later in the year) compared with October: lessening from an average of 6.4 to 4.6 days apart.
The phenomenon was dubbed "the McClintock effect" and is widely held as the first example of pheromones—unconscious chemical signals that influence behavior and physiology—among humans.
Many subsequent researchers went on to reproduce the results from McClintock's original experiment in people, rats, hamsters and chimpanzees. But a cohort of studies that found no evidence for menstrual synchrony began to grow, too.
The father–son team of Leonard and Aron Weller, both at Bar-Ilan University in Israel, conducted the most studies on humans; they looked at college dorm roommates, athletes, lesbian couples, mothers, sisters, friends and even office colleagues throughout the 1990s. Sometimes they found signs of synchrony and other times not, with no explanation why. "The answer is not clear," the elder Weller says. "At one time before we started doing our research it was sort of a truism. But if it exists it is certainly not ubiquitous."
In 1992 H. Clyde Wilson, now an emeritus professor of anthropology at the University of Missouri–Columbia re-analyzed McClintock's first experiment, along with a few others that used a similar design. He found that all had inflated the difference between period start dates at the beginning of their studies. Correcting this and other methodological errors stripped away significance from McClintock's original results, he wrote.
And McClintock's former colleague, psychologist and mathematical modeler Jeffrey Schank at the University of California, Davis, found in a highly controlled rodent pheromone study that their model of two pheromones—one that pulls ovulation forward and one that delays it—driving synchrony didn't work. "That was very disappointing to me," he says. "I really wanted those models to work out."
The insurmountable hurdle in all the studies, he says, is that women often have persistent cycles of different lengths. As such, they can never truly synchronize, just randomly phase in and out of synchrony over the months as their cycles diverge and converge.
Last year, he co-authored a study in Human Nature following 186 female Chinese students living in dorms for an entire year, the longest menstrual synchrony study yet. He saw no evidence for the phenomenon, but plenty of random overlaps that could be seen as synchrony if viewed through a shorter time window.
McClintock, however, remains resolute. Focusing on narrow definitions of precise synchrony misses the greater point, she says: whether the social environment of women can affect the timing of ovulation, not menstruation per se, no matter in which direction or what pattern. "I don't think there is any doubt that social interaction among women and body compounds from women can change the way the ovary functions," she says.
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20 Comments
Add CommentGreat article!
Reply | Report Abuse | Link to thisSomehow it makes sense that women would NOT co-ordinate their menstrual cycles, because if we all ovulated at the same time, there may not be enough healthy men to go around ... Synchronization due to differing lengths of menstrual cycles is a more viable explanation for the apparent synchronization at certain times of the year.
Reply | Report Abuse | Link to thisVery interesting article. Thank you
Marie-Louise Oosthuysen de Gutierrez
Mexico City
Synchronization also doesn't make sense because during their mentrual cycles, women often experience lack of energy. These spells of low energy among women in a tribe would be detrimental to a hunter-gatherer lifestyle. Furthermore, if all of the women get pregnant at the same time, they won't be able to help each other.Given our anthropological history, evolution should select that women do not cycle together.
Reply | Report Abuse | Link to thisWhen my 9 month pregnant, 30 yr. old daughter began pre labor contractions, I began my period after being in peri menopause for 2 months. As her contractions got stronger the next few days my period got worse. On my day of heavy cramping and bleeding my daughter had heavy contractions and had the baby! We think that I made her have the baby or she made me start my periods again. Please comment! :)
Reply | Report Abuse | Link to thismy 2 teenager grand daughters live here with me also does their 33 yr old motherone teen has her period on 15 and the mother on about 1st well one day i ask mother whats wrong with teen she replies oh she is on her period since i am i really dont believe the old saying when 1 on the period all is if living in same house hold is this true
Reply | Report Abuse | Link to thisI absolutely believe this they synchronization exists. I served in the military and during basic training all the women in the platoon stayed in an open bay. We worked, ate and slept together and by month 2 we were all synced up. That is right all of us, I can't remember how many of us there were but it was between 30 ad 45 females.
Reply | Report Abuse | Link to thisPerhaps the military would be a good place to do a proper study on this.
Even now, in the software world I share an office with another female. We work about 50 -60 hours a week in the same room and both start on the same day. I just don't see how that can be coincidence.
I think it is highly possible that this does exist as I have personally experienced this. I have never had regular periods and in 2004 at the age of 19 I was diagnosed with Poly Cystic Ovaries Syndrome due to not having periods hardly ever and if I did they were perhaps every 3 to 6 months. In June 2009 I moved in with my friends parents after alot of family problems and we became very close so close I count them as my parents. I became very close with my new mum and for the first time ever I was having a period every month at the exact same time each month. I moved out in February 2010 into my own place and although I have still been having periods every month since I moved out they have not been as regular and predictable as they were while I was living with my new mum. I can not think of any other explaination for this happening other than period synchronization.
Reply | Report Abuse | Link to thishopefully this kind of synchronization really exists and is true. it would be a great help for women who suffers from irregular menstrual cycle.
Reply | Report Abuse | Link to thisif this would be true, it would be a great help for women who suffers from irregular menstrual cycle.
Reply | Report Abuse | Link to thisI sometimes get cramps after a few minutes of being near another girl when I am not on my period. When I ask, I find out that the other girl is on her period. Once, I got cramps when I was with a pregnant woman. They feel the same as menstrual cramps, with the low back pain as well as abdominal pain. Can anyone explain this to me?
Reply | Report Abuse | Link to thisI recently experienced this and is why I am commenting. I have always been SUPER regular with my cycle. Only twice did I notice a change. First was a few years back when I worked in a restaurant with many female employees. I was five days late but when I started, I realized that the other ladies I worked with had started too! The Most recent was last week. I have been working as a summer intern and live with two other girls. One girl started, the other a day or two later. Oddly enough, I just finished my period a week and a half before they started, but as soon as started sharing the Midol, I started again!! It was very frustrating and bizarre. I really think it started again soon after because the other girls both started
Reply | Report Abuse | Link to thisIf this is true, and I believe it is, because I've experienced this for myself along with other women in my past, then your friendships can even determine when you'll get pregnant and, coincidentally, what day your child will be born. Kind of like the butterfly effect: That a butterfly gently flapping its wings in the jungles of Madagascar can indirectly cause a typhoon off the coast of Jakarta. So, each person has an effect on you and vice versa.
Reply | Report Abuse | Link to thisI also believe, for what ever reason, that this does happen. My sister and I were always on the same cycle. What prompted me to look at this now is my oldest daughter. When she finally started her period (I knew it was on the horizon), she happened to start it on the 4th day of my cycle. What are the odds of that, being that there are 28-31 days in each month? Sorry, not much for statistical analysis here. I used to be 28 days like clockwork, but as I've gotten closer to 40, I've now gone 30-31 days. However, this month (daughter's second period) I went only 26 days, and she started the day after I did (she went 23 days)! It may just all be a big coincidence, but I really feel that there is 'something' to it. I'll be watching next month closely too. It will be very interesting when my twin girls hit puberty...Will we all be on the same cycle? Will the twins be on the same cycle? Will just the 3 sisters be on the same cycle (as I'll be closer to 50 by then)? Hmmmm, looking forward to that (I think!).
Reply | Report Abuse | Link to thisAstrology is not real. Ever read King Lear by Shakespeare? Outer forces do not determine your character.
Reply | Report Abuse | Link to thisI believe that a better study may be done on whether pairing of a female who is very irregular to a female who is body is like clock work causes synchronization or at the very least more regular period.
Reply | Report Abuse | Link to thisMy periods are extremely irregular. In fact most of the time, I am in amenorrhia. I was married for 4 years and had extremely frequent unprotected sex with my husband, (5 plus times a week). During that time I probably ovulated twice.
When I left him, and moved in with a female room mate whose cycle worked like clockwork. During that time, I ovulated almost every 6-8 weeks almost immediately after I moved in. I continued to have sex with my husband, (sorry ladies, I could not resist, the sex really just that great) though on 1-2 a week sometimes every 2 weeks. Withing 6 months, I was pregnant.
I am a lesbian woman, who has been dating someone for 5 months now. Our periods first synced up after about 3 months. The odd thing is, I am in Afghanistan and she is in the U.S. We have had some short visits with each other, but for the most part we are apart. We do skype, but I'm almost positive you can't smell pheromones through the internet yet =)
Reply | Report Abuse | Link to thisVery interesting article. But I like to know if some one did the research or have any data.
Reply | Report Abuse | Link to thisOne female “A” living alone and later one second “B” lady move in. In some time later their menstruate become sync. Do the B lady change to sync with A or A change to B?
What if 2 or 3 female move in the house? Will the A have to change to them?
Most of the research is done females live in same home or dorm. Is it same thing when women work together in same office of factory?
Second part of the question is. The one whose periods change is she submissive or dominant. Will the submissive become leader or dominant become leader. Dose it have any baring on their lifestyle?
Someone mentioned our tribal ancestors. Well, if several females cycle closely together, conceive around the same time and give birth around the same time that could be beneficial in terms of childcare. Something happens to one or more of the mothers, another mother(s) can nurse the abandoned offspring. Couldn't do that unless they were already lactating.
Reply | Report Abuse | Link to thisEven though it doesn't seem logical, I believe there's some truth to it. I usually don't get my period because my hormones are messed up and the person I'm usually around the most is my mother, who has gone through menopause. For the past week I've been living with my sister, and the day after she gets her period, I get mine, which hasn't come in more than half a year. This has happened several times too; when my sister gets her period and I've been around her for a long time then I get mine. In certain times in history, women would come together during their menstrual cycles, to get away from the men or the man who run their lives otherwise, and it would instill a sense of bonding. Humans are social animals, and we bond through certain ways in order to maintain a sense of cohesiveness to the social organism they are a part of. The very act of talking about your menstrual cycle with another woman does send out that feeling of sharing something, a knowledge not known or rarely understood by men.
Reply | Report Abuse | Link to thisI totally believe in females having their cycle at the same time let me tell you why. I have two daughters age 15 (J) and 11 1/2 (L), me 39. When one starts her menstrual cycle it is a matter of a day to a week and then the other two will start. I am the mom, so there has been numerous times L will start then I will, two weeks later J will start and I will start again, this has happened numerous times. My cycle is pretty on cue every 28 days, but if all us girls in the house do not have our periods within the same week and one of the girls has theirs two weeks later or three weeks later I will start again this has happened 4 times this year, because usually we are all at the same time. So, my question is how is this possible if females being synchronized is not true? Anyone have the answers to this?
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