Reexamination of the relation between menstrual cycle and kampo diagnosis, yin-yang

Several Chinese herbal medicine textbooks describe that a short menstrual cycle indicates "yang" status and a long cycle indicates "yin" status. However, we sometimes encounter yang patients with a long cycle or yin patients with a short cycle in daily practice. Therefore, we reviewed the relationship between yin-yang and length of menstrual cycle. A questionnaire addressing both menstrual cycle and several parameters for determining yin-yang was completed at the time of the patients' visit to the hospital. Patients were divided into yang or yin groups, and menstrual cycle was compared between the two groups. A short menstrual cycle was mostly observed in yin patients (27.42 +/- 1.73, 95% CI: 26.32-28.52, n = 12) and a long cycle was mostly observed in yang patients (31.63 +/- 3.96, 95% C.I: 29.51-33.74, n = 16). The difference in menstrual cycle between the two groups was significant (p = 0.002), and this result was entirely opposite to the traditional theory. This study identified a discrepancy between the traditional theory and the actual menstrual cycle findings in this small population. Current reexamination of the relationship between yin-yang and menstruation in a larger population is warranted.