Menstrual Factors and Stroke Incidence in Japanese Postmenopausal Women: The Ohasama Study

Background: The association between stroke and menstrual factors, for example, age at the time of menarche and age at the time of menopause, has not been well studied so far and the findings are inconsistent. We sought to examine this association in Japanese postmenopausal women. Methods: We followed 1,412 postmenopausal women aged ≥35 without a history of stroke in Ohasama, Japan. Baseline data were collected using a self-administered questionnaire. Adjusted hazard ratios (HRs) and 95% CIs of each menstrual factor for stroke incidence were calculated using the Cox proportional hazard model. Results: During a median follow-up of 12.8 years, 143 participants developed a stroke for the first time. Women aged ≤13 at the time of menarche had a significantly higher probability of encountering a stroke incidence in their lives compared with women aged 15 at the time of menarche (HR 1.83; 95% CI 1.04-3.22). The same was also true for cerebral infarction (HR 2.34; 95% CI 1.18-4.66). While early menopause was not significantly associated with stroke incidence, women aged ≤45 at the time of menopause faced a higher risk for cerebral infarction compared with women aged 50 years at the time of menopause (HR 3.25; 95% CI 1.54-6.86). Conclusions: Early menarche and its associated features might be a useful tool for future intervention strategies targeting modifiable factors that trigger menstrual onset.