Fact or Fiction: Women Who Room Together, Cycle Together

My roommate and I are polar opposites in many ways: she’s a tall blonde with a gregarious personality; and I’m a petite brunette who may admire J.D. Salinger a bit too much; but late one Tuesday night, we suddenly felt like sisters.

Tired, moody and PMSing, we bundled into the car in our PJs and drove to the local ice cream parlor for a salted caramel cookie crunch cure-all. In stereotypical fashion, we bemoaned the less exciting aspects of womanhood and wondered if we had fallen into sync with each other’s cycles. Naturally, we did a little digging…

The Evidence

For:

In 1971, based on a phenomenon called the Lee-Boot effect, which describes the influence of pheromones on the oestrous (reproductive hormone) cycles of mice, Dr. Martha McClintock surveyed 135 women in a college dorm to see if a similar phenomenon occurred in humans.  She found that women who spent the most time together had closer onset dates for their periods. Follow-up studies showed comparable results.

25 years later, Dr. McClintock conducted another study and found that the sweat from women in the follicular (egg maturation) phase of their cycles led other women to have shorter menstrual cycles; while sweat from women in their ovulatory (egg release) phase, lengthened the menstrual cycles of other women. She continues her work today.

Against:

Critics of the menstrual synchrony theory cite problems with studies like Dr. McClintock’s, including: flawed assumptions, unsound statistical methods, and sampling biases. In a critical review done by Dr. H. Clyde Wilson of the original McClintock study, correcting these “errors” erased the observation of significant levels of menstrual synchrony.

Furthermore, it’s hard to eliminate pure coincidence. Two women’s periods are, in fact, statistically likely to overlap. The average woman has a 28-day cycle, thus the maximum amount of time that two women may be out of phase would be 14 days. Given that information, on average, the onset of the two women’s periods would be seven days apart, and fifty percent of the time they would be even closer. Since a women’s period usually lasts for about five days, an overlap is almost to be expected!

The Verdict

Speculation remains over if, why and how this phenomenon occurs in humans. Nonetheless, some studies suggest that there is a sliding scale of sensitivity to certain pheromones, such as 5alpha-androst-16-en-3alpha-ol, which may affect the presentation of menstrual synchrony.

References

McClintock MK. 1971. Menstrual Synchrony and Suppression. Nature. 291:244-245.

Morofushi M, Shinohara K, Funabashi T, Kimura F. 2000. Positive relationship between menstrual synchrony and ability to smell 5alpha-androst-16-en-3alpha-ol. Chem Senses. 25(4):407-11.

Rudis J. 2008. True or False: Women Who Live Together Tend to Have Synchronized Menstrual Periods [Internet]. Beth Israel Deaconess Medical Center web site. [cited in 2014 Nov 30]. Available from: http://www.bidmc.org/YourHealth/Therapeutic-Centers/Womens-Self-Care.aspx?ChunkID=156991

Wilson HC. 1992. A Critical Review of Menstrual Synchrony Research. Psychoneuroendocrinology. 17(6):565-591.