Menstrual synchrony in female undergraduates living on a coeducational campus

Abstract (1) The study investigated whether or not menstrual synchrony would develop in a sample of female undergraduates living on a coeducational university campus. (2) Seventy-nine subjects (aged 17–21 yr) recorded their menstrual cycles for 4 months from the beginning of the autumn semester. (3) A significant decrease in the difference between pairs' onset dates (i.e. a trend toward synchrony) was found for closest friends, but no significant effect occurred for neighbours or randomized pairs. (4) No significant correlation emerged between (a) cycle length, or (b) duration of menstruation, and the amount and nature of social interaction with males. (5) Only 16% of the subjects reported awareness of their closest friends' cycles. (6) The amount of time that individuals spent together, and not similar living conditions, was the significant factor in synchrony.