Menstrual synchrony under optimal conditions: Bedouin families

Ovarian cycles of females living and interacting together have been shown to synchronize in a number of species. In humans, the related phenomenon of menstrual synchrony has been reported among roommates and best friends. Menstrual data were collected prospectively for 3 months from 27 Bedouin nuclear families living under conditions optimally conducive for synchrony: (a) women living together for many years, (b) a highly sexually segregated society, (c) standard living conditions, and (d) minimal use of oral contraceptives. Results show unequivocally the existence of menstrual synchrony: A 20%-25% shift toward synchrony was found for sisters-roommates, sisters-roommates who are close friends, and the family (all women in the family between 13 and 50 years of age).