Many of us females have had this conversation. We live in the freshman dorms, and it seems like everyone is menstruating at the same time. I remember someone my freshman year saying something to the effect of, "It's not just our floor, it's our dorm!" Many of us who have sisters have experienced the same thing--we menstruate at the same time. And guys, you may have noticed that once a month many of the girls are grumpy at the same time (thank you progesterone!).
Of course not all women living together menstruate at the same time, and not everyone reacts to menstruation in the same way (some don't PMS at all). And some of you may have read the last paragraph and had an intense negative reaction to it--maybe you thought that the evidence for menstrual synchrony is anecdotal, or maybe you thought of those women who don't PMS or don't menstruate. Others may have read the last paragraph and agreed with it completely, or remembered having a similar conversation.
So which reaction is scientifically supported? What exactly is menstrual synchrony, and does it exist, and if it does, why? To answer the first question, menstrual synchrony is exactly what it sounds like--the proposed process whereby menstrual cycles of women who live with or have close relationships with one another synchronize their menstrual cycles. The larger question is whether or not it exists and, if it exists, what causes it.
Unfortunately, science has failed to answer the first question: researchers still debate the existence of menstrual synchrony. Although Martha McClintock in 1971 found that social interaction in college dormitories strongly affected menstrual cycles, and although her results have been verified in some subsequent studies, many other studies have found the opposite results (that women do not experience menstrual synchrony). My general observations from my fairly brief research is that many (but, of course, NOT all) of the older studies support the existence of menstrual synchrony, whereas many (but, again, of course NOT all) of the later studies refute it. It is interesting, though, that many of these later studies did not control for the use of birth control in their samples (Ziomkiewicz, 2006; Yang & Schank, 2006), even though birth control use dropped 24% in 1979 due to health risks and was not approved for acne treatment until 1997 (after McClintock's study) or protected under the Equal Employment Opportunity Commission until 2000 (Nikolchev, 2010; meaning that birth control use could have changed dramatically due to decreased safety risk and more general uses since this older research was conducted). Thus, although the research shows mixed results, I suggest that some time/cultural trends may be behind this debate (possibly an interesting research topic if someone wants to respond/comment or even has an endocrinological or social lab research interest). [Note: The affirmative studies of menstrual synchrony have also been critiqued because of their methods, but I don't want to get too far into that because the critiques have also been criticized (i.e. see: Graham, C. A. (2002). Methods for obtaining menstrual-cycle data in menstrual-synchrony studies: Commentary on Schank (2001). Journal of Comparative Psychology, 116, 313-316. doi: 10.1037/0735-7036.116.3.313.)]
I know this blog was kind of all over the place, but that's because the research is. I decided to post it anyway because I think it's an example of how research--whether in the lab or online research--often leads to more questions than answers.
References:
McClintock, M. K. (1971). Menstrual synchrony and suppression. Nature, 229, 244-245. doi: 10.1038/229244a0
Morofushi, M., Shinohara, K., Funabashi, T., & Kimura, F. (2000). Positive relationship between menstrual synchrony and ability to smell 5a-Androst-16-en-3a-ol. Chemical Senses, 25, 407-411. doi: 10.1093/chemse/25.4.407
Nikolchev, A. (2010, May 7). A brief history of the birth control pill. The New York Times. Retrieved from http://www.pbs.org/wnet/need-to-know/health/a-brief-history-of-the-birth-control-pill/480/
Yang, Z., & Schank, J. (2006). Women do not synchronize their menstrual cycles. Human Nature, 17, 433-447. doi: 10.1007/s12110-996-1005-z
Shannon,
ReplyDeleteI have to say I am guilty of letting out a few chuckles while reading your post because I have been living with only women for all of my post-pubescent life, and the trend of “syncing-up” is almost always mentioned in ladies room talk. Although, I never gave it much scientific thought, but your post intrigued me! After looking at some of the articles and publications you mentioned, I found a brief article that brought up the theory of coincidental timing. It mentioned that if the menstrual cycle is approximately 28 days, then the furthest two women living together could be out of “phase” from each other is 14 days. Therefore, as the number of women living together increases, so does the probability of cycles overlapping (Wilson, 1992; Strassmann, 1997). That is probably why the pattern of menstrual synchrony became so evident once in a dorm hall with much larger numbers of women.
But, I loved your point that research often leads to more questions than answers, which inspired me to pose some of my own questions in relation to this possible hypothesis. As you know, we recently picked our topics for our EPs in class and I chose to do mine about the effects of psychological stress. As I was trying to come up with an explanation for the hypothesis of menstrual synchrony I thought about the similarities of living environments between women, and stress factors that they may have in common that could also attribute to this synchronizing trend. I have heard before that stress can affect the menstrual cycle, making them either longer or shorter or absent completely and how this could possibly explain women falling out of their normal cycle and “matching up” with women around them if their stress levels are rising and falling at similar times. For example, most of my roommates are in their first year of nursing school so they have similar exam and clinical schedules that result in fluctuating stress throughout the month. If they were to stress their reproductive system enough to knock it out of allostasis then maybe when their body was attempting to return to homeostatic balance it would occur at similar times in cycle. Unfortunately, as you saw from your own research there is still much uncertainty about this topic as one study I found saw no significant difference between menstrual cycle and the effects of acute stress (Barsom. S, 2004). But the questions are still there and remain to be tested to see why these trends seem to be showing up.
I hope to be able to look further this semester in just how these psychological stressors trigger a stress response in the body that lead to these functions. My initial thoughts are a stress perception in the brain, specifically suppression in the hypothalamus, leading to a disruption or change in the pituitary functions in hormones that ultimately affect the reproductive system that is resulting in these changes in menstrual cycles. Like I said, my hopes are to learn more about these systems and the relationship with psychological stress.
Thanks for your intriguing post that helped spark my own random search of information!
References:
Barsom, S., Mansfield, P., Koch, P., Gierach, G., & West, S. G. (2004). Association between psychological stress and menstrual cycle characteristics in perimenopausal women. Women's Health Issues, 14(6), 235-241. doi:10.1016/j.whi.2004.07.006
McClintock, M.K. (1971) Menstrual synchrony and suppression. Nature, 229, 244–245.