Female reproductive factors are associated with the risk of newly diagnosed bipolar disorder in postmenopausal women

Changes in the levels of female sex hormones are associated with mood disorders in middle-aged women. This study investigated the association between female reproductive factors and the development of newly diagnosed bipolar disorder (BD). We used a South Korean nationwide medical records database. Postmenopausal women aged 40 or older who underwent health examinations were identified and followed for the occurrence of BD. We identified female reproductive factors including the age at menarche and menopause, parity, history of breastfeeding, oral contraceptive (OC) use, and hormone therapy (HT), and investigated their association with the occurrence of newly diagnosed BD. During an average of 8.32 years (SD 0.83) of follow-up, the incidence of BD was 0.50 per 1000 person-years in postmenopausal women. Compared to women with menopause at an age of 40 years or younger, those with menopause at an age of 45 years or older showed decreased risks of BD. Compared to women who had never breastfed, those who had breastfed for more than 12 months showed a decreased risk of BD. Compared to women who never received HT, those who received HT showed an increased risk of BD in a time-dependent manner. Among postmenopausal women, later menopause and breastfeeding for more than one year were associated with a decreased risk of BD occurrence, and receiving HT was associated with an increased risk.